Dissertations / Theses: 'Poly (lactic acid)'

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Wang, Peiyao. "Stereopure Functionalized Poly(lactic acid)." University of Akron / OhioLINK, 2013. http://rave.ohiolink.edu/etdc/view?acc_num=akron1366631276.

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Shyamroy, S. "Synthesis of biodegradable poly (lactic acid) polymers." Thesis(Ph.D.), CSIR-National Chemical Laboratory, Pune, 2003. http://dspace.ncl.res.in:8080/xmlui/handle/20.500.12252/2861.

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Lei, Xia. "Blends of High Molecular Weight Poly(lactic acid) (PLA) with Copolymers of 2-bromo-3-hydroxypropionic Acid And Lactic Acid (PLB)." University of Akron / OhioLINK, 2013. http://rave.ohiolink.edu/etdc/view?acc_num=akron1367402061.

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Yan, Jialu. "Enzymatic Polyesterification to Produce Functionalized Poly(Lactic Acid) and Poly(n-Hydroxyalkanoic Acid)s." University of Akron / OhioLINK, 2013. http://rave.ohiolink.edu/etdc/view?acc_num=akron1375415868.

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Li, Yonghui. "Biodegradable poly(lactic acid) nanocomposites: synthesis and characterization." Diss., Kansas State University, 2011. http://hdl.handle.net/2097/8543.

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Doctor of Philosophy
Department of Grain Science and Industry
X. Susan Sun
Biobased polymers derived from renewable resources are increasingly important due to acute concerns about the environmental issues and limited petroleum resources. Poly(lactic acid) (PLA) is such a polymer that has shown great potential to produce biodegradable plastics. However, low glass transition temperature (Tg), low thermal stability, slow biodegradation rate, and high cost limit its broad applications. This dissertation seeks to overcome these limitations by reinforcing PLA with inorganic nanoparticles and low-cost agricultural residues. We first synthesized PLA nanocomposites by in situ melt polycondensation of L-lactic acid and surface-hydroxylized nanoparticles (MgO nanocrystals and TiO2 nanowires) and investigated the structure-property relationships. PLA grafted nanoparticles (PLA-g-MgO, PLA-g-TiO2) were isolated from the bulk nanocomposites via repeated dispersion/centrifugation processes. The covalent grafting of PLA chains onto nanoparticle surface was confirmed by Fourier transform infrared spectroscopy and thermalgravimetric analysis (TGA). Transmission electron microscopy and differential scanning calorimetry (DSC) results also sustained the presence of the third phase. Morphological images showed uniform dispersion of nanoparticles in the PLA matrix and demonstrated a strong interfacial interaction between them. Calculation based on TGA revealed that more than 42.5% PLA was successfully grafted into PLA-g-MgO and more than 30% was grafted into PLA-g-TiO2. Those grafted PLA chains exhibited significantly increased thermal stability. The Tg of PLA-g-TiO2 was improved by 7 °C compared with that of pure PLA. We also reinforced PLA with low-value agricultural residues, including wood flour (WF), soy flour (SF), and distillers dried grains with solubles (DDGS) by thermal blending. Tensile measurements and morphological images indicated that methylene diphenyl diisocyanate (MDI) was an effective coupling agent for PLA/WF and PLA/DDGS systems. MDI compatibilized PLA/WF and PLA/DDGS composites showed comparable tensile strength and elongation at break as pure PLA, with obviously increased Young’s modulus. Increased crystallinity was observed for PLA composites with SF and DDGS. Such PLA composites have similar or superior properties compared with pure PLA, especially at a lower cost and higher biodegradation rate than pure PLA. The results from this study are promising. These novel PLA thermoplastic composites with enhanced properties have potential for many applications, such as packaging materials, textiles, appliance components, autoparts, and medical implants.

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Corre, Yves-Marie. "Poly (lactic acid) foaming assisted by supercritical CO2." Lyon, INSA, 2010. http://theses.insa-lyon.fr/publication/2010ISAL0106/these.pdf.

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The poly (lactic acid) (PLA), through its organic origin and its biodegradation properties, can be a good alternative to petroleum-based polymers. To this end, the foaming of PLA by supercritical CO2 was evaluated in this study as an alternative to expanded polystyrene (EPS) for the production of food packaging. Because low rheological properties of this type of polyester, a first chain extension step was necessary to ensure a good foaming ability of PLA. Following a full characterization in physicochemical, rheological and thermal domain, a batch foaming assisted with supercritical CO2 was achieved. The influence of the foaming parameters, the extent of chain modificaton as well as the contribution of crystallization on cell morphology was evaluated. Based on these parameters, structures ranging from micro to macro-cellular-cell were obtained
Le polylactide (PLA), par son origine bio sourcée et ses propriétés de biodégradation, peut être une bonne alternative aux polymères issus du pétrole. Dans cet objectif, le moussage du PLA par CO2 supercritique a été évalué dans cette étude comme substitution au polystyrène expansé (PSE) pour la production d'emballages alimentaires. Du fait des propriétés rhéologiques faibles de ce type de polyester, une première étape d'extension de chaînes a été nécessaire afin de garantir des bonnes aptitudes au moussage du PLA. Suite a une caractérisation complète dans le domaine physico-chimique, rhéologique et thermique, une étude de moussage en mode batch sous CO2 supercritique a été réalisée. Les paramètres de moussage, le taux de modification du matériau ainsi que de l'apport de la cristallisation sur la morphologie cellulaire ont été évalués. En fonction de ces différents paramètres, des structures allant du micro-cellulaire au macro-cellulaire ont été obtenues

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Gonçalves, Carla Maria Batista. "Barrier properties of poly(lactic acid) based films." Doctoral thesis, Universidade de Aveiro, 2014. http://hdl.handle.net/10773/14296.

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Doutoramento em Engenharia Química
In recent years, the search for a environmentally friendly products has increased. One of the major challenges has been the demand for biodegradable materials that can replace plastic. If a few decades ago, plastic replaced, for example, the ivory in billiard balls, and in other products, saving the lives of thousands elephants, nowadays a replacement for that plastic is being searched, to prevent the change of the environmental conditions, essential to life in harmonly with the fauna and flora that the human specie has, in recent years, destroyed. Plastic is a petroleum derivate, whose price has been growing exponentially, mainly due to the fact of beind a cheap material and also to enable the production of products that are essential to modern life. Therefore, the petrochemical era is going to come to an end and a new environmentally sustainable era, based on biodegradable materials from renewable sources, will follow. The change to green routes only will be possible with the support of the major companies, and the implementation of drastic governmental law. Poly(lactic acid), PLA, is produced from the lactose present in the corn or sugarcane and has been intensively studied in recent years because if some limitants properties required its extrusion are overcome, it has the potential to replace the traditional polymers. PLA have high brittleness, low toughness and low tensile elongation. In this work, natural antioxidant (alpha-tocopherol) and synthetics antioxidants (BHT ant TBHQ) were added to the PLA with the aim not only to improve their flexibility, but also to create an active packaging to extend the shelf life of the foods and improve the organoleptic properties by preventing food losses. The impact of the addition of antioxidants into the PLA films, in its mechanical, thermal and barrier properties were studied by FTIR, DSC, SEM, AFM, DMA, TGA, QCM and time-lag techniques.
Nos últimos anos temos assistido à procura de produtos amigos do ambiente. Um dos maiores desafios tem sido a procura de materiais biodegradáveis que possam substituir materiais vulgarmente designados por “plástico”. Se há dezenas de anos o plástico veio, por exemplo, substituir o marfim nas bolas de bilhar, salvando vidas de milhares de elefantes, hoje, procuramos um substituto para esse plástico, de forma a preservar as condições ambientais que nos permitem viver harmoniosamente com a restante fauna e flora, e que a espécie humana tem, nos últimos anos, vindo a destruir. O plástico é um derivado do petróleo, cujo preço tem vindo a crescer exponencialmente, devido ao facto de ser barato e possuir propriedades que permitem desenhar produtos essenciais à vida quotidiana. Por isso, precisamos de sair da era petroquímica e entrar numa nova era ambientalmente sustentável, baseada em materiais biodegradáveis provenientes de fontes renováveis. Esta mudança para rotas “verdes”, só será possível com o apoio de grandes empresas, e medidas governamentais drásticas. O poliácido láctico, PLA, produzido a partir da lactose presente no amido ou no açúcar, tem sido intensivamente estudado nos últimos anos e possui potencial para substituir os tradicionais polímeros derivados do petróleo, se forem melhoradas algumas propriedades necessárias ao processamento por extrusão. O PLA, é muito frágil, pouco resistente e pouco flexível. Neste trabalho foram adicionados antioxidantes naturais (alfa-tocoferol) e sintéticos (BHT e TBHQ) ao PLA com o objetivo não só de melhorar as suas propriedades mecânicas, mas também de criar uma embalagem ativa que prolongue o prazo de validade dos alimentos e melhore as suas propriedades organoléticas prevenindo alterações ou perda de sabor. O impacto da adição destes antioxidantes nas propriedades originais do PLA a nível mecânico, térmico e de barreira foi estudado pela utilização das técnicas de FTIR, DSC, SEM, AFM, DMA, TGA, QCM e time-lag.

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Rasal, Rahul M. "Surface and bulk modification of poly(lactic acid)." Connect to this title online, 2009. http://etd.lib.clemson.edu/documents/1246558434/.

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Oliveira, Juliana de. "Poly(Lactic acid) production by conventional and microwave polymerization of lactic acid produced in submerged fermentation." reponame:Repositório Institucional da UFPR, 2016. http://hdl.handle.net/1884/46421.

