Dissertations / Theses on the topic 'Plastic foams'

Title from PDF of title page (University of Missouri--Columbia, viewed on Feb 25, 2010). The entire thesis text is included in the research.pdf file; the official abstract appears in the short.pdf file; a non-technical public abstract appears in the public.pdf file. Dissertation advisor: Dr. Fu-hung Hsieh. Vita. Includes bibliographical references.

Thesis (Ph. D.)--Hong Kong University of Science and Technology, 2002.
Includes bibliographical references (leaves 154-166). Also available in electronic version. Access restricted to campus users.

Thesis (M. S.)--Materials Science and Engineering, Georgia Institute of Technology, 2009.
Committee Chair: Gall, Ken; Committee Co-Chair: McDowell, David; Committee Member: Guldberg, Robert; Committee Member: Sanderson, Terry; Committee Member: Shofner, Meisha; Committee Member: Tannenbaum, Rina.

A series of four water-blown flexible polyurethane foams was produced in which the water content was varied from 2 to 5 pph at a constant isocyanate index of 110. A portion of each foam was thermally compression molded into a plaque. The morphology of the foams and plaques was investigated using DMS, DSC, FTIR, TEM, SEM, swelling, WAXS, and SAXS. A high degree of phase separation occurs in these foams and the degree of phase separation is independent of water (hard segment) content. In the foam with the lowest water content the morphology is similar to that of typical segmented urethane elastomers. Small hard segment domains are present with a correlation distance of roughly 7.0 nanometers. When the water content is increased a binodal distribution of hard segments appears. There are the small hard segment domains typical of segmented urethane elastomers as well as large hard segment aggregates greater than 100 nanometers in diameter. The large domains are thought to be aggregates of polyurea that precipitated during the manufacture of the foam. The foam making process successfully incorporated the trifunctional polyols into a network indicating a high degree of polymerization for the hydroxyl-isocyanate reaction. Unreacted isocyanate is present in the foams a month after curing. It is believed to be trapped in the large urea aggregates. WAXS patterns of the foams suggest hard segment ordering that may be of a paracrystalline nature but certainly lacking in true crystallinity.
Master of Science

Thesis (M. Phil.)--Hong Kong University of Science and Technology, 2004.
Includes bibliographical references (leaves 63-67). Also available in electronic version. Access restricted to campus users.

Thesis (M. S.)--Mechanical Engineering, Georgia Institute of Technology, 2009.
Committee Chair: Colton, Jonathan; Committee Member: Schultz, John; Committee Member: Zhou, Min. Part of the SMARTech Electronic Thesis and Dissertation Collection.

Excessive settlement and foundation instability are some of the main problems commonly encountered in fills and embankment structures built on a soft soil of low bearing capacity.The Expanded Polystyrene(EPS)replacement method, by partially or fully replacing the conventional fill material with extremely lightweight EPS geofoam, may solve these problems. In this thesis, experimental and theoretical work have been carried out to investigate the behaviour of EPS under various loading conditions in geotechnical applications and the effectiveness of EPS replacement technique has been studied using numerical models.Several tests were performed for this study and the results of these tests are given
Doctor of Philosophy (PhD)

In the packaging industry, cushioning products are usually made of plastic materials, such as polystyrene. The insulation and lightweight character make it more popular and convenient to use. However, the extensive use of it creates more waste leading to an environmental problem. Usually the cushioning foams are discarded after being used for inbox protection as packaging material; eventually they end up in a landfill. Most plastic foams are not biodegradable, which cannot be composted and will create more and more waste that affects the ecological system. In the mean time, foams made up of bio-degradable materials are considered. In general, biodegradable plastics are starch-based or cellulose-based, and the biodegradable components can be found in corn (e.g. corn starch, and corn cob). Instead of extracting the corn component, here popped corn kernel will be investigated for its suitability in packaging applications.

The use of cellular foam as a core material in light-weight structural applications is of considerable interest. However, advances in this technology have been limited due to the lack of information concerning the macroscopic material behavior of cellular foams. Of particular interest in the design of composite structures is the shear modulus, G, of the core material, which must be established with a high degree of accuracy. Current ASTM test methods for shear modulus determination were researched and found inadequate for testing cellular foam materials. The difficulty in testing foam and the inaccuracies associated with the standard test methods established the need for the development of a test method for these materials. The test method (test fixture and test procedure) developed for cellular foam materials is presented. The design of the test fixture and the finite element analysis performed to determine fixture accuracy are discussed in detail. Additionally, the test procedure is presented, as well as the results for the 32 tests performed.

Excessive settlement and foundation instability are some of the main problems commonly encountered in fills and embankment structures built on a soft soil of low bearing capacity.The Expanded Polystyrene(EPS)replacement method, by partially or fully replacing the conventional fill material with extremely lightweight EPS geofoam, may solve these problems. In this thesis, experimental and theoretical work have been carried out to investigate the behaviour of EPS under various loading conditions in geotechnical applications and the effectiveness of EPS replacement technique has been studied using numerical models.Several tests were performed for this study and the results of these tests are given

This thesis addresses a new technique of foaming on polymer-paperboard composites which combines the advantages of traditional polymeric foam with the environmental benefits of paperboard. Paperboard is sandwiched between two extruded polymeric layers of different densities. On application of heat, one face is foamed by the evaporating moisture in the board; the other face serves as a barrier. This work is directed at gaining a better understanding of the fundamental processes in foaming polymers on paperboard. The ultimate goal is to be able to produce uniform bubbles of a predetermined size on the surface so as to give optimum heat insulation and good tactile properties. Bubble growth was studied as a function of paperboard properties, polymer melt index, extrusion speed, polymer thickness, temperature and moisture content. The foam quality (thickness) is also related to the cell size distribution and various factors affecting it are identified. A combination of experimental techniques such as high speed imaging, infrared thermography and scanning electron microscopy is used for this purpose. Foaming on paper-polymer composites is caused by water vapor escaping through the pores present in the paperboard substrate and then foaming the polymer. The vapor driving force which dominates foaming and overcomes the less significant viscoelastic and surface tension opposition forces depends on the paperboard properties as well as on the ability of the polymer to bond with the paperboard. It was found that the bubble size distribution directly relates to the pore size distribution on the paperboard. The bubble size was also controlled by the thickness of the polymer layer and its ability to bond with the paperboard. Coalescence subsequently led to thicker foams due to the formation of larger sized bubbles.

