Effect of Coblowing Agent on the Supercritical CO2 Foaming Behavior of Polyvinyl Chloride: Induced Plasticization, Regulated Gelation, and Enhanced Mechanical Performance

Abstract

This work investigates the effects of coblowing agents (n-pentane, methyl acetate, n-butanol, and propionic acid) on the plasticization, gelation degree, and foaming behavior of polyvinyl chloride (PVC) using supercritical CO2. The results demonstrate that coblowing agents exhibit excellent plasticizing effects and a remarkable capacity to regulate the gelation degree of PVC. Specifically, the CO2/propionic acid system decreases the glass transition temperature (Tg) of PVC by 19.8 °C while simultaneously increasing the gelation degree by 20.3%. The introduction of coblowing agents enhances apparent blowing-agent solubility and decreases the gas apparent desorption diffusion coefficient. The enhanced plasticization significantly lowers the initial and optimal foaming temperatures by 10 and 20 °C, respectively. Under the optimized gelation degree and processing conditions, the expansion ratio increases from 11.1 to 16.5. For foams with an expansion ratio of approximately 10, the compressive strength and compressive modulus of the foam prepared using the CO2/propionic acid system increase by 123.3 and 294.4%, respectively. In summary, modulating the polarity of coblowing agents and their interactions with the polymer matrix not only effectively broadens the processing window but also provides a viable strategy for fabricating high-expansion and high-performance PVC foams.