Dissertations / Theses on the topic 'Nanofilled composites'

2013/2014
The present thesis focused on nanofilled dental resins. The first year activity focused on depth of cure analysis of nanofilled composites. The second year activity focused on hardness, depth of cure and shrinkage stress analysis of bulk fill resin composites. The third year focused on degree of conversion and hardness of nanofilled resin cements.
XXVII Ciclo
1980

Carbon nanofillers such as graphite nanoplatelets (GNPs) and vapour grown carbon nanofibres (VGCNFs) have enormous potential for developing thermal interface materials (TIMs), mainly due to their high thermal conductivity. In this project GNPs, VGCNFs and carbon black (CB) fillers were dispersed in the compliant polymer matrices, rubbery epoxy and silicone, to form composites. Mechanical mixing, dual asymmetric centrifuge speed mixing, three-roll milling or combined sonication and solvent mixing were used to produce composites. The effects of processing technique, wt.% offiller(s), particle size and silane-functionalisation of fillers on the properties of composites were studied. Composites were characterised mainly in terms of morphology, texture, thermal conductivity, electrical conductivity and mechanical properties. The interfacial thermal transport performance of carbon nanofiller/polymer composites was studied using a steady state method, with a view to their use as 'thermal interface adhesives and thermal pads. Roll milling was found to be the best method for producing composites with superior transport properties. GNP/rubbery epoxy and GNP/silicone composites produced by roll milling have thermal conductivities in the range of 1-3 W/m.K with 8-25 wt.% GNP. The thermal conductivities of the composites increase with increasing GNP loading and particle size but slightly decrease with silane-functionalisation of GNPs. Composites produced using GNPs ) synthesised (in-ho~se) via graphite, oxidation and thermal exfoliation offered improved transport properties compared to corresponding composites produced with commercial GNPs. Development of good interconnects between carbon nanofillers was found to be vital for producing composites with improved transport properties. GNP/silicone composites are more compliant materials than GNP/rubbery epoxy composites. VGCNF/rubbery epoxy composites have thermal conductivities in the range of 0.2-1.8 W/m.K with 2-40 wt.% VGCNF. VGCNFs increase the compressive strength of both rubbery epoxy and silicone without compromising their compliant nature. The thermal conductivity of CB/polymer composites reached ~O.2-0.3 W/m.K with 8-36 wt.% CB, depending upon the CB used. CB incorporation improved dispersion of GNPs in hybrid CB/GNP/rubbery epoxy composites and produced a thermal paste-type morphology. Similarly, VGCNFs improved the dispersion of GNPs in GNPNGCNF/rubbery epoxy hybrid composites but reduced the density of interconnects between GNPs. GNP/rubbery epoxy and VGCNF/rubbery epoxy composites offered the best performance as thermal interface adhesives compared to CB/rubbery epoxy and commercial thermal interface adhesive. The thermal contact resistance of the adhesives depends on their viscosity/conformability, bond line thickness, filler particle size, surface roughness of the substrate and thermal conductivity.

PONTIFÍCIA UNIVERSIDADE CATÓLICA DO RIO DE JANEIRO
COORDENAÇÃO DE APERFEIÇOAMENTO DO PESSOAL DE ENSINO SUPERIOR
PROGRAMA DE SUPORTE À PÓS-GRADUAÇÃO DE INSTS. DE ENSINO
PROGRAMA DE SUPORTE À PÓS-GRADUAÇÃO DE INSTITUIÇÕES COMUNITÁRIAS DE ENSINO PARTICULARES
O nanocompósito estudado com função de revestimento anticorrosivo é constituído de Epóxi Novolac Tipo II aditivado com grafeno, sintetizado através do processo de esfoliação/redução do grafite empregando microondas. O sistema epóxi utilizado é composto pelos componentes: A, baseado em bisfenol F e cargas inorgânicas, e o B, endurecedor baseado em um polímero aminado. A síntese do grafeno e sua aditivação no componente A, foram realizadas pelo CTNano - UFMG. O principal objetivo desta dissertação é o estudo da aplicabilidade do nanocompósito, onde o grafeno é utilizado como aditivo complementar em matriz polimérica (epóxi), como alternativa de maximizar a proteção anticorrosiva. Foram estudadas diferentes aditivações: CR (sem aditivo), e aditivadas (0.1 por cento e 0.5 por cento). O substrato utilizado foi o aço carbono 1020, cuja superfície foi preparada com jateamento abrasivo e em seguida revestida com uma pistola de ar comprimido e com solvente para auxiliar o processo. Para avaliar a eficiência destes revestimentos foram realizados ensaios de corrosão (Célula Atlas e Ensaios Cíclicos), teste de aderência (Pull Off), medida de espessura (MEV) e rugosidade do substrato através do rugosímetro analógico e microscopia óptica. Para a dispersão do grafeno foi adicionado diglidil éter de bisfenol A (DGEBA) como um diluente. Os resultados obtidos indicaram que o grafeno apresentava boa dispersão na matriz polimérica. Concentrações de grafeno acima de 0,1 por cento em massa levam à falha da proteção anticorrosiva. Este comportamento pode estar relacionado à presença de solvente residual ou DGEBA não reagido no sistema com grafeno, além de possível atuação de grafeno agregado como ponto de tensão. O mecanismo de adesão revestimento/substrato permaneceu inalterado para todas as aditivações estudadas.
The studied nanocomposite with anticorrosive coating function is composed of Novolac Type II epoxy added with graphene, synthesized through the process of exfoliation / reduction of graphite using microwaves. The epoxy system used consists of the following components: A, based on bisphenol F and inorganic fillers, and B, hardener based on an amino polymer. The synthesis of graphene and its additivation in component A were performed by CTNano - UFMG. The main objective of this dissertation is the study of the applicability of the nanocomposite, where graphene is used as complementary additive in polymer matrix (epoxy), as an alternative to maximize anticorrosive protection. Different additives were studied: CR (without additive), and additives (0.1 percent and 0.5 percent). The substrate used was carbon steel 1020, the surface of which was prepared with abrasive blasting and then coated with a compressed air and solvent gun to aid the process. To evaluate the efficiency of these coatings were performed corrosion tests (Atlas Cell and Cyclic Tests), Pull Off test, thickness measurement (MEV) and roughness of the substrate through the analogous rugosimeter and optical microscopy. For the dispersion of graphene, diglycidyl ether of bisphenol A (DGEBA) was added as a diluent. The results indicated that graphene showed good dispersion in the polymer matrix. Concentrations of graphene above 0.1 percent by mass lead to failure of the anticorrosive protection. This behavior may be related to the presence of residual solvent or unreacted DGEBA in the graphene system, in addition to the possibility of aggregated graphene as voltage point. The coating / substrate adhesion mechanism remained unchanged for all additives studied.