Thesis (MBA)--Stellenbosch University, 2001.
ENGLISH ABSTRACT: The polystyrene foam tray manufacturing industry started with a monopoly in 1954, and lasted for more than 29 years. During the last ten years the industry has grown extremely competitive, seeing many new players enter (and exit) and a reduction in industry profitability. This mini thesis attempts to analyze the polystyrene foam tray manufacturing industry in its current form and to quantify the external, new challenges it currently faces. It attempts to identify potential pitfalls for new entrants to the industry and to construct an ideal strategy suited best for the industry, based on an industry analysis. The polystyrene foam container industry background is discussed to determine its origins in South Africa. An industry and competitive analysis is done to assess the strategically relevant aspects of the industry's macro environment. A technique developed by Thompson and Strickland (1998: 68) is utilized. The scope of the macro environment in the mini-thesis was limited to the South African scenario. Ultimately, an ideal strategy, which would deal with all the relevant challenges of the industry, is proposed. The industry and competitive analysis revealed important dominant economic traits. Competition is concentrated in the country's economic hub, namely Gauteng, but regional manufacturing bases leads to extended market share in those areas. The product range spans over several hundred coloured, printed and laminated trays, but the fiercest competition across the board takes place in a few sizes white, commodity flat trays to the meat industry, which also forms the bulk of sales to the industry. The growth rate has been organic for the last few years, mainly due to the mature status of polystyrene foam tray products and the introduction of alternative (though more expensive) media. The external macro economic environment has also not been conducive to abnormally high growth (GDP in South Africa has drifted between 1% and 3% for the last few years). Five competitors exist, and two of these competitors have 80% of the market share, but are also the furthest away from the largest part of the market, namely Gauteng. Customers are divided into two groups, distributors and end users. Small competitors make extensive use of distributors (since they do not own their own distribution channels), while large competitors limit the use of distributors to limit the potential buying power of distributors. The barrier to entry for a new entrant wanting to acquire up to 5% of market share is around R 10m, which includes working capital. The industry profitability varies from losses to extreme profits in some years. This becomes a vicious circle, since the latter attracts new entrants, which in turn causes price wars. Rivalry amongst competitive sellers is excessive, specifically when new entrants appear on the scene. Price cutting, although a very blunt tool, is used almost exclusively to obtain a volume advantage. Substitute products do not really pose a threat in the South African economic situation where cost is all-important. No other packaging medium can compete with the wide range of applicability, low cost and strength of polystyrene foam. Where end-user markets are more affluent, substitute products may have a minor impact. The power of suppliers in the industry is limited, since there is a manufacturing over capacity in the country, and there are no switching costs when changing from one supplier to another. The power of buyers, specifically ones that buy in bulk (distributors and the like), is thus quite strong. The main drivers of change include excessive movement in market pricing, product innovation, technological changes, increasing globalisation of the industry and changing societal concerns. Movement in market pricing is by far the most important and has the greatest affect on industry profitability, since the complete product range is affected. The latter four drivers affect mostly branded and speciality product. Strategic group mapping, combined with an in-depth analysis of each competitor, revealed that the largest two players, Kohler Versapak and Atlantic Forming, are definitely in the strongest position from a financial point of view. Although drawbacks such a corporate red tape, shareholder pressure and geographic location exist for these competitors, sheer financial strength to survive price wars will give them an edge. With the current amount of competitors and over capacity in the market there is bound to be some consolidation in the manufacturing industry. It seems that one of the larger two players (Kohler Versapak or Atlantic Forming) may acquire one of the smaller manufacturers in a bid to stabilize market prices. The most important key success factor is the ability to produce polystyrene foam trays at the lowest possible cost. The absence of switching costs, price wars and a manufacturing over capacity are all causes of the preceding success factor. Other less important success factors are distribution related (being close to the market is an advantage) and technology related (being able to develop advanced branded and functional trays). In its current status, where there is a supply-demand imbalance, the industry does not seem attractive. Although negative external forces such as environmental pressure, are limited, growth potential is limited and competition is fierce. In summary none of the competitors have attempted to utilize other tools than pricecutting to protect market share. From a geographic location point of view, Airshield and Mainpack are positioned best, but do not possess the financial momentum to optimally utilise their location in terms of finished product distribution and raw material acquisition. Atlantic Forming and Kohler Versapak seem to have expanded their product ranges to low profit and unprofitable products, while the other competitors have stayed focused on a few high volume items. It seems that it may have been a better idea for the larger players to utilize existing resources on other profitable media rather than expanding its interests in polystyrene foam trays.
