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ABSTRACT:In this work, the shear-induced crystalline layers of isotactic polypropylene (i-PP), developed in a slit die, were characterized by different techniques. Rheological studies made in a strain-controlled rheometer, at different crystallization temperatures, T c , allowed us to observe that the induction time for the beginning of the shear-induced crystallization, t i , decreased as the shear rate increased, whereas at a given shear rate, the higher the T c , the higher the t i . The thickness of the shear-induced crystallized layer, after extrusion through the slit die, was found to decrease with the increase of the die temperature, T d , at a given flow rate, Q, and to increase with the increase in Q, at a given T d. Regarding the die length, it was found that only at T d ϭ 169°C, the thickness of this layer increased with the length. By polarized light optical microscopy (PLOM), five different crystalline layers were observed along the thickness of the sample. By scanning and transmission electron microscopy (SEM and TEM), respectively, and wide-angle X-rays (WAXS), it was found that layer 1, the nearest to the wall, was formed mainly by very small and oriented ␣-crystallites, while layer 2 was mainly composed of ␤-crystallites; also it was found that the amount of the ␤-phase decreased as the shear rate decreased. Key words: crystallization; polypropylene; morphology; rheology; extrusion INTRODUCTIONThe morphology along the thickness of semicrystalline polymers after extrusion or injection molding is usually formed by crystalline layers of different sizes and forms. Near the wall, very small and highly extended crystallites or cylindrites are observed, while near the center, large and unoriented spherulites are seen. In the intermediate region, columnar-or transcrystallinetype crystals can be observed. This morphology is called skin-core type. The skin is highly oriented due to the large shear rates that are developed near the wall, while the core is spherulitic because of the zero or minimum shear rates. This skin is also known as the shear-induced crystalline layer, while the core is known as the quiescent crystalline layer. The effect of the shear rate gradient on the morphology can also be better visualized in the injection molding of immiscible polymer blends, 1 where the disperse phase deforms according to this gradient. Although it is known that elongational flows enhance crystallization better than shear flows, 2,3 we will limit in this work to the study of only shear-induced crystallization.Eder et al. 4 were one of the first to formulate a kinetic theory for the development and understanding of this shear-induced crystalline layer. Their main as-

in Wiley InterScience (www.interscience.wiley.com).ABSTRACT: Conventional and chain extended-modified solid-state polymerization (SSP) of postconsumer poly(ethylene terephthalate) (PET) from beverage bottles was investigated. SSP was carried out at several temperatures, reaction times, and 2,2 0 -bis-2-oxazoline (OXZ) or pyromellitic anhydride (ANP) concentrations. The OXZ was added by impregnation with chloroform or acetone solution. Higher molecular weights were reached when the reaction was carried out with OXZ, resulting in bimodal distribution. The molecular weights of the flakes reacted at 230 C for 4 h were 85,000, 95,000, and 100,000 for samples impregnated with 0, 0.5, and 1.25 wt % OXZ solution, respectively. In the case of reactions with ANP, branched chains were obtained. The thermal and thermal-mechanical-dynamic properties of these high-molecular-weight recycled PET were determined. For OXZ-reacted samples, the reduction of crystallinity was observed as the reaction time was increased, becoming evident the destruction of the crystalline phase. The chain extended samples did not show changes in thermal relaxations or thermal degradation behavior.

impróprios, e tem contribuído para entupimentos da rede de esgoto e para a formação de enchentes, propiciando a proliferação de vetores e gerando graves problemas ambientais, como por exemplo, poluição de rios e nascentes e mesmo em aterros sanitários, o chorume que se forma causa a contaminação de aqüíferos e lençóis freáticos. Aliado a isto, a baixíssima degradabilidade dos mesmos e o seu elevado volume fazem com que os rejeitos plásticos ocupem vastos espaços por tempo muito longo, diminuindo o tempo de vida útil dos aterros sanitários. Sendo assim, o estudo do resíduo sólido urbano, de seus componentes e da viabilidade técni-ca e econômica da sua reciclagem é de fundamental importância no contexto da sociedade contemporânea [2,3,4] . Apesar do PEAD estar sendo amplamente utilizado em aplicações como pavimentação (reciclado misturado com asfalto), madeira plástica, construção civil (eletrodutos, conduítes, etc.), IntroduçãoAs crescentes aplicações do polietileno de alta densidade (PEAD), principalmente no setor de embalagens de rápido descarte, vêm tornando-o um dos plásticos mais consumidos no mercado mundial. Estudos realizados sobre a composição dos resíduos sólidos urbanos no Brasil, indicaram que o PEAD encontra-se em aproximadamente 30% do total dos plásticos rígidos coletados, perdendo o primeiro lugar apenas para o poli (tereftalato de etileno), PET, com 60% [1] . Apesar do plástico ter conquistado aos poucos seu espaço como material de grande importância para a sociedade, atualmente seu descarte é um problema para o mundo e principalmente para o Brasil. A falta de gerenciamento adequado para os resíduos urbanos, pode resultar em descartes Resumo: Neste trabalho, as propriedades reológicas de blendas de PEAD virgem e PEAD reciclado, em diferentes porcentagens, foram avaliadas em regime permanente, transiente e dinâmico de cisalhamento utilizando-se reometria cone-placa e reometria capilar. Embalagens de PEAD pós-consumo foram coletadas e submetidas aos processos básicos de recuperação de plásticos: lavagem, moagem e secagem. Formulações, previamente estabilizadas, contendo 0, 25, 50, 75 e 100% de material reciclado, adicionado à resina virgem, foram reprocessadas por extrusão e posterior injeção. Das medidas das propriedades reológicas foi possível concluir que a incorporação de material reciclado proveniente de resíduo pós-consumo à resina virgem promove, neste caso, uma diminuição da massa molar e aumento na sua distribuição. Além disso, um estudo das propriedades reológicas permite a predição de seu comportamento frente ao processamento de resinas recicladas pós-consumo. Palavras-chave: Reciclagem, resíduos pós-consumo, PEAD, propriedades reológicas. Evaluation of Rheological Properties of Virgin HDPE/Recycled HDPE BlendsAbstract: In this study, the incorporation of a high density polyethylene (HDPE) resin in a virgin resin was assessed by means of its rheological properties with the use of shear steady, transient and dynamic flows using cone and plate and capillary rheometry. HDPE post-consumer p...

Poly(propylene-co-ethylene) composites with rice husk were prepared in a corotating intermeshing twin-screw extruder using four different coupling agents. While modified maleic anhydrides such as maleated polypropylene (MAPP) and maleated polyethylene (MAPE) are commonly used as compatibilizers to improve interfacial adhesion between lignocellulosic filler and matrix, in this study, polypropylene grafted with acid comonomer (CAPP) and high-density polyethylene grafted with acid comonomer (CAPE) were also used. The morphologies and the thermal and mechanical properties of the composites were characterized using scanning electron microscopy, thermogravimetric analysis, differential scanning analysis, tensile and impact tests. The results indicate that the base resin of the compatibilizer is an important factor in determining the effectiveness of compatibilizers for composites. Composites with PP-based compatibilizers are more effective than PE-based compatibilizers due to the improved wetting of the former compatibilizer in the matrix polymer.