The main aim of this work was to investigate the process-structure-property relationship of high density polyethylene (HOPE)/carbon nanofiller composites. A secondary aim was to develop thin thermoplastic films with enhanced electrical and mechanical properties for the potential use in aerospace applications. Three types of carbon nanofillers with different dimensions, multi-walled carbon nanotubes (MWCNTs), graphite nanoplatelets (GNPs) and carbon black (CB) respectively, were used to reinforce the polymer matrix. The melt-mixed HOPE/carbon nanofiller composites were processed by compression moulding, biaxial stretching and blown film extrusion, and the structure and properties of the resulting composites were characterised. The crystallinity and melting temperature of the material are barely influenced by the addition of carbon nanofillers, while the crystallization temperature is slightly increased due to a heterogeneous nucleation effect. The incorporation of carbon nanofillers has a positive effect on the modulus of the composites studied and a negative effect on the stress at break and strain at break. The relative effectiveness of generating rheological and conductive networks in the polymer is as follows: GNPs < CB < MWCNTs. The inclusion of carbon nanofillers led to significant strain hardening during the biaxial stretching of the material. The carbon nanofillers were further dispersed in the matrix by biaxial stretching. The mechanical properties of all the HOPE/carbon nanofiller composites were clearly improved after biaxial stretching. However, the volume resistivity of biaxially stretched HOPE/carbon nanofiller composites, at loadings lower than 4 wt%, was increased due to the deagglomeration of nanofillers and increased inter-particle distance. Blown films of the HOPE/MWCNT composites were manufactured at blow-up-ratios (BURs) of 2 to 3. The stress at break and strain at break of the composite films increases steadily with increasing BURs. Blown film extrusion also has a destructive effect on the conductive network of MWCNTs. However, there is no significant increase in the resistivity of the composite containing 8 wt% MWCNTs after film blowing at increasing BURs due to a sufficient density of nanotubes forming a robust conductive network .

Microfibrillar composites (MFCs) are advantageous polymer-polymer composites with in situ formed reinforcing fibrils. The range of applications of MFCs is limited by their low thermal resistance and me-chanical parameters of polymeric microfibres, which are formed by melt or cold drawing of the polymer blend. This study addresses improving MFCs based on HDPE matrix with 20% polyamide 6 microfibrils using organophilized montmorillonite. The complex effect of the nanofiller on the structure and parameters of the MFCs is investigated. When you are citing the document, use the following link http://essuir.sumdu.edu.ua/handle/123456789/35451

L’utilisation de composites à matrice thermodurcissable et fibres continues est en constante progression dans le secteur aéronautique, ferroviaire, et automobile. Afin d’améliorer les composites obtenus, notamment leur résistance à l’impact et leur conductivité électrique, des nanocharges organiques ou inorganiques peuvent être ajoutées. Les nanotubes de carbone (CNT) font partie des candidats les plus prometteurs pour le renforcement de composites à multi-échelle. Cependant, il s’avère difficile de contrôler la dispersion, la répartition et l’orientation des CNT, après les avoir mélangés aux prépolymères. Une nouvelle stratégie d’insertion des CNT dans un composite consiste à combiner des fibres de CNT avec des fibres de carbone. L’orientation et l’organisation structurelle des CNT au sein de la fibre permettent d’obtenir d’excellentes propriétés mécaniques et électriques. Dans notre étude, les propriétés de fibres contenant exclusivement des CNT, obtenues par direct spinning, ont été comparées à celles de fibres de carbone (non-ensimées, ensimées, et CNT en surface). Différentes interfaces entre les fibres de CNT, fibres de carbone et deux types de matrices époxy (de TG très différentes) ont été générées et testées par des essais de fragmentation de fibre dans la matrice. La contrainte de cisaillement interfaciale fibre/matrice a été évaluée afin de déterminer l’influence des diverses fibres et ensimages sur les performances mécaniques de composites à matrice organique et à fibres continues. En outre, la nature de l’adhésion et la qualité de l’interphase entre la matrice et la fibre ont été caractérisées par plusieurs techniques d’analyses et d’observations à multi-échelles
Nowadays, polymer-matrix composites reinforced with carbon fibers are increasingly used in the whole transport sector (aerospace, automotive and railway industries). However, the obtained parts still suffer from low impact resistance and low damage tolerance. To improve these properties, the matrix precursors have to be combined with organic or inorganic compounds to lead to multi-phased matrices. Among them, carbon nanotubes (CNT) are especially promising for targeting multi-scale reinforcement. Since high quality of the parts are required, continuous-fibers-reinforced composites can be produced by resin transfer molding (RTM) which also offers a reduced cost if compared with high temperature- and high pressure-based processes. However, RTM requires a very low viscosity of the polymer precursors and CNT-filled precursors are far too viscous to be injected on dry performs. In addition, this strategy does not allow for a control of the CNT location and orientation in the final part. In this study, innovative ways have been developed to insert CNT in the preform with local positioning and defined orientation. Deliveries of CNT in the matrix, from a neat carbon multi-nanotubes fiber produced by direct spinning, or from a CNT grown on carbon fiber were investigated in two types of epoxy matrices (with very different TG). Different polymer matrix/fiber interfaces have been generated using neat carbon multi-nanotubes fiber, CNT grown on carbon fiber and conventional carbon fiber, with or without sizing. A fine mechanical characterization of various fibers and particularly the measurement of single fiber interfacial properties have been performed in order to determine mechanical performance of continuous fiber reinforced composites. In addition, the nature of adhesion and quality of matrix/fiber interface have been fully evaluated by different multi-scale analyses and suitable microstructural observations

