Advanced polycarbonate foam: Enhancing foamability and mechanical properties with toughened polycarbonate using nanofibrillation method and crosslinked rubbery EPDM networks

Abstract

The main objective of this study is to develop advanced composite technologies aimed at enhancing the foamability of Polycarbonate (PC) and simultaneously elevating ductility and toughness. During the foaming process with plasticizing blowing agents, amorphous PC undergoes crystallization, which results in a stiffened and excessively brittle PC state that restricts achieving a high expansion ratio. The embrittled cell walls of PC foam tend to open during the foaming process, leading to inadequate mechanical properties. This research leverages the in-situ nanofibrillation method, incorporating a rubbery nanofibrillar network to augment the properties of PC-based foams. PC-nanofibril ethylene-propylene-diene-monomer (EPDM) composites are manufactured initially manufactured through a twin-screw extruder, followed by a spunbond system. The advantageous effects of the crosslinked rubber phase induced by gamma irradiation, alongside nanofibrillation processing, serve as pivotal contributors to property improvement. These processes lead to an augmentation of the expansion ratios and cell densities. The presence of EPDM nanofibrils relaxes the local tensile stresses caused by shrinkage from the crystallized PC molecules, resulting in the successful prevention of cell opening. Additionally, the presence of soft EPDM nanofibrils also relaxes the stiffened PC matrix, resulting in significantly higher expansion ratios compared to the neat PC. Nanofibril rubber serves as a solution to this challenge: PC-nanofibril rubber composite foams exhibit a low density (10-fold), alongside high toughness and stiffness.