Effects of extraction conditions and alkali type on yield and composition of wheat straw hemicellulose

Abstract

The utilization of various alkaline regimes for the optimal extraction and isolation of hemicellulose and cellulose from wheat straw was extensively examined. Factors investigated include varying concentrations of one alkali (KOH) and H3BO3, varying temperature and time of extraction, and varying the nature of the alkali: calcium hydroxide, sodium hydroxide, lithium hydroxide, and liquid ammonia were examined in this context. For example, a preferred extraction of hemicellulose from holocellulose preparations utilized a solution of 24% KOH/2% H3BO3 at 20°C for 2 h. This produced yields for hemicellulose and cellulose of 34.23 and 35.96%, respectively. The neutral sugar composition of the various hemicellulose fractions was found to vary slightly with treatment regime. In all hydrolysates of hemicellulose preparations, xylose was by far the predominant sugar, comprising around 80% of the material. Minor constituents were arabinose, galactose, glucose, and uronic acids. The composition of phenolic acids and aldehydes in extracted wheat straw hemicellulose was also studied. The average molecular weights of the hemicellulose isolates ranged from 12,000 for the 30% KOH/2% H3BO3 (20°C, 2 h) extract to 27,000 for the extract obtained using 5% KOH/2% H3BO3 (20°C, 2 h). © 1996 John Wiley & Sons, Inc.