The thesis takes inspiration from the worldwide issues related to the shortage of critical raw materials (CRMs) and the need of finding sustainable alternatives to CRMs within fields and sectors strategic to the well-being and economy of industrialized countries. The research activity has been focused on the fabrication of Cu-matrix composites reinforced with carbon nanofillers, nano-graphite and graphene in particular. This class of composites attracts considerable interest as a consequence of the broad spectrum of applications Cu-MCs could find due to their thermal and electric conductivities, self-lubricating properties of graphite, cost-effectiveness and availability. Ball milling (BM) and spark plasma sintering (SPS) have been combined to provide an innovative methodology to fabricate Cu-MCs reinforced with carbon nanofillers enabling the fine dispersion of nanoparticles into the Cu matrix. Specifically, a two-stage cycle involving BM first and, then, SPS has been shown to result in the dispersion of graphite particles in relatively large Cu grains. The iteration of cycles allows the refinement of graphite nanoparticles and their dispersion in Cu powders on the microscopic scale, mostly at grain boundaries, and the subsequent incorporation of nanoparticles into Cu grains due to grain growth mechanisms activated and promoted by high temperatures during SPS. Molecular level mixing has been also tested to obtain Cu-MCs reinforced with graphene starting from liquid solutions of Cu nanoparticles and graphene. In particular, graphene was dispersed during the redox synthesis to obtain Cu nanopowder, subsequently consolidated by SPS. Despite the intrinsic different between the two methods, it has been possible to prepare Cu-MCs with graphite nanoparticles and graphene as dispersoids. Structural and microstructural characterization indicate that dispersoids are finely dispersed into the Cu matrix. Nanoindentation measurements clearly demonstrate the significant enhancement of mechanical properties, thus providing an important clue to the validity of the methodology developed.

Yes
This study investigates the interfacial characteristics between aggregates and cement paste matrix in nanofillers modified concrete. A three-point bend test on the specimens composed of two pieces of aggregates bonded with a thin layer of cement pastes with/without nanofillers was carried out to characterize the interfacial bond strength of the composites. The scanning electron microscope observations and energy dispersive x-ray spectrometry analysis were also performed to characterize the interfacial microstructures and compositions of the composites. The experimental results indicated that the nanocomposites have higher interfacial bond strength and narrower interfacial transition zone thickness as well as more optimized intrinsic compositions and microstructures than that of composites without nanofillers. Specifically, the interfacial bond strength of nanocomposites can reach 7.67 MPa, which is 3.03 MPa/65.3% higher than that of composites without nanofillers. The interfacial transition zone thickness of nanocomposites ranges from 9 μm to 12 μm, while that of composites without nanofillers is about 18 μm. The ratio of CaO to SiO2 in the interface of composites without nanofillers is 0.69, and that of nanocomposites increases to 0.75–1.12. Meanwhile, the nanofiller content in nanocomposite interface is 1.65–1.98 times more than that in the bulk matrix. The interfacial microstructures of nanocomposites are more compact and the content and crystal size of calcium hydroxide were significantly reduced compared with that of composites without nanofillers.
The National Science Foundation of China (51978127 and 51908103), and the China Postdoctoral Science Foundation (2019M651116).

Carbon fibre reinforced polymer (CFRP) composites are high performance materials which are widely used in various applications, such as aircraft and aerospace structures, satellites, advanced marine vessels, fuel tanks, sports equipment, high-end automobile structures and many other strength/weight critical applications. It is well known that CFRP composites are stronger in tension (in the fibre direction) than in compression, typically 30-40% higher. This is due to the fact that the compressive strength depends on the properties of the matrix and quality of the laminate, such as alignment of the fibres embedded in the matrix and void content. In theory, stiffer, stronger and tougher matrices provide better support to the carbon fibres (better resistance to fibre instability or microbuckling), hence enhancing the compressive properties of the CFRP composites. The aim of this study is to improve the properties of the CFRP composite by carefully selecting and incorporating nanofillers in the epoxy resin. The nanomodified-epoxy is then combined with continuous carbon fibres, which results in better overall structural response. The thesis is made up of two main parts i.e., examination of the thermal and mechanical properties of nanomodified-epoxies and investigation of mechanical properties of the nanofilled-CFRP composite with an emphasis on compressive behaviour. In the first part, a systematic experimental investigation is conducted in order to identify the optimum content and dispersion of nanofillers in the resin systems to be used in the fabrication of CFRP composite laminates. The effect of silica nanospheres, carbon nanotubes and clay nanoplatelets on the compressive, tensile, flexural and fracture toughness properties of epoxy polymers were studied. Two types of epoxy resin were used: Epikote 828 and Cycom 977-20. In addition, the thermal properties of the nanomodified-epoxies compared to the neat systems were also investigated. The results showed that the addition of nanosilica into the epoxy significantly enhanced the compressive, tensile and flexural moduli. Additionally, strength and fracture toughness properties were also improved without any significant reduction in failure strain and thermal properties of the epoxy. It was found that the mechanical performance of nanosilica-modified Epikote 828 system was comparable to that of the commercial high-performance Cycom 977-20 polymer. The Halpin-Tsai model was modified to include the effect of particle volume fraction on the shape factor ~ that appears in the equation for predicting the Young's modulus of the nanoreinforced-resin. In the second part of the investigation, the effect of nanosilica on the compressive and in-plane shear properties of HTS40/828 CFRP composite was studied. A number of [O]s and [±45b laminates were fabricated using dry filament winding, wet resin impregnation and vacuum bagging techniques. The quality of the laminate such as fibre distribution, fibre misalignment, void content, fibre and nanosilica volume fraction was examined and measured. Static uniaxial compression and tensile tests on [O]s and [±45b laminates were performed. It was found that the compressive and in-plane shear properties of nanomodified CFRP were better than the neat system. For example, the addition of 7 vol% nanosilica improved the unidirectional (UD) compressive modulus and strength of the HTS40/828 composite by 40% and 54%, respectively. The compressive strength was also predicted using several analytical models based on fibre micro buckling and fibre kinking fracture mechanisms. One of the existing fibre microbuckling models was modified in this work to better account for the non-linear resin response. The predicted values showed that the UD nanomodified-FRP laminate exhibited a better compressive strength compared to that of the neat composite system. In addition, the results demonstrated that the performance of the nanosilica-filled HTS40/828 composite was comparable to that of the commercially available HTS40/977-2 system, which is currently used by the aircraft industry.

