Modificação da opacidade de copolímero heterofásico de polipropileno

Abstract

Heterophasic copolymers, or impact copolymers are obtained in sequential reactors, in which the polypropylene (PP) is obtained in the first reactor as matrix and the rubber phase of ethene-propene (EPR) is obtained in the second reactor. The rubber phase provides great impact properties to the material, but it makes it more opaque when compared to PP homopolymer. The opacity reduction of impact copolymers is a desired property for the application in rigid and flexible packaging. The objective of this study is to test different methodologies for modifying the crystallization process and rubber fraction of the heterophasic copolymer to achieve opacity reduction. The polymer provided by Braskem S.A used in this study has a flow rate of 26 g/min (230°C/2,16Kg), density of 0,900g/cm3 and average opacity of 90% for the commercial product. The processes studied to obtain opacity reduction were: a) Grafting of itaconic acid in the polymer chain through reactive extrusion; b) Neutralization with sodium hydroxide of the polymer grafted with itaconic acid to obtain the sodium itaconate salt grafted in the polymer matrix; c) Dispersion of the synthetized sodium itaconate salt as a nucleating agent. The techniques used for characterization of the materials were: DSC, MOLP, AFM, FTIR, RMN, XRF, Haze Percent and DMA. The neutralization process of grafted itaconic acid gave the material opacity results of 42%, which means an opacity reduction of 53% comparing to the commercial product.