Preparation of modified cellulose films from waste cotton fabrics under microwave energy

Abstract

Cellulose-enrich residue from waste cotton fabric was modified into bioplastic by esterification reaction under microwave irradiation. The cellulose is acetylated by using stearic acid as esterifying agent, toluenesulfonyl chloride and pyridine as catalyst in homogenous system of lithium chloride-N,N-dimethylacetamide (LiCl-DMAc). This synthetic method was based on the using of mixed p-toluenesulfonic/stearic acid anhydride as active species. Under an optimum condition, approximately 71% of the free hydroxyl groups in cellulose were acetylated and 155% of weight were increased under microwave irradiation at 270 watt for 3.30 min. Cellulose stearate film was easily obtained by casting method in chloroform solution. After esterification, it was found that % esterification of cellulose stearate had marked influences on the properties of esterified product. The morphology of cotton stearate reveals aggregation of acyl group on surface of cotton stearate powder. The melting transitions attributed to side chain crystallization of acetyl groups of stearic acid reveal the possibility to enhance melt-processible of cotton stearate. In addition, the wettability and water absorption were dependent on both residue hydrogen bonding and hydrophobic acetyl groups of stearic acid. Similarly, tensile stress at maximum and modulus at break of cotton stearate films increased with % esterification, as a result of side chain crystallization of substitution of stearic acid. While, elongation at break slightly increased. For biodegradability of the film, it was found that an increase in substitution of acetyl groups of stearic acid on hydroxyl groups of cotton helped promoting the biodegradability of cotton stearate film. This results can be confirmed from an increase in % weight loss and cavities on the film surface after soil burial test for 30 days.