Ever since the discovery of carbon nano materials like carbon nanotube (CNT) and graphene, this class of materials has gained significant attention due to their exotic properties. The principle idea of my present research project is to understand the novel improvements induced in polymer matrices with inclusion of the nanofillers. This thesis is thematically divided into three parts. In the first part we introduce principle materials that we use for preparation of composites. Methods of nanofiller preparation and different nanocomposites as previously reported in literature are discussed to formulate the basis of our study. Different dispersion techniques are discussed which facilitate uniform nanofiller distribution. A variety of experimental methods are described which were employed to investigate the structure and properties of the composites. In the second part we discuss in details polyamide-12 (PA12) composites using CNT and graphene as fillers. A marked improvement is recorded in the toughness of the films with incorporation of CNT, dispersed in PA12 using a surfactant. Electrical percolation is also achieved in the otherwise insulating matrix. With PA-12 fibers we explored the effect of fiber processing and CNT incorporation in the mechanical properties. Extensive wide angle x-ray diffraction was carried out to interpret the structural modifications brought about by CNT in the matrix. The final part of the thesis deals with a thermosetting polymer, epoxy composites. CNT, Graphene and also a mixture of the two nanofillers were used as reinforcing agents. Appreciable improvement was recorded in the mechanical properties, electrical and thermal conductivity of the composites. Detailed optical and electron microscopy was carried out to get a vivid idea of the micro-structure and dispersion. The presented work demonstrates the significant ability of carbon nanofillers to reinforce polymer matrices enhancing their mechanical, electrical and thermal properties and opening a wide horizon for a variety of applications.

This thesis designed and tested a series of titanate nanofillers enhanced polycaprolactone (PCL) composites. The significance of the homogeneity of the nanofiller in terms of printability and mechanical strength were evaluated. By grafting functional groups, the nanofiller surface has shown an improved hydrophobicity, which improved their dispersion in the PCL matrix. Therefore, the addition of functionalized nanofillers has not only enhanced the mechanical properties of the composites but has also made the composites 3D printable. Besides, the PCL composites have shown minimal cell toxicity indicating a great potential in the field of customized 3D printing for biomedical applications.

2012 - 2013
Inspection and Maintenance are important aspects when considering the availability of aircraft for revenue flights. Modern airframe design is exploiting new exciting developments in materials and structures to construct ever more efficient air vehicle able to enable efficient maintenance. The improvement in the aircraft safety by advanced structures and protecting nanofillers is a revolutionary approach that should lead to the creation of novel generation of multifunctional aircraft materials with strongly desired properties and design flexibilities. In recent years, the development of new nanostructured materials has enabled an evolving shift from single purpose materials to multifunctional systems that can provide greater value than the base materials alone; these materials possess attributes beyond the basic strength and stiffness that typically drive the science and engineering of the material for structural systems. Structural materials can be designed to have integrated electrical, electromagnetic, flame resistance, and possibly other functionalities that work in synergy to provide advantages that reach beyond that of the sum of the individual capabilities. Materials of this kind have tremendous potential to impact future structural performance by reducing size, weight, cost, power consumption and complexity while improving efficiency, safety and versatility. It is a well-known fact that, actually, also a very advanced design of an aircraft has to take required inspection intervals into account. An aircraft with inherent protective abilities could help to significantly extend the inspection intervals, thereby increasing aircraft availability. The challenge in this research is to develop and apply a multifunctional composite for structural applications. The aim of this project is the formulation, preparation and characterization of structural thermosetting composites containing dispersed protective nanofillers. This project specifically targets composites tailored for multifunctional applications such as lightning strike protection, and flame resistance. These composites were designed to enable their application on next generation aircrafts. With regard to the objectives of this PhD project the multifunctional composite systems were developed with the aim of overcoming the following drawbacks of the composite materials: • reduced electrical conductivity; • poor flame resistance. The thermosetting material was projected considering compatibility criteria so that to integrate different functions into a material that is capable of bearing mechanical loads and serves as a structural material element. [edited by author]
XII n.s.

This masters’s thesis study electric properties of nanocomposites based on epoxy resins, production of samples and measuring their electrical properties. In this thesis there are observed temperature dependences of the dissipation factor, relative permittivity and internal resistivity.

