Sustainable starch-based biocomposites: Effect of inorganic fillers on the structure and properties

• Thermoplastic starch (TPS) composites were prepared from plasticized starch. • Inorganic fillers reinforce TPS due to strong interactions. • Shrinkage of TPS composites decreases considerably. • Basalt fiber has a more pronounced effect on reinforcement and shrinkage. • Fiber fracture and pull-out during deformation are the dominating processes. Thermoplastic starch composites incorporating isotropic calcium carbonate and anisotropic basalt fiber as inorganic fillers were produced through injection molding, covering a broad range of compositions. We focused on the structure of the composites, the interfacial interactions between components, mechanical properties, and dimensional stability. Interfacial adhesion and reinforcement were assessed through model calculations, while local deformation processes were monitored using acoustic emission measurement. The addition of fillers led to a notable reinforcing effect, with a remarkable increase of 1076 % and 234 % in tensile modulus and strength, respectively. Adding 25 V/V % of basalt fiber reduces shrinkage from 12.5 % to 2 % and minimizes deterioration of stiffness and strength in humid conditions. The improvement was particularly significant when basalt fiber was used as fiber reinforcement.