Sustainable packaging solutions: harnessing primary sludge cellulosic fibres in foamed starch materials via injection moulding

Abstract

Driven by stringent environmental regulations and keen social awareness, the pulp and paper industry is increasingly challenged by the growing volume of residues generated, highlighting the need for more comprehensive plants and to find solutions to transform biowastes into value-added products. Tackling this problem while replacing synthetic polymer packaging with natural alternatives is challenging, but it also provides an opportunity to address both issues. The main objective of this study was to develop sustainable packaging solutions using primary sludge, a major cellulose fibre residue from the paper industry. For the purpose, the sludges were combined with starch, a natural polymer, to produce foamed trays via injection moulding, using water as plasticizing and blowing agent. The injection moulding conditions were optimized, and the physical properties and microstructure of the resulting materials were evaluated. The results showed that foamed trays could be successfully produced using formulations with up to 28% wt of primary sludge incorporated into a starch matrix through injection moulding. The resulting trays had a cellular foamed structure with a dense hard hydrophobic surface layer, displaying a water contact angle greater than 115°. The foamed inner structure contributed for the low density of about 0.500 g cm⁻³ and the high-water absorption capacity. The packaging material revealed flexural stress values varying in the order of 5.0–7.0 MPa and flexural modulus of 370–450 MPa. This study demonstrated that sustainable 3D foamed packaging materials can be produced from natural and waste materials using injection moulding, representing a shift from earlier thermopressing methods traditionally used for manufacture starch-based biocomposites.