Effect of Injection Molding on the Performance of EDTAD-Functionalized Oat Protein Bioplastics as Water-Absorbent Materials

Sustainable water-absorbent materials derived from renewable resources represent an attractive alternative to petroleum-based counterparts. Oat protein concentrate (OPC), an underutilized plant protein, has considerable potential for this purpose, although its processing into injection-molded bioplastics has not previously been reported. While chemical functionalization has been explored to enhance the water affinity of protein-based materials, the combined influence of functionalization and thermomechanical processing on oat protein bioplastics remains unexplored. In this study, OPC was functionalized with ethylenediaminetetraacetic dianhydride (EDTAD) and processed by injection molding to investigate the combined effects of formulation, chemical functionalization, and mold temperature on the rheological, mechanical, thermal, and water-absorption properties of the resulting bioplastics. Among the formulations evaluated with glycerol (Gly) as plasticizer, OPC/Gly-70/30 showed the best balance between mechanical performance, water uptake, and soluble matter loss and was selected for functionalization. FTIR analysis showed spectral changes consistent with the introduction of additional carboxyl-containing groups after EDTAD treatment. Functionalization reduced the viscoelasticity of the protein/Gly doughs before processing but increased the viscoelastic moduli of the injection-molded bioplastics, showing that the effect of functionalization on the viscoelastic response depended on the processing stage. Although functionalized bioplastics molded at 120 °C exhibited lower water uptake than the native materials, reducing the mold temperature to 60 °C increased their water uptake capacity from approximately 115% to 232%, whereas the native bioplastics remained essentially unchanged. These findings highlight the interplay between chemical functionalization and thermomechanical processing, with mold temperature emerging as a key design parameter. The enhanced water uptake was accompanied by a reduction in tensile properties, highlighting the need to balance absorbency and mechanical performance when developing these materials for specific applications.