Sappan Natural Dyed Biocomposites from Poly(Lactic Acid) and Aluminum Silicate Synthesized via Sol-Gel Method from Rice Husk Ash

Precipitated silica synthesized via the sol-gel method from rice husk ash was used as the solid support for Sappan dye, extracted from natural Sappan heartwood. The precipitated silica was transformed into aluminium silicate in order to fix the natural dye onto the solid support for better high-temperature resistance during polymer melt compounding. The novel synthesized natural dye pigments were mixed into poly(lactic acid) (PLA) via the melt compounding using a pigment loading of 5 wt% and injection molded into specimens. Three types of compatibilizers as tetraethyl orthosilicate (TEOS), gamma-glycidyloxypropyltrimethoxysilane (GPTMS) and gamma-aminopropyltriethoxysilane (APTES) have been studied on the effect on different color shade and the improvement of compatibility by better interfacial adhesion between PLA and the pigments. Based on FTIR spectra, natural dye adsorption onto aluminium silicate was illustrated. It was found that the Sappan (red color) dyed pigments treated with GPTMS had the highest tensile modulus, while those treated with APTES provided the brightest color of the biocomposites. Thermal resistant of the biocomposites were improved when compared with pure PLA due to presence of silica.