AFRIKAANSE OPSOMMING: Polistireen skuim houer vervaardiging het in 1954 met 'n monopolie begin wat vir 29 jaar staande gebly het. Gedurende die laaste tien jaar het die polistireen skuim industrie baie kompeterend geraak, met heelwat kompeterende maatskappye wat die mark betree het (en uitgetree het), en 'n gevolglike afname in industrie profyt gehad het. Hierdie minitesis poog om die polistireen skuim bakkie industrie te analiseer in sy huidige vorm en om die eksterne uitdagings wat tans bestaan, te identifiseer. Die tesis poog verder om potensiele probleme te identifiseer wat nuwe kompeterende maatskappye in die industrie mag teëkom, en dan om 'n ideale strategie saam te stel, gebasseer op 'n industrie analise. Die polistireen skuim houer industrie is bespreek, sodat die oorsprong van die industrie in Suid-Afrika bepaal kon word. 'n Industrie en kompeterende analise is gedoen om die strategies belangrike aspekte van die industrie se makro omgewing te bepaal. Vir die bogenoemde analise is 'n tegniek soos ontwikkel deur Thompson en Strickland (1998: 68) gebruik. Die omvang van die makro omgewing in hierdie minitesis is beperk tot die Suid- Afrikaanse omgewing. Die uiteindelike ideale strategie sal al die relevante uitdagings van die industrie aanspreek. Die industrie en kompeterende analise het belangrike dominante ekonomiese eienskappe blootgelê. Markgerigte kompetisie is gekonsentreerd in die land se ekonomiese enjin, naamlik Gauteng, maar streeks gebaseerde vervaardigings aanlegte lei gewoonlik tot 'n verbeterde mark aandeel in 'n spesifieke streek. Die produk reeks bestaan uit honderde gekleurde, gedrukte en gelamineerde houers, maar die grootste kompetisie vind plaas oor slegs 'n paar plat, wit vleis bakkies - wat ook die grootste volume verkope in die industrie beslaan. Die groei tempo was organies vir die laaste paar jaar, hoofsaaklik as gevolg van die volwasse stand van polistireen skuim produkte en die bekendstelling van alternatiewe produkte. Die eksterne makro ekonomiese omgewing het ook nie bygedra tot bogemiddelde groei nie (BBP in Suid-Afrika het tussen I% en 3% gewissel vir die laaste paar jaar). Vyf produseerders van polistireen skuim houers ding mee in die mark, en twee van hulle besit 80% van die totale mark aandeel, alhoewel hulle ook die verste vanaf grootste mark, naamlik Gauteng, is. Kliënte word in twee groepe verdeel, naamlik verspreiders en eind-gebruikers. Klein produseerders maak meestal gebruik van verspreiders omdat hulle nie oor hulle eie verspreidings kanale beskik nie. Groter produseerders beperk die gebruik van verspreiders om uiteindelik potensiële koopkrag van verspreiders te beperk. Vaste kapitaal, asook lopende kapitaal om ongeveer 5% van die mark te bekom, is ongeveer R10m. Die industrie profyt variëer tussen verliese tot oorgrote profyt in sommige jare. Hierdie variasie vorm 'n afbrekende sirkel, aangesien oorgrote profyt potensiële nuwe produseerders aantrek wat dan weer tot prys oorloë lei. Mededinging tussen kompeterende produseerders is oormatig sterk, spesifiek wanneer nuwe produseerders die mark betree. Alhoewel prys verlaging 'n redelike kru metode is om markaandeel te bekom, word dit amper uitsluitlik gebruik. Alternatiewe, duurder vervangings produkte is nie werklik 'n gevaar vir polistireen skuim produkte in Suid-Afrika nie, aangesien prys die belangrikste element is. Geen ander verpakkingsmedia kan meeding met die toepasbaarheid, lae koste en sterkte van polistireen skuim nie. Slegs in sekere wel-gestelde segmente van die mark kan alternatiewe produkte 'n minimale impak op die polistireen skuim mark toon. Die mag van verskaffers in die industrie is beperk, aangesien daar 'n geweldige oorkapasiteit in die land is en omdat daar geen oorskakelingskoste bestaan wanneer daar van een verskaffer tot 'n ander geskuif word nie. Die mag van kopers, en spesifiek die wat in grootmaat koop, is dus redelik sterk. Die hoofdrywers van verandering sluit in sterk beweging in mark pryse, produk innovasie, tegnologiese veranderinge, toenemende globalisering van die industrie en veranderende sosiale standaarde. Variëerende beweging van markpryse is by verre die belangrikste en het ook die grootste effek op industrie profyt, aangesien die hele produk reeks geraak word. Die laaste vier drywers affekteer meestal handelsmerk produkte en spesialiteits produkte. Strategiese groep kaarte, gekombineerd met 'n indiepte analise van elke produseerder, het aangedui dat die twee grootste kompeteerders, Kohler Versapak en Atlantic Forming, definitief in die sterkste posisie is vanaf 'n finansiële oogpunt gesien. Alhoewel negatiewe punte soos korporatiewe sloering, aandeelhouer druk en geografiese posisie teen die twee mededingers tel, sal blote finansiele mag om prys oorloë te deurstaan hulle die oorhand gee. Met die huidige hoeveelheid oorkapasiteit in die mark moet daar uiteraard konsolidasie in die vervaardigings industrie plaasvind. Dit is waarskynlik dat een van die groter spelers (Kohler Versapak of Atlantic Forming) van die kleiner mededingers mag bekom in 'n poging om die mark te stabiliseer. Die mees belangrike sleutel sukses faktor is die vermoë om polistireen skuim bakkies teen die laagste koste te vervaardig. Die afwesigheid van oorskakelingskoste, die aanwesigheid van prys oorloë en vervaardigings oorkapasiteit is almal oorsake van die genoemde sukses faktor. Ander minder belangrike sukses faktore is verspreidings verwante (om nabyaan die mark te wees is 'n voordeel) en tegnologie verwante (om handelmerk produkte en moderne funksionele produkte te kan ontwikkel) faktore. In die mark se huidige vorm is daar nie 'n vraag-aanbod balans nie, en lyk die industrie nie aantreklik nie. Alhoewel negatiewe eksterne kragte soos omgewings druk beperk is, is groei potensiaal ook beperk en kompetisie agressief. Opsommendergewys het geen van die mededingers ander metodes as prys verlaging probeer gebruik om mark aandeel te beskerm nie. Vanaf 'n geografiese oogpunt gesien, is Airshield en Mainpack die beste geposisioneer, maar hulle het nie die finansiële momentum om hulle posisie optimaal te benut in terme van klaar produk verspreiding en rou material aankope nie. Atlantic Forming en Kohler Versapak het hulle produk reeks uitgebrei na lae profit en verlies-lyende produkte, terwyl ander mededingers gefokus gebly het op 'n paar hoë volume items. Dit lyk asof dit beter sou gewees het vir die groter spelers om bestaande bronne te gebruik het op ander winsgewinde media as om verder uit te brei in polistireen skuim.

