The purpose of this thesis was to evaluate orthogonal cutting as a method to determine the fracture toughness of low and high density polyethylene and wood plastic composites. A test fixture was developed to capture normal and tangential cutting forces at variable depth and rake angle. A tool interface method (TIM) is proposed to separate forces on both sides of the tool from the energy needed to propagate the crack. Also investigated were shear plane models of chip failure, which seek to measure toughness by modeling internal stresses in the chip. These results are compared to current methods of determining essential work of fracture (EWF). It is found that cutting requires much less energy than current methods of EWF. Further work is suggested to better parameterize failure. / Graduation date: 2013

The effects of polyethylene, (PE), type, compatibilizer type and organoclay type on the morphology, rheological, thermal, and mechanical properties of ternary low density polyethylene (LDPE), high density polyethylene (HDPE), and linear low density polyethylene (LLDPE), matrix nanocomposites were investigated in this study. Ethylene &ndash / Methyl acrylate &ndash / Glycidyl methacrylate terpolymer (E-MAGMA) and Ethylene &ndash / Butyl acrylate- Maleic anhydrate terpolymer (E-BA-MAH) were used as the compatibilizers. The organoclays selected for the study were Cloisite 30B and Nanofil 8. Nanocomposites were prepared by means of melt blending via co-rotating twin screw extrusion process. Extruded samples were injection molded to be used for material characterization tests. Optimum amounts of ingredients of ternary nanocomposites were determined based on to the mechanical test results of binary blends of PE/Compatibilizer and binary nanocomposites of PE/Organoclay. Based on the tensile test results, the optimum contents of compatibilizer and organoclay were determined as 5 wt % and 2 wt %, respectively. XRD and TEM analysis results indicated that intercalated and partially exfoliated structures were obtained in the ternary nanocomposites. In these nanocomposites E-MA-GMA compatibilizer produced higher d-spacing in comparison to E-BA-MAH, owing to its higher reactivity. HDPE exhibited the highest basal spacing among all the nanocomposite types with E-MA-GMA/30B system. Considering the polymer type, better dispersion was achieved in the order of LDPE&lt / LLDPE&lt / HDPE, owing to the linearity of HDPE, and short branches of LLDPE. MFI values were decreased by the addition of compatibilizer and organoclay to the matrix polymers. Compatibilizers imparted the effect of sticking the polymer blends on the walls of test apparatus, and addition of organoclay showed the filler effect and increased the viscosity. DSC analysis showed that addition of compatibilizer or organoclay did not significantly affect the melting behavior of the nanocomposites. Degree of crystallinity of polyethylene matrices decreased with organoclay addition. Nanoscale organoclays prevented the alignment of polyethylene chains and reduced the degree of crystallinity. Ternary nanocomposites had improved tensile properties. Effect of compatibilizer on property enhancement was observed in mechanical results. Tensile strength and Young&rsquo / s modulus of nanocomposites increased significantly in the presence of compatibilizers.

No description available.

published_or_final_version / abstract / Physics / Doctoral / Doctor of Philosophy

published_or_final_version / Dentistry / Doctoral / Doctor of Philosophy

No description available.

No description available.

by Luk Wai Hi. / Thesis (M.Phil.)--Chinese University of Hong Kong, 1978. / Includes bibliographical references (leaves 111-112).