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Orientador : PhD. Luciana Porto de Souza Vandenberghe
Coorientadores : PhD. Carlos Ricardo Soccol e PhD. Sônia Faria Zawadzki
Tese (doutorado) - Universidade Federal do Paraná, Setor de Tecnologia, Programa de Pós-Graduação em Engenharia de Bioprocessos e Biotecnologia. Defesa: Curitiba, 09/06/2016
Inclui referências : f. 115-128
Área de concentração: Agroindústria e biocombustíveis
Resumo: Poli(ácido lático), poliéster, é um polímero biodegravável aplicado em produtos como embalagens, têxteis, médicos e farmacêuticos. Pode ser obtido a partir do monômero ácido lático (AL) por meio da reação de policondensação direta e pela polimerização por abertura de anel do lactídeo. O AL é um ácido orgânico que apresenta diversas aplicações principalmente na indústria alimentícia, assim como na indústria farmacêutica, química e de polímeros. A produção do AL por fermentação oferece vantagens tais como a produção do isômero opticamente puro. As necessidades nutricionais da bactéria aumentam o custo de produção do AL, portanto substratos alternativos tem sido estudados por apresentarem uma alternativa econômica para este processo. O objetivo deste trabalho foi a produção de ácido lático por Lactobacillus pentosus em fermentação submersa utilizando subproduto do processamento da batata e caldo de cana como substratos para a obtenção de poli(ácido lático). Estes sub-produtos porque possuem alta concentração de fonte de carbono e volumes significativos são gerados anualmente, o que justifica sua a re-utilização e valorização. O sub-produto do processamento da batata foi submetido a hidrólise ácida com o objetivo de converter o amido em glucose. A produção de AL foi otimizada utilizando etapas de planejamento experimental estatístico envolvendo a seleção de bactérias do gênero Lactobacillus, definição da composição do meio de cultivo e estudos de cinética em frascos de Erlenmeyer e biorreator do tipo tanque agitado. A produção de AL chegou a 150 g/L utilizando sub-produto do processamento da batata e 225 g/L utilizando caldo de cana em 96 horas de fermentação. O uso da célula inteira de levedura de panificação como fonte de nitrogênio e a condição de fermentação não estéril demostraram ser boas alternativas para um processo industrial de produção de AL. O processo de separação e recuperação do AL do caldo fermentado foi desenvolvido para obtenção da molécula purificada e estudos de polimerização com o monômero obtido. O processo desenvolvido consistiu no aquecimento do caldo fermentado seguido pela etapa de centrifugação. A etapa de clarificação foi realizada utilizando carvão ativado em pó seguida pela precipitação a baixa temperatura e acidificação do lactato de cálcio para conversão em ácido lático. O processo foi efetivo para remoção de contaminantes que estavam presentes no caldo fermentado. A concentração final de AL em solução aquosa foi de 416 g/L com um rendimento de 51%. Os estudos de polimerização foram desenvolvidos utilizando a técnica de policondensação direta do AL, por meio de dois diferentes sistemas de aquecimento, convencional e micro-ondas. Um polímero com massa molar de 6330 g/mol e 61% de rendimento foi obtido a partir de um AL comercial e utilizando o AL obtido por fermentação resultou em um polímero com massa molar de 2370 g/mol. O processo de aquecimento por micro-ondas proporcionou um maior rendimento, 79% e 76% para o AL comercial e obtido por fermentação, respectivamente. Porém, foi obtida menor massa molar que o processo convencional, 2070 para o AL comercial e 1450 para o AL obtido por fermentação. As propriedades físico-químicas do poli(ácido lático) demonstraram aplicação em encapsulamento de compostos bioativos e engenharia de tecido. As perspectivas de sequência de estudos são a aplicação em encapsulamento de moléculas, modificações do polímeros e desenvolvimento de compósitos. PALAVRAS CHAVE: Poli(ácido lático), sub-produto do processamento da batata, caldo de cana, policondensação
Abstract: Poly (lactic acid) (PLA) is a polyester, which has a predominant role as biodegradable plastic, that is applied in packaging, textile, medical and pharmaceutical products. It can be obtained from lactic acid by direct polycondensation and by ring-opening polymerization (ROP) of lactide. Lactic acid (LA) is an organic acid that presents diverse applications mostly in food industry, as well as in pharmaceutical, chemical industries and polymers. The production of LA by fermentation offers the advantage of producing optically high pure LA. Nutritional requirements of bacteria increase the cost of LA production so alternatives substrates have been studied to bring an economical alternative for this process. The aim of this work was the production of LA by Lactobacillus pentosus in submerged fermentation using potato processing waste and sugarcane juice as substrate in order to obtain poly(lactic acid). The fermentation process was developed using potato processing waste and sugarcane juice because of their high carbon source concentration. Important volumes of both sub-products were generated, which is another reason for their re-use and valorization. Potato processing waste was submitted to hydrolysis in order to convert starch to glucose. LA production by fermentation was optimized using, statistical experimental design approach steps of optimization involved the screening of bacteria of the genus Lactobacillus and definition of medium composition kinetics studies in Erlenmeyer flask and stirred tank reactor were also carried out. LA production reached 150 g/l using potato processing waste, it was and 225 g/l with sugar cane juice after 96 hours of fermentation. The use of baker's yeast as a source of nitrogen and nonsterile conditions demonstrated good alternatives for an industrial production process of LA. The separation and recovery process of LA from fermented broth was developed to obtain a purified molecule for further polymerization studies. The developed process consisted in heating the fermented broth, then a centrifugation step was conducted for removal of the cells and suspended solids. A clarification step was included with powered activated carbon with further precipitation at low temperature and acidification of calcium lactate to convert to LA. The process was effective for removal of contaminants that were present in the fermentation medium. Final concentration of LA in aqueous solution reached 416 g/l and a yield of 51%. Polymerization studies were then carried out using direct polycondensation of LA, that were carried out with two different heating systems, conventional and microwave heating. A polymer with 6330 g/mol of molecular weight and 61% of yield was obtained from commercial LA and using fermented LA resulted in 2370 g/mol. Microwave heating process provided a higher yield, 79% and 76% for commercial and fermented LA, respectively. Nevertheless, the molecular weight was lower than conventional process, 2070 for commercial LA and 1450 for fermented LA. Physicochemical properties of PLA demonstrated application in encapsulation of bioactive compounds and tissue engineering. Perspectives of sequence of the studies: application on encapsulation of molecules, modifications of polymer and development of composites. KEYWORDS: Poly(lactic acid); potato processing waste; sugarcane juice; polycondensation

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Sinclair, Fern. "Modification of poly(lactic acid) via olefin cross-metathesis." Thesis, University of Edinburgh, 2017. http://hdl.handle.net/1842/28896.

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Poly(lactic acid), PLA, is a viable replacement to petroleum derived polymers due to its renewable feedstock, biodegradability and bioassimilability, yet improvements in its physical, thermal and mechanical properties are required before it can fully enter all commodity markets. This thesis investigates olefin cross-metathesis (CM) as a synthetic strategy to modify the properties of PLA. The use of novel lanthanide and actinide catalysts on the microstructure control of PLA are also explored. The Tebbe reagent was used in a new synthetic strategy to produce a novel olefin derivative of lactide (MML). Olefin CM of MML with hex-1-ene was successful but polymerisation pre- and post-CM was unsuccessful due to monomer instability. CM of another olefin derivative of lactide, 3-methylenated lactide (3-ML) was successful with aliphatic alkenes; hex-1-ene to dodec-1-ene. To overcome competing alcoholysis of the functionalised monomers, which prevented polymerisation, hydrogenation was used to remove the olefin entity followed by successful ring-opening polymerisation (ROP) to produce polymers of low glass-transition temperatures (Tg). Post-polymerisation CM on an olefin containing polymer P(β-heptenolactone) P(β-HL), with methyl acrylate and an epoxide, generated functionalised homopolymers with increased Tg’s. Co-polymerisation of lactide with β-HL generated novel gradient-copolymers. Olefin CM with 15 different cross-partners produced functionalised copolymers with different thermal properties. Based on this route a new methodology was created to introduce two unique functionalities into the polymer backbone by manipulation of the olefin reactivities. Finally, in a collaborative project, uranium and cerium catalysts, Me3SiOU(OArP)3 and Me3SiOCe(OArP)3 - designed out-with the group- were tested and compared as ROP catalysts for lactide. Both catalysts were active in living polymerisations of L-lactide and under immortal conditions the activity and rates of the catalysts were switched, accounted for by a change in the coordination sphere due to ligand displacement. ROP of rac-lactide using the uranium analogue produced heterotactic-biased PLA with a Pr = 0.79.

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Jalali, Amirjalal. "Quiescent and flow-induced crystallization of poly(lactic acid)." Thèse, Université de Sherbrooke, 2017. http://hdl.handle.net/11143/9892.

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Le poly(acide lactique), PLA, est un polymère biocompatible et biodégradable, qui peut être produit à partir de ressources renouvelables. En conséquence, il a soulevé une attention toute particulière en tant que remplacement éventuel des polymères à base de pétrole. C’est un polyester aliphatique ayant des propriétés telles que module élevé, haute résistance, biocompatibilité et est donc un matériau prometteur pour diverses applications telles que les implants, l’encapsulation de médicaments et l'emballage. A cause de sa faible température de transition vitreuse, le PLA a une faible résistance thermique et les applications sont donc limitées à celles qui ne sont pas associées à des températures élevées. En outre, ce polymère souffre d'un faible degré de cristallinité. L'augmentation du taux de cristallinité dans de nombreuses techniques de mise en forme, telles que le moulage par injection, est nécessaire. Il y a plusieurs façons d'augmenter le niveau de cristallinité du PLA. Ces procédés comprennent l'utilisation d'agents nucléants, de plastifiants, ou de combinaisons d'agents plastifiants et de nucléation. La cristallisation du PLA à l'état fondu se présente sous deux formes cristallines légèrement différentes connues sous les noms α et α'. Cette étude compare la capacité d'auto-nucléation de ces deux formes cristallines par auto-nucléation. Ceci est réalisé en comparant les températures de cristallisation lors du refroidissement des échantillons préalablement cristallisés à diverses températures, puis de nouveau chauffé à une température dans la plage de fusion partielle du PLA. Dans la deuxième étape, l'effet des paramètres cinétiques et le poids moléculaire du PLA sur l'efficacité de nucléation des PLA phases cristallines a été étudié. Cette partie de l’étude ouvre une nouvelle voie pour comprendre le rôle des modifications cristallines du PLA qui mènent aux conditions optimales pour la cristallisation du PLA. La mise en forme des polymères implique des contraintes de cisaillement et d’élongation, ce qui implique une cristallisation induite par l’écoulement et la solidification qui s’en suit. Les propriétés mécaniques des produits finals dépendent du degré de cristallisation et de la nature des cristaux formés. Par conséquent, l'optimisation du procédé nécessite une bonne compréhension de la façon dont l’écoulement influence la cristallisation. Le type d'écoulement peut jouer un rôle important sur la cristallisation. Par exemple, l'écoulement élongationnel provoque l’orientation et l’étirement des molécules dans le sens de l'extension, comme dans le cas de la mise en forme de fibres et le soufflage de film, en aidant le processus de cristallisation induite par l'écoulement. Une littérature abondante existe sur la ii cristallisation des thermoplastiques classiques induite par l'écoulement. Cela dit, moins d'attention a été accordée à l'effet de l'écoulement de cisaillement et d'allongement sur la cristallisation du PLA. Comme étudié dans la dernière partie de ce document, l'effet du poids moléculaire sur la cristallisation induite par cisaillement du PLA est rapporté. Pour cela, trois différents PLA à faible, moyen et haut poids moléculaire ont été préparés par réaction d'hydrolyse. Ensuite, en utilisant un rhéomètre oscillatoire, l’effet du cisaillement sur la cinétique de cristallisation du PLA a été examiné.
Abstract : Poly(lactic acid), PLA, is a biocompatible and biodegradable polymer that can be produced from renewable resources. As a result, it has raised particular attention as a potential replacement for petroleum-based polymers. It is an aliphatic polyester with properties such as high modulus, high strength, and biocompatibility and is thus a promising material for various applications such as implants, drug encapsulation, and packaging. In the wake of low glass transition temperature, PLA has a low heat resistance and its application is limited to those not associated with high temperatures. In addition, this polymer suffers from a low degree of crystalinity. Increasing the crystallization rate in many processing operations, such as injection molding, is required. So far, many routes have been found to improve the crystallinity of PLA. These methods include using nucleating agents, plasticizers, and combination of nucleating agents and plasticizers together. PLA crystallization in the melt state results in two slightly different crystalline forms known as α and α’forms. This thesis compares the self-nucleation ability of these two crystal forms by self-nucleation. This is achieved by comparing crystallization temperatures upon cooling for samples previously crystallized at various temperatures and then re-heated to a temperature in the partial melting range for PLA. In the second step, we study the effect of molecular weight of PLA on the nucleation efficiency of PLA crystalline phases. This part of the investigation opens a new pathway to understand the role of PLA crystalline phases on the optimal condition for its crystallization kinetics. Polymer processing operations involve mixed shear and elongational flows and cause polymer molecules to experience flow-induced crystallization during flow and subsequent solidification. The mechanical properties of the final products are significantly dependent upon the degree of crystallization and types of formed crystals. Therefore, optimization of any polymer process requires a good understanding of how flow influences crystallization. The type of flow can play a significant role in affecting crystallization. For example, elongational flow causes molecules to orient and stretch in the direction of extension, as in the case of fiber spinning and film blowing, helping the process of flow-induced crystallization. An extensive body of literature exists on flow-induced crystallization of conventional thermoplastics. Having said that, less attention has been paid to the effect of shear and elongational flow on the PLA crystallization kinetics. As investigated in the final part of this thesis, the effect of iv molecular weight on the shear-induced crystallization of PLA is reported. For this, low, medium and high molecular-weight PLAs were prepared from a high molecular weight one by a hydrolysis reaction. Next, by means of a simple rotational rheometry, effect of the shear flow was examined on the crystallization kinetics of these three PLAs.

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Lenti, Mattia. "Triethyl citrate-based oligomeric plasticizers for poly(lactic acid)." Master's thesis, Alma Mater Studiorum - Università di Bologna, 2018. http://amslaurea.unibo.it/15760/.