In this study, polypropylene (PP) based nanocomposites were prepared by incorporating different kinds and amounts of silica nanoparticles and graphite nanoplatelets (GNP). The role of various percentages of compatibilizer polypropylene grafted with maleic anhydride (PPgMA) into PP nanocomposites was also investigated. In order to analyze the effect of the manufacturing process on the material’s properties, the samples were produced by (i) melt compounding and compression molding and (ii) extrusion and injection molding. It was found that injection molding provides significantly greater stiffness and strength compared to compression molding for all types of PP nanocomposites. Several characterization techniques were used in order to correlate the microstructure to the physical and mechanical properties of the materials. Both silica and GNP were found to be effective nucleating agents, significantly increasing the crystallization rate during isothermal crystallization and favoring the nucleation of the the β- phase, which manifests superior impact strength and toughness compared to the most common α-form crystals. Graphite nanoplatelets were found more efficient in inducing polymorphism and favoring the formation of a transcrystalline phase on the filler surface. A significant correlation between the tensile modulus, glass transition temperature and the amount of constrained phase, as assessed through tensile and DMA analyses, revealed the presence of a secondary reinforcing mechanisms, which, concurrently to the primary stiffening effect of the high modulus filler, contributes to the enhancement of the bulk properties. A complex constrained phase, responsible for providing a secondary reinforcing mechanism, was modeled as immobilized amorphous and transcrystalline regions located at the filler surface. The non-linear viscoelastic creep of the composites, successfully studied by the application of the time strain superposition principle (TSSP), showed a considerable enhancement of the creep stability in nanocomposites with respect to unfilled PP, especially for higher creep stresses. The study of creep dependance on the temperature showed that the stabilizing effect provided by the nanoparticles was more effective at high temperatures and, considering the time temperature superposition principle (TTSP), at long loading times. The equivalence between the time strain- and time temperature- superposition principle was substantiated by comparing the correspondent superimposed master curves. The nanofilled PP matrices have also been used for the preparation of microcomposites reinforced with short glass fibers (GF). Interfacial shear strength (ISS) was measured by means of the single fiber fragmentation test on various PP/GF microcomposites. Results show that the strength at the fiber/matrix interface can be remarkably increased when using nanocomposite systems, especially in the case of dimethyldichlorosilane-functionalized silica nanoparticles and GNP platelets, and that the improvement is further increased when the nanoparticles are used in combination with PPgMA. The thermodynamic fiber/matrix work of adhesion, estimated by contact angle measurements, showed a good correlation with the ISS values. Hybrid composites reinforced with short glass fibers and nanofillers were produced and characterized in order to investigate how the morphology and the mechanical properties of the composites were affected by the combined effect of two fillers of rather different size scales (i.e. micro- and nano- scale). The stronger fiber/matrix adhesion combined with the enhancement of the matrix properties resulted in superior tensile properties and impact resistance and improved viscoelastic behavior. As means of comparison, thermosetting hybrid composites based on epoxy resin were also produced by incorporation of GNP and short GF.

Orientador: Debora Alves Nunes Leite Lima
Dissertação (mestrado) - Universidade Estadual de Campinas, Faculdade de Odontologia de Piracicaba
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Resumo: O objetivo deste estudo in vitro foi avaliar as propriedades físicas de uma resina composta nanoparticulada submetida ao envelhecimento artificial acelerado (AAA), ação de agentes clareadores e manchamento extrínseco. O estudo foi dividido em 2 experimentos. O experimento 1 avaliou a influência do AAA e do peróxido de carbamida a 16% com diferentes espessantes na retenção do brilho (GU), cor (?E), microdureza (KHN) e rugosidade média (Ra) de superfície do compósito. A análise qualitativa da superfície de resina foi realizada através de microscopia de força atômica. Cem amostras cilíndricas (7,0mm x 2,0mm) foram confeccionadas e distribuídas aleatoriamente em 10 grupos (n=10). Somente metade dos grupos foram envelhecidos. Para o tratamento clareador/espessante, os grupos com e sem AAA foram divididos em: peróxido de carbamida 16% (PC) com carbopol, PC com natrosol, gel de carbopol, gel de natrosol e sem tratamento (controle). Os dados obtidos foram analisados por meio de ANOVA dois fatores e teste de Tukey. Para o ?E as comparações múltiplas foram realizadas pelos teste de Tukey e Dunnett. Os valores de rugosidade foram analisados pelos testes de Kruskal Wallis, Dunn e Mann Whitney. O nível de significância considerado foi de 5%. O PC com carbopol promoveu redução apenas na microdureza do compósito, diferindo estatisticamente do controle. Para o PC com natrosol esta alteração não foi observada. O PC com carbopol aumentou a rugosidade e diminuiu o brilho das resinas envelhecidas, enquanto o natrosol só o briho foi reduzido, diferindo estatisticamente do grupo controle. O Experimento 2 avaliou a influência dos tratamentos clareadores em diferentes concentrações e manchamento com café na propriedades físicas anteriormente citadas da resina nanoparticulada, submetidas ou não ao AAA. Duas amostras representativas de cada grupo foram avaliadas em microscopia eletrônica de varredura. Cento e vinte amostras cilíndricas foram confeccionadas, semelhante ao estudo anterior, distribuídas em 12 grupos (n=10). Metade das amostras foram envelhecidas artificialmente. Para o tratamento clareador/pigmentação, os grupos com e sem AAA, foram divididos em: peróxido de carbamida a 10% (PC 10%), peróxido de hidrogênio a 35% (PH 35%) e sem tratamento clareador, com e sem pigmentação por café. Os dados foram coletados e submetidos a ANOVA três fatores e teste de Tukey para comparações múltiplas. Para o ?E as comparações múltiplas foram realizadas pelos testes de Tukey e Dunnett (?=0,05). Nas resinas sem envelhecimento, os agentes clareadores reduziram a microdureza do compósito, entretanto a rugosidade, brilho e cor não apresentaram alterações. Após o envelhecimento, o PC 10% aumentou a rugosidade e diminuiu o brilho comparado ao PH 35%. A pigmentação também reduziu a microdureza das resinas sem e com envelhecimento e alterou a cor das resinas envelhecidas (?E>25). Portanto, a ação dos géis clareadores reduziu a microdureza do nanocompósito, sendo que a composição do gel clareador influenciou nessa alteração. O AAA promoveu significativas alterações nas propriedades físicas avaliadas, além de favorecer uma maior degradação da superfície da resina pelo agente clareador e este efeito contribuiu para um maior manchamento extrínseco
Abstract: The aim of this in vitro study was to evaluate the physical properties of a nanocomposite subjected to artificial accelerated aging (AAA), to the action of bleaching agents and to extrinsic staining. This study was divided into two experiments. Experiment 1: evaluate the influence on a composite surface of AAA and 16% carbamide peroxide with different thickeners, in gloss retention (GU), color (?E), microhardness (KHN) and roughness (Ra). Qualitative analysis of the resin surface was performed by atomic force microscopy. One hundred cylindrical samples (7.0mm x 2.0mm) were prepared and randomly divided into 10 groups (n = 10). Only half of the groups were aged. For the bleaching/thickening treatment, the groups with and without AAA were divided into groups/ treatments: 16% carbamide peroxide (PC) with carbopol, PC natrosol, carbopol gel, natrosol gel and untreated (control). Data were submitted to two-way ANOVA and Tukey¿s test for multiple comparisons. The multiple comparisons for ?E were performed by using Tukey¿s and Dunnett¿s tests, and roughness values was analysed by using Kruskal-Wallis, Dunn¿s, and Mann-Whitney¿s tests (? =0.05). The PC with carbopol promoted a decreased in the composite microhardness differing significantly from the control. As for CP + natrosol this change in the microhardness was not observed. The treatment with CP + carbopol increased the roughness and decreased the gloss of the aged resins, whereas natrosol reduced only the gloss which differed statistically from the control. Experiment 2: evaluate the influence of bleaching treatments with different concentrations and coffee staining, in the physical properties of nanocomposite, submitted or not to AAA. Two representative samples of each group were evaluated in scanning electron microscopy (SEM). One hundred twenty cylindrical samples were prepared similar to the previous study and divided into 12 groups (n = 10). Half of specimens were artificially aged. For the bleaching/pigment treatment, groups with and without AAA, were divided into the following groups: 10% carbamide peroxide (10% CP), 35% hydrogen peroxide (35% PH) without bleaching treatment, with and without pigmentation of coffee. Data were submitted to three-way ANOVA and Tukey¿s test for multiple comparisons. The multiple comparisons for ?E were performed by using Tukey¿s and Dunnett¿s tests (?=0,05). The resins without aging, the bleaching agents promoted a reduction in the composite microhardness, however, in the roughness, gloss and color this changes were not observed. After aging, the pigmentation also reduced the microhardness of the resins with and without aging and altered the color of the aged resins (?E> 25). 10% PC increased roughness and decreased gloss compared to 35% PH. Pigmentation also reduced the microhardness of the resins with and without aging and change the color of the aging resins (?E> 25). The action of bleaching agents reduced the microhardness of the nanocomposite, and this alteration was influenced by the composition of the bleaching gel. The AAA promoted significant changes in the evaluated physical properties and favored the further deterioration of the resin surface by the bleaching, contributing to a greater extrinsic staining
Mestrado
Dentística
Mestra em Clínica Odontológica

