Thesis (MTech (Chemistry))--Cape Peninsula University of Technology, 2007. / The continuous development of new materials and the improvement of existing ones ensure a balance between technological growth and environmental sustainability. With the above trade-offs, the quality of life for humankind is continually being improved. Polymeric materials are some of our most valued commodities in our everyday lives. They continue to be developed and improved in a variety of ways; one of which is to improve their properties by preparing nanocomposites. Polymer-based nanocomposites (PNCs) is a way of getting novel properties and enhancing existing one in polymer matrices, by incorporating additives on a nano-scale. The most significant advantage of PNCs is the potential to design and tailor properties for a specific application, since the control of the structure can be done at the molecular level. Therefore, a fundamental understanding of the relationships between the structure and the properties of PNCs is of utmost importance. Amongst the most studied and researched PNC materials, polymer-layered silicate nanocomposites (PLSNs) have recently enjoyed attention from academia and industry. In the current study structure-property relationships of PLSNs were investigated. Polystyrene (PS) was chosen as the base polymer due to its wide use in many articles such as in packaging. It was also a material of choice based on its poor mechanical properties in its natural state (unfilled), so as to contribute in its property improvement. Montmorillonite (MMT) was a layered silicate (clay) of choice, as much research has been done on it, and it is available worldwide, as a main component in Bentonite (a natural material). Clays are composed of sheet-like, layered particles, which, when in a suitable environment, can delaminate into single, nano-sized sheets. The sheets are held together by van der Waals forces and between the sheets are exchangeable cations. The clays are hydrophilic in nature and cannot readily delaminate in a hydrophobic polymer matrix due to the differences in surface energies. A MMT surface was functionalized to be hydrophobic by conducting an ion exchange reaction with alkyl ammonium surface active agents (surfactants). Polymerizable surfactants (surfmers) were used to enhance the interfacial interaction between the PS matrix and MMT silicate layers. The organically modified clays (organoclays) were used in synthesizing polystyrene-layered silicate nanocomposites (PS-LSN) by an in-situ intercalative polymerization method. The polymerization of the nanocomposites was conducted in bulk. The morphologies of the nanocomposites were characterized using small-angle X-ray scattering (SAXS), transmission electron microscopy (TEM), Fourier transform infrared spectroscopy (FTIR) and gel permeation chromatography (Ope). The study was further expanded to the investigation of the effects of the nanocomposite structure, type of organic modifier, and amount of clay loading on the properties of the materials. The properties were studied by dynamic mechanical analysis (DMA), thermomechanical analysis (TMA) and dielectric analysis (DEA). The properties were dependent on the interfacial processes between the clay layers and the polymer matrix. The changes in properties compared to the PS homopolymer showed time and temperature dependent effects, as determined by DEA. Even though the dynamics of the interfacial interactions are still not fully understood, the nanocomposites showed improvements in properties compared to the homopolymers.

No description available.

Multiblock [-A-B-]_n copolymers of bisphenol-A polycarbonate (I) and several poly(arylether sulfones) (II) have been investigated. The copolymers [see document for a diagram of copolymers (I) and (II)] were prepared from hydroxyl terminated oligomers (4,000 < M̅_n < 30,000) by an interfacial technique which utilized phosgene as the coupling agent. Characterization of the oligomers and copolymers included end group analysis, membrane osmometry, and gel permeation chromatography. One of the most interesting aspects of block copolymers is their ability to undergo microphase separation above a critical block length. Either one or two phase block copolymers can be prepared by controlling the molecular weights of the parent oligomers. In the bisphenol-A polycarbonate/bisphenol-A polysulfone system, for example, strictly one phase materials, with only one intermediate glass transition temperature, were obtained at block lengths of less than 10,000 g/mole. Two-phase copolymers resulted when blocks exceeding 20,000 g/mole were coupled. Copolymers comprised of intermediately sized blocks (M̅_n ≃16,000) could be obtained as either single or multiphase systems depending upon their previous thermal history. Homogeneous films, with a single intermediate Tg, were obtained via solution casting, whereas compression molding provided films exhibiting two Tg's. Subsequent DSC studies pointed out that microphase separation could be thermally, and irreversibly, induced by annealing above the Tg of the polysulfone blocks (190°C). Since polycarbonate and polysulfone are leading examples of tough, amorphous thermoplastics, the effects of microphase separation on the tensile, impact, and melt flow properties of the copolymers were investigated. A novel falling weight impact tester was designed and constructed to meet the needs of this study. The device was fully instrumented to provide a deceleration-time plot of the impact process by means of an accelerometer mounted in the projectile. Fracture energies for commercial homopolymers and graphite reinforced composites, in addition to polysulfone-polycarbonate block copolymers, were calculated from the impact curves. Both the tensile and impact properties of the copolymers improved with increasing polycarbonate content. Both single and multiphase materials were ductile and transparent as opposed to physical blends of the two. oligomers which were opaque and possessed poor mechanical properties. No differences due to microphase separation were observed in either the tensile or impact studies. The homogeneous copolymers displayed melt viscosities and activation energies nearly equal to those of the homopolymers. Much greater viscosities and activation energies were exhibited by the phase separated materials indicating that the heterogeneity was retained in the melt. / Ph. D.

