Biodegradable composites of starch/polyvinyl alcohol/soybean hull (Glycine max L.) produced by thermoplastic injection

Abstract Soybean hull is an agro‐industrial residue produced abundantly both in Brazil and worldwide. It is generated during the dehulling of the grains for oil production. This work aimed to develop materials using low‐cost, abundant, and biodegradable raw materials, as soybean hull, corn starch, polyvinyl alcohol (PVA), and glycerol. Five formulations of thermoplastic starch (TPS) were produced containing between 4% and 19% of ground soybean hull and another five formulations of the same composition but with 6% PVA added. The materials were extruded and injected to produce specimens. They were analyzed by FTIR‐ATR, mechanical tests, mass loss in water, and dimensional variations. The addition of hull to the TPS did not affect the processability of the materials, and the PVA improved the processability. Hull concentration from 8% to 15% increased the tensile strength of the materials, and the PVA reduced them. Soybean hull provided greater dimensional stability to the specimens, especially with PVA and with the highest hull contents (15% and 19%).Content of soy hulls between 8% and 15% acted as a structural reinforcer of TPS materials, forming a composite, as it increased the tensile strength, reduced the elongation, increased the stiffness, and improved the dimensional stability of the materials.