Il trattamento efficace della pulpite e/o della parodontite continua ad essere una sfida nella pratica clinica soprattutto in relazione all’invecchiamento della popolazione. Quest’ultimo è un fenomeno fisiologico che si verifica con il tempo e che impedisce la normale funzionalità degli organi, ostacolando l'omeostasi dei tessuti e delle attività fisiologiche. Inoltre, è ben noto che le cellule senescenti influenzano significativamente il loro microambiente, poiché secernono molecole pro-infiammatorie e degradative. Gli approcci di medicina rigenerativa potrebbero soddisfare le necessità di nuove terapie per tali patologie e di conseguenza risulta importante poter valutare sia le ripercussioni legate età sulle potenzialità di Cellule Stromali/Staminali Mesenchimali (MSC) nonché gli effetti legati al microambiente. Nello specifico, poiché le cellule Staminali/Stromali derivate dalla Polpa Dentale (DPSC) rappresentano un buon candidato per le terapie restaurative del cavo orale, lo studio del loro potenziale rigenerativo età correlato potrebbe essere fondamentale per lo sviluppo di trattamenti sempre più personalizzati in una società che invecchia. I nostri studi in vitro sono stati inizialmente indirizzati a valutare i cambiamenti morfologici, proliferativi e differenziativi verso i fenotipi mesenchimali, odontoblastici e neuronali di cellule della polpa dentaria (hDPSC) isolate da soggetti di età diversa. Successivamente, abbiamo studiato gli effetti di un microambiente età correlato sul comportamento biologico di hDPSC ottenute sia da individui giovani che da soggetti anziani. Dalle analisi citofluorimetriche, immunoistochimiche, e di espressione genica mediante Real Time PCR (qRT-PCR) e western blotting è emerso un declino sia della capacità proliferativa che e del potenziale differenziativo con l'avanzare dell’età dei donatori. Inoltre, è stato possibile riscontrare modificazioni età correlate della capacità di mineralizzazione della matrice extracellulare in seguito a stimoli odontogenici e osteogenici. Anche il differenziamento in senso neuronale ha evidenziato cambiamenti età correlati. Infine, la presenza di un microambiente età-correlato ha mostrato effetti significativi sul comportamento di hDPSC isolate da soggetti giovani e anziani. Successivamente, nell’ottica di combinare l'odontoiatria restaurativa convenzionale con le recenti tecniche rigenerative, si è voluta testare la biocompatibilità in vitro di un composito dentale nanoriempito di ultima generazione (Filtek Supreme XTE), comunemente usato in odontoiatria. Anche in questo caso sono stati analizzati la capacità proliferativa, l'apoptosi e il potenziale differenziativo in senso odontogenico delle hDPSC, nonché la loro capacità di mineralizzare la matrice. I nostri dati hanno dimostrato che Filtek Supreme XTE influenza e/o ritarda i processi di differenziamento e mineralizzazione della matrice da parte delle hDPSC rispetto ai controlli rappresentati sia cellule messe a contatto con la dentina sia da hDPSC coltivate in plastica. Questa sperimentazione preliminare, eseguita con cellule provenienti da individui giovani, pone le basi per futuri studi con cellule ottenute da soggetti anziani utili allo sviluppo di materiali bioattivi adatti ad una popolazione che invecchia. In conclusione, i nostri studi hanno confermato che le caratteristiche biologiche delle hDPSC possono risultare compromesse dai fenomeni di invecchiamento, probabilmente anche in relazione a fattori presenti nel microambiente in grado di modulare l’attività cellulare. Queste osservazioni risultano utili per lo sviluppo di terapie personalizzate che mirano alla rigenerazione di osso, polpa dentaria e dentina, nonché per l’applicazione in medicina rigenerativa del trattamento di disturbi neurologici. Nell’ambito dell’odontoiatria conservativa, è da tenere inoltre in considerazione che l’esposizione a lungo termine delle hDPSC con i compositi nanoriempiti sulle potrebbe ritardare in modo significativo e perfino interrompere il loro di differenziamento in senso odontogenico e/o la mineralizzazione della matrice extracellulare. Questi dati sono di rilevanza clinica, poiché nelle lesioni traumatiche o cariose, le cellule della polpa potrebbero avere una ridotta capacità rigenerativa in un tessuto dentale vulnerabile, specialmente in un soggetto anziano.
Uncomplicated dental treatments for pulpitis and periodontitis continues to be challenging especially in elderly, and regenerative approaches could meet this contingency. Ageing is a physiologic phenomenon occurring with time, which hamper the organs’ functional capacity that normally maintains tissue homeostasis and physiological responses. Moreover, it is well known that aged cells significantly affect their microenvironment, as they secrete pro-inflammatory and matrix-degrading molecules. The impact of these factors on Mesenchymal Stem/Stromal Cells (MSCs) could be also of interest for a better understanding of the age-related regenerative potential. Since Dental Pulp Stem/Stromal cells (DPSCs) represent a good candidate for oral restorative therapies, the study of age-related changes in their recovering capability could be crucial for developing customized treatments for an ageing society. In our in vitro investigations, we firstly analysed changes in the morphology, proliferation, and differentiation toward mesenchymal, odontoblastic and neuronal phenotypes of human DPSCs (hDPSCs) harvested from differently aged donors. Then, we studied the effects of an age-related microenvironment on the biological performances of hDPSCs isolated from young and old subjects. Cytofluorimetric, immunohistochemical, quantitative reverse‐transcription polymerase chain reaction (qRT‐PCR), and western blot analyses were performed. We observed a decline in hDPSCs proliferation and differentiation potential with age. Moreover, these cells showed distinct age‐related mineralization capabilities as well as neurogenic differentiation. In addition, cell-conditioned media from an age-related microenvironment was able to modify the behaviour of hDPSCs isolated from young or old subjects. Later, aimed to combine the conventional restorative dentistry with the recent regenerative techniques, the in vitro impact of a commonly used nanofilled composite (Filtek Supreme XTE) on hDPSCs was taken into account. In this research, proliferation, apoptosis, differentiation ability as well as matrix mineralization, of hDPSCs cultured in the presence of a nanofilled composite were examined. Our data demonstrated that Filtek Supreme XTE affects and delays hDPSCs differentiation and mineralization processes when compared to a control group with dentin-slices as well as in tissue culture plates. This initial approach performed with young cells paves the ways for future studies with hDPSCs derived from old subjects, in order to develop a bioactive material customised for an ageing population In conclusion, our results confirmed that ageing differently impaired hDPSCs biological properties and local factors may modulate these processes. Our observations represent a valid tool for the development of tailored regenerative strategies in an ageing society.