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Poly(lactic acid) (PLA) is a bio-based, biocompatible, biodegradable polymer that can be produced from renewable resources including starch from corn and potatoes, sugar from beets and sugar cane. Poly(lactic acid) and its copolymers have attracted significant attention in environmental, biomedical, and pharmaceutical applications and as alternatives to petroleum-based polymers. Due to the relatively high glass transition temperature (55°C) and low crystallization rate which respectively result in a brittle behaviour and low production efficiency, the use of a plasticizer is critical to meet technological requirements. Low molecular weight plasticizers show migration issues over time while blending PLA with lower Tg polymers may result in phase separation. Our approach to tackle those issues was to synthetize a novel type of plasticizer containing an oligomeric PLA chain to which a triethyl citrate functionality is grafted as end-chain group. This system guarantees maximum compatibility with the polymeric matrix while still providing an improvement in the material properties. Triethyl citrate (TEC) is a bio-based and biocompatible compound so the “green” properties of PLA are retained. Synthesis and characterization of the plasticizer are described in this research project. The thermal properties of the plasticizers have been investigated using Thermogravimetric Analysis (TGA) and Differential Scanning Calorimetry (DSC). Upon addition of the plasticizer PLA shows a decrease in the glass transition temperature and an increase in the crystallinity which results in a higher storage modulus.

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Bahcecioglu, Gokhan. "Poly(l-lactic Acid) (plla)-based Meniscus Tissue Engineering." Master's thesis, METU, 2011. http://etd.lib.metu.edu.tr/upload/12613968/index.pdf.

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Meniscus is a fibrocartilaginous tissue which plays an important role in joint stability, lubrication, and load bearing and transmission. Meniscal tears are commonly encountered in sports activities, or caused by degeneration of the cartilage with ageing. They lead to pain, loss of work, disturbed biomechanics of the knee and inability to walk or even move the legs. As the meniscal tissue is avascular in the inner portion, injury to this part does not heal by itself, and therefore treatments are needed. In some cases when complex tears occur, the tissue cannot be successfully treated with the conventional methods. Tissue engineering appears to be a promising alternative to treat such complex tears. It includes the application of cells on scaffolds (or cell carriers), and provision of bioactive agents to the site of injury in order to regenerate the damaged tissue. The cells and the bioactive agents are involved in the synthesis of the new tissue, while the scaffold acts as a support to guide the cells until the new tissue is formed, and it is slowly absorbed by the body leaving the new tissue behind. Thus, a natural tissue is generated at the end. Few studies have been reported on the tissue engineering of meniscus, but neither of them was able to completely mimic the meniscus structure, nor could they succeed in constructing scaffolds with sufficiently high tensile properties. In the current in vitro study, a novel 3D construct was proposed, in which the natural tissue is perfectly mimicked. The 3D construct consisted of aligned collagen fibers embedded within a foam network which stabilizes the structure. The foam was prepared by freezing a polymer solution with a certain concentration, and lyophilizing it. Aligned fibers were aimed to improve the tensile properties. The construct was impregnated in alginate gel, which was then crosslinked, to improve the compressive properties. The foam was prepared from (poly(L-lactic acid)/poly(lactic-co-glycolic acid) (PLLA/PLGA) solutions of various concentrations (2%, 2.5%, 3%, and 4% w/v) and at different freezing temperatures (-20oC or -80oC) to select the best preparation condition. After analysis of the microstructure and mechanical properties, foams prepared from 3% polymer solution frozen at -20oC were found to be the most appropriate for use as scaffold for the 3D construct, since they had large pores, high and interconnected porosity, as well as high mechanical strength. The 3D constructs were seeded with human meniscus cells and incubated for 21 days. Cell behavior on the constructs was examined. Cell attachment and proliferation was found to be better with the constructs not coated with alginate. However, the constructs coated with alginate demonstrated higher compressive strength. It was also found that incorporation of collagen fibers significantly improved the tensile properties. All the constructs were shown to lead to the production of extracellular components specific for fibrocartilages, and thus it was concluded that they were promising for use in meniscal replacement.

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Tan, Bowen. "Poly(lactic acid) nanocomposites : water barrier properties and electrospinning." Thesis, Loughborough University, 2016. https://dspace.lboro.ac.uk/2134/24611.

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The PhD thesis investigated poly(lactic acid) nanocomposite in terms of water barrier properties and electrospinning. The thesis addresses two different but related topics. The first topic is improvement of the water vapour barrier properties of PLA films. The effect of montmorillonite clay and its alignment on water vapour permeability and the effect of crystallinity (introduced by annealing) on nanoclay alignment and barrier properties were investigated (Chapter 4). PLA nanocomposites containing 0 to 5 wt.% montmorillonite layered silicate were prepared. Both amorphous and semi-crystalline PLA nanocomposite films were obtained by compression moulding. Thermal properties of the samples were measured by DSC. The nanoclay dispersion was measured using TEM and WAXD. Water vapour transmission rates through the films were measured at 38℃ and at a relative humidity of 90%. A new tortuous path model was developed to quantify the effect of crystallinity, nanoclay concentration and nanoclay alignment on water vapour permeability and showed a good fit with the experimental data from the annealed PLA nanocomposites.

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15

Zhang, Zheng. "Synthesis of Pegylated Poly(lactic acid) Via Radical Coupling." University of Akron / OhioLINK, 2015. http://rave.ohiolink.edu/etdc/view?acc_num=akron1430759091.

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16

Singla, Rajendra Kumar. "Studies on poly (lactic acid) based blends and composites." Thesis, IIT Delhi, 2017. http://localhost:8080/xmlui/handle/12345678/7228.

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17

Fischer, Anna Magdalena [Verfasser]. "Branched and star copolymers based on poly(glycolic acid) and poly(lactic acid) / Anna Magdalena Fischer." Mainz : Universitätsbibliothek Mainz, 2017. http://d-nb.info/1133301150/34.

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18

Hagan, Susan Anne. "Poly(lactic acid)-poly(ethylene glycol) copolymers for use as drug delivery systems." Thesis, University of Nottingham, 1998. http://eprints.nottingham.ac.uk/30646/.

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Block copolymers of polylactide and poly( ethylene glycol) (PLA-PEG) were investigated as biodegradable drug delivery systems. They are defined by the differing molecular weight ratios of polylactide to poly( ethylene glycol). Copolymers containing more hydrophilic PEG than hydrophobic PLA per molecule self-dispersed in water giving spherical nonionic micelles. Purification by gel permeation chromatography gave two peaks. The first peak only formed micelles (the second was PLA-depleted). Analysis by dynamic light scattering (DLS) and transmission electron microscopy (TEM) gave diameters of IS.6nm and 18.9nm for 1.5:2 and 2:5 PLA-PEG micelles respectively. PLA-PEG copolymers with more PLA than PEG per molecule (4:2 and 6:2 PLA-PEG) formed "solid particles" by the solvent-precipitation method. GPC purification again gave two peaks, but smaller second peaks. DLS analysis gave diameters of 15.1 nm and 20.8nm for 4:2 and 6:2 PLA-PEG particles respectively (confirmed by TEM and atomic force microscopy (AFM)). Static secondary ion mass spectrometry and X-ray photoelectron spectroscopy showed PEG at the surface of 4:2 and 6:2 PLA-PEG in water and acetone. Stability testing to salt suggested sterically stability. Rheological measurements determined PEG chain layer thicknesses, with the thickest chain for 2:5 PLA-PEG (where PEG chain length is 5000gmol-1 compared with 2000gmol-1). Testosterone and sudan black B (SBB), were used as "model" drugs with different hydrophobicities. Ultracentrifugation sedimentation velocity studies confirmed drug incorporation. Aromatic SBB loaded readily (≥59.0%w/w) compared with steroidal testosterone <2%w/w). Loading of testosterone esters of varying hydrophobicity into PLA-PEG particles showed little difference compared to between testosterone and SBB, suggesting that aromaticity is more significant. In vitro release studies (4:2 PLA-PEG particles/SBB) showed a small burst release, then linear release to twenty eight days. In vivo studies in the rat, using a radioactive marker, demonstrated extended blood circulation times for PLA-PEG micelles during the three-hour study, with increased blood levels and lower liver uptake for 1.5:2 over 2:5 PLA-PEG micelles. PLA-PEG particles were directed to the liver.

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19

Prévot, Flavie. "Valorization of vegetables wastes for the poly(lactic acid) bioproduction." Thesis, Strasbourg, 2015. http://www.theses.fr/2015STRAE008/document.

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Cette thèse s’articule autour de la valorisation de la biomasse lignocellulosique pour la production d’un polymère biosourcé, le poly(acide lactique) PLA. Lors d’une première étude, deux prétraitements de la biomasse lignocellulosique ont été réalisés pour libérer les sucres fermentescibles. Puis plusieurs stratégies de fermentations ont été mises en place et un criblage microorganisme / biomasse a été réalisé en vue de sélectionner la meilleure stratégie de fermentation et le meilleur couple biomasse / microorganisme pour la production d’acide lactique. Les bactéries lactiques, Lactobacillus casei et Lactobacillus delbrueckii et le son de blé ont été retenus pour produire l’acide lactique lors d’une fermentation en milieu liquide sur l’hydrolysat produit par une hydrolyse à l’acide dilué du son de blé. Lors d’une seconde étude, la stratégie choisie a été optimisée et a subi un « scale-up » afin d’augmenter la concentration en acide lactique. Les fermentations en milieu liquide ont été effectuées au sein d’un bioréacteur afin de contrôler les paramètres de croissance bactérienne et de production d’acide lactique (pH, pO2, agitation, production d’acide lactique). Puis une purification de l’acide lactique a été menée par chromatographie échangeuse d’ions. Cette technique a été réalisée en deux étapes clés utilisant successivement une colonne cationique forte et une colonne anionique faible. L’acide lactique purifié a été polymérisé par ouverture de cycle (ROP). Durant toutes ces recherches, la chimie verte a été mise au premier plan d’une part par le sujet de l’étude (valorisation de la biomasse végétale) mais aussi d’autre part par le choix des méthodes employées (pas de solvants, peu de produits chimiques, méthodes propres, économiques et renouvelables)
This thesis is articulated around the lignocellulosic biomass valorization to develop a fully sustainable, green and cheap route of PLA production. During a first study, two pretreatments have been realized on the lignocellulosic biomass in order to release the fermentable sugars. Several fermentations strategies have been considered and a screening of the couples microorganisms / biomasses has been performed in order to select the best strategy and the best couple microorganism / biomass for lactic acid production. The lactic acid bacteria, Lactobacillus casei and Lactobacillus delbrueckii and wheat bran have been selected to produce lactic acid via a liquid state fermentation on the acid hydrolysate obtained thanks to a diluted acid pretreatment on the wheat bran. During a second study, the chosen strategy has been optimized and scaled-up in order to increase the lactic acid concentration. Liquid state fermentations have been made in a bioreactor in order to control parameter needed for the optimal growth and consequently the optimal lactic acid production (pH, pO2, agitation, acid lactic production). Then, the lactic acid purification has been performed by ion exchange chromatography. This technic was made in two key steps using a strong cationic column and a weak anionic column successively. Finally, the purified lactic acid was then polymerized by ring opening polymerization (ROP). During all the researches, the green chemistry has been placed in the first plan in one hand by the choice of the topic of the study (biomass valorization) and in a second hand by the choice of each employed method (no solvent; few chemical products; sustainable, cheap and green methods)

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20

McLauchlin, Andrew R. "Development of a novel organoclay for poly(lactic acid) nanocomposites." Thesis, Loughborough University, 2009. https://dspace.lboro.ac.uk/2134/10298.

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This thesis describes a programme of work whose aim was to develop and characterise a novel organoclay derived from montmorillonite clay and the amphoteric surfactant cocamidopropylbetaine (CAB), a plant oil derivative, and to test its compatibility with poly(lactic acid) (PLA). Clay minerals such as montmorillonite increase the mechanical and physical properties of polymers when well dispersed within the polymer matrix, a condition that is more easily achieved when the clay layers are coated with a surfactant such as a quaternary alkyl ammonium compound (QAC). In the first part of the thesis the structure, purity and thermal behaviour of the CAB were characterised and the solubility parameter of the molecule was calculated and compared with that of a surfactant used in a commercial organoclay. The effects of concentration and pH on the uptake of the surfactant by montmorillonite were characterised by analytical and spectroscopic methods including X-ray diffraction analysis. The effect of surfactant loading on the thermal stability of the organoclay was studied using thermogravimetric analysis (TGA). The possibility of a reaction between CAB and PLA was also investigated by thermal and spectral methods. In the second part of the thesis, composites of the novel organoclay and PLA were manufactured by solution casting from chloroform, and melt compounding using a torque rheometer. It was found that intercalated/exfoliated nanocomposites could be made by either method. The biodegradability of the nanocomposites in composting conditions was also investigated. The study showed that CAB can be used to manufacture organoclays that confer useful improvements in the properties of PLA in terms of thermal stability and mechanical strength and on this basis merits further study. It also showed that organoclays based on CAB are a useful addition to the range of tallow-derived organoclays currently available.