Orientador: Silvana Artioli Schellini / Resumo: Esta pesquisa foi realizada com o objetivo de se avaliar o comportamento do polietileno gel como um material para ser usado para a reposição de volume ou aumento de tecidos moles e para se estudar as reações teciduais que se seguem à sua injeção no subcutâneo dorsal de ratos. Material e método: uma injeção de 01 cc de polietileno gel (Makron Biopolímeros Ltda. - Mogi das Cruzes - SP - Brasil) foi efetuada na região subcutânea dorsal de 24 ratos brancos, machos, pesando cerca de 200 gramas cada um, sob anestesia geral, tricotomia e assepsia. Os animais foram separados em oito grupos e foram sacrificados 7 (G1), 15 (G2), 30 (G3), 45 (G4), 60 (G5), 90 (G6), 180 (G7) e 365 (G8) dias após a injeção da substância a ser estudada. Os espécimes foram removidos e preparados para o exame histopatológico. Este foi realizado ao microscópio óptico e foi realizada também a análise morfométrica dos dados obtidos. Os resultados foram submetidos à análise estatística (Kruskal-Wallis). Resultados: a comparação entre os grupos revelou que o polietileno gel esteve presente através de todo o período experimental, provocando escassa reação tecidual, com poucas células inflamatórias, principalmente na periferia do material e no começo do experimento. Posteriormente, essa reação foi mais densa, avançando para o centro do material e também com poucas células inflamatórias. Nenhum sinal de infecção foi observado durante o período experimental. Conclusões: a manutenção do PG, com reação inflamatória muito discreta e sem sinais de rejeição ou infecção, leva-nos a considerar este material como sendo uma boa opção para reposição de volume e para aumento de tecidos moles. / Abstract: This research was performed in order to evaluate the effects of gel polyethylene as a material to be used for reposition of lack of volume or soft-tissue augmentation and to study the tissue reactions following the injection of this substance into the dorsum subcutaneous region of rats. Material and methods: an injection of 1 cc of gel polyethylene (Makron Biopolímeros Ltda.- Mogi das Cruzes - SP - Brasil) was performed into the dorsal subcutaneous region of 24 white male rats, weighting about 200 grams each one, under general anesthesia, skin shaving and asepsis. The animals were separated into eight groups and they were sacrificed 7 (G1), 15 (G2), 30 (G3), 45 (G4), 60 (G5), 90 (G6), 180 (G7) and 365 (G8) days after the injection of the substance to be studied. The specimens were removed and they were prepared for the histopatologic examination, under optical microscopy. It was also performed the morphometric analysis of the observed data. The results were submitted to the statistic analysis (Kruskal-Wallis). Results: the comparison among the groups revealed that the maintenance of the presence of the gel polyethylene occurs throughout the experimental period, provoking a slack tissue reaction, with few inflammatory cells, mainly at the beginning of the experience. Later, the tissue reaction became denser, advancing to the center of the material, with also few inflammatory cells. The integration with the host was progressive and no sign of infection was observed throughout the experimental period. Conclusions: the injected gel polyethylene was present throughout the complete study, provoking a very slight inflammatory reaction and with a good integration with the host, taking us to consider that material as a good option for soft-tissue augmentation and lack of volume replacement. / Mestre

Filmes de polietileno (PE) contendo aditivo pró-degradante à base de um composto de cobalto foram expostos a intemperismo natural por 12 meses, em Canoas, RS (30º S, 59º W), sob condições de umidade ambiente e saturação de umidade. Procurou-se desenvolver condições de ensaio adequado para a degradação abiótica e biótica, visando monitorar alterações na estrutura da cadeia e propriedades mecânicas. Obtiveram-se valores crescentes de índice de carbonila com o aumento do tempo de exposição ao intemperismo natural, por meio de espectroscopia de infravermelho por transformada de Fourier (FTIR). A massa molar ponderal média decresceu de 170.000 para próximo de 8.000 g mol-1 com 4 – 5 meses de exposição, com fragilização progressiva das amostras e diminuição da resistência mecânica. A degradação biótica dos resíduos de PE originados a partir da degradação abiótica foi realizada em células fechadas, a 58º C. Após 90 dias de ensaio, as amostras de PE tiveram 12 % do seu carbono convertido a CO2, contra 70% obtidos com celulose (padrão positivo). Mesmo com essa diferença elevada em relação ao padrão positivo, a biodegradabilidade desenvolvida pelo PE pode ser considerada muito boa, uma vez que a biodegradação dessa poliolefina sem aditivo promotor de degradaçao é extremamente pequena. Assim, o aditivo pródegradante teve uma eficiência significativa em acelerar a degradação abiótica dos filmes de PE expostos ao intemperismo natural, em condições de umidade ambiente ou saturação de umidade. / Plastic bags of polyethylene (PE) containing cobalt prodegradant additive were exposed to natural weathering for 12 months, in Canoas, RS (30° S, 59º W). An appropriate test methodology for monitoring abiotic and biotic degradation was chosen, with evaluation of changes in the structure of the polymeric chain, mechanical parameters and biodegradation. Increasing results of carbonyl index demonstrated accelerated oxidation of the samples. The molar mass (weight average) decreased from 170.000 to 8.000 g mol-1 after 4 – 5 months of exposure, being followed by fragilization and mechanical resistance decrease. Biotic degradation tests of PE bags residues were performed in closed vessels, at the temperature of 58 ºC. According to the tests, residues of PE films reached a mineralization of 12% after 90 days, compared to 70 % for cellulose. That degree of biodegradation may be considered high, because biodegradation of PE films not containing prodegradant additives is very slow. Thus, the additive was showed efficient to accelerate the abiotic degradation, conferring biodegradability to PE films.