The use of polymer brushes (long polymer chains anchored at their end to a surface or an interface) as a robust approach to control surface properties has generated significant interest in recent years. The stretched conformation of polymer brushes results in unique aggregation, phase, and dynamic behaviors, therefore, they have been used to stabilize colloidal particles and applied in numerous innovative biomedical applications: targeted magnetic hyperthermia, targeted drug delivery, and genotyping. The main goal of this thesis is to shed light on the key factors that affect the formation of these brushes in solution on solid surfaces. In Chapter 3, attenuated total reflectance infrared spectroscopy (ATR-IR) is used to directly measure the rates of the copper-catalyzed azide-alkyne cycloaddition (CuAAC) reactions between alkyne-terminated polystyrene and poly(n-butyl acrylate) and azide-functional substrates in the good solvent DMF. Four regimes of behavior are observed: initially, the reaction rate is diffusion-controlled scaling with t^1/2; in the crossover regime at the onset of chain overlap, the rate scales with ln(t); the rate then accelerates briefly; and finally, in the terminal or penetration-limited regime, the logarithm of areal density scales linearly with time. Kinetic behavior in the diffusion-limited, crossover, and penetration-limited regimes corresponds well to the predictions of Ligoure and Leibler. The blob model suggests that the acceleration in rate is due to lateral chain contraction during the mushroom to brush transition. A theory is presented which predicts that the areal density at saturation should scale as Σsaturation ∼ MW^1.2 for good solvents, and experimentally we find MW^(−0.93±0.04) scaling. In Chapter 4, the effect of symmetry of the CuAAC reaction is investigated for the reaction of end-functional polystyrene and solid surfaces modified with self-assembled monolayers (SAMs). The polymer grafting density on azide-functional substrates is about two times higher than the polymer density on alkyne-functional surfaces. This asymmetry in the reaction density is caused by the difference in the mobility of the alkyne groups between the two systems. While the reaction stoichiometry requires one alkyne and one azide, the reaction mechanism involves two alkyne groups and one azide group in the formation of a stable triazole ring. When the alkyne groups are on the surfaces, their mobility is significantly reduced, preventing the formation of the triazole rings and consequently decreasing the amount of polymer grafted. Increasing the alkynes’ mobility by either extending the thickness of the alkyne monolayer or adding free 1-pentyne improves the polymer density on alkyne-functional silica substrates. The presence of free 1-pentyne also increases the polymer density on alkyne-functional wafers containing a preexisting polymer brush. This study shows that the placement of each functional group in the CuAAC reaction is important in surface modification applications. In Chapter 5, a universal model to quantify the amount of tails vs. loops during brush formation of telechelic polymers is proposed. This model involves the synthesis of telechelic polymers bearing a degradable unit in the middle of each chain via ATRP. Several reaction schemes are suggested for the synthesis of the required bi-functional ATRP initiators with degradable units. The amount of singly (tails) vs. doubly (loops) bound chains is quantified by comparing the brush heights, measured by ellipsometry, before and after degradation.

No description available.

The goal of this research is to develop an integrated polymer embossing module, with which difficult-to-emboss polymer microstructures and microparts can be fabricated in a cost-effective manner. In particular, the research addresses three major limitations of the hot embossing process, namely, long cycle time, difficulty in producing shell patterns, and difficulty in building up a high embossing pressure on thick substrates. To overcome these limitations, three new technical approaches two-station embossing, rubber-assisted embossing, and through-thickness embossing were developed and investigated. Fundamental understanding of these new embossing techniques were achieved through extensive experimental and theoretical studies involving parametric experiments, rheological characterization, surface investigation, mathematical modeling, and computer simulation.

Thesis (Ph.D)--Chemical Engineering, Georgia Institute of Technology, 2010. / Committee Chair: Meredith, Carson; Committee Member: Bucknall, David; Committee Member: Fuller, Tom; Committee Member: Griffin, Anselm; Committee Member: Koros, William. Part of the SMARTech Electronic Thesis and Dissertation Collection.