Ce travail de thèse porte sur la compréhension du rôle polyvalent des liquides ioniques (LIs) phosphonium comme agents de nanostructuration et interfaciaux pour la matrice polymère fluorée poly(fluorure de vinylidène-chlorotrifluoroéthylène) (P(VDF-CTFE)). Dans un premier temps, deux LIs phosphonium avec des fonctionnalités différentes générant un encombrement stérique et des fonctions dipolaire additionnelles sont tout d'abord incorporés dans la matrice P(VDF-CTFE) pour préparer des films de polymère additives. La structure de la phase cristalline, la morphologie issue de la dispersion et le comportement de cristallisation sont finement caractérisés dans le but de fournir une compréhension fuie et complète du rôle joué par le LI sur la nanostructuration. Dans un second temps, le rôle d’agent interfacial du LI est étudié avec un LI phosphonium fluoré comprenant un cation combinant trois phényles et une chaîne fluorée courte.Ce LI est utilise pour modifier la surface de l'oxyde de graphène (GO) et de l'oxyde de graphène réduit (rGO) afin de rendre ces nanocharges fonctionnelles et les incorporer dans la matrice P(VDF-CTFE). Ainsi, des films composites de P(VDF-CTFE)/graphène avec différentes teneurs en nanocharges sont préparés et une caractérisation fuie de la structure et des propriétés est entreprise afin de mieux comprendre les mécanisme d’interaction interfaciale et leurs influences sur les films composites, tels que la structure de la phase cristalline, le comportement de cristallisation, la relaxation des chaînes, la morphologie et les propriétés diélectriques finales
This thesis work deals with an understanding of the versatile roles of phosphonium ionic liquids (ILs) as nanostructuration and interfacial agents for the fluorinated polymer matrix, i.e.,poly(vinylidene fluoride-chlorotrifluoroethylene) (P(VDF-CTFE)). In this context, two phosphonium ILs with different functionalities in steric hindrance and extra dipolar groups are firstly incorporated in P(VDF-CTFE) matrix to prepare polymer films. The crystalline phase structure, dispersion morphology and crystallization behavior are finely characterized with the goal of providing a full and deep understanding of the versatile and tunable nanostructuration effect of phosphonium ILs. Subsequently, in order to elucidate the mechanism of interfacial influence of IL, a fluorinated phosphonium IL with a cation structure combining three phenyls and a short fluorinated chain is added on the surface of graphene oxide (GO) and reduced graphene oxide (rGO), making them as functional nanofillers to be incorporated into P(VDF-CTFE) matrix. Thus,P(VDF-CTFE)/graphene composite films with different filler contents are prepared in order to investigate the mechanism of interfacial interaction and its influence on the composite films, such as crystalline phase structure, crystallization behavior, chain segmental relaxation behavior, dispersion morphology and the final dielectric properties

