Joyce Azevedo

Effect of reprocessing cycles on the degradation of PP/PBAT-thermoplastic starch blends

The solid waste management problems caused by the accumulation of plastics require measures to mitigate the environmental damage, and mechanical recycling of plastics is among the possible solutions. In this context, the present study aimed to evaluate the effects of mechanical recycling on the properties of a polypropylene/poly(butylene adipate co-terephthalate)-thermoplastic starch blend (PP/PBAT-Thermoplastic starch blend) when it was subjected to seven reprocessing cycles by a single-screw extruder. The observations by infrared spectroscopy indicated that the chemical structures of the blend and the polypropylene matrix did not present significant changes with the reprocessing cycles. The X-ray diffraction analyses showed that the PP crystals were most affected when reprocessed in their pure form. The observations by thermogravimetry and differential scanning calorimetry indicated that the thermal stability of the blend was higher than that of polypropylene during the extrusion cycles. The scanning electron microscopy images indicated a weak interfacial interaction between the components of the blend, and the mechanical properties showed that the reprocessing improved the elasticity modulus and yield stress, with a consequential decrease of the impact strength.

Heterogeneities and physical properties of ethylene-vinyl acetate foams containing calcium carbonates

This work investigated the effect of type (natural or precipitated) and content of calcium carbonate in ethylene-vinyl acetate foams produced by compression moulding. This processing technique generates various types of heterogeneities in the product, like differences between the skin and the core. The differences in temperature on the mould surface also have a major influence in foam properties. The hardness was shown to vary widely from place to place in moulded samples, and this was related to local variations in temperature. The analysis of the effect of calcium carbonate showed that the precipitated one yield better physical properties like density, hardness and elastic modulus.

Efeito de reticulante na morfologia e propriedades físico-mecânicas de espumas poliméricas obtidas com EVA e EPDM

Polymer foams are biphasic materials prepared with a polymer matrix and a gaseous phase from a foaming agent. Products based on this type of material are currently in a good market position due to the good mechanical properties, low density and competitive cost. Blending EVA with elastomers is a feasible alternative to enhance the properties of the expandable compounds. Among the elastomers used as a blend component with EVA, EPDM has a high potential since it has a good compatibility with polyolefins. Considering that during the foam processing there are simultaneous crosslinking reactions and the formation of gases, the balance between these two effects has a strong influence over the physical characteristics of the final product. In this study the effect of a crosslinking agent on EVA/EPDM foams was investigated. The physical, mechanical and rheometric properties, as well as the foam morphology, were analyzed as a function of dicumil peroxide, used as a crosslinking agent. The results showed that this additive has a strong influence in the crooking and expansion of the compounds, affecting their properties.

Caracterização de compósitos obtidos a partir de polímero biodegradável e casca de arroz utilizando duas técnicas de processamento

A adicao de fibras naturais a uma matriz de polimero biodegradavel tem sido uma alternativa para obter compositos com melhores propriedades termicas e mecânicas. Tendo em vista que as propriedades dos compositos possam ser influenciadas pelas condicoes de processamento, tipo e concentracao da fase dispersa, este trabalho teve como objetivo obter compositos a partir de uma blenda comercial constituida de Poli (butileno adipato co-tereftalato) - PBAT/ Amido (EB), de carater biodegradavel, e casca de arroz (CA). Inicialmente foram preparados compositos com PBAT/Amido contendo 10,20 e 30% de (CA) utilizando extrusora de dupla rosca e misturador interno. Posteriormente, foram determinadas propriedades mecânicas e termicas dos sistemas obtidos. Os resultados das propriedades mecânicas mostraram que o modulo elastico dos compositos foi afetado pelo tipo de processamento empregado, os compositos obtidos em extrusora apresentam maior modulo que os compositos obtidos no misturador: 92% maior em compositos com 10% de carga, e 38% maior em compositos com 30% de carga. A resistencia ao impacto diminuiu significativamente e a resistencia a tracao aumentou moderadamente com o teor de casca de arroz, independente do tipo de processamento utilizado. A resistencia ao impacto de compositos com 30% de carga e aproximadamente 33% da resistencia ao impacto da blenda pura. Ja na resistencia a tracao, observou-se um aumento de 25% nos compositos com 30% de carga. Analises de MEV indicam que as particulas de carga foram adequadamente molhadas pela matriz e que a adesao carga/matriz e boa. A avaliacao dos resultados obtidos com as analises de DSC indicou que a adicao de CA nos compositos extrusados altera a temperatura de cristalizacao, variando de 75oC da amostra pura, para 101oC para as amostras com casca de arroz, resultado atribuivel ao efeito nucleante causado pela maior dispersao da carga neste tipo de processamento.

Biodegradation Evaluation of Composites with Natural Fiber by Weight Loss and CO2 Production

The biodegradable polymers pass by a degradation process resulting from action of microorganisms such as bacteria, fungi and algae. These polymers are being used as matrix in the composites obtained with natural fibers seeking to improve the mechanical and thermal properties without amending the biodegradability characteristics of the product. Thus, this study evaluated the biodegradation of composites obtained from commercial blends of poly (butylene adipate-coterephthalic) (PBAT) and starch as matrix and rice husk (CA) using two different techniques. PBAT starch systems with 10, 20 and 30% RH were obtained in an internal mixer and evaluated by weight loss by biodegradation test in the simulated ground, using the Sturm test. The tests for weight loss indicates that the attack of microorganisms occurs preferentially in the matrix. However, the atmosphere used in the Sturm test to evaluate the degradation was favorable biodegradation of samples of rice husk.