Thesis (Ph.D.) -- University of Western Sydney, Nepean, 2001.
A thesis submitted for the degree of Doctor of Philosophy, School of Civic Engineering and Environment, University of Western Sydney, Nepean, January, 2001. Bibliography : p. 215-225.

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Dissertação (Mestrado)
IPEN/D
Instituto de Pesquisas Energeticas e Nucleares - IPEN/CNEN-SP

As espumas de polietileno são amplamente utilizadas. Suas aplicações vão de aparelhos domésticos a artefatos médicos, incluindo aplicações nas indústrias de construção civil e automobilística. As propriedades das espumas dependem da densidade e da sua estrutura celular, em outras palavras, da quantidade de células abertas e fechadas, da distribuição e do tamanho das células. Os métodos de produção de espumas de polietileno reticulado são classificados em dois tipos, de acordo com o método de reticulação. Um dos métodos é a reticulação química, que utiliza peróxidos como agente reticulante, O outro método é a reticulação por irradiação, utilizando feixe de elétrons. As espumas obtidas a partir do polietileno reticulado pelo processo de irradiação apresentam superfície lisa e homogênea, e são formadas basicamente por células fechadas. O objetivo deste trabalho foi utilizar a radiação ionizante para a formação de ligações cruzadas entre as moléculas de polietileno de baixa densidade (LDPE), que permitiu a obtenção das espumas. As suas propriedades mecânicas, térmicas e morfológicas foram avaliadas. As amostras de polietileno com densidade de 0,946 g/cm3, contendo 5% de azodicarbonamida (ADCA), agente expansor, foram irradiadas com feixe de elétrons de alta energia com doses de radiação de 10, 20, 30, 40, 50, 60, 80 e 100 kGy. Após a irradiação, as amostras de LDPE foram colocadas em um forno para expansão térmica e formação das espumas. Foi determinado o grau de reticulação das espumas. Algumas amostras também foram envelhecidas termicamente. O desempenho mecânico das amostras de espumas foi avaliado por meio de ensaios de tração e deformação, dureza, deformação permanente por compressão e resiliência. Também foram realizados ensaios de termogravimetria (TGA) e de microscopia eletrônica de varredura (MEV). Os resultados mostraram que no intervalo de doses de radiação estudadas, a resistência à tração aumenta com o aumento do grau de reticulação. Nos ensaios de resistência à compressão, a partir da dose de radiação de 40 kGy, observou-se um decréscimo nos valores obtidos. Já a resiliência sofreu pouca aheração. De acordo com a análise morfológica pode-se concluir que a dose de radiação de 30 kGy foi a que promoveu a formação de espumas com estrutura celular fechada e mais homogênea.
The polyethylene foams are widely used. Their main applications are used for both home appliances to medical equipments. Beside that, they have applications in building and automotive industries. The foam properties depend on the density and its cellular structure, that is, the amount of open and closed cells, of the distribution and size of them. The methods of the crosslinking polyethylene foam production are classified in two types, according to the crosslinking method. One method is based on the chemical crosslinking, which utilizes peroxide as crosslinking agent. In the other method, the crosslinking is induced by electron beam radiation. The foams obtained from the crosslinking polyethylene by irradiation process presented a smooth and the homogeneous surface, and are formed basically by closed cells. The aim of this study was to apply the ionizing radiation from electron beam to crosslink low density polyethylene (LDPE), to obtain foams. Their morphological, thermal and mechanical properties were studied to evaluate the obtained samples. The samples of low density polyethylene (0,946 g/cm3), containing 5% of azodicarbonamide (ADCA), as expander agent, were irradiated with electron beam with doses of 10, 20, 30, 40, 50, 60, 80 and 100 kGy. After the irradiation, these LDPE samples were put into an oven to obtain the foams. It was determined the crosslinking degree of the foams. Some samples were also thermically aged. The mechanical performance of the foams samples was evaluated by means of the tensile strenght, compression, hardness, permanent deformation by compression and resilience. It was also carried out thermogravimetry and scanning electron microscopy (SEM). The results have shown that, in the interval of radiation doses studied, that the tensile strength increases with the increase of the crosslinking degree. The compression resistance results obtained from with samples with to radiation dose of 40 kGy showed significant decreasing. The resilience measurements have shown only little variations. According to the morphological analysis it can be concluded that foams with radiation dose of 30 kGy have closed cellular structure more homogeneous and smooth morphology.

Physical properties and morphology of extruded semicrystalline polymers can be significantly affected by modification and change in die design and melt viscosity of the molten polymer. Further modifications to physical properties (i.e. density and open cell fraction) of foamed material occur, following the modification of melt viscosity by melt blending of polypropylene and high density polyethylene). The main object of this research project was to carry out a systematic examination of rheological properties of polymer/gas mixture, affect of die design, polymer molecular weight (melt viscosity), and processing conditions on density, open cell fraction, cell morphology (i.e. cell size and cell size distribution) and micromorphology of polyolefin foams. Also attention was given to method of stabilisation of extruded foam, where, it was found support of the extrudated foam (by adding a specially designed die adapter to the end of the die) prior to entering the cooling tank could result not only to a specimen with uniform cross section, but also due to drop in melt temperature, the cell walls are to some extent rigidized, hence, the collapse of bubbles are limited. From commercial point of view control of cell collapse, density and open cell fraction, will make these foamed materials valuable for their filtration characteristics. Microstructural analysis of polypropylene (unfoamed state) by X-ray diffraction and Differential Scanning Calorimetry revealed 13-spherulites are only formed in skin layer, and beneath the thickness of 500 pm from the surface, the crystal structure of this polymer is only consist of B-spherulites. On the other hand, the chemical blowing agent (Hydrocerol CF-20), was found to have nucleating affect on microstructure of polypropylene, where, it has resulted in reduction of size of spherulites together with a drop in recrystallisation temperature and formation of P and a spherulites through the thickness of extrudated foam. The foregoing chemical blowing agent was found to have no significant affect on the crystal structure of the high density polyethylene.

