Effects of burning temperature and K2O on preparation of silica from rice husk ash for anti-blocking application in LLDPE film

Abstract

Amorphous silica (SiO) in rice husk ash (RHA) was transformed to cristobalite with some amount of tridymite at over 900 degree celsius. The RHA included about 2 wt% of potassium oxide (K[subscript 2] O). The K[subscript 2]O played an important role in reducing the melting temperature of SiO[subscript 2] in RHA and in re - crystallization of amorphous silica to cristobalite at lower temperature. The RHA from rice mill factory was transformed to cristobalite/tridymite by heat treatment at 1,200 degree celsius for 4 h. Such resulting powder was ground with air jet mill and mixed to make a masterbatch with linear low density polyethylene (LLDPE) by twin-screw extruder. LLDPE film was prepared by a common film blowing extruder. Film properties containing commercial grade anti-blocking cristobalite was compared with the film containing cristobalite from rice husk, prepared in this study. It was found that transparency and mechanical tensile strength of the two film types were relatively the same. However, some reports published in other countries indicate that cristobalite is considered as a carcinogenic material. Amorphous silica is, so far, another candidate for use as anti-blocking agent in plastic films. From this study, amorphous silica could be produced by a similar process as compared to that for cristobalite, but at lower burning temperature of 650 degree celsius for 1 h. The optical and tensile properties of the films with amorphous SiO[subscript 2] is equivalent to those containing cristobalite.