E. Hage

Effects of processing conditions on the phase morphology of PC/ABS polymer blends

The phase morphology of PC/ABS blends can be significantly affected by its processing conditions. Blends prepared in a mixing chamber at different conditions show a strong influence of mixing time and temperature on its morphology. The blend morphology changes from a well-dispersed PC phase surrounded by the ABS matrix phase to a cocontinuous morphology with increase in the mixing time. Higher blending temperatures promote changes in the PC/ABS morphology, probably due to thermal degradation. The rotor speed has not shown much influence on the blend phase morphology. The cocontinuous phase morphology of the PC/ABS blends obtained after mixing for 10 min was shown to be unstable as detected by the heat treatment. A melt annealing for a few minutes showed a significant change in the morphology.

Compósitos termoplásticos com madeira

Resumo: Dentre muitas fibras naturais de interesse tecnologico, o residuo de madeira substitui com vantagens as cargas e reforcos tradicionalmente empregados em compostos e compositos polimericos, particularmente os de ori- gem mineral, tais como talco, CaCO 3 e fibra de vidro. A tecnologia dos chamados Wood-Plastic Composites (WPCs) envolve conceitos de compatibilidade e processabilidade e apresenta grandes desafios tecnologicos para a formula- cao e estabilizacao da mistura devido a baixa estabilidade termica da celulose. Muitos dos avancos tecnologicos em WPCs dependem de uma analise criteriosa das caracteristicas fisicas de seus componentes e das condicoes de processamento do sistema, particularmente aspectos relacionados a sua compatibilizacao. No presente trabalho sao apresentados estudos sobre a reatividade do polipropileno modificado com anidrido maleico (PP-MAH) utilizado como compatibilizante em compositos termoplasticos de polipropileno com farinha de madeira. A influencia da carga celulosica e a eficiencia do compatibilizante nas propriedades reologicas, termicas, mecânicas e morfologicas do sistema foi avaliada atraves de medidas de rigidez, grau de cristalinidade, temperatura de cristalizacao e fusao cristalina levando-se em conta as caracteristicas da resina, a distribuicao granulometrica e o teor de umidade da farinha de madeira. Observou-se que os compositos compatibilizados com PP-MAH apresentaram ganhos significa- tivos de rigidez em relacao aos compositos nao-modificados independentemente do tipo de farinha de madeira em- pregada. As propriedades termicas do polimero mostraram-se sensiveis a distribuicao granulometrica e algumas com- posicoes apresentaram tendencia ao escurecimento e a elevacao da temperatura de cristalizacao do polimero na presenca do reforco celulosico. Imagens obtidas por microscopia eletronica de varredura ilustram o molhamento da fibra celulosica pela resina termoplastica quando na presenca do compatibilizante indicando a possivel ocorrencia de reacoes de esterificacao na interface polimero-madeira. Palavras-Chave: Compositos termoplastico-celulosicos, tecnologia polimero-madeira, compatibilizacao, reometria de torque, analise termica. Wood-Plastic Composites Abstract: Wood waste fibers (WWF), mostly known as wood flour, can replace mineral fillers such as talc, CaCO 3 and fiberglass in the reinforcement of thermoplastics with great advantage. Wood-plastics composites (WPCs) technol- ogy includes concepts of compatibility and processing and yet presents technical challenges in grade formulation and stabilisation of the composite system. Owing to thermal constraints in wood flour processing, commodities such as polyolefins (PP, PEAD/PEBD), styrenics (PS e HIPS) and vinyls (PVC) represent the bulk of the thermoplastics used in WPCs applications. In the present work, a brief overview of the latest developments in WPCs processing technol- ogy is discussed in the light of technical characteristics and performance of this novel class of thermoplastics com- posites in emerging applications. Some investigations on compatibilizing efficiency of the polypropylene modified with maleic anhydride (PP-MAH) are presented for polypropylene formulations compounded with different types of pinus wood waste. The influence of the cellulosic filler and the efficiency of compatibilizers on thermal, mechanical and morphology of the composite system was evaluated through stiffness measurements, degree of cristallinity, crystallization and melt temperatures in regard to the resin intrinsic properties and sawdust characteristics. Electron microscopy micrographs illustrate in great detail the filler wetting by the resin in the presence of the maleic anhy- dride in the polypropylene used as compatibilizer suggesting that sterification reactions may take place at the wood- polymer interface.