Misturas de poliacetal (POM), polímero de engenharia com boas propriedades mecânicas, com poliuretano termoplástico (TPU), um polímero composto por uma fase rígida e outra flexível visam buscar alternativa de materiais a serem utilizadas em bandas externas de roldanas, visando a diminuição da emissão de ruído das roldanas quando utilizadas em sistema de movimentação de portas de armários, em contato com um trilho metálico. Neste trabalho foram avaliadas as propriedades mecânicas, físicas, térmicas e morfológica de misturas de POM/TPU nas proporções 100/0, 80/20, 70/30, 60/40, 50/50, 40/60 e 0/100 (m/m). As misturas foram preparadas em extrusora dupla rosca corrotante e após os corpos de prova foram injetados em injetora convencional. O aumento dos teores de TPU nas misturas promoveu o aumento da resistência ao impacto, à abrasão e diminuição na dureza do material. Houveram aumentos da temperatura de deflexão térmica das misturas com o aumento do teor de POM. Através da microscopia eletrônica de varredura (MEV) pode ser analisada uma mistura homogênea com partículas dispersas de TPU em formato de gotículas. A avaliação de emissão de ruído mostrou que com a diminuição do módulo de elasticidade, com o aumento da quantidade TPU na mistura, ocorre a redução da emissão de ruído do mesmo, esta redução fica evidente em frequências acima de 1kHz, ocorrendo uma redução da emissão de ruído de 2-5dB. / Submitted by Ana Guimarães Pereira (agpereir@ucs.br) on 2015-02-20T16:45:11Z No. of bitstreams: 1 Dissertacao Celso Roman Junior.pdf: 3205658 bytes, checksum: 028ff664a71b2d23dd502892c15b0e08 (MD5) / Made available in DSpace on 2015-02-20T16:45:11Z (GMT). No. of bitstreams: 1 Dissertacao Celso Roman Junior.pdf: 3205658 bytes, checksum: 028ff664a71b2d23dd502892c15b0e08 (MD5) / Bolsa Desenvolvimento de Tecnologia e Inovação / Polyoxymethylene (POM), an engineering polymer with good mechanical properties, blended with thermoplastic polyurethane (TPU), a polymer composed by a flexible and a rigid phase, are an alternative of materials to be used in external bands of pulleys, aiming to reduce the noise emission of pulleys when used in system drive cabinets doors, occurring pulleys contact with a metallic rail. In this work, the mechanical, physical, thermal and morphological properties of POM/TPU blends were evaluated in the proportions of 100/0, 80/20, 70/30, 60/40, 50/50, 40/60 and 0/100 (w/w). The blends were prepared in a twin screw extruder and after the samples were injected in a conventional injector. The increase in the levels of TPU on the blends promoted a rise in the impact resistance, abrasion and a decrease in the material hardness. There was an increase in the deflection heat temperature of the blends with enhanced content of POM. Through scanning electron microscopy (SEM) was observed a blend with the presence of dispersed TPU particles. The noise emission showed that with the decrease in the modulus of elasticity of the polymer occurs a reduction of noise emission. This reduction is evident in frequencies above 1 kHz, causing 2-5dB reduction of noise emission.

