Study On The Separation And Thermal Stability Of Hemicelluloses From Bamboo Stem Aged Six Months And Twelve Months

As the continuous depletion of the fossil fuels such as oil, natural gas, and coal, the subject of transforming renewable biomass resources into the new energy, new materials and pharmaceutical fine chemicals has become more and more important both at home and abroad. The main components of biomass are cellulose, hemicellulose and lignin. Hemicellulose accounts for about 20-35% of the total biomass. As an inexhaustible supply of natural renewable resources, hemicellulose is widely used in chemical, food, paper and pharmaceutical industries. It has broad development and application prospects. However, only at the premise of isolating hemicellulose from the plants can we study the chemical composition and structural characteristics of the hemicellulose in-depth and explore ways of improving the additional values of the hemicellulose. So it is very important to study the fractional isolation, purification and the characterization of the hemicellulose.In this paper, for the purpose of efficiently using the hemicellulose of bamboo stem resources which is rich in hemicellulose, The single factor tests were first used to study the main process parameters of the ultrasound-assisted alkaline extraction on the bamboo hemicellulose extraction and isolation. The influences of the KOH solution concentration, extraction temperature and ultrasonic time on the overall yield of bamboo hemicellulose were investigated. Then the Box-Behnken experimental design method was used to further optimize the extraction process. According to the response surface analysis, the best extraction process parameters were:3.1% KOH concentration,1:20 solid to liquid ratio,54.4℃extracton temperature,120 min extraction time where 56 min were with ultrasonic treatment. The yield of hemicellulose was 19.22%. Extraction temperature and alkali concentration were significant factors, but the effect of the ultrasonic treatment time on yield was not significant.Fractional extraction and individual organic solvent extraction methods were employed for the 6 months and 12 months old bamboo stems for obtaining water-soluble, alkali-soluble hemicellulose A, B, and DMSO soluble hemicellulosic components. The yields of each component were compared and analyzed. The characteristics of the components were investigated using FT-IR, ion-exchange chromatography, and GPC technology. The results showed that the acetyl group were still remained intact in the water-soluble and DMSO soluble hemicelluloses. The yield of alkali-soluble hemicelluloses were high, but the acetyl group had been completely hydrolyzed. The content of the associated lignin in the water-soluble and DMSO soluble were low, while the alkali-soluble hemicellulose A, B components had a relative higher content of the associated lignin. The bamboo stem hemicelluloses consisted ofβ-linkage between the pentose units, and had some part of the uronic acid composition. DEAE-Cellulose 52 elution curve appeared as a single peak shape which could effectively separate the neutral and acidic components. The results of molecular weight analysis showed that the molecular weight of the water-soluble hemicellulose was slightly larger than the alkali-soluble components. The hemicelluloses components obtained from fractional isolation had been degraded to some extent.In this study, thermal gravimetric analysis (TGA) was employed to explore the thermal decomposition characteristics of various bamboo hemicellulose components. The results showed that bamboo hemicelluloses had a wide weight loss temperature range, and the thermal stability was poor. The main weight loss temperature range were from 180 to 400℃. TG-DTG curve indicated that the maximum weight loss occurred between 250 and 300℃. There was a shoulder peak between 400 and 500℃in the water-soluble and alkali-soluble components, which is associated to the remaining lignin. The average residue of