Vapor-foamed injection molding of polycarbonate using sodium chloride and active carbon as nucleating agents

This paper presents a new process for producing vapor-foamed polycarbonate (PC) parts using water vapor as the physical blowing agent and two kinds of nucleating agents, namely, sodium chloride (NaCl) particles and active carbon (AC) powder. The effects of these two nucleating agents on the surface roughness, mechanical properties, and microstructure of solid and foamed parts were characterized. The results were compared with microcellular injection molded parts using supercritical fluid (SCF) nitrogen as the physical blowing agent without a nucleating agent. The water vapor-foamed PC parts with NaCl as the nucleating agent had a smooth surface comparable to that of solid injection molded parts. Foamed PC parts with AC had desirable specific mechanical properties as well as an advantageous average weight reduction of 16.4 wt%. AC powder, serving as nucleating agents, water carrier, and reinforcing fillers, positively improved the microcellular structure and mechanical properties of vapor-foamed PC parts. Based on infrared spectrometry (IR) and gel permeation chromatography (GPC) results, the melt compounding processing to incorporate the nucleating agent and the vapor-foaming process caused minor thermal degradation and hydrolytic degradation, respectively. Without the nucleating agent, vapor-foamed PC parts exhibited much larger and fewer bubbles within the molded parts.