Bio-foams for thermal packaging applications

Abstract

A liquid foaming technology was developed to produce bio-foams for packaging applications. Liquid foaming consists in the transformation of a liquid foamed solution into a porous solid polymer through liquid removal. Five bio-based liquid foaming formulations systems were explored in this research: starch-PVA-calcium sulfate, starch-gelatine, gelatine hydrogel, gelatinecomposites and hydrogel alternatives to gelatine. Gelatine hydrogel-composite foams secondary materials included bio-mass powders from agriculture waste, expanded vermiculite particles, silica aero-gel powders and honeycomb sandwich panels. The hydrogel foams alternative to gelatine were based on agar and gellan gum as main biopolymers. The feasibility of each formulation system was explored, and the key parameters of formulation and process conditions were identified. The role of different formulation (e.g. biopolymer content, gelatine strength, surfactant type and content, among others) and processing (e.g. expansion ratio, processing temperature and drying process, among others) factors on foaming and drying behaviour of the liquid foam, and the impact on foam structure and properties (density, drying shrinkage and mechanical, thermal and acoustic properties) of the solid foams were investigated. Hydrogel-foams with comparable densities and thermal conductivity to conventional polymeric foams were produced. Gelatine foams made with both surfactants “A” and C2 exhibited desirable properties for being a strong alternative to conventional plastic foams. Low densities (<20 kg/m3), thermal conductivity (≈0.039 W/k·m), and relatively low shrinkage level were achieved. Production upscale research would need to consider drying process optimization for drying time reduction and drying shrinkage minimization.