Evaluation of nano-mechanical properties and morphology of filled polypropylene modified by irradiation

Martin Ovsik,Martin Reznicek,Michal Stanek,N Mastorakis,V Mladenov,A Bulucea

doi:10.1051/matecconf/201712502042

Abstract

This paper describes the effect of electron beam irradiation on the surface properties (nano-indentation test) of glass fiber filled polypropylene (30%). These nano-mechanical properties were measured by the DSI (Depth Sensing Indentation) method on samples which were non-irradiated and irradiated by different doses of the β – radiation (33, 66 and 99 kGy). The purpose of the article is to consider to what extent the irradiation process influences the resulting nano-mechanical properties measured by the DSI method. The polypropylene tested showed significant changes of indentation hardness and modulus. The best results were achieved by irradiation at doses of 99 kGy (increase about 35%) by which the highest nano-mechanical properties of filled polypropylene were achieved. These changes were examined and confirmed by X-ray diffraction and Gel content.

Highlights

Polypropylene (PP) is a stereospecific polymer prepolyamydered by polymerization using an organometallic catalyst system
Commercial polypropylenes have up to 95% isotactic content, which means that pendant methyl groups are almost all on the same side of the chain
If the radical is formed on the pendant methyl, the resulting reaction is cross-linking

Summary

Introduction

Polypropylene (PP) is a stereospecific polymer prepolyamydered by polymerization using an organometallic catalyst system. Commercial polypropylenes have up to 95% isotactic content, which means that pendant methyl groups are almost all on the same side of the chain. When polypropylene is exposed to ionizing radiation, free radicals are formed and these cause chemical changes. Since PP is highly crystalline, these radicals are relatively immobile, and may not be available for reaction for long periods of time. Upon irradiation the free radicals are formed along with evolution of hydrogen gas. If the radical is formed on the pendant methyl, the resulting reaction is cross-linking. If the radical is formed in the main chain, the chain end may react with hydrogen, causing an irreversible scission. The processes of chain scission and cross-linking occur simultaneously, and even though the net effect is crosslinking, the overall effect is the loss of mechanical strength. The processes of chain scission and cross-linking occur simultaneously, and even though the net effect is crosslinking, the overall effect is the loss of mechanical strength. [1-3]

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