Crystallization behavior of PBT/ABS polymer blends

Poly(butylene terephthalate) (PBT) crystallization behavior is modified by blending it with acrylonitrile-butadiene-styrene copolymers (ABS). The effects of ABS on melting and crystallization of PBT/ABS blends have been examined. Most ABS copolymers of different rubber content and styrene/acrylonitrile ratios studied showed little effect on the melting behavior of PBT crystalline phase. However, ABS copolymer with high acrylonitrile content had a significant effect on the crystallization behavior of the PBT/ABS blends. The nucleation rate of the PBT crystalline phase decreased due to the presence of the high acrylonitrile content ABS, whereas the spherulitic growth rate increased significantly. These phenomena are attributed to changes in nucleation and growth mechanisms of PBT crystalline phase promoted by ABS.

Influence of notching and molding conditions on determination of EWF parameters in polyamide 6

Abstract The evaluation of the fracture toughness of polymers is highly relevant, particularly because of the ongoing development of new polymeric blends, most of which are aimed at increasing the impact resistance of engineering plastics. The toughness evaluation method, known as essential work of fracture (EWF), is a relatively simple method, useful for application on both brittle and ductile materials. This study investigated the effect of thickness, processing and testing conditions on the fracture behavior of polyamide 6. To this end, test specimens of the DDENT (double deeply notched tensile) geometry were tensile-tested under low (uniaxial tension) and high (tensile-impact) strain rates. The results, which are presented in terms of the variation of total fracture energy according to the ligament length, revealed that injection molded specimens without a pre-cracked notch offered the best choice. The geometrical criterion established by the ESIS protocol (test of the European Structural Integrity Society) for application of the EWF was also reviewed.

Thermal properties of nylon6/ABS polymer blends: Compatibilizer effect

Nylon6/ABS binary blends are incompatible and need to be compatibilized to achieve better performance under impact tests. Poly(methyl methacrylate/maleic anhydride) (MMA-MA) is used in this work to compatibilize in situ nylon6/ABS immiscible blends. The MA functional groups, from MMA-MA copolymers, react with NH2 groups giving as products nylon molecules grafted to MMA-MA molecules. Those molecular species locate in the nylon6/ABS blend interfacial region increasing the local adhesion. MMA-MA segments are completely miscible with the SAN rich phase from the ABS. The aim of this work is to study the effects of ABS and compatibilizing agent on the melting and crystallization of nylon6/ABS blends. This effect has been investigated by differential scanning calorimetry (DSC) and dynamic mechanical thermal analysis (DMTA). Incorporation of this compatibilizer and ABS showed little effect on the melting behavior of the PA6 crystalline phase, in general. DMTA analysis confirmed the system immiscibility and showed evidence of compatibility between the two phases, nylon6 and ABS, produced by MMA-MA copolymer presence. The nylon6/ABS blend morphology, observed by transmission electron microscopy (TEM), changes significantly by the addition of the MMA-MA compatibilizer. A better dispersion of ABS in the nylon6 phase is observed.

Evolução da morfologia de fases de blendas PA6/AES em extrusora de dupla rosca e moldagem por injeção

The evolution of phase morphology in non-reactive vs reactive blends with polyamide and ethylene-propylene-diene elastomer grafted with styrene-acrylonitrile copolymer (AES) in a co-rotating twin-screw extruder was investigated. The morphological evolution of these blends along a twin-screw extruder was monitored by quickly collecting small samples from the melt at specific extruder barrel locations and characterizing them with a transmission electron microscope (TEM). The copolymers methyl methacrylate-co-maleic anhydride (MMA-MA) and methyl methacrylate-co-glycidyl methacrylate (MMA-GMA) were used as compatibilizing agents. The maleic anhydride and the epoxy groups of the copolymers can react with the polyamide end groups during melt processing and improve the interphase interaction in the PA6/AES system. The uncompatibilized blends showed a coarse phase morphology where the AES phase is not well dispersed in the PA6 matrix due to lack of adequate interaction between the components. The addition of MMA-GMA compatibilizer neither promoted good phase dispersion or improved the mechanical properties of the blends, probably because the possible reactions are very slow and may not occur inside the extruder. On the other hand, the addition of the MMA-MA copolymer promotes better impact strength and good phase dispersion in the blend. The AES particles undergo significant reduction in the first stages of the mixture inside the extruder. The morphology observed for the injection molded specimens was correlated with the mechanical properties.

