Chemical blowing agent-based processing of integral-skin polypropylene cellular composites in rapid rotational foam molding

Abstract

The traditional rotational molding process is the most widely implemented technology for low-cost fabrication of low-volumes of hollow/double-walled large-sized, seamless and virtually stress-free, single-piece plastic articles with complex shapes and/or moderate undercuts. However, demanding industrial end-use applications often require lightweight rotationally molded articles that could resist harsh environments while simultaneously demonstrating buoyancy, enhanced mechanical strength, thermal and/or acoustic insulative properties, as well as improved strength-toweight ratios. In response to this need, over the years, several design modifications of the traditional rotational molding process advantageously enabled the manufacture of rotationally foam molded cellular composites having a distinct integral solid-skin that is fully encapsulating a foamed inner core or layer. Although the resulting cellular composite moldings were attributed with significantly enhanced properties compared to their hollow non-foamed predecessors, the inherent disadvantages of the traditional parent process, such as the very lengthy and energy-intensive processing cycle times and the very limited means for real-time process control, were only further aggravated. This paper focuses on a recently patented process that alleviates these drawbacks by replacing the close interactions between foamable and nonfoamable polymeric resins to their effective independence. It is referred to as Rapid Rotational Foam Molding (RRFM). An experimental study in the domain of processing polypropylene (PP)-based integral-skin cellular composites using the RRFM technology is presented in details. In this context, by successfully decoupling (segregating) the skingenerating/article-shaping processing phase from the foamed-core-processing segment, RRFM proved to provide a viable solution to the common previously faced challenges in the manufacture of PP foams surrounded by an integral-solid-PPskin with a desired shape.