Effect of ultra-violet cross-linking on the properties of boric acid and glycerol co-plasticized thermoplastic starch films

Abstract

Abstract Thermoplastic starch (TPS) is a potential alternative to non-degradable plastics. However, the hydrophilic nature and relatively weak mechanical properties is a major hurdle to its commercial application. In this study, Ultra-violet (UV) irradiation based cross-linking was investigated for its effect on the mechanical properties of TPS films plasticized by boric acid, and glycerol. Spray dried amorphous powder was compressed to obtained TPS films. All the samples were amorphous under dry conditions (RH0%) while retro-gradation was resisted at the relative humidity (RH) of50% and 100% for all the films. The concentration of the plasticizers influenced the moisture uptake ability of TPS films. UV irradiation showed no effect on the crystallinity of TPS films. However, it enhanced the mechanical strength and lessened the solubility and degree of swelling. Boric acid plasticized and co-plasticized samples revealed improved mechanical properties before and after UV irradiation compared to glycerol but showed more moisture sensitivity before cross-linking. The UV irradiated starch with 30% boric acid as plasticizer (30BA.UV.PS) showed highest tensile strength (4.28 MPa) among all the samples at 50% relative humidity. Moreover, the strain at break of the same sample decreased from 12.53% to 9.12% at 50% relative humidity.