Compatibilização de blendas de poliamida 6/ABS usando os copolímeros acrílicos reativos MMA-GMA e MMA-MA. Parte 1: Comportamento reológico e propriedades mecânicas das blendas

Polyamide 6 (PA6) is a semicrystalline polymer suitable to be used in engineering applications with a number of advantages, but its processing instability and relatively low impact strength are limiting aspects. The addition of acrylonitrile-butadiene-styrene (ABS) as an impact modifier to PA6 can improve these properties. However, this blend is immiscible and incompatible, hence the use of an adhesion promoter is necessary to improve the interfacial interaction between the phases. This study focuses on the influence of poly(methyl methacrylate-co-glycidyl methacrylate) (MMA-GMA) and poly(methyl methacrylate-co-maleic anhydride) (MMA-MA) copolymers as compatibilizers for PA6/ABS blends. These copolymers are miscible with SAN phase of ABS due to the presence of PMMA and they have also the esther and anhydride functional groups capable of reacting with polyamide end groups. PA6/ABS/MMA-MA blends showed an excellent impact performance, being super-tough at room temperature and maintaining a good ductility in subambient temperatures.

Análise do desenvolvimento morfológico da blenda polimérica PBT/ABS durante as etapas de mistura por extrusão e moldagem por injeção

The aim of this work was to observe the development of the phase morphology of the PBT/ABS blends during their extrusion mixing and injection molding steps. The evolution of the blend morphology during the mixing stage was analyzed using a specially designed co-rotational twin-screw extruder with a collecting device located along the barrel. Blend samples were collected in-line along the length of the extruder barrel during the blending process. Blend morphology was also observed from specimens molded through injection molding. All the samples were observed by transmission electron microscopy (TEM). They were prepared by cryo-ultramicrotomy and the rubbery phase of the ABS contained in the blends was stained with osmium tetroxide (OsO4). A special function was established and is proposed to analyze the blend morphology trends through image analysis. In binary blends, the ABS phase showed better dispersion after the mixture passed through the extruder die. However, a coalescence phenomenon was observed during the next molding step. Compatibilized PBT/ABS blends showed better dispersion than binary blends, even after injection molding. The special function used to quantify the dispersion throughout the mixing and molding steps showed an excellent performance.

Determinação de temperatura de transição dúctil-frágil de plásticos através de testes de impacto instrumentado

Nesse trabalho e realizada uma analise descritiva do teste de impacto tipo Izod instrumentado e sao mostradas suas vantagens em relacao ao impacto convencional na obtencao de diagramas de forca e energia de fratura em tempo-real. Estes diagramas alem de fornecerem dados do material em termos de sua resistencia ao impacto tradicional, contem informacoes detalhadas sobre os mecanismos de fratura e as principais caracteristicas apresentadas durante a propagacao da trinca no corpo de prova. A medida da variacao da resistencia ao impacto com a temperatura pode ser utilizada como uma forma de se determinar a existencia de transicoes ductil-frageis ou alternativamente a suscetibilidade de materiais polimericos a concentracao de tensoes, i.e., profundidade e raio da extremidade do entalhe. As curvas de carga e energia, obtidas a varias temperaturas, sao utilizadas na determinacao de parâmetros do material e da temperatura de transicao ductil-fragil de um copolimero de acrilonitrila-butadieno-estireno (ABS). A analise da superficie de fratura por microscopia eletronica de varredura, (MEV) permitiu a correlacao da forma das curvas de impacto com o modo de fratura observado e detalhes da microestrutura do material.

Influência das condições de processamento na obtenção de blendas PBT/ABS

In order to correlate processing conditions in intermeshing co-rotational twin-screw extrusion (ICTSE) and properties of PBT/ABS blends, devices have been developed to obtain extruded strips from PBT/ABS blends. The PBT/ABS blend compatibilized with reactive copolymer methyl methacrylate- glycidyl methacrylate (MGE) has shown higher viscosity, lower heat of fusion and lower ductile-brittle transition temperature (DBTT) when compared to the non compatibilized PBT/ABS blend, possibly due to chemical reactions between MGE epoxy groups and the molecule end groups from PBT. Concerning the screw rotation, the compatibilized blend processed with 120 rpm has shown higher viscosity, lower heat of fusion and better impact strength properties than the one processed with 240 rpm. This could be a consequence of degradation of the blend components, caused by higher screw rotation. The feeding rate has presented itself as the processing parameter with the greater influence on blend properties. A feeding rate of 3.5 kg/h has severely compromised impact strength properties, reduced the viscosity and increased the heat of fusion, in contrast to a feeding rate of 7.0 kg/h. These observations can be attributed to a higher residence time, with the blend being submitted to higher temperature and shear for a long time, leading to the degradation of blend constituents.