Influence of Exothermic and Endothermic Chemical Foaming Agents on the Physical and Mechanical Properties of the Polypropylene-Based Thermoplastic Structures

Abstract

Using a chemical foaming agent (CFA) along with a thermoplastic polymer in a foam extrusion process has a significant effect on the density and thickness of the final product so that highly light-weight and low-cost structures could be achieved. In this experimental study we have investigated the thermal and chemical behavior of two different types of CFA and their effect on the foam quality and physical/mechanical properties of the final product in an extrusion foaming process. A polypropylene-based thermoplastic (PP) sheet was produced via a plastic extrusion machine with 12″ width and 4mm thickness. An exothermic foaming agent Azodicarbonamide (EV AZ-3.0) was added into the PP pellets in 5 wt%. They were completely mixed and melted inside the extruder to decompose and liberate gas. The melt temperature and pressure must be high enough to guarantee a total decomposition of the foaming agent and make the generated gas dissolved inside the polymer melt until it exits from the die opening. The same trial was conducted with an endothermic CFA named Styrene-Ethylene/Butylene-Styrene (PN-40E). Our thermal TGA analysis and physical tests demonstrate that each of the foaming agents has its own unique specifications which could be utilized based on the operating temperature and pressure. However, using the exothermic CFA is recommended for the PP-based thermoplastic foams as it can build up the product with low weight and high specific stiffness.