Effect of kraft lignin and esterified lignin on the properties of thermoplastic starch

In order to improve the mechanical properties and the resistance to water absorption of thermoplastic starch (TPS), kraft lignin (KL) and esterified lignin (EL) were used as fillers for the TPS matrix. EL was produced via esterification of the KL hydroxyl groups. The TPS/lignin composites were prepared using compression molding. The amount of each of the lignins used in the composites was 5 wt.% (dry starch basis). The TPS and composites were investigated using Fourier transform infrared spectroscopy (FTIR), water absorption and tensile testing. The FTIR spectra showed that the interaction between the TPS and each lignin caused the peak of the OH stretching shift to lower wavenumber. This result indicated that both the TPS/KL and the TPS/EL composites had improved mechanical properties over TPS. The tensile strength of the TPS/KL and TPS/EL composites was higher than for the TPS by about 17% and 32%, respectively. In addition, the presence of lignins in the TPS matrix significantly decreased the water absorption properties.