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Melo, Priscila Cristina Soares. "Electromechanical Poly(L-lactic acid) PLLA platforms for regenerative medicine." Master's thesis, Universidade de Aveiro, 2014. http://hdl.handle.net/10773/15135.

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Mestrado em Materiais e Dispositivos Biomédicos
The discovery of piezoelectricity in bone by Fukada brought to light the idea of using piezoelectrics to enhance bone growth. Piezoelectric polymers like poly (L-lactic) acid (PLLA), a synthetic semi-crystalline polyester combining adjustable biodegradability and physical properties, stands out and therefore can be used as scaffolds for bone regeneration. In addition, some PLLA products have been approved for implantation in human body by the Food and Drug Administration (FDA). In the present work PLLA films with different crystallinities and thicknesses were produced in order to improve the dielectric properties and cellular adhesion. The maximum crystalline degree obtained was 35%. A complete characterization of PLLA films with different thicknesses and crystallinities was performed. The dielectric analysis included permittivity, dielectric loss and polarization. The highest relative permittivity value was 52.58 for amorphous samples at 120 ºC and 153 kHz. Dielectric loss reached its maximum at 27 ºC for a frequency of 1 MHz, being the value 1.64 on crystalline films. Polarization was studied by the technique Thermal Stimulated Depolarization Currents (TSDC), a method that measures polarization through thermal stimulus. In terms of polarization, the values increase proportionally with crystallinity, being the highest values 180 μC/cm2 on crystalline samples polarized during half an hour. In addition to cell-based assays, exists the metabolomics studies, a powerful tool since it can provide detailed information on the specific metabolic pathways responding and adapting to each of the selected material formulations. The work carried out in this project is the first stage of a wider program including in vitro biological characterization. It is presented the first metabolomics study using human osteoblasts in contact with piezoelectric PLLA, on PLLA standard films with 3% crystallinity, negatively poled.
A descoberta da piezoeletricidade no osso por Fukada levou à ideia de usar materiais piezoeléctricos para melhorar o crescimento ósseo. Polímeros piezoeléctricos como o poli (L-ácido láctico) (PLLA), um poliéster semicristalino sintético que combina biodegradabilidade e propriedades físicas ajustáveis, destacam-se pois podem ser utilizados como estruturas temporárias para a regeneração óssea. Para além disso, alguns produtos feitos à base de PLLA estão já aprovados para implantação no corpo humano pela Food and Drug Administration (FDA).Neste trabalho foram produzidos filmes de PLLA com diferentes cristalinidades e espessuras com o intuito de melhorar as propriedades dielétricas do material e a adesão celular. O grau de cristalinidade máximo obtido foi de aproximadamente 35%. Efectuou-se uma caracterização completa dos filmes com diferentes cristalinidades e espessuras. As medidas dielétricas realizadas abrangeram permitividade relativa, perda dielétrica e polarização. O valor mais alto de permitividade relativa medido foi de 52,58 para o filme amorfo, a 120 ºC e 153 kHz. A perda dielétrica atingiu o seu máximo nos filmes cristalinos aos 27 ºC para uma frequência de 1 MHz, com o valor de 1,64. A polarização foi estudada segundo a técnica TSDC (Thermal Stimulation Depolarization Current), um método que mede a polarização do material através do estímulo térmico. Em termos de polarização os valores aumentaram proporcionalmente com a cristalinidade, sendo o mais elevado 180 μC/cm2 para as amostras cristalinas polarizadas durante meia hora. Para além dos ensaios celulares, existe a metabolómica, hoje em dia uma ferramenta poderosa pois pode fornecer informações detalhadas sobre as vias metabólicas específicas que respondem e permitem a adaptação celular a cada uma das formulações de materiais selecionados. O trabalho realizado neste projecto constitui a primeira etapa de um programa mais amplo de caracterização biológica in vitro. É apresentado o primeiro estudo de metabolómica, utilizando osteoblastos humanos, em contato com o piezoelétrico PLLA, utilizando filmes de PLLA standard, 3% de cristalinidade, polarizados negativamente.

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22

Juikham, Sukunya. "Design and characterisation of novel blends of poly(lactic acid)." Thesis, Aston University, 2012. http://publications.aston.ac.uk/16523/.

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This thesis is concerned with the effect of polymer structure on miscibility of the three component blends based on poly(lactic acid) (PLA) with using blending techniques. The examination of novel PLA homologues (pre-synthesised poly(a-esters)), including a range of aliphatic and aromatic poly(a-esters) is an important aspect of the work. Because of their structural simplicity and similarity to PLA, they provide an ideal system to study the effect of polyester structures on the miscibility of PLA polymer blends. The miscibility behaviour of the PLA homologues is compared with other aliphatic polyesters (e.g. poly(e-caprolactone) (PCL), poly(hydroxybutyrate hydroxyvalerate) (P(HB-HV)), together with a series of cellulose-based polymers (e.g. cellulose acetate butyrate (CAB)). The work started with the exploration the technique used for preliminary observation of the miscibility of blends referred to as “a rapid screening method” and then the miscibility of binary blends was observed and characterised by percent transmittance together with the Coleman and Painter miscibility approach. However, it was observed that symmetrical structures (e.g. a1(dimethyl), a2(diethyl)) promote the well-packing which restrict their chains from intermingling into poly(L-lactide) (PLLA) chains and leads the blends to be immiscible, whereas, asymmetrical structures (e.g. a4(cyclohexyl)) behave to the contrary. a6(chloromethyl-methyl) should interact well with PLLA because of the polar group of chloride to form interactions, but it does not. It is difficult to disrupt the helical structure of PLLA. PLA were immiscible with PCL, P(HB-HV), or compatibiliser (e.g. G40, LLA-co-PCL), but miscible with CAB which is a hydrogen-bonded polymer. However, these binary blends provided a useful indication for the exploration the novel three component blends. In summary, the miscibility of the three-component blends are miscible even if only two polymers are miscible. This is the benefit for doing the three components blend in this thesis, which is not an attempt to produce a theoretical explanation for the miscibility of three components blend system.

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23

Rahman, Nelly. "Studies on Crystallization of Poly(Lactic Acid) and Related Polymers." 京都大学 (Kyoto University), 2009. http://hdl.handle.net/2433/124553.

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24

Kumar, Navdeep. "Studies on biodegradable nonwovens and biocomposites prepared from nettle and poly (lactic acid) fibers." Thesis, IIT Delhi, 2017. http://localhost:8080/xmlui/handle/12345678/7248.

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25

Liggins, Richard. "Paclitaxel-loaded poly(L-lactic acid) microspheres, characterisation and intraperitoneal administration." Thesis, National Library of Canada = Bibliothèque nationale du Canada, 1998. http://www.collectionscanada.ca/obj/s4/f2/dsk2/tape17/PQDD_0012/NQ34582.pdf.

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26

Liu, Tong. "Enzymatic Synthesis of Poly(lactic acid) Based Polyester Capable of Functionalization." University of Akron / OhioLINK, 2015. http://rave.ohiolink.edu/etdc/view?acc_num=akron1430749638.

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27

Polam, Anudeep. "Thermal and Draw Induced Crystallinity in Poly-L-Lactic Acid Fibers." Cleveland State University / OhioLINK, 2015. http://rave.ohiolink.edu/etdc/view?acc_num=csu1439843418.

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Saeidlou, Sajjad. "Cinétique de cristallisation, structure et applications des stéréocomplexes de PLA." Thèse, Université de Sherbrooke, 2014. http://savoirs.usherbrooke.ca/handle/11143/161.

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Résumé : Le poly(acide lactique) ou PLA est une famille de polyester thermoplastique linéaire qui a connu un essor commercial important durant la dernière décennie. L'enthousiasme pour le PLA vient de sa nature biosourcée, de ses bonnes propriétés mécaniques comme un module élastique élevé et de la possibilité de le biodégrader. Toutefois, certaines carences comme une faible résistance thermique et une faible élasticité à l’état fondu limitent son champ d’application. Fait à noter, le monomère d’acide lactique possède deux stéréo-isomères (L et D). Il est possible de polymériser les isomères L ou D pour former respectivement le PLLA ou le PDLA mais de façon surprenante, le mélange de PLLA et de PDLA permet la formation d’une structure cristalline distincte appelée le stéréocomplexe. Cette forme cristalline a un point de fusion 50[degré]C plus élevé par rapport aux formes cristallines du PLLA ou de PDLA d’où un premier intérêt pour augmenter la résistance thermique du matériau. Dans ce travail, l’usage de petites quantités (0-5 % massique) de PDLA comme additif dans une phase majeure de PLLA sera analysé. L’effet du stéréocomplexe formé à haute température sur la nucléation du PLLA et sur les propriétés rhéologiques du mélange sera plus particulièrement étudié. La présente thèse comprend une revue de littérature sur la cristallisation des PLA suivie de quatre parties expérimentales, conclusions et recommandations. La revue de littérature a pour objectif de réinterpréter l’ensemble des données disponibles sur la cristallisation du PLA afin d’en tirer des conclusions claires. La première partie expérimentale porte sur la cinétique de formation du stéréocomplexe à l'état fondu. Il a été constaté que la formation du stéréocomplexe est lente aux températures usuelles de mise en forme du PLLA ( 180[degré]C). De plus, la coexistence d’une morphologie baptisée dans ce travail « structure en réseau » et d’une morphologie sphérulitique a été révélée pour la première fois. Il a été démontré que la structure de réseau a une température de fusion moins élevée que la structure sphérulitique. Dans la seconde partie du travail, la cinétique de stéréocomplexation a été améliorée significativement pour adapter celle-ci aux cycles de refroidissement courts typiques des méthodes de mise en forme à l’état fondu. Ceci a été réalisé en ajoutant des agents nucléants qui initient la cristallisation à plus haute température et des agents plastifiants qui viennent augmenter la mobilité des polymères. Cette stratégie a permis de réduire le temps de cristallisation d’un ordre de grandeur. Dans un troisième temps, l'effet du stéréocomplexe sur les propriétés rhéologiques d’un mélange PDLA/PLLA a été investigué. En raison de son point de fusion élevé, le stéréocomplexe peut être préservé dans une matrice PLLA fondue et ainsi changer significativement les propriétés rhéologiques. La présence du stéréocomplexe a mené à une augmentation significative de la viscosité et de l'élasticité du PLA expliqué par la formation de points de « réticulation physique » dans la matrice amorphe. Enfin, dans la dernière partie expérimentale, le stéréocomplexe a été utilisé pour améliorer le comportement en moussage du PLA. Des expériences de visualisation et de moussage en mode discontinu ont montré que la présence de stéréocomplexe augmente la densité de nucléation de bulles et améliore significativement la morphologie de la mousse finale grâce à un effet de nucléation et à l’augmentation de l’élasticité du fluide. La revue de littérature et les trois premières parties expérimentales sont présentées sous forme d’articles scientifiques. La dernière partie expérimentale est à titre prospectif pour la suite du projet et ne sera pas soumise pour publication. // Abstract : Poly(lactic acid), or PLA, is a family of linear thermoplastic polyesters that has experienced strong market growth over the past decade. The enthusiasm for PLA originates from its bio-based nature, its good properties and its biodegradability. However, some of PLA deficiencies such as low thermal resistance and low melt elasticity have limited the development of this polymer. It is noteworthy that the lactic acid monomer has two stereo-isomers (L and D) that can be polymerized respectively into PLLA and PDLA but surprisingly, blending of PLLA and PDLA can lead to the formation of a “stereocomplex” which has a distinct crystalline structure from that of the homopolymers. This crystalline form has a melting point 50 oC greater than the crystalline PDLA or PLLA forms, thus it has by itself an interest in terms of heat resistance. In this work, the use of small amounts of PDLA (0-5%) in a matrix of PLLA will be explored. Particular emphasis will be on the nucleating ability of the stereocomplex (formed at high temperature) on PLLA crystallization and on its effect on the blends rheological properties. The current thesis comprises a literature review on PLA crystallization followed by four experimental sections. The objective of the literature review was to reinterpret the large body of data available on PLA in order to draw clear conclusions on PLA crystallization. The first experimental part of the work focused on the kinetics and conditions of stereocomplex formation in the melt state. It was found that stereocomplex formation is slow in the melt processing temperature range of PLLA (180 oC). Co-existence of a so-called “network structure” with a spherulitic structure was revealed for the first time. It was shown that the network structure has a lower melting point than the spherulitic one. In the second part of the work, stereocomplexation kinetics was improved significantly to match it with the fast cooling cycles typical of melt processing techniques. This was achieved by adding nucleating agents that initiated crystallization at higher temperatures and plasticizers that enabled more polymer fluidity. This strategy enabled an order of magnitude decrease in crystallization time. The third part of the work was the investigation of rheological properties upon formation of the stereocomplex structure in 0-5% PDLA in PLLA blends. Due to its higher melting point, the stereocomplex can be preserved in molten PLLA and alter significantly the blend melt rheology. Stereocomplex formation was monitored through rheological measurements and compared to classical calorimetry data. The presence of the stereocomplex lead to a significant increase in viscosity and in melt elasticity explained through the presence of physical crosslink points in the amorphous matrix. Finally, in the last experimental part of the work, the stereocomplex was employed to enhance PLA foaming behavior. Foaming visualization experiments as well as batch foaming tests showed that the presence of the stereocomplex can increase bubble nucleation density and led to a finer and more uniform foam morphology due to its nucleating effect and to the increased melt elasticity. The literature review and the three first experimental sections are presented in Peer-reviewed journal format. The last experimental section is meant as an exploratory and prospective part for the project and will not be submitted for publication.

