Improving of impact copolymer PP (ICP) blends properties via compounding

Abstract

Polypropylene is one of the well-known and multi-use thermoplastic materials because of its distinctive mechanical properties. On the other hand, it has deficiencies in the impact property at low temperatures. Several methods have been proposed and introduced to improve and overcome such deficiencies; one of them is the combination of isotactic homopolymer polypropylene and ethylene-propylene random copolymer (EPR) with a high ethylene content, which is usually created by consecutive polymerization in at least two reactors, to form a polymer called impact copolymer polypropylene (ICP). The distinctive properties of this type of ICP polymer made it an important material in various fields. The standard polypropylene impact copolymer, or “ICP,” is created as described above with a high ethylene content. However, the markets for these applications are calling for better levels of performance than those offered by PP homopolymer “HPP”. Notwithstanding the benefits of ICPs over HPP, there may be even more particular requirements for ICP features such impact/stiffness balance (I/S) and others, depending on the ultimate application. The maximum EPR level and highest isotacticity from the homopolymer continuous phase to manage the I/S balance, however, are both constrained by existing technology. The majority of earlier studies attempted to improve the ICP by melt blending it with materials that had the desired qualities, ideally materials from the same family, such as polyolefin or other families. In this study, ICP and PP homopolymer have been blended in a variety of ways and using the same weight percentages (Wt%). Different HPP grades with different melt flow, i.e., molecular weights, were utilized as a discontinuous phase in the final blend at a level of about 0.25%. Different ICP grades with varying ethylene-rubber phase and molecular weight were used as the continuous phase. The final blends were compounded, pelletized, and injection molded to manufacture finished components and/or samples for laboratory testing and analysis. Surprisingly, it has been discovered that discontinuous phases with varying molecular weights from the same family can operate as impact boosters or “plasticizer” at levels below 0.5% weight to enhance the impact resistance. Additional details on the improved sample, with different percentage of blends such as 0.5% and 1%, have been performed to investigate whether a further change in mixture composition could further improve the impact strength properties; the obtained values confirm that the improvement occurs when the level of the particular minor phase, i.e., HPP, is below 5 wt.%. The acquired findings were assessed and concluded that, for a given formulation, they revealed a well-dispersed rubber composition and consistent particle size distribution, which clearly improved the impact resistance by around 33% above the value of the virgin ICP.