Thermoplastic starch biocomposites reinforced with hemp shives obtained via extrusion

Biodegradable and sustainable materials are becoming increasingly important in response to environmental concerns associated with traditional petroleum-based plastics. The objective of this study was to assess the feasibility and efficiency of incorporating hemp shives as a filler in thermoplastic wheat starch, aimed at promoting environmental sustainability and reducing reliance on non-renewable resources. The biocomposites, prepared by extrusion, consisted of pure starch, different hemp shives concentrations (10%, 20%, 30%, 40%, 50%, and 70%), with water and glycerol as plasticizers. The results revealed that the incorporation of shives notably enhanced the mechanical properties of the biocomposite, reaching an optimal performance at 40% shives concentration (resulting in a maximum tensile strength of 11.5 MPa and Young's modulus of 1621 MPa). In this concentration, ESEM images unveiled robust adhesion between hemp shives and the matrix, indicating starch penetration into the shives' parenchymatous cells. At higher concentrations, however, the resulted high pressures during extrusion collapsed the shive cells, impairing their adhesion with starch and reducing the biocomposite strength. The hemp shives addition reduced the water uptake, thereby enhancing the dimensional stability. Conclusively, this study offers pivotal insights into the development and characteristics of starch/hemp shives biocomposites, with structure-process-properties relationships, suggesting their potential applicability in the creation of eco-friendly packaging materials and small objects, presenting a viable alternative to traditional materials.