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Jasti, Bhaskara Rao. "Characterization of polymorphic forms and in vitro release of etoposide from poly-DL-lactic and poly-DL-lactic-co-glycolic acid micromatrices." Scholarly Commons, 1995. https://scholarlycommons.pacific.edu/uop_etds/2654.

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Etoposide has been shown to be effective in the treatment of testicular and small-cell lung cancers, lymphoma, leukemia and Kaposi's sarcoma. Several clinical investigations have suggested that the prolonged maintenance of greater than 1 $\mu$g/ml concentration in plasma would provide better therapeutic response in patients. Thus use of a sustained/controlled release formulation of etoposide was indicated. This investigation focused on the potential for the development of a sustained/controlled release dosage form of etoposide for a 7-15 day delivery using selected polylactic and polylactic-co-glycolic acid polymers. During the course of studies involving the enhancement of aqueous solubility of etoposide in our laboratory evidence of a potential thermally induced polymorphic transition was detected. Therefore, further characterization of this phenomenon was also included in this investigation. Thermal behavior of etoposide was characterized by differential scanning calorimetry, thermal gravimetric analysis, X-ray diffractometry, mass spectroscopy, IR spectra and HPLC analyses. A method for the preparation of micromatrices of etoposide was developed utilizing a suspension and solvent evaporation technique. DSC, IR and NMR investigations did not indicate any potential etoposide-polymer interaction. Etoposide I, a monohydrate, underwent a dehydration reaction between 85-115$\sp\circ$C to yield Etoposide Ia, which upon further heating melted at 198$\sp\circ$C and crystallized to a new polymorph, Etoposide IIa at 206$\sp\circ$C. Etoposide IIa was found to melt at 269$\sp\circ$C and converted to its hydrated form, Etoposide II when exposed to atmosphere at room temperature. The polymorphic transition was found to be irreversible and monotropic. Etoposide I, the currently marketed drug was used in all delivery systems examined. Formulation studies with polylactic acid polymers indicated that the molecular weight of the polymer was a key parameter in influencing the percent of drug entrapped in the micromatrices, particles size distribution and the drug release profiles. Glycolide-containing polymers demonstrated control of etoposide release only at low drug loadings: larger micromatrices showing better control. Polylactic acid 50,000 at 1:5 and 1:15 drug to polymer ratios exhibited maximum rate of drug release of 1.57 mg/hr. At this release rate, a delivery system containing 350 mg of etoposide could be expected to maintain a plasma concentration of 1.08 $\mu$g/ml over a period of 7 days. Additionally, drug release profile of polylactide-co-glycolide (85:15, 75-180 $\mu$m) microsphere formulation with 1:10 drug to polymer ratio, was found to be more appropriate for a 15-day release system based upon 700 mg of etoposide.

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30

Tommey, Tyler. "Synthesis and Characterization of Free-acid Derivatives and Corresponding Ionomers of Poly(L-lactic acid)." University of Akron / OhioLINK, 2020. http://rave.ohiolink.edu/etdc/view?acc_num=akron1596234685966831.

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31

Kim, Junseok. "Improved Properties of Poly (Lactic Acid) with Incorporation of Carbon Hybrid Nanostructure." Thesis, Virginia Tech, 2016. http://hdl.handle.net/10919/81415.

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Poly(lactic acid) is biodegradable polymer derived from renewable resources and non-toxic, which has become most interested polymer to substitute petroleum-based polymer. However, it has low glass transition temperature and poor gas barrier properties to restrict the application on hot contents packaging and long-term food packaging. The objectives of this research are: (a) to reduce coagulation of graphene oxide/single-walled carbon nanotube (GOCNT) nanocomposite in poly(lactic acid) matrix and (b) to improve mechanical strength and oxygen barrier property, which extend the application of poly(lactic acid). Graphene oxide has been found to have relatively even dispersion in poly(lactic acid) matrix while its own coagulation has become significant draw back for properties of nanocomposite such as gas barrier, mechanical properties and thermo stability as well as crystallinity. Here, single-walled carbon nanotube was hybrid with graphene oxide to reduce irreversible coagulation by preventing van der Waals of graphene oxide. Mass ratio of graphene oxide and carbon nanotube was determined as 3:1 at presenting greatest performance of preventing coagulation. Four different weight percentage of GOCNT nanocomposite, which are 0.05, 0.2, 0.3 and 0.4 weight percent, were composited with poly(lactic acid) by solution blending method. FESEM morphology determined minor coagulation of GOCNT nanocomopsite for different weight percentage composites. Insignificant crystallinity change was observed in DSC and XRD data. At 0.4 weight percent, it prevented most of UV-B light but was least transparent. GOCNT nanocomposite weight percent was linearly related to ultimate tensile strength of nanocomposite film. The greatest ultimate tensile strength was found at 0.4 weight percent which is 175% stronger than neat poly(lactic acid) film. Oxygen barrier property was improved as GOCNT weight percent increased. 66.57% of oxygen transmission rate was reduced at 0.4 weight percent compared to neat poly(lactic acid). The enhanced oxygen barrier property was ascribed to the outstanding impermeability of hybrid structure GOCNT as well as the strong interfacial adhesion of GOCNT and poly(lactic acid) rather than change of crystallinity. Such a small amount of GOCNT nanocomposite improved mechanical strength and oxygen barrier property while there were no significant change of crystallinity and thermal behavior found.
Master of Science

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32

Guan, Xin. "Fabrication of Poly-Lactic Acid (PLA) Composite Films and Their Degradation Properties." University of Toledo / OhioLINK, 2012. http://rave.ohiolink.edu/etdc/view?acc_num=toledo1333779869.

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33

Singh, Shikha. "Properties of poly(lactic acid) in presence of cellulose and chitin nanocrystals." Doctoral thesis, TDX (Tesis Doctorals en Xarxa), 2020. http://hdl.handle.net/10803/671766.

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Plastic based materials are widely used for packaging applications. However, disposal of such petroleum-based materials e.g. polyethylene (PE) and polypropylene (PP) has become a huge threat to the environment due to its non-biodegradable behavior and complexity for waste management. For a sustainable industrial and economic development, it is indeed an urgency to develop packaging materials, which are environmentally benign, easy for waste treatment and recycling, and less/non-toxic. However, developing suitable and efficient plastic-substituents needs multiple requirements to be fulfilled viz., logistics and cost-effectiveness, good mechanical, thermal, optical and barrier properties, structural integrity of the constituents and morphological properties of the films. In this regard, utilizing bio-based polymers such as poly(lactic acid) (PLA), which originates from the natural resources, can be a viable and practical option due to its low toxicity, biodegradability, and eco-friendly behavior. Moreover, PLA has good optical and mechanical properties, which are similar or comparable to the some of the petroleum-based materials. However, pristine PLA possess few challenges such as slow crystallization rate, low crystallinity, poor toughness, and poor barrier properties, which need to be modified and fine-tuned. Utilizing nano-reinforcements, such as nanocellulose and nanochitin, is a promising approach for modifying PLA because of raw materials abundancy; easily obtainable from forest-based and bio-waste, hence, utilizing such materials also help the sustainable bioeconomy. Chitin nanocrystals (ChNCs) and cellulose nanocrystals (CNCs) possess unique properties, such as, low density, biodegradability, low toxicity, good mechanical, and barrier properties; therefore, can act as suitable nano-reinforcements for PLA. First segment of the research was aimed to understand and gain an insight about the role of ChNCs on the crystallization behavior of PLA and optimize the isothermal crystallization conditions. ChNCs, due to large surface area, acted as better nucleating agent and improved the overall crystallization rate of PLA by reducing the crystallization time and size of the spherulites. In second part of the research, knowledge gained about crystallization behavior was further explored to produce isothermally crystallized films at larger scale. The effect of crystallinity on the thermal, optical, barrier, and hydrolytic degradation properties of the nanocomposites were investigated. Noticeably, at 110ºC, the highest rate of crystallization achieved within 5 min. Furthermore, homogenous crystallization and smaller spherulite size (7 nm) of PLA achieved with ChNCs, significantly improved the crystallinity, thermal, barrier, and hydrolytic degradation properties. Third part of the research involved the study of mechanical properties of oriented films (PLA/ChNCs) achieved by a combination of solid-state and melt-state drawings. These oriented PLA nanocomposites films exhibited excellent mechanical properties. For example, a tensile strength with 360%, elongation at break with 2400%, and the toughness with 9500% increment achieved as compared to un-oriented nanocomposite films. The degree of crystallinity of highly oriented nanocomposite films increased from 8% to 53% with respect to the un-oriented nanocomposite films and smaller crystallites sizes were observed. Finally, in the fourth part, mechanical properties of the surface modified PLA/CNCs nanocomposites were investigated by a conventional tensile test and compared with the small punch test. Surface modification of CNC facilitated the dispersion of CNC into PLA matrix and increased the elastic modulus of the PLA/CNC nanocomposites. Knowledge and results gained in this thesis demonstrate the potential path for the development of the PLA nanocomposites with higher properties for packaging applications.
Para un desarrollo industrial y económico sostenible, es urgente disponer de materiales para envases y embalajes que sean ambientalmente benignos, cuyos residuos sean fáciles de tratar y reciclar y que sean atóxicos. Sin embargo, el desarrollo de sustituyentes plásticos adecuados y eficientes requiere que se cumplan múltiples requisitos, a saber, rentabilidad y buenas propiedades mecánicas, térmicas, ópticas y de barrera, así como integridad estructural de los constituyentes. En este sentido, la utilización de polímeros biobasados, como el ácido poliláctico (PLA), que se obtiene de fuentes renovables, puede ser una opción viable debido a su baja toxicidad, biodegradabilidad y baja huella de carbono. Además, el PLA tiene buenas propiedades ópticas y mecánicas, que son similares o comparables a algunos de los materiales obtenidos a partir del petróleo. Sin embargo, presenta algunos inconvenientes, como su lenta velocidad de cristalización, baja cristalinidad, fragilidad y deficientes propiedades barrera, que deberían modificarse y ajustarse para su uso industrial extensivo. La utilización de nano-refuerzos, como la nanocelulosa y la nanoquitina, es un enfoque prometedor para modificar y mejorar el desempeño del PLA. Estos refuerzos proceden de materias primas abundantes, son fácilmente obtenible a partir de residuos forestales y biorresiduos, por lo que la utilización de dichos materiales también ayuda al desarrollo de una economía más sostenible. Los nanocristales de quitina (ChNC) y los nanocristales de celulosa (CNC) poseen propiedades únicas, como baja densidad, biodegradabilidad, baja toxicidad, buenas propiedades mecánicas y de barrera; por lo tanto, pueden actuar como nano-refuerzos adecuados para mejorar el PLA. La primera etapa de la investigación tuvo como objetivo comprender el papel de las ChNC en el proceso de cristalización del PLA y optimizar las condiciones de cristalización isotérmica. Los ChNC, debido a su gran área superficial, actuaron como un buen agente nucleante y mejoraron la tasa de cristalización general de PLA al reducir el tiempo de cristalización y el tamaño de las esferulitas. En la segunda parte de la tesis, se exploró más a fondo el conocimiento adquirido sobre el comportamiento de la cristalización para producir películas cristalizadas isotérmicamente a mayor escala. Se investigó el efecto de la cristalinidad sobre varias propiedades de los nanocompuestos obtenidos. Se puede destacar que a 110ºC, en 5 min se alcanzó la mayor tasa de cristalización. Además, la cristalización fue homogénea y se obtuvo el tamaño esferulítico de PLA más pequeño (7 nm), mejoraron significativamente las propiedades térmicas, barrera y la degradación hidrolítica. En tercer lugar, se estudiaron las propiedades mecánicas de películas de (PLA / ChNC) orientadas, obtenidas mediante una combinación de estiramiento en estado sólido y en estado fundido. Estas películas de nanocomposites de PLA orientado exhibieron excelentes propiedades mecánicas, con incrementos del 360% de la resistencia a la tracción, 2400% de la elongación a la rotura y 9500% de la tenacidad en comparación con las películas de nanocompuestos no orientados. El grado de cristalinidad de las películas de nanocompuestos altamente orientados aumentó del 8% al 53% con respecto a las películas no orientadas y se observaron tamaños de cristalitas más pequeños. Finalmente, se investigaron las propiedades mecánicas de nanocompuestos PLA / CNC mediante ensayos de tracción convencionales y se compararon con los resultados de los ensayos de "small punch" (SPT). La modificación superficial de los CNC facilitó su dispersión en la matriz de PLA e incrementó el módulo elástico de dichos materiales. El conocimiento y resultados obtenidos con esta tesis demuestran el potencial para desarrollar nanocomposites de PLA con altas propiedades para aplicaciones de envase y embalajes.