Orientadores: Cecília Amélia de Carvalho Zavaglia, Vanessa Petrilli Bavaresco / Tese (doutorado) - Universidade Estadual de Campinas, Faculdade de Engenharia Mecânica / Made available in DSpace on 2018-08-23T08:52:06Z (GMT). No. of bitstreams: 1 Lima_LonetaLauro_D.pdf: 3772105 bytes, checksum: ad6e43883313d496e11ffb1ce6a798d9 (MD5) Previous issue date: 2013 / Resumo: A área de biomateriais tem crescido e desenvolvido tecnologias para acompanhar e suprir as demandas que tem surgido a cada dia na área médica. Os novos biomateriais são produtos versáteis que atuam, combatem ou reparam inúmeras limitações e patologias. Dentro da classe de biomateriais poliméricos os hidrogéis têm sido cada vez mais estudados devido as suas características serem adequadas para várias aplicações biomédicas, dentre elas a cartilagem articular. As tecnologias de fabricação também tem acompanhado o desenvolvimento dos biomateriais. A prototipagem rápida tem impulsionado as pesquisas na área biomédica e permitido a biofabricação de estruturas complexas que existe no corpo humano e de animais. A biofabricação integra os fundamentos da engenharia e o conhecimento da área biomédica para produzir dispositivos biocompatíveis que possam ser utilizados na área biomédica. Esse trabalho é um estudo para verificar a viabilidade de fabricar substratos de poli (metacrilato de 2-hidroxietila) (pHema) usando um equipamento desenvolvido pelo grupo de pesquisadores do INCT Biofabris da Unicamp. Esse equipamento de biofabricação utiliza os princípios da estereolitografia por irradiação direta com luz UV-Visível para fabricar dispositivos médicos Os substratos foram produzidos utilizando seis diferentes composições químicas, para verificar a influência da composição química nas propriedades mecânicas, biológicas e biotribológicas dos hidrogéis. Foi verificado que os substratos produzidos com maior densidade de reticulação promove maior proliferação celular / Abstract: The development of biomaterials area has grown and has developed technologies aimed to satisfy the demands that emerge every day in the medical field. New biomaterials are versatile products that act and repair numerous limitations and diseases. Within the class of polymeric biomaterials, hydrogels have been increasingly studied due to their characteristics that are suitable for various biomedical applications, such as articular cartilage. Manufacturing technologies have also followed the development of biomaterials. Rapid prototyping has driven research in the biomedical field and has allowed the biomanufacturing of complex structures that exist in the human and animals' body. The biomanufacturing integrates the fundamentals of engineering and biomedical knowledge to produce biocompatible devices that can be used in the biomedical field. This work is a study to verify the feasibility for fabrication of substrates of poly (2-hydroxyethyl methacrylate) (pHema) using an equipment developed by the research group of INCT Biofabris Unicamp. This equipment is based on the principle of stereolithography by direct irradiation with UV- visible light to fabricate medical devices. The substrates were produced using six different chemical compositions in order to verify the influence of the chemical composition on the mechanical properties, biological and biotribological properties of hydrogels. It was found that the substrate produced with higher crosslinking density promotes greater cell proliferation / Doutorado / Materiais e Processos de Fabricação / Doutora em Engenharia Mecânica

Misturas de poliacetal (POM), polímero de engenharia com boas propriedades mecânicas, com poliuretano termoplástico (TPU), um polímero composto por uma fase rígida e outra flexível visam buscar alternativa de materiais a serem utilizadas em bandas externas de roldanas, visando a diminuição da emissão de ruído das roldanas quando utilizadas em sistema de movimentação de portas de armários, em contato com um trilho metálico. Neste trabalho foram avaliadas as propriedades mecânicas, físicas, térmicas e morfológica de misturas de POM/TPU nas proporções 100/0, 80/20, 70/30, 60/40, 50/50, 40/60 e 0/100 (m/m). As misturas foram preparadas em extrusora dupla rosca corrotante e após os corpos de prova foram injetados em injetora convencional. O aumento dos teores de TPU nas misturas promoveu o aumento da resistência ao impacto, à abrasão e diminuição na dureza do material. Houveram aumentos da temperatura de deflexão térmica das misturas com o aumento do teor de POM. Através da microscopia eletrônica de varredura (MEV) pode ser analisada uma mistura homogênea com partículas dispersas de TPU em formato de gotículas. A avaliação de emissão de ruído mostrou que com a diminuição do módulo de elasticidade, com o aumento da quantidade TPU na mistura, ocorre a redução da emissão de ruído do mesmo, esta redução fica evidente em frequências acima de 1kHz, ocorrendo uma redução da emissão de ruído de 2-5dB. / Bolsa Desenvolvimento de Tecnologia e Inovação / Polyoxymethylene (POM), an engineering polymer with good mechanical properties, blended with thermoplastic polyurethane (TPU), a polymer composed by a flexible and a rigid phase, are an alternative of materials to be used in external bands of pulleys, aiming to reduce the noise emission of pulleys when used in system drive cabinets doors, occurring pulleys contact with a metallic rail. In this work, the mechanical, physical, thermal and morphological properties of POM/TPU blends were evaluated in the proportions of 100/0, 80/20, 70/30, 60/40, 50/50, 40/60 and 0/100 (w/w). The blends were prepared in a twin screw extruder and after the samples were injected in a conventional injector. The increase in the levels of TPU on the blends promoted a rise in the impact resistance, abrasion and a decrease in the material hardness. There was an increase in the deflection heat temperature of the blends with enhanced content of POM. Through scanning electron microscopy (SEM) was observed a blend with the presence of dispersed TPU particles. The noise emission showed that with the decrease in the modulus of elasticity of the polymer occurs a reduction of noise emission. This reduction is evident in frequencies above 1 kHz, causing 2-5dB reduction of noise emission.