Ce travail a porté sur la caractérisation et la quantification en 3D de la répartition de charges de différents types (nanoparticules, nanotubes, etc.) dans des matrices polymères. Nous nous focalisons sur les techniques de tomographie en microscopie électronique. Une approche multiple en tomographie électronique a été réalisée : la tomographie en FIB/MEB (faisceau d’ions focalisé/microscope électronique à balayage), la tomographie en MEB et la tomographie en MET (microscope électronique en transmission). Les nanocomposites polymère sont généralement élaborés aux fins d’améliorer les propriétés physiques (mécanique, électrique, etc.) du matériau polymère constituant la matrice, grâce à une addition contrôlée de charges nanométriques. La caractérisation de tels matériaux, et l’établissement de corrélations précises entre la microstructure et les propriétés d’usage, requièrent une approche tri-dimensionnelle. En raison de la taille nanométrique des charges, la microscopie électronique est incontournable. Deux systèmes de nanocomposite polymère ont été étudiés par une approche multiple de tomographie électronique : P(BuA-stat-S)/MWNTs (copolymère statistique poly (styrène-co-acrylate de butyl) renforcé par des nanotubes de carbone multi-parois), et P(BuA-stat-MMA)/SiO2 (copolymère statistique poly(butyl acrylate-co-methyl methacrylate) renforcé par des nanoparticules de silice). Par combinaison de divers techniques, la caractérisation et la quantification des nanocharges ont été possibles. En particulier, la taille, la fraction volumique et la distribution des charges ont été mesurées. Cette étude a ainsi fourni des informations en 3D qui contribuent à mieux comprendre les propriétés des nanocomposites. Une attention particulière a été portée aux artefacts et causes d’erreur possibles durant l’étape de traitement 3D. Nous avons également essayé de comparer les différentes techniques utilisées du point de vue de leurs avantages et inconvénients respectifs, en dégageant des possibilités d’amélioration future
This work is focused on the characterization and quantification of the 3D distribution of different types of fillers (nanoparticles, nanotubes, etc.) in polymer matrices. We have essentially used tomography techniques in electron microscopy. Multiple approaches to electron tomography were performed: FIB-SEM (focused ion beam/scanning electron microscope) tomography, SEM tomography and TEM (transmission electron microscope) tomography. Polymer nanocomposites are basically synthesized in order to improve the physical properties (mechanical, electric, etc.) of the pure polymer constituting the matrix, by a controlled addition of fillers at the nanoscale. The characterization of such materials and the establishment of accurate correlations between the microstructure and the modified properties require a three-dimensional approach. According to the nanometric size of the fillers, electron microscopy techniques are needed. Two systems of polymer nanocomposites have been studied by multiple electron tomography approaches: P(BuA-stat-S)/MWNTs (statistical copolymer poly(styrene-co-butyl acrylate) reinforced by multi-walled carbon nanotubes) and P(BuA-stat-MMA)/SiO2 (statistical copolymer poly(butyl acrylate-co-methyl methacrylate) reinforced by silica nanoparticles). By combining various techniques, the characterization and the quantification of nanofillers were possible. In particular, statistics about size, distribution and volume fraction of the fillers were measured. This study has then provided 3D information, which contributes to a better understanding of properties of the nanocomposites. Attention has been paid to analyze carefully original data, and artifacts and causes of errors or inaccuracy were considered in the 3D treatments. We also attempted to compare benefits and drawbacks of all techniques employed in this study, and perspectives for future improvements have been proposed

碩士
國立聯合大學
電機工程學系碩士班
104
In power systems, insulators can ensure the isolation between the transmission line and the ground, therefore the stability of the power systems is closed related to the insulation characteristics of insulators. Insulation characteristics of the insulators mainly depend on the material used in insulator manufacturing, the shape design of the insulators and the coating conditions on the surface of insulators. In addition to the traditional porcelain insulators, the polymer insulators are also widely used in power systems. The contour design can improve the tangential electric field of the surface of the insulators to decrease the probability of the surface flashover of the insulators. The coating on the surface of the insulators can enhance the hydrophobicity on the surface of the insulators to improve the insulation performance of insulators. After measuring the samples of the epoxy resin filled with nanoparticles, the breakdown voltage increases with the thickness of the samples. The dielectric constant of samples are positive correlated to the density of the filler in the samples. The samples with 5 wt% SiO2 nanoparticles have the highest breakdown voltage and the samples with 5 wt% Al2O3 nanoparticles have the more stable failure rate. In the samples groups of 5 wt% nanoparticles, the samples with calcination of mixed SiO2 and Al2O3 have higher dielectric constant. The contour design of insulators is performed by the genetic algorithm merged with the charge simulation method. The optimal contour of the insulators changes with the constraints. The results of insulator coating with RTV silicone rubber shows that the BaTiO3 3 wt% filled can get the best hydrophobicity, and the smallest leakage current occurs at the BaTiO3 10 wt% filled.

Over the past years, research efforts have focused on adding highly conductive nanoparticles, such as carbon nanotubes (CNTs) and graphene nanoplatelets (GNPs), into polymers to improve their electrical conductivity or to tailor their piezoresistive behavior. Resultant materials are typically described by the weight or volume fractions of their nanoparticles. The weight/volume fraction alone is a very global quantity, making it a poor evaluator of a doping configuration. Knowing which particles actually participate in improving electrical conductivity can optimize the doping strategy. Additionally, conductive particles are only capable of charge transfer over a very short range, thus most of them do not form part of the conduction path. Thus, understanding how these particles are arranged is necessary to increase their efficiency. First, this work focuses on polymers loaded with CNTs. A computational modeling strategy based on a full morphological analysis of the CNT network is presented to systematically analyze conductive networks and show how particles are arranged. A definition of loading efficiency is provided based on the results obtained from this morphology analysis. This study provides useful guidelines for designing these types of materials based on important features, such as representative volume element, nanotube tortuosity and length, tunneling cutoff distance, and efficiency. Second, a computational approach is followed to study the conductive network formed by hybrid particles in polymer nanocomposites. These hybrid particles are synthesized by growing CNTs on the surfaces of GNPs. The objective of this study is to show that the higher electrical conductivity of these composites is due to the hybrids forming a segregated structure. Polymers loaded with hybrid particles have shown a higher electrical conductivity compared with classical carbon fillers: only CNTs, only GNPs or mixed CNTs and GNPs. This is done to understand and compare the doping efficiency of the different types of nanoparticles. Finally, some parameters of the hybrid particle are studied: CNT density on GNPs, and CNT and GNP geometries. Recommendations to further improve the composite’s conductivity based on these parameters are presented. It is noted that this work is the first time the hybrid particle is studied through a computational approach.