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34

Tanpichai, Supachok. "Micromechanics of microfibrillated cellulose reinforced poly(lactic acid) composites using Raman spectroscopy." Thesis, University of Manchester, 2012. https://www.research.manchester.ac.uk/portal/en/theses/micromechanics-of-microfibrillated-cellulose-reinforced-polylactic-acid-composites-using-raman-spectroscopy(51fc47fa-fcb4-43cd-accc-3c559b5a0a2e).html.

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Microfibrillated cellulose (MFC) is an alternative material that has been widely studied to enhance the mechanical properties of a polymer matrix due to a number of perceived advantages over traditional plant fibre forms. Mechanical properties of MFC networks were found to depend on parameters such as the modulus of fibrils, bonding strength, porosity, degree of crystallinity, contact area of fibrils and possibly the modulus of the cellulose crystals of the raw materials (cellulose I or II). Even though the longer processing time used to produce MFC was found to yield networks with fewer fibre aggregates, finer fibrils and higher density, some properties, for instance thermal stability and degree of crystallinity, decreased due to the degradation of fibrils caused by the harsh treatment. The aims of this thesis were to assess the mechanical properties and interfaces of composites produced using of a range of MFC materials, prepared using different treatments and from different sources. Raman spectroscopy has been used to detect the molecular orientation of cellulose chains within an MFC network, and to monitor the deformation micromechanics of MFC networks. The Raman band initially located at ~1095 cm-1 obtained from MFC networks was observed to shift towards a lower wavenumber position upon the application of tensile deformation. The intensity of this band as a function of rotation angle of MFC networks was similar, indicating randomly oriented networks of fibrils. From the Raman band shift rate data, the effective moduli of MFC single fibrils produced from pulp were estimated to be in the range of 29-41 GPa. Poly(lactic acid) (PLA) composites reinforced with MFC networks were prepared using compression moulding. Enhanced mechanical properties of MFC reinforced composites were reported, compared to neat PLA films. The mechanical properties of these composites were found to mainly depend on the interaction of the PLA matrix and the reinforcement phase. The mechanical properties of the composites reinforced with dense networks were shown to be dominated by the network properties (fibril-fibril interactions), while matrix-fibril interactions played a major role where more opened networks were used to reinforce a polymer matrix. The penetration of the matrix into the network was found to depend on the pore sizes, fibre width and porosity within the network. It was found that the matrix easily penetrates into the network with a range of mean fibril dimensions, rather than for networks with only fine fibrils present. The stress-transfer process in MFC reinforced PLA composites was monitored using Raman spectroscopy. Greater Raman band shift rates with respect to tensile deformation for the composites were observed compared to pure MFC networks. This indicates that stress is transferred from the PLA matrix to MFC fibrils, supporting the enhancement of the mechanical properties of the composites.

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35

Deng, Yixin. "Optimising properties of poly(lactic acid) blends through co-continuous phase morphology." Thesis, Loughborough University, 2017. https://dspace.lboro.ac.uk/2134/33338.

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This PhD project investigated the effects of a co-continuous phase structure on the ductility of poly(lactic acid) (PLA) blends. An empirical model was used to predict the phase inversion point of the blends. The co-continuous phase morphology was first observed in polybutylene succinate(PBS)/PLA blends. With as little as 10 wt% of PBS, PBS/PLA blends achieved a dramatic improvement in ductility, over 250% elongation-to-break. Clay additives were incorporated in PBS/PLA blends. Clay was found out to affect the compatibility and co-continuous phase morphology of PBS/PLA blends. The clay dispersion was found to have an intercalated and exfoliated structure at a PBS/PLA composition ratio of 20/80. The clay particles increased the mixing conditions between the polymers by producing a finer structure, but also destroyed the co-continuous phase morphology, resulting in a substantial decrease in elongation-at-break. PLA was then blended with Poly(butylene adipate-co-terephthalate) (PBAT) to examine whether the co-continuous phase model could also be applied to other PLA-polymer blends. From the melt viscosity ratio of PLA and PBAT in the processing regime used in the study, the predicted phase inversion value was 19 wt% of PBAT. This value was verified by the results of mechanical properties, where results for elongation-to-break show a dramatic rise from around 10% up to 300% in the composition range between 10 and 20wt% of PBAT. Polyhydroxyalkanoate (PHA) was also blended with PLA and this project investigated how co-continuous phase morphology affects the blends of two brittle polymers. It was found that when PHA content ranged from 10 to 20wt%, the brittle-brittle polymer blends showed ductile behaviour due to a plane stress effect.

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36

Kim, Jung Ho. "Estudo experimetal comparativo da histotoxicidade entre o copolímero de poli (ácido láctico-co-glicólico) e a blenda poli (ácido láctico-co-glicólico) / poli (isopreno)." reponame:Biblioteca Digital de Teses e Dissertações da UFRGS, 2012. http://hdl.handle.net/10183/131198.

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Introdução: A aplicação clínica de biomateriais está se expandindo para diversas especialidades médicas. Dentre os diversos tipos de biomateriais, os classificados como temporários merecem atenção especial, pois são assimilados pelo organismo após exercerem sua função, evitando, assim, procedimento cirúrgico para sua retirada. O copolímero de poli (ácido láctico-co-glicólico) (PLGA) é um tipo de biomaterial temporário, rotineiramente utilizado na medicina na forma de fios de sutura e implantes ortopédicos. A mistura do PLGA com o poli (isopreno) resulta em uma blenda (PLGA / PI), de alta resistência e tenacidade, que foi desenvolvida pelo Laboratório de Biomateriais do Instituto de Engenharia da UFRGS. Entretanto, não existem estudos “in vivo” testando a reação óssea desta blenda. Objetivo: Testar a histotoxicidade da blenda de PLGA / PI em relação ao biopolímero já consagrado PLGA. Método: Foram utilizados 46 ratos machos wistar (Rattusnorvegicus - linhagem albina), divididos em 2 grupos conforme o material implantado (PLGA ou PLGA / PI) na calota craniana, e subdivididos em tempos de morte (15, 30, 60 e 90 dias). Os procedimentos foram realizados na Unidade de Experimentação Animal (UEA) do Hospital de Clínicas de Porto Alegre (HCPA). Após a morte, a calota craniana foi retirada, submetida ao exame histopatológico e aplicado o escore de Dadas e cols (14) modificado. Resultados: A diferença da histotoxicidade dos dois materiais não foi significativa nos períodos 15, 30 e 90 dias, porém foi significativa no período 60 dias. Conclusão: A histotoxicidade do PLGA / PI, ao final do estudo (90 dias), foi semelhante ao PLGA, demonstrando equivalência em longo prazo. O período de 60 dias pós-cirúrgico (grupo da blenda) foi o único em que a histotoxicidade mostrou-se significativamente maior. Mais estudos devem ser feitos para melhorar o entendimento desta variação.
Introduction: Clinical application of biomaterials is expanding to various medical specialties. Among the different types of biomaterials, those classified as temporary deserve special attention because they are assimilated by the body after exercising their function, thereby avoiding surgical procedure for their removal. Co-polymer poly (lactic-co-glycolic acid) (PLGA) is a type of temporary biomaterial, routinely used in medicine as suture threads and orthopedic implants. The mixture of PLGA with poly (isoprene) results in a high-strength and thoughness blend (PLGA / PI), developed by the Biomaterials Laboratory of the Engineering Institute/ UFRGS. However, there are no studies “in vivo” testing the bone reaction of that blend. Objective: To Test histotoxicity of PLGA / PI blend over the already established biopolymer, PLGA. Method: Forty six male Wistar rats (Rattus norvegicus – albino strain), divided into 2 groups according to the material (PLGA or PLGA / PI) implanted in the skull and sub divided into periods of death (15, 30, 60 and 90 days). The procedures were developed in the Animal Experiment Unit (AEU) of Hospital de Clínicas de Porto Alegre (HCPA). After death, the skull was removed, submitted to histopathologic examination and the modified Dadas’ et all score was used (14). Results: The histotoxicity difference of the two materials was not significant in the periods of 15, 30 and 90 days, but it was significant in the period of 60 days. Conclusion: At the end of the study (90 days), the PLGA / PI histotoxicity was similar to PLGA, showing longterm equivalence. The 60-day post-surgical period was the only one in which histotoxicity was significantly higher (blend group). More studies shall be done in in order to better understand that variation.

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Quirk, Robin Andrew. "Surface engineering of biodegradable polymers to create materials with biological mimicking activity." Thesis, University of Nottingham, 2000. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.342477.

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38

Hsin-PingChen and 陳欣平. "Spherulitic Morphology and Lamellar Assembly in Nonequimolar Mixtures of Poly(L-lactic acid) with Poly(D-lactic acid) and Solution-Cast Poly(L-lactic acid) Films." Thesis, 2017. http://ndltd.ncl.edu.tw/handle/ajvqb8.

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碩士
國立成功大學
化學工程學系
105
Investigations on the morphology resulted from melt-crystallization of nonequimolar blends of PLLA with PDLA with regard to the prior melting temperature and crystallization temperature were conducted. When crystallized after melting at 190 oC, the PLLA/PDLA (95/5) blend exhibits large radiating-stripe spherulites surrounded by tiny spherical crystals. When crystallized after melting at 240 oC, the radiating-stripe spherulites appear with negative-type spherulites. Melting observation show that radiating-stripe spherulites belong to PLLA α-crystals, while negative-type spherulites belong to sc-PLA crystals. From the top surfaces of radiating-stripe spherulites, the lamellae are arranged at an angle of 60o with radial direction on the main stalk, while lamellae on the region between main stalks are arranged perpendicular to the main branch. Because of the difference in lamellar assembly, the blend shows different birefringence in the same quadrant, resulting in special morphology. For neat PLLA crystallized by solvent evaporation, PLLA exhibits ring-banded morphology at 26~30 oC with tetrahydrofuran as solvent. The top surface of ring-banded spherulites shows lamellae arranged in dendritic shape. Lamellae inside spherulites arrange in radial direction, and show layer structure from lateral view.