Development of foam cutting machines for rapid prototyping and manufacturing purposes began shortly after the first additive manufacturing machines became commercialised in the late 1980s. Increased computer power, the development and adoption of CAD/CAM software and rising demand for customisation has caused the rapid prototyping industry to grow swiftly in recent decades. While conventional rapid prototyping technologies are continuing to improve in speed and accuracy the ability to produce large (> 1m³) prototypes, moulds or parts it is still expensive, time consuming and often impossible. Foam cutting rapid prototyping and manufacturing machines are ideally suited to fulfil this niche because of their high speed, large working volumes and inexpensive working materials. Few foam cutting rapid prototyping machines have been commercialised to-date leaving significant opportunities for research and development in this area. Thermal plastic foam cutting is the material removal process most commonly used in foam cutting rapid prototyping to shape or sculpt the plastic foam into desired shapes and sizes. The process is achieved by introducing a heat source (generally a wire or ribbon) which alters the physical properties of the plastic foam and allows low cutting forces to be achieved. In thermal plastic foam cutting the heat source is generated via Joule (electrical) heating. This study investigates the plastic foam cutting process using experimental cutting trials and finite element analysis. The first part of this thesis presents an introduction to conventional foam cutting machines and rapid prototyping machines. It is suggested that a market opportunity lies out of reach of both of these groups of machines. By combining attributes from each, foam cutting rapid prototyping machines can be developed to fill the gap. The second part of this thesis introduces the state-of-the-art in foam cutting rapid prototyping and investigates previous research into plastic foam cutting mechanics. The third part of this thesis describes cutting trials used to determine important factors which influence plastic foam cutting. Collectively over 800 individual cutting tests were made. The cutting trials included two main material sets, expanded polystyrene and extruded polystyrene, three different wire diameters, two hot-ribbon configurations and a wide range of feed rates and power inputs. For each cut the cutting force, wire temperature and kerf width was measured as well as observations of the surface texture. The data was then analysed and empirical relationships were identified. An excel spreadsheet is established which allows the calculation of important outcomes, such as kerf width, based on chosen inputs. Quantitative measurements of the surface roughness and form, of cuts made with hot-tools, will not be addressed in this thesis. This body of work is currently under investigation by a colleague within the FAST group. The fourth part of this thesis describes the formation of a nonlinear transient two-dimensional heat transfer finite element model, which is developed for plastic foam cutting simulations. The conclusion is that the cutting trials contributed to a better understanding of plastic foam cutting mechanics. A new parameter was identified called the mass specific effective heat input, which is a function of the foam material and the cutting tool, it allows the prediction of cutting conditions with given cutting parameters and hence provides the necessary relationships needed for adaptive automated foam sculpting. Simulation results were validated by comparison with experimental data and provide a strong base for further developments including optimisation processes with adaptive control for kerf width (cut error) minimization. This study has added considerably to the pool of knowledge for foam cutting with a hot-tool. In general, much of the work reported herein has not been previously published. This work provides the most advanced study of foam sculpting work available to date.

Tableau d'honneur de la Faculté des études supérieures et postdorales, 2015-2016
Le but de ce travail est de produire et de caractériser des structures sandwich à trois couches asymétriques avec ou sans cœur moussé. Pour ce faire, le travail est divisé en deux sections. Dans la première partie, l'effet de la variation des quantités d'agent de couplage et de fibres sont étudiés. La microscopie et la caractérisation mécanique sont utilisées pour évaluer l'effet du polyéthylène greffé d’anhydride maléique (MAPE) sur l'amélioration de la compatibilité entre les fibres de chanvre et le polyéthylène de haute densité (HDPE). Les résultats montrent que les propriétés mécaniques optimales (tension, flexion, torsion et impact) sont obtenues à 9% en poids de MAPE. Dans la deuxième partie, des structures sandwich asymétriques à trois couches, avec ou sans cœur moussé, sont produites par extrusion suivi par un moulage en compression. Les effets de paramètres tels que la densité du cœur, la concentration en chanvre dans les peaux, les épaisseurs des couches et la séquence d'empilage sur leurs comportements en flexion et en impact sont étudiés. Les effets combinés de tous les paramètres mènent à contrôler les propriétés mécaniques (traction, torsion, flexion et impact) des structures sandwich asymétriques.
The aim of this work is to produce and characterize asymmetric three-layer sandwich structures with and without foam core. In order to do so, the work is divided in two sections. In the first part, the effect of coupling agent and fiber content is investigated. Micrographs and mechanical characterizations are used to show that the addition of maleic anhydride polyethylene (MAPE) improved the compatibility between hemp and high density polyethylene (HDPE). It is found that the optimum mechanical properties (tension, flexion, torsion and impact) are obtained with 9% wt. of MAPE in the composite. In the second part, asymmetric three-layer sandwich structures with and without foam core were produced using extrusion followed by compression molding. The effect of different parameters such as core density, skin hemp content, layer thickness, and stacking sequence on their flexural and impact behaviors are studied. The combined effect of all the parameters was found to control the mechanical properties (tension, torsion, flexion and impact) of asymmetric sandwich structures.

