EFFECTS OF EXTRACTION CONDITIONS AND ALKALI TYPE ON YIELD AND COMPOSITION OF WHEAT-STRAW HEMICELLULOSE

The utilization of various alkaline regimes for the optimal extraction and isolation of hemicellulose and cellulose from wheat straw was ext ensively examined. Factors investigated include varying concentrations of one alkali (KOH) and H3BO3, varying temperature and time of extrac tion, 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 ho locellulose preparations utilized a solution of 24% KOH/2% H3BO3 at 20 degrees C for 2 h. This produced yields for hemicellulose and cellulo se of 34.23 and 35.96%, respectively. The neutral sugar composition of the various hemicellulose fractions was found to vary slightly with t reatment regime. In all hydrolysates of hemicellulose preparations, xy lose was by far the predominant sugar, comprising around 80% of the ma terial. Minor constituents were arabinose, galactose, glucose, and uro nic acids. The composition of phenolic acids and aldehydes in extracte d wheat straw hemicellulose was also studied. The average molecular we ights of the hemicellulose isolates ranged from 12,000 for the 30% KOH /2% H3BO3 (20 degrees C, 2 h) extract to 27,000 for the extract obtain ed using 5% KOH/2% H3BO3 (20 degrees C, 2 h). (C) 1996 John Wiley & So ns, Inc.