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39

Jau-Yan, Li, and 李兆彥. "Thermal degradation of poly (lactic acid)." Thesis, 2006. http://ndltd.ncl.edu.tw/handle/04298834317877617273.

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碩士
高苑科技大學
高分子環保材料研究所
94
英文摘要 In this study, the thermal stability for the different molecular weight of poly (lactic acid)s (PLAs) were investigated. The characteristics of PLA were examined by elementary analysis (EA), soild nuclear magnetic resonance (NMR), different scanning calorimeter (DSC), fourier transform infrared spectrophotometer (FTIR), x-ray diffractometer (XRD), thermomechanical analyzer (TMA) and dynamic mechanic analysis (DMA). The thermal degradation behaviors of PLA ( 5,000 and 10,000 g/mole) were carried by dynamic thermogravivetric method and isothermal thermo- gravivetric method under three various condition gas. The experimental results of poly(lactic acid)s are showed that as following : Firstly, physical and morphological properties such as function groups and weight loss were characterized by FTIR, NMR, EA. Secondly, physical and morphological properties such as crystalline melting point, glass transition point, crystallization temperature, softing temperature , degradation behavior and mechanical properties were characterized by DSC, XRD, TMA and DMA. Thirdly, according to Flynn-Wall analytical model, the TGA experimental results showed that the activation energies of dynamic heating of PLA ( 5,000 g/mole) were 91, 158 and 201 kJ/mole and PLA ( 10,000 g/mole) were 141, 224 and 226 kJ/mole under nitrogen, air and oxygen, respectively. Moreover, the thermal degradation behavior activation energies of poly (lactic acid) increase with increase molecular weight and increase with content percentage of oxygen, and it was decreased with increase the weight remaining fraction. Fourthly, according to Flynn-Wall analytical model, the TGA experimental results showed that the activation energies of isothermal of PLA ( 5,000g/mole) were 73, 91, and 108 kJ/mole and PLA ( 10,000g/mole) were 82, 115, and 125 kJ/mole under nitrogen, air and oxygen, respectively. Moreover, the TGA showed that the activation energy increase with molecular weight, and increase with content percentage of oxygen in the weight lossing fraction in the range from 0.05 to 0.75.

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LingChang and 張靈. "Lamellar Assembly and Stereocomplex Structuring in Mixtures of Poly(L-lactic acid) and Poly(D-lactic acid)." Thesis, 2011. http://ndltd.ncl.edu.tw/handle/11011741637354234634.

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41

Yi-KwanChen and 陳伊寬. "Adsorption and Reactions of Lactic Acid and Poly(lactic acid) on Powdered TiO2." Thesis, 2010. http://ndltd.ncl.edu.tw/handle/24267332960729017883.

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碩士
國立成功大學
化學系碩博士班
98
Fourier-transform infrared spectroscopy has been employed to investigate the adsorption and reactions of lactic acid and poly(lactic acid) on powdered TiO2(35 ℃). Lactic acid can dissociate when exposed to the surface of TiO2. The carboxyl group deprotonates to form a carboxylate or the hydroxyl group breaks the O-H bond to form an alkoxy group on TiO2. As the temperature is raised higher than 250 ℃ in the absence of O2, it is found that propionate is formed, with minor acetate and gaseous CO2. In the presence of O2, acetate and CO2 are the only products detected after the lactic acid decomposition. Dehydration of lactic acid on TiO2 to form acrylate dose not occur. In the case of absorption of poly(lactic acid) on TiO2, the polyester chains are broken, forming carboxylate species, when exposed to the surface. Poly(lactic acid) has the same thermal decomposition products as those of lactic acid on TiO2. Poly(lactic acid) on TiO2 is subjected to photooxidation. Approximately 55% of poly(lactic acid) decompose to form acetate and CO2 under UV irradiation for four hours in the presence of O2. Possible decomposition mechanisms for lactic acid and poly(lactic acid) on TiO2 are proposed.

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42

Yuryev, Yury. "Nucleation and crystallization of poly(lactic acid)." Thesis, 2011. http://spectrum.library.concordia.ca/974024/1/Yury_Yuryev_PhD_thesis_final_submission.pdf.

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Poly(lactic acid) is one of the most promising “green” polymers, having huge potential for use as a packaging and construction material. The lack of knowledge about polylactide-specific crystallization behaviour is one of the barriers to widespread industrial use. In the present thesis, different aspects of one of the most important phenomena in polylactide crystallization were studied. In the series of articles included in this thesis, parameters of quiescent and field-induced crystallization were investigated. Significant attention was paid to the spherulitic morphology, growth rates, and stereocomplexation phenomenon that are intrinsic to polylactide, due its optical activity. A novel technique for growth rate measurements based on ultrafast heating and cooling of cast films, was suggested and validated. Melt crystallization of polylactide was studied using rheological methods. A new advanced model allowing the relation of complex viscosity to melt crystallinity was proposed and verified. The physical cross-linking phenomenon was introduced and quantified in the frame of the proposed model. Also, a new technique allowing the determination of the induction time of crystallization was presented and successfully validated. A proposed technique allowed dramatically improved precision of the measurement of induction time for both quiescent and field-induced crystallization. The phenomena of surface crystallization that had previously gone unexamined by the research community were investigated in detail. A theoretical model was suggested and its predictions were supported by extensive computer simulations. The simulation program used for research was developed during this study. It was found that surface crystallization can have an immense effect on crystallization kinetics and dramatically distort the observed thermal analysis results. Custom-designed experiments allowed the application of these results to polylactide crystallization. Extensive studies of shear-induced crystallization were done in this work. The novel techniques developed in the research allowed for a better understanding of the field-induced phenomenon. New techniques allowing the implementation of rheological measurements to discover and quantitatively assess electric field-induced polylactide crystallization were investigated in this study as well. It was shown that a DC electric field significantly promotes homogeneous nucleation of polylactide and enhances crystallization. An explanation to this observation based on the dipole moments of repeat units in the polylactide chain was offered and validated.

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43

"Poly (lactic acid) (PLA)/clay/wood nanocomposites." Tulane University, 2010.

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Poly (lactic acid) (PLA) is a promising substitute for conventional petroleum-based polymer materials as a result of its environmentally benign quality and suitable physical properties. However, there are also problems associated with properties, such as brittleness, low heat deflection temperature, low melt viscosity, as well as cost that prevent wide-range applications of PLA This work reports on melt extrusion preparation of PLA/clay/wood nanocomposites involving various compatibilizers, resulting in remarkable improvements in mechanical as well as in thermal material properties. In particular, the tensile and flexural moduli of PLA/clay/wood nanocomposites with 30 wt. % wood flour and 5 wt. % nanoclay respectively increased from 3.75 to 7.08 GPa and from 3.83 to 6.01 GPa compared to neat PLA. The thermal decomposition temperature improved by about 10°C compared to that of PLA/wood composites A mathematical model was developed based on Eshelby's equivalent inclusion method and Mori-Tanaka's background analysis to successfully predict longitudinal elastic moduli of complex structured nanocomposite materials
acase@tulane.edu

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44

Hsiao, An-Chih, and 蕭安智. "Toughening Poly(lactic acid) with α-Cellulose." Thesis, 2011. http://ndltd.ncl.edu.tw/handle/17791976078765282287.

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碩士
崑山科技大學
材料工程研究所
99
The PLA/α-cellulose composites have been fabricated using twin-screw extruder. The α-cellulose in this study will play the role of toughening the PLA matrix, and the contents of α-cellulose in PLA matrix will range from 0.2 to 10 wt%. To achieve this purpose α-cellulose was first subjected to surface modification with stearic acid to impart a good interfacial compatibility between the PLA matrix and α-cellulose. The resulting PLA/α-cellulose composites exhibit softer characteristics than the neat PLA. The mechanical properties, including ultimate tensile strength (UTS) and Young’s modulus (E), of the PLA/α-cellulose composites are much lowered at lower α-cellulose contents, and then these properties would climb up gradually at higher α-cellulose contents. However, the values of UTS and E of the resulting composites are significantly lower than those of the neat PLA polymer. Meanwhile, the ε (elongation at break) values of PLA/α-cellulose composites for all of the α-cellulose contents are higher than that of the neat PLA. It is intentional that the inclusion of α-cellulose into PLA matrix is aimed to increase the microcrack length and to improve the toughness of the PLA polymer. The SEM micrographs show that the fractural surfaces for the PLA/α-cellulose composites present the dimple-like morphology as compared to the somewhat flatten-like for the neat PLA polymer. The impact test shows that the impact strength for PLA/α-cellulose composite filled with 2 wt% modified α-cellulose would obtain an enhancement about 310% as compared to that of the neat PLA. Moreover, the damping factor from the DMA test for PLA/α-cellulose composite filled with 4 wt% modified α-cellulose is higher than that of the neat PLA by 28.6%. From the results of impact and DMA tests, the inclusion of α-cellulose could substantially and significantly increase the microcrack length and, as a result, improve the toughness and damping characteristics of the PLA polymer. Furthermore, α-cellulose modified with stearic acid would exhibit better performance in toughering property than that of the unmodified counterparts. As for the isothermal crystallization behavior of the PLA/α-cellulose composites, the inclusion of α-cellulose would decrease the spherulite dimensions and increase the growth rates of spherulite of the resulting composites. Moreover, there is a max. radial growth rate of spherulite for neat PLA and PLA/α-cellulose composites. The inclusion of α-cellulose could significantly increase the crystallinities Xc and the crystallization growth rates K of the resulting composites. Furthermore, irrespective of neat PLA and PLA/α-cellulose composites, there are double melting (Tm1，Tm2) occurrences for the crystallization temperatures between 95~115oC. As the temperatures raising higher than this range, the PLA molecules would possess enough kinetic energy to undergo the melt-recrystallization process, and under this condition the unsteable Tm1 would vanish and the Tm1，Tm2 come into single melting peak. The investigations on the non-isothermal crystallization kinetic behavior have been conducted by means of differential scanning calorimeter. The Avrami, Ozawa, and combined Avrami and Ozawa equations were applied to describe the crystallization kinetics and to determine the crystallization parameters of the α-cellulose filled PLA composites. It is found that the inclusion of α-cellulose can decrease the growth rate Zc due to hindrance of the polymer chain mobility. On the other hand, the composites show a higher Avrami value than that of the neat PLA, implying a more complex crystallization configuration. Moreover, the combined Avrami and Ozawa equation can successfully describe the crystallization model under the non-isothermal crystallization.

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45

Li, Kan-Rung, and 李侃融. "Characteristics of Biodegradable Poly(lactic acid) / Poly(butylenes succinate) Blends." Thesis, 2010. http://ndltd.ncl.edu.tw/handle/36793164916684276295.

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碩士
萬能科技大學
材料科技研究所
98
The poly(lactic acid)/poly(butylenes succinate) blends(PLA/PBS) were here in prepared by a method of melting blend, and had PBS content from 10 to 90wt%. The PLA/PBS characteristics for the phase transition regions, compatibility and morphology were investigated by DSC, DMA and SEM; and the effects of the characteristics on the tensile property were determined by the tensile strength. The various PLA/PBS blends present three regions of phase transition, including the glass transition region of PBS at -31~-37℃, the glass transition region of PLA at 52~-58℃ and the melting region of crystal at 108~110℃. The morphologies of PLA/PBS were a dispersive two-phase structure involved the sphere, layer and random dispersive morphology. The random dispersive morphology for the PLA/PBS had the random dispersive morphology, which presented a high ultimate elongation at 460% according to the analysis of tensile strength. Because a serious interface occurred at the dispersive phase of PLA sphere resulted from the process of nucleation and growth, it exhibited the low compatibility and tensile strength. Furthermore, as the PBS content was increased the Tan δ value and tensile strength were increased, indicating that the toughness of PLA was improved by the PBS blended with PLA.

