Enhancing the Thermo-Mechanical Properties of Thermoplastic Starch Films Using Rice Straw Fibers as Reinforcement

Nowadays, the need for biodegradable plastics is increasing because they are environmentally friendly and can replace petroleum-based non-degradable plastics that pollute the environment. Starch-based bio-plastics have huge potential to replace synthetic polymer-based plastics due to their economic and environmental advantages. However, the poor thermo-mechanical properties and high moisture sensitivity limited their application. In this study, potato peels that were readily available in the area were utilized to extract pure starch, which was then employed as a polymer matrix to develop starch-based composite films. Since rice straw is one of the most abundant agro-industrial residues worldwide, cellulose obtained from rice straw through chemical treatments was used as reinforcement. Using a simple domestic blender, the crude cellulose was disintegrated into cellulose nanofibers to boost the reinforcing efficiency. The starch-based composite films were fabricated using a simple solution casting method. The cellulose nanofibers in the composite films were at 1, 3, 5, 10, and 15 weight ratios. Thus obtained starch-based composite films were characterized in terms of their transparency, chemical structure, thermal stability, mechanical strength, and moisture sensitivity. The tensile strength of the thermoplastic composite films is remarkably enhanced by the inclusion of cellulose fibers as reinforcement. For the neat starch film, the tensile strength is 0.714 MPa and the value reaches 11.12 MPa for 10 wt% cellulose fiber addition. Increasing the concentration of the cellulose above 10 wt% reduced the tensile strength. The reason can be attributed to the fiber aggregation in the composite film, which resulted in poor interfacial interaction between the fillers and the stretch matrix. The fracture strain of the composite films was also linearly increased up to 10 wt% cellulose fiber inclusion. As the TGA data revealed, the thermal stability of the composite films was significantly enhanced due to the reinforcement effect of cellulose fibers. The addition of cellulose fibers up to 10 wt% also enhanced the moisture resistance of starch films, and the lowest water-holding composite film was obtained when the cellulose fiber content of the composite was 10 wt%. All the analysis in this work indicates that 10 wt% cellulose fibers is the optimum concentration to reinforce thermoplastic starch-based films for better industrial applications.