Syindiotactic polypropylene/EPDM blends, influence of processing and of thermal history in the physical and mechanical properties / Blendas de polipropileno sindiotatico com EPDM : influencia do processamento e da historia termica nas propriedades fisicas e mecanicas

AUTOR(ES)
DATA DE PUBLICAÇÃO

2005

RESUMO

The sPP containing 30 % of racemic pentads is a semicrystalline polymer presenting different crystalline polymorphs which depend on the thermo-mechanical history. Under heating sPP can recrystallize in a more perfect and thermodynamically stable form. The polymorphs differ in the density and also in the lamella thickness. The insertion of defects in the crystalline phase is not kinetically favorable, but it can happen under isothermal crystallization at low temperatures. Blends of sPP containing up to 50 wt % of EPDM prepared by melting mixture are immiscible, semicrystalline and compatible, presenting morphology of EPDM disperse phase in the sPP matrix. EPDM acts as toughness agent for sPP. The physical and mechanical properties of sPP/EPDM blends depend on the morphology of blends and on the crystalline characteristics of sPP. The conditions of mixing have an important influence on the blends morphology and also on the crystalline phase of sPP. Blends processed in a twin screw extruder show a better EPDM dispersion than blends prepared in a single screw extruder. The injection molding induces the formation of the metastable trans-planar mesomorphic phase of sPP, which can recrystallize in a more stable crystalline form under heating. The presence of chains with trans-planar conformation improves the toughness of sPP compared with the sPP containing chains with helix conformation. Annealing at 70 °C has no influence on the blends morphology, but it induces conformational changes of chains from trans-planar to helix and this can be the cause of the increase in the toughness of the blends. The annealing at 105 °C induces changes on morphology of the blends and on the sPP crystalline phase, wich are accompanied by a significant improvement of the elongation at break mainly for blends containing 20 and 30 wt % of EPDM. It is important to note that the crystalline degree of sPP and of its blends is independent of the thermo-mechanical history and the macroscopic properties of these materials are strongly related to the features of the sPP crystalline phase.

ASSUNTO(S)

epdm cristais - estrutura polimeros - morfologia spp crystal structure polymer morphology

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