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46

Tsou, Chi-hui, and 鄒智揮. "Investigation of preparation and Properties of Poly (lactic acid) / Biodegradable Polymer and Poly(lactic acid)/ Ethylene Glycidyl Methacrylate Copolymer." Thesis, 2012. http://ndltd.ncl.edu.tw/handle/50555601599675029440.

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博士
國立臺灣科技大學
材料科學與工程系
100
this study, Poly (lactic acid) (PLA) is modified with Poly (butylene adipate-co- terethphlate) (PBAT), Ethylene and Glycidyl Methacrylate Copolymer (EGMC) and FePol to improve the mechanical properties, respectively. The corresponding PLA blends were prepared by melt-blending PBAT, FP and EGMC with PLA. Several investigations, including Fourier transform infrared spectroscopy, Differential scanning calorimetry (DSC) , wide angle X-ray diffraction (WAXD), and thermal, dynamic, mechanical, and weight loss percentage analysis of the PLA/PBAT, PLA/FP and PLA/EGMC blends were performed to understand the significantly improved mechanical properties of the specimens. The presented work was divided into three parts: In the first part, the percentage crystallinity (Xc), peak melting temperature (Tm) and onset re-crystallization temperature (Tonset) values of PLA/PBAT specimens reduce gradually as their PBAT contents increase. However, it is worth noting that the Tg values of PLA molecules found by DSC and DMA analysis reduce to the minimum value as the PBAT contents of PLAxPBATy specimens reach 2.5 wt%. Further morphological and DMA analysis of PLA/PBAT specimens reveal that PBAT molecules are compatible with PLA molecules at PBAT contents equal to or less than 2.5 wt%, since no distinguished phase-separated PBAT droplets and tan δ transitions were found on the fracture surfaces and tan δ curves of PLA/PBAT specimens, respectively. In contrast to PLA, the PBAT specimen exhibits highly deformable properties. After blending proper amounts of PBAT in PLA, the inherent brittle deformation behavior of the PLA specimen was successfully improved. In the second part, the percentage crystallinity, peak melting temperature and onset re-crystallization temperature values of PLA/FP specimens reduce gradually as their FP contents increase. However, the glass transition temperatures of PLA molecules found by DSC and DMA reduce to the minimum value as the FP contents of PLAxFPy specimens reach 6 wt%. Further DMA and morphological analysis of PLA/FP specimens reveal that FP molecules are compatible with PLA molecules at FP contents equal to or less than 6 wt%, since no distinguished phase-separated FP droplets and tan δ transitions were found on fracture surfaces and tan δ curves of PLA/FP specimens, respectively. In contrast to PLA, the FP specimen exhibits highly deformable and tearing properties. After blending proper amounts of FP in PLA, the inherent brittle deformation and poor tearing behavior of PLA was successfully improved. In the third part, the tensile and tear strength values of PLAxEGMCy blown-film specimens in machine and transverse directions improve significantly, and reach their maximal values as their EGMC contents approach an optimum value of 6 wt. %. The melt shear viscosity values of PLAxEGMCy resins, measured at varying shear rates, are significantly higher than those of the PLA resin, and increase consistently with their EGMC contents. Differential scanning calorimetry (DSC) and dynamic mechanical analysis (DMA) of PLA and PLAxEGMCy specimens reveal that the percentage crystallinity, peak melting temperature, and onset re-crystallization temperature values of PLAxEGMCy specimens reduce gradually as their EGMC contents increase. In contrast, the glass transition temperatures of PLAxEGMCy specimens increase gradually in conjunction with their EGMC contents. Further DMA and morphological analysis of PLAxEGMCy specimens reveal that the EGMC molecules are compatible with PLA molecules at EGMC contents equal to or less than 2 wt. % because no phase-separated EGMC droplets and tan δ transitions were found on fracture surfaces and tan δ curves of PLAxEGMCy specimens, respectively.

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47

Rathi, Sahas R. "Toughening semicrystalline poly(lactic acid) by morphology alteration." 2013. https://scholarworks.umass.edu/dissertations/AAI3603142.

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For the first time, a physical method based on polymer crystallization is employed, to overcome the inherent brittleness of poly (L-lactic acid) (PLLA) by kinetically trapping a low Tg continuous amorphous phase. The decrease in mobility as a result of polymer crystallization is used to arrest the remaining polymer in the amorphous phase. This is achieved by melt blending and co-crystallizing a triblock copolymer with a configuration of the form PDLA-soft block-PDLA with PLLA. When crystallized from a temperature Tb, such that TmPLLA < Tb < Tm stereocomplex, the slow quiescent crystallization of PLLA and the preferential crystallization of the PLA stereocomplex results in formation of a morphology that can be described as stereocomplex crystals dispersed in a soft continuous amorphous phase containing the amorphous PLLA and the non-crystallized triblock copolymer. A systematic investigation of the effect of various parameters on the stereocomplex crystallization, morphology and properties of the PDLA-softblock-PDLA triblock copolymer/ PLLA blends is performed. These parameters include the chemical nature of the midblock, the triblock composition and the triblock architecture. The effect of addition of a molecular plasticizer as a third component to the blend to modify the properties of the amorphous phase is also investigated. Finally, varying functionality epoxy oligomers are investigated as additives to improve the hydrolytic stability and durability of the poly(lactic acid) based blends developed. Based on these studies, poly(lactic acid) based flexible, rubbery, semicrystalline materials containing a physically cross-linked network with the stereocomplex crystals acting as physical cross-links and the amorphous PLLA, triblock and plasticizer acting as mobile amorphous chains between the cross-links has been developed.

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48

Chen, Hsuan-Po, and 陳宣伯. "The Phase-Equilibria Thermodynamics and Dynamic Behavior of Poly(L-lactic acid)-Polyether-Poly(L-lactic acid) Triblock Copolymers in Aqueous Solutions." Thesis, 2019. http://ndltd.ncl.edu.tw/handle/a92b23.

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碩士
國立臺灣科技大學
材料科學與工程系
107
In this study, polyethylene glycol and L-lactide were used to synthesize poly(L-lactide)-poly(ethylene glycol)-poly(L-lactide) (PLLA-PEG-PLLA) triblock copolymers by ring-opening polymerization. The degree of polymerization of the hydrophilic segment PEG was fixed at 91. The molecular weight of the copolymers was analyzed by gel permeation chromatography (GPC), and the degree of polymerization of the hydrophobic segment PLLA was calculated to be 20, 40, and 75, respectively. The critical gelation concentration and the solution-precipitation phase transition temperature of each copolymer were measured by tube-inverting method. It was found that the copolymers favored the formation of a gel phase and possessed for solution-precipitation phase transition when the degree of polymerization of the hydrophobic segment of the copolymer increased. The rheological measurement was used to find the gel-solution phase transition temperature of the copolymers of different concentrations. It was found that copolymer solution was not conducive to the gel to solution phase change when the copolymer concentration was increased. The phase boundary in phase diagram was predicted by the Flory-Huggins mean-field theory. However, the precipitate phase of the copolymers in aqueous solutions at a high temperature could not be predicted. The phase boundary was shifted to the left as the degree of polymerization of the hydrophobic segment increased, and the Flory-Huggins interaction parameter at the critical point between copolymer and water changed from entropy control to enthalpy control as the degree of polymerization of the hydrophobic segment increased. The amphiphilic copolymer formed micelle in a selective solvent. Thus, the critical micelle concentration could be measured by the fluorescent probe and the Gibbs free energy of micellization was calculated. It was found that the copolymers favored the formation of the micelle when the degree of polymerization of the hydrophobic segment of the copolymer increased. The dynamic light scattering was used to find that in the aqueous solutions of the copolymers at the infinitely dilute concentration, as the degree of polymerization of the hydrophobic segment increased, the correlation length increased, the dynamic correlation delay time increased, and the tracer diffusion coefficient decreased. In dilute and semi-dilute solutions, the correlation length increased as the copolymer concentration increased, whereas oppositely the correlation length decreased as the homopolymer concentration increased. There was a significant difference between the copolymer and the homopolymer. We inferred that triblock copolymer produced the microstructure, and the repulsive force between the hydrophobic segments and the hydrophobic segments caused a shielding effect on copolymer-water interaction. At semi-dilute concentrations, the dependencies of correlation length upon temperature, degree of polymerization of the hydrophobic segment, and concentration were used to calculate the enthalpy of micelle aggregation. It was found that with the degree of polymerization of the hydrophobic segment increased, micelles were conducive to the aggregation. We found the enthalpy of micelle aggregation was smaller than that of gel-solution phase transition, and the enthalpy of gel-solution phase transition was smaller than that of solution-precipitation phase transition. Thus we knew the enthalpy changes of the copolymer molecules during the course of each phase transition. In dilute and semi-dilute solutions, as the concentration increased, the dynamic correlation delay time increased, and the cooperative diffusion coefficient decreased, whereas the cooperative diffusion coefficient of the homopolymer increased with the increase of the concentration. We concluded that this was due to the difference in the relative force between the polymer-solvent thermodynamic interaction and the polymer-solvent friction. However, as the concentration rose to concentrated regime, the cooperative diffusion coefficient of the copolymer increased with increasing concentration, which exhibited the same tendency as the homopolymer. It was also found that the correlation length of the concentrated solutions decreased with temperature, but the correlation length began to rise at higher temperatures, which was supposed to be caused by the sol-precipitation phase transition. Finally, the phase structures of various regions in the phase diagram was inferred from the change of the correlation length with the concentration and temperature in concentrated solutions.

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49

Li, Yung-Chung, and 黎元中. "The study of photocrosslinked poly(D,L-lactic acid-ethylene glycol-D,L-lactic acid) diacrylate nanogel." Thesis, 2004. http://ndltd.ncl.edu.tw/handle/czt2e3.

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50

Tsai, Hsien-Chi, and 蔡憲麒. "Electrospun Biomedical Nanocomposite Fibers of Poly(Lactic Acid)/Hydroxyapatite." Thesis, 2013. http://ndltd.ncl.edu.tw/handle/58139976746914203905.

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碩士
東海大學
化學工程與材料工程學系
102
The main purpose of this research is using a simple technique of electrospinning to prepare the PLA nano fibers and HA-PLA nano composite fibers, which as a scaffold of the three elements of tissue engineering for culturing osteoblast. The research divides into two parts: (A)The preparation of the fiber and composite fiber: To investigate the effect of solvent on electrospinning. DMF was added to chloroform in the ratio of D:C=1:4, the overall volatility of solvent was found decrease, and so that electrospinning can be carried out. Then the effects of various operating parameters were investigated. The images of SEM, showed that the diameter of spinning was mainly determined by the concentration of solution and the inner diameter of needle. Thus, approriate operating conditions were chosen in order to produce spun fibers with diameter approximating 400, 600 and 800 nanometers. By kepping the linear speed of the collecting drum at approximatedly 0.13, 5.17 and 10.50 m/s fiber membranes with orientational order parameter tensors approximately 0.06, 0.23 and 0.34 were obtained. To prepare composite fibers HSA was used as a surfactant to ensure the suspension of HA powder in chloroform and the suspension was then used to dissolve PLA until homogenous mixture was formed. The mixture was electrospun into nano composite fibers at the same conditions previously described. (B)The characterization of fibers: The content of HA powder in the composite fibers were calculated from the results of the TGA analysis. DSC analysis showed the degree of crystallinity increased with increasing fiber diameter. Crystallinity was also found increasing as the orientational order parameter tensors approached 0.5. The results of tensile analysis showed that when the orientational order parameter increased, Young’s modulus gained an increase of 200% to 300%. The Young’s modulus had a higher values when the diameter of fibers is smaller. In XRD analysis, the characteristic peaks of PLA and HA powder showed that the coexistence of both crystals with their inherent lattices. The final chapter, records the research about the effect of fibers orientation on the growth of osteoblast. The result showed that to an improved the survival or proliferated capacity of osteoblast accompanied with the increasing orientational order parameter of fibers, and the cell preferentially grew along the axis of fiber.

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