Sustainable foamed starch biocomposites produced by injection moulding: Effect of fibrous reinforcement material and inorganic filler

In this study, environmentally friendly starch-based foamed material was obtained by injection moulding using simple and sustainable formulations with only four natural components. The basic formulation contains starch (75–85% wt.) as the main matrix, cellulose fibres as reinforcing material (0–20% wt.), kaolin (0–10% wt.) as an inorganic filler, and water (40–60% wt.), as multifunctional agent promoting gelatinization, plasticization and foaming. The importance of cellulosic fibre origin (hardwood or softwood, sulphite or kraft pulp) and the load of inorganic filler at the predetermined water content in the formulation were highlighted within the context of detected structure-properties relationships. Lightweight foamed biocomposites, with a density of 0.37–0.44 g∙cm −3 and displaying a hydrophobic surface and a highly porous hydrophilic core, were successfully fabricated. Water, at levels between 40 and 60% ( w /w), plays a crucial role in the processability, microstructure, and flexural properties of the biocomposites. Cellulosic fibres enhance the strength of foamed composites when incorporated up to 10% ( w /w) of the dry formulation. Additionally, the inclusion of kaolin as an inorganic filler increases porosity and mechanical strength, with most favourable effects observed at filler contents up to 5% ( w /w) on a dry matter basis. The best compromise in properties was obtained for the formulation containing (wt.) 10% of cellulosic fibres, 5% of kaolin, 85% of corn starch, as dry matter, and 50% of water. The proposed all-natural foamed composites are seen as an environmentally friendly prospect for packaging solutions, an alternative to conventional synthetic polymer foamed materials produced from fossil resources. • Four-component formulations included starch, cellulosic fibres, kaolin and water. • The formulations were processed by injection moulding using water as blowing agent. • Composite morphology consisted of a hydrophobic surface and a highly porous core. • Cellulosic fibres affect the morphology and the strength of starch-based composites. • Kaolin contributes to the rigidity and porosity of foamed starch materials.