PEER-REVIEWED ARTICLE bioresources.com Ndazi et al. (2007). “Rice husk stability, alkali treatment,” BioResources 3(4), 1267-1277. 1267 CHEMICAL AND THERMAL STABILITY OF RICE HUSKS AGAINST ALKALI TREATMENT Bwire S. Ndazi, * Christian Nyahumwa, and Joseph Tesha Chemical and thermal stability of rice husks against alkali treatment with 2 to 8% w/v NaOH are presented and discussed in this paper. The thermal stability of the rice husks was examined by using a thermal gravimetric analysis instrument. Chemical stability was evaluated by examining the organic components of rice husks using proximate analysis. The results indicated that the proportion of lignin and hemicellulose in rice husks treated with NaOH ranging from 4 to 8% decreased significantly by 96% and 74%, respectively. The thermal stability and final degradation temperatures of the alkali-treated rice husks were also lowered by 24-26°C due to degradation of hemicellulose and lignin during alkali treatment. Absence of the onset degradation zones in the alkali-treated rice husks was a further indication that hemicellulose and other volatile substances degraded during alkali treatment. This leads to a conclusion that alkali treatment of rice husks with more than 4% NaOH causes a substantial chemical degradation of rice husks, which subsequently decreases their thermal stability. Keywords: Alkali treatment; Cellulose; Chemical content; Degradation; Hemicellulose; Lignin; Rice husks Department of Engineering Materials, University of Dar es Salaam, P.O. Box 35131 Dar es Salaam, Tanzania; *Corresponding author: bndazi@udsm.ac.tz INTRODUCTION Rice husks, which are by-products of the rice hulling industry, are amongst the few agricultural residues that can be readily obtained in huge amount at one location. Researchers have made use of this advantage and have addressed the disposal nuisance caused by rice husks by developing various products from rice husks. Rice husks, like other agricultural residues, are quite fibrous and require relatively little input energy to be processed into various products, including panel boards. However, because of inconsistent properties of rice husks compared, for example, to wood particles, manufacture of panel boards from these residues has yielded undesirable properties (Chen 1979). Rice husks contain a high proportion of lignin, and about 20% of their outer surfaces are covered with silica (Houston 1972; Juliano 1985), which is deposited onto this surface as monosilicic acid to form a silicon-cellulose membrane (Yoshida et al. 1962). Adhesion of agricultural fibres with thermosetting resins involves either or both chemical and physical interactions. Chemical interaction can be achieved through hydrogen or covalent bonding between the reactive OH groups available on the cellulosic fibres and compatible functional groups on the thermosetting resins. A high proportion of