Els materials porosos polimèrics, també denominats escumes sòlides, són materials sòlids de baixa densitat i elevat volum de porus. Són ben coneguts per la seva varietat d’aplicacions i constitueixen una part integral de diverses formes de dosificació. La xarxa porosa és important per determinar fenòmens relacionats amb l’administració de medicaments, tals com la dissolució, adsorció i difusió de fàrmacs. S’ha descrit l’ús de materials mesoporosos per incorporar i posteriorment alliberar diverses molècules d’interès farmacèutic i s’ha demostrat que molècules de diferents mides poden quedar atrapades als porus mitjançant un procés d’impregnació i alliberades a través d’un mecanisme controlat per difusió. En aquest context, els materials porosos tenen característiques molt interessants com són superfícies elevades, mida de porus ajustable amb una baixa polidispersitat i propietats superficials ben definides, permetent així l’adsorció i alliberament de certs tipus de fàrmacs d’una manera més reproduïble i predictible. La majoria de mètodes per fabricar materials porosos donen lloc a estructures poroses jeràrquiques, però són processos laboriosos amb diverses etapes i, per aplicacions industrials es requereixen mètodes més simples. Com a alternativa als mètodes convencionals es poden obtenir materials porosos mitjançant sistemes col·loidals, generant un sistema bifàsic i polimeritzant posteriorment la fase externa. Les entitats col·loidals serveixen per a formar la porositat en el material final i després són eliminades del sistema. Depenent de la naturalesa del sistema col·loidal (emulsions, microemulsions, etc.), la grandària dels porus generats pot ser des de nanòmetres fins a centenars de micres. En aquesta tesi doctoral s’han seleccionat quatre polímers biocompatibles per desenvolupar materials nanoestructurats a partir d’emulsions altament concentrades: poliestirè-divinilbenzè (PS-DVB), poliacrilamida (PAM), quitosan (QS) i àcid hialurònic (HA). Els materials de poliestirè-divinilbenzè i els de poliacrilamida s’han obtingut mitjançant una reacció de polimerització de l’estirè amb divinilbenzè en el primer cas i d’acrilamida i bisacrilamida en el segon cas, fent servir com a plantilla (template) l’estructura de les emulsions altament concentrades. Per a l’obtenció de materials de poliestirè-divinilbenzè s’han emprat emulsions altament concentrades W/O i pels materials de poliacrilamida, emulsions O/W, degut a les diferents solubilitats de l’estirè i l’acrilamida en els components de les emulsions i per afavorir les reaccions de polimerització a la fase externa. Els altres polímers s’han incorporat directament preformats a les emulsions O/W i s’han utilitzat agents reticulants (cross-linkers) per mantenir l’estructura. El reticulant emprat pel quitosan ha estat la genipina i per a l’àcid hialurònic, el butandiol diglicidil éter (BDDE). La caracterització d’aquests nous materials i l’estudi de la incorporació de fàrmacs i la cinètica d’alliberament és fonamental pel desenvolupament de formes farmacèutiques segures i eficaces. És per això que s’ha desenvolupat un sistema de control senzill basat en l’equip de dissolució que ens ha permès comparar les característiques del diferents materials sense haver de recórrer a tècniques complexes que suposarien un cost excessiu per a la fabricació industrial d’aquests nous materials per a ús farmacèutic. S’han preparat materials porosos de poliestirè-divinilbenzè (PS-DVB), partint d’emulsions altament concentrades W/O preparades pel mètode PIT o pel mètode de les addicions successives. Les diferents característiques de les emulsions i dels materials obtinguts han permès comprovar que les emulsions efectivament han servit de plantilla per a l’estructura porosa dels materials, obtenint-se porus més petits i homogenis quan les emulsions es preparen pel mètode PIT. És possible augmentar la hidrofília de la superfície d’aquests materials hidrofòbics amb un tractament amb plasma atmosfèric a baixa temperatura. Les escumes sòlides que s’han format per polimerització de monòmers a la fase continua de l’emulsió altament concentrada, materials de PS-DVB i PAM, tenen una estructura més compacta i els porus són més ordenats i interconnectats. Quan es produeix la polimerització en un sistema col·loidal compartimentat, la reacció té lloc d’una manera més ordenada i les estructures que es formen tenen un grau d’ordenació més elevat. Els materials obtinguts conserven l’estructura de l’emulsió, són majoritàriament macroporosos, amb més d’un 90% de porositat, i tenen una baixa densitat. Els resultats de porosimetria han evidenciat la possibilitat de modificar les característiques dels materials porosos, mida de por i superfície específica, mitjançant canvis en la mida de gota de l’emulsió de partida, per canvis en la composició o en el mètode de preparació. Els resultats obtinguts en l’estudi dels mètodes d’incorporació de principis actius als monòlits han permès comprovar que es pot realitzar una impregnació eficient, uniforme i en profunditat dels monòlits hidròfobs de PS-DVB i QS pel mètode d’immersió en una solució hidroalcohòlica d’aigua/etanol (1:1, p/p). El mètode de degoteig es va reservar pels materials d’HA degut a la seva fragilitat. També s’ha comprovat que les solucions més concentrades en principi actiu permetien la incorporació de quantitats més elevades de fàrmac. La posada a punt d’una metodologia per a la presa de mostres de manera automàtica amb l’equip de dissolució ha permès establir les condicions per a un mostreig fiable i reproduïble, per realitzar els assaigs d’alliberament de fàrmacs des dels materials polimèrics. L’automatització de l’equip ha permès assajar vàries mostres simultàniament i obtenir resultats més fiables. Els dispositius basats amb bossa de diàlisi, cel·la d’immersió i cistell perforat (mètode 1 de la Real Farmacopea Española) són adequats per avaluar la cessió de principis actius des de materials porosos polimèrics fins una solució receptora; no obstant, aquest darrer mètode te l’avantatge de que l’alliberament es realitza directament a la solució receptora sense interferència de cap membrana i és el més adient per comparar diferents materials o diferents principis actius. Les escumes sòlides hidròfobes de PS-DVB produeixen un alliberament retardat de fàrmacs lipòfils com el ketoprofèn (KP) i afecten en menor grau a la cessió de fàrmacs hidròfils com el clorhidrat de clindamicina i el sulfat de salbutamol, que queden menys retinguts pel material porós. El retard en l’alliberament de KP des dels materials hidròfobs és molt significatiu en comparació amb formes sòlides orals comercialitzades d’aquest mateix principi actiu. La retenció dels fàrmacs pels materials porosos estudiats està influenciada per l’estructura de l’emulsió que ha fet de plantilla perquè condiciona la morfologia de l’estructura porosa, per la composició dels materials porosos i la seva afinitat pels principis actius incorporats i per la rigidesa o fragilitat dels materials, que condiciona els mètodes per a la seva impregnació. Considerar aquestes característiques permetrà modular les propietats de les escumes sòlides per adaptar-les als perfils de cessió més adequats per cada principi actiu.

Thesis (M.S.)--West Virginia University, 2008.
Title from document title page. Document formatted into pages; contains xiii, 101 p. : ill. (some col.). Includes two zip files of TIF images. Includes abstract. Includes bibliographical references (p. 93-94).

