Sustainable Polylactic Acid Foam Development Via Solid-State Processing and Cross-Linking

Plastics have played a vital role in global materials industries for the past 80 years, but their contribution to climate change and their inability to biodegrade when disposed of the environment has generated great cause for concern. Bioplastics have replaced some of the traditional petroleum-derived materials over the recent years, with room for a wider range of applications and extensions. One important category of plastic material is polymer foams, which have widespread applications in insulation, packaging, and storage. The work covered in this project aims to generate, test, and analyze bio-based polylactic acid (PLA) polymer foams that undergo solid-state processing, such as solid-state shear pulverization (SSSP) and cryogenic milling, as a pre-process prior to foaming. Solid-state processing has been shown to enhance crystallization kinetics of PLA, which theoretically enables better PLA foaming by allowing PLA to crystallize quicker and therefore capture more gas. This study focuses on foaming through a chemical foaming method, using an exothermic, nitrogen-based chemical foaming agent (CFA). Melt extrusion and compression molding are used to generate the foams after initial solid-state processing. It is determined whether the enhanced properties through solid-state processing support chemical foaming to a sufficient extent to enable PLA foams that are comparable with those that use petroleum-derived cross-linkers such as dicumyl peroxide (DCP) and tryallylisocyanurate (TAIC), which are currently the industry standard.