Effect of Mold Temperature on the Impact Behavior and Morphology of Injection Molded Foams Based on Polypropylene Polyethylene⁻Octene Copolymer Blends.

Santiago Muñoz-Pascual,Cristina Saiz-Arroyo,Miguel Angel Rodriguez-Perez,Eduardo Lopez-Gonzalez

doi:10.3390/polym11050894

Santiago Muñoz-Pascual, Cristina Saiz-Arroyo + Show 2 more

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https://doi.org/10.3390/polym11050894

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Journal: Polymers	Publication Date: May 15, 2019
Citations: 11	License type: CC BY 4.0

Affiliation: University of Valladolid

Abstract

In this work, an isotactic polypropylene (PP) and a polyethylene–octene copolymer (POE) have been blended and injection-molded, obtaining solids and foamed samples with a relative density of 0.76. Different mold temperature and injection temperature were used. The Izod impact strength was measured. For solids, higher mold temperature increased the impact resistance, whereas in foams, the opposite trend was observed. In order to understand the reasons of this behavior, the morphology of the elastomeric phase, the crystalline morphology and the cellular structure have been studied. The presence of the elastomer near the skin in the case of high mold temperature can explain the improvement produced with a high mold temperature in solids. For foams, aspects as the elastomer coarsening in the core of the sample or the presence of a thicker solid skin are the critical parameters that justify the improved behavior of the materials produced with a lower mold temperature.

Highlights

Polypropylene (PP) is a polymer with relatively low cost and excellent properties such as low density, easy processability, good recyclability, moisture resistance, high thermal stability or excellent chemical and corrosion resistance
The impact strength and the morphology of foamed materials produced from PP/polyethylene–octene copolymer (POE) blends have been studied
A 24% density reduction was obtained and this density reduction promoted, on average, a 60% reduction of the impact resistance

Summary

Introduction

Polypropylene (PP) is a polymer with relatively low cost and excellent properties such as low density, easy processability, good recyclability, moisture resistance, high thermal stability or excellent chemical and corrosion resistance. These versatile properties make this material one of the most used commodity plastics, and this is the reason why the mechanical performance of PP arouses scientific interest. Unless highly selective nucleating agents are used, PP typically crystallizes in the α-form, this morphology being the one obtained in this study [5] Another common strategy is to blend PP with other polymers, especially

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