Characterization and comparison of cellulose fiber extraction from rice straw by chemical treatment and thermal steam explosion

Abstract

Rice straw is one of the major agricultural wastes in Thailand. It can potentially be processed to extract natural fibers from which environmentally sustainable products, e.g. papers, can be subsequently made. This research studied the characteristics of cellulose fibers extracted from rice straw by two different treatments: (i) chemical treatment and (ii) thermal steam explosion. For the chemical treatment, sodium-hydroxide (NaOH) solutions with varying concentration were applied to treat fibers. Life Cycle Assessment (LCA) was used to evaluate and compare the potential environmental impacts of the natural-fiber thermal insulation pads produced by different rice-straw cellulose extraction processes. The morphological results show that an increase of NaOH concentration decreases the fibers' average diameter and length and fiber yielding; however, the aspect ratio of length-to-width increases with increasing NaOH concentration. For the thermal steam explosion, the cellulose fibers were extremely broken down resulting in significant reduction in the fiber diameter and length. The results of Fourier transform infrared spectrometer (FTIR) spectrum analyses reveal that both treatments only lightly dissolved lignin and hemicellulose from the cellulose fibers. Thermal insulation pads were produced from the extracted cellulose fibers using natural rubber as a binder. The thermal conductivity coefficient of the natural-fiber thermal insulations was in the range of 0.11–0.14 W/m-K. The LCA results showed that the thermal steam explosion process potentially reduced the environmental impacts as compared to the chemical extraction treatment due to a significant reduction in an eco-toxicity impact and a higher fiber yielding. However, the energy consumption of the thermal explosion process is a main issue that needs to be improved for the further development of eco fiber insulation pads produced from extracted rice-straw cellulose.