The New Zealand Structural Loading Standard, until its latest revision, was using the structural displacement ductility factor as a measure of the deformation demand of all potential plastic hinges in a structure. In the revised version of New Zealand Structural Loading Standard for Earthquake Actions (NZS 1170.5:2004) the detailing of potential plastic regions is determined according to the local inelastic deformation demand in these regions. The change has been prompted by evidence that the structural ductility factor gives a poor indication of the demand on individual plastic regions. This is a major paradigm shift in international design codes. This new approach has been adopted by the New Zealand Concrete Structures Standard (NZS 3101:2006) which classifies potential plastic regions into three categories (namely ductile, limited ductile and nominally ductile) based upon their inelastic deformation demand which has been specified in terms of material strain limits in the form of curvatures or shear deformations. The values of material strain limits currently used in New Zealand Concrete Standard (NZS 3101:2006) to categorise the plastic regions are based on limited evidence and need a closer revision. This research attempts to obtain more justifiable values of material strain limits through experimental data existing in literature. Moreover, experimental testing is also conducted to compensate for a lack of data in the nominally ductile range of detailing. The experimental work explores the effects of transverse reinforcement arrangement, reinforcing steel grade and plastic hinge type. Together the literature review and experimental work provide a sound basis for re-defining the material strain limits for different plastic regions.

This thesis presents the development of a novel robotically effected plastic foam sculpting system for rapid prototyping and manufacturing purposes. The developed system is capable of rapidly sculpting physical objects out of expanded and extruded polystyrene using an electrically heated Nichrome sculpting tool. An overview of current conventional rapid prototyping systems indicated that the main disadvantages lie in the limited size of objects which can be built, the relatively long time involved to produce one part and the high cost of the systems and materials. An extensive literature and technology review was conducted on work which was similar to the novel system presented in this thesis. The literature provided many good ideas which could be applied. Two sections of experimental work were conducted. The first was aimed at simply proving the concept of robotically effected sculpting of plastic foams. A crude procedure was developed which proved to be rather tedious and manual, especially in terms of generating the tool paths. Qualitative observations of the cut surfaces were used to change the testing parameters to explore their effects and discover which parameters produced accurate and smooth sculpted surfaces. 12 tests were documented and proved that the sculpting of satisfactory surfaces was achievable. The second section of experimental work involved developing the aforementioned crude procedure to make it more automated, especially in terms of the tool path generation and optimisation step. An innovative five step procedure was developed which if followed can produce accurately sculpted artefacts using CAD models of the artefacts as the primary input. Two artefacts were successfully sculpted using the developed procedure. The first was a simple lofted surface; the CAD model of which was created in SolidWorks. The second artefact was a patient customised medical radiation therapy head and neck support; the CAD model of which was created by scanning the back of the author's head and neck with a 3D scanner. The sculpted support fitted the author perfectly. The implementation of the procedure in the two tests highlighted several points including the speed in which the whole process can be carried out. The time taken from the scanning of the authors head and neck with the 3D scanner through to the physical sculpted artefact, was a mere 80 minutes; of which only 13 minutes was consumed in the actual setup and sculpting step! This is extremely quick when compared to conventional rapid prototyping systems and CNC milling. Several areas of future work were outlined and included, tool and fixture design, automation and integration of the system procedure, tool pathing strategy for foam cutting and robot control system issues. The work presented in this thesis provides an excellent foundation for future development of the robotic foam sculpting system.

This thesis focuses on the design, development, and evolution of a novel patent-pending plastic processing technology entitled “Rapid Rotational Foam Molding” with special emphasis on the processing of polyethylene (PE) integral-skin foamed core moldings. Rapid Rotational Foam Molding is a technology deliberately designed to address the intrinsic disadvantage of conventional rotational foam molding, i.e., its very long cycle times. In this context, a physical system that exploits the positive synergistic effects of innovatively combining extrusion melt compounding and rotational foam molding was designed and built. The fundamental processing steps of this system comprise (i) rotationally molding a non-foamable PE powder in a lab-scale oven while, (ii) simultaneously melt compounding and foaming a pre-dry blended foamable PE and chemical blowing agent (CBA) formulation in an on-line lab-scale extruder, and then (iii) filling the newly created foaming material into the non-chilled hollow article thereby created in the mold through a special interface. Two varieties of PE resins ranging from linear low density PE (LLDPE) to high density PE (HDPE) were selected for experimentation with melt flow rates (MFR) ranging from 2.0 to 3.6 g/10min. The implemented CBA was Celogen OT. The materials were characterized using thermal analysis techniques such as differential scanning calorimetery (DSC) and thermogravimetric analysis (TGA) to ensure their correct operating temperatures ranges. Scanning electron microscopy (SEM) was utilized for characterizing the quality of the foam samples and achieved skin-foam interface for the final moldings. Improvements to the achieved molding quality were accomplished through various system and process modifications described throughout this research work.

Rotational moulding is a low pressure, high temperature manufacturing method and is considered to be the best for making large hollow shape plastic parts. Due to its long heating cycle, mould rotation during heating and slow cooling rate, it is completely different from injection or other moulding processes. The mechanical properties of rotationally moulded plastics are totally dependent on unique heating or cooling cycles. With the growing demand for rotationally moulded plastics in load bearing and other applications, a better understanding of their fracture properties is essential. In the rotational moulding process, multilayer plastic products such as skin-foam-skin three layered sandwich structures can be manufactured in a single manufacturing step without any joints. It exhibits relatively high stiffness, strength-to-weight ratios and is used increasingly in various applications such as automotive and marine. During the lifetime of the sandwich material, it may face multiple or repeated impact events. Therefore, the aim of this work is to develop a better understanding of the fracture behaviour of rotationally moulded plastics in order to use them in skin-foam-skin sandwich structure and reduce in-service failures due to impact. Here, rotationally moulded two different commercially available Polyethylene (PE) and Polypropylene (PP) plastics are tested. Microstructural details of the plastics are investigated here. Fracture properties, particularly fracture toughness properties are studied using J-integral elastic-plastic fracture mechanics approach to identify the fracture initiation point. Impact properties are also investigated at a wide range of temperatures. PE materials are found to have better fracture properties. It is observed that with the fracture toughness plastic’s microstructure particularly crystal and amorphous region thickness are related. The understanding from these works is followed by the manufacture of rotationally moulded skin-foam–skin sandwich structure and testing of low velocity impact properties of this structure from 20 J to 100 J energy level with a drop weight impact testing machine. PE is used for both in skin and core layer and sandwich samples are manufactured at four different skin-core thickness combinations. Impact force resistance and bending stiffness are found to be increased with an increase of both skin and core layer thickness. Low velocity repeated impact properties of the rotationally moulded sandwich samples are also investigated from 20 J to 50 J energy level at the end of this project to understand the effect of repeated impact on the sandwich structure. The samples are subjected to single impact event repeatedly up-to penetration at each energy level. Impact energy-impact number curve obtained from repeated impact test provides an equation for prediction of the number of repeated impacts for the penetration of the sandwich samples at each energy level.

