Morphology, Rheology and Crystallization in Relation to the Viscosity Ratio of Polystyrene/Polypropylene Polymer Blends.

Salim Hammani,Mikhael Bechelany,Nadji Moulai-Mostefa,Alain Dufresne,Pieter Samyn,Ahmed Barhoum

doi:10.3390/ma13040926

Abstract

Microfibrillar and droplet morphology of polypropylene (PP) phase dispersed in polypropylene (PS) was fabricated by using melt-extrusion. This morphology was obtained by introducing isotactic PP (20 wt.%) with different viscosity in the PS matrix (80 wt.%). Furthermore, the rheological properties of the blend investigated as a function of the viscosity ratio K. The variations in blend morphology were related to crystallization, melting properties, and viscoelasticity. The blends with K >> 1 develop a fine morphology with PP microfibrils along the flow direction, while diameters of the dispersed PP droplets gradually increase with lower values of K = 1, or K << 1. Crystallinity of the prepared blends significantly decreases compared to neat PP, while the microfibrillar morphology induces homogeneous crystallization with small crystallites. This is reflected in a decrease of the crystallization temperature, small loss in the crystallinity, and lower melting temperature of the PS80/PP20 blend compared to neat PP. The storage moduli, loss moduli, and complex viscosity are highest for the microfibrillar morphology that presents retarded relaxation. The rheological properties are dominated by the dispersed phase (K > 1), or matrix (K < 1). The variation in blend properties with microfibrillar morphology can be clearly distinguished from heterogeneous blends containing PP droplets, providing an efficient tool to create a binary blend with unique properties.

Highlights

Polymer blending is a simple and economically viable route to develop composite materials with superior properties than the parent phases
The morphology of PS80/PP20 blends with different viscosity ratios is shown in SEM micrographs in Figure 1, taken in a transverse direction to the flow
A high viscosity ratio will result in large deformed droplets and a coarse morphology, whereas a low or matching viscosity ratio could result in fine fibrils and uniform morphology during melt-spinning [48]

Summary

Introduction

Polymer blending is a simple and economically viable route to develop composite materials with superior properties than the parent phases. While some properties of immiscible binary blends such as homogeneity, elongation, and impact strength improve by interface compatibilization, the tensile strength for non-compatibilized binary blends of polystyrene (PS) with polypropylene (PP) remains superior in the non-compatibilized form [1]. Besides extensive research on chemical interface compatibilization [3], the PS/PP blends were less frequently studied in their non-compatibilized form [4]. The formation of finely dispersed particles frequently occurs in ternary blends as a result of wetting effects, but it is more difficult to induce a fine morphology in immiscible binary blends that present a rather island-like phase organization [8] or a bimodal distribution [9]

Methods

Results

Conclusion