Dynamic Mechanical Analysis of in situ Microfibrillar Composites Based on PP and PET

Microfibrillar composites (MFCs) based on polypropylene and poly (ethylene terephthalate) were prepared by a three step process namely blending (extrusion), fibrilization (drawing) and isotropization, using different draw ratios (viz. 2, 5, 8 and 10). The drawn (stretched) blend was injection moulded at a temperature between the melting points of the two polymers, leading to isotropization. During this step PET microfibrils got randomly distributed in an isotropic PP matrix to complete the formation of microfibrillar in situ composites. The dynamic mechanical properties such as storage modulus (E′), loss modulus (E″) and mechanical loss factor (tan δ) of PP, neat blend and in situ composites were investigated. The E′ values were found to increase up to a stretch ratio of 8. The glass transition temperature (Tg) of PP in the MFC was found to shift to higher values with an increase in stretch ratio. The presence of microfibrils showed a positive effect on the modulus at temperatures above Tg of PP, especially for the samples drawn at stretch ratio 5 and 8. The tan δ and E″ modulus spectra indicated a strong influence of the microfibrils on the magnitude of α and β relaxations of PP. The effect of test frequency on storage modulus, loss modulus and tan δ was studied.

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