The Unsettled Object is an installational art project that considers the instability of objects in regards to their assembly, classification, and presentation, underpinned by the context of the museum and supported by Michel Foucault’s notion of the classificatory grids he discusses in The Order of Things: an archaeology of the Human Sciences. (Foucault,1970) The artefacts are being fabricated as a response to the corporeal body-on-display; its surfaces, spaces and volumes. An underlying notion of temporality and mutability is indicated in the processes of making, the objects, material responsiveness and the devices employed in the presentation of the work.

For several years, research work has been carried out at the University of Canterbury aimed at the development of a rapid prototyping and manufacturing process referred to as Robotic Foam Sculpting (RFS). This system uses a six-axis industrial robot and electrically-heated hot-wire and hot-blade tools to sculpt desired parts from blocks of polystyrene foam. The vision for this system is that it will be able to rapidly create large volume foam models at low cost, for a range of potential applications. Parts produced by the RFS system can potentially be used as investment casting patterns, cores for sculptures and architectural details, demonstration and testing models, wind tunnel test models, and many other potential applications. At the beginning of the work reported in this thesis, there was very little understanding of the nature of the surfaces produced by hot-tool cutting of foam, very little knowledge of the range of input cutting conditions that affected the surface quality, and almost no understanding of the relationships between the cutting strategy and the nature of the surfaces being produced. In addition, there was little evidence of published work on these subjects that was sufficiently robust to be applicable to the RFS system. This research was concerned with rectifying this gap in the existing knowledge. There were a number of different focal areas for this research. These included the surface texture of surfaces cut with hot tools, the effects of cutting strategy on the surface quality in single-pass cutting of foam, the effects of cutting strategy on the surface quality in multi-pass cutting, and the application of a current-control system to control the surface quality in real time during a cut. In each of the focal areas the goal was to develop a detailed understanding of the nature of the different aspects of surface quality, to map the factor interactions and dependencies that controlled these aspects of surface quality, to develop methods for predicting the expected surface quality based on cutting strategy (and vice versa) and to develop techniques for minimising the surface errors. The detailed investigation of the surface texture of surfaces produced with hot-tool cutting is presented in Chapter 4. This chapter explores the characteristic nature of foam surfaces, presents the development of a method of measuring the surface texture of foam, and investigates the usefulness of a range of standard texture parameters for assessing foam surface quality. It is concluded in this chapter that common texture parameters based on the relative heights of surface features are not capable of reliably discriminating between different foam surfaces, so a new texture parameter (the 10%-Height Contiguous Diameter) is developed and implemented. Using this parameter, it is possible to reliably predict the surface texture to be expected for a given set of cutting conditions. Investigations of the cutting strategy in single-pass cutting are presented in Chapter 5. This chapter identifies the two key aspects of surface quality in single-pass cutting, the kerfwidth and the surface barrelling. Experimental work is carried out to investigate the relationships between these errors and the cutting strategy, and the factors that influence each of them are identified. In addition, statistical models are developed for the kerf along the length of a cut so that the kerf can be predicted based on cutting conditions. This chapter also includes a study of the cutting force in single-pass cutting, and develops models that allow the prediction of the expected cutting force for a given cutting strategy. A detailed study of the cutting strategy for multi-pass cutting is presented in Chapter 6. This study identifies the most significant surface errors in multi-pass cutting and determines the causes of each of these errors and the factor interactions and dependencies that have to be considered when developing a multi-pass cutting strategy. Once again, statistical models that allow the prediction of these surface errors based on cutting strategy, or the evaluation of cutting strategy parameters to achieve a desired surface quality, are developed. The models for cutting force in single-pass cutting are applied to multi-pass cutting, and it is found that these models can accurately predict the force in multi-pass cutting as well. The characterisation of the acoustic output in hot-tool cutting forms the subject matter of Chapter 7. This study establishes that the magnitude of the acoustic output is proportional to the cutting force experienced during the cut, and is therefore potentially suitable for use as a trigger signal for feedback current control. This would allow an acoustic signal to be used instead of the current force signal, which has a number of drawbacks that will be discussed in Chapter 2, the Background Material chapter. The specific trigger signal identified as being of most use is the acoustic output in the 4 – 12 kHz band, where the presence of any non-zero acoustic output above background noise is a reliable and repeatable indicator of the presence of thermomechanical cutting. The work presented in this thesis provides a detailed, quantitative, evidence-based and reliable understanding of the nature of the cutting strategy in hot-tool cutting of foam. The key cutting strategy parameters and the important aspects of surface quality for different cutting types are identified, the relationships between all these parameters are mapped, and quantitative models are developed that allow the output metrics like the surface quality or the cutting force to be predicted with a high degree of accuracy based on the input cutting strategy conditions. Armed with this understanding, it is possible to determine the most suitable cutting strategy for sculpting a given part, and to assess whether a given part can be sculpted with the RFS system. As such, the research problem posed at the start of this thesis has been largely solved, and the stage is set for further research to optimise the cutting strategy for sculpting different parts and to correct the remaining drawbacks of the RFS system to complete the development of a commercially-useful manufacturing system.

Etude du vieillissement de polymeres renforces ou non de fibres de verre ou de mousses syntactiques immerges dans l'eau sous des pressions de 0 a 300 bars. Adsorption d'eau, proprietes mecaniques, eclatement des microspheres dans les mesures syntactiques