Improved cell morphology and thermal properties of expanded polypropylene beads by the addition of PP with a high melting point

Abstract

ABSTRACTExpanded polypropylene (EPP) beads have attracted attention in recent years due to their potential use in fabricating complex, three dimensional structures. In this study, a small amount of polypropylene (PP) with a higher melting temperature (HPP) was blended with low melting point PP (LPP) to regulate the cell morphology and thermal behavior peaks of the resulting blends. These materials were then foamed to produce EPP beads in an autoclave with CO2 at different temperatures, producing EPP beads. The rheological, thermal, and foaming properties of the LPP/HPP blends were characterized. The melt strength and elasticity of LPP/HPP were improved because of rapid crystallization and increase in crystal number with increasing HPP content. These results were attributed to the physical crosslinks and nucleation sites provided by the HPP. These enhanced properties were leveraged to produce regular foams without through‐holes, decreased cell size, and increased cell density. Furthermore, the lower melting point decreased with increasing HPP content, producing a wider temperature range over which steam‐chest molding could occur. Thus, the addition of HPP is a facile method for regulating the cell morphology and thermal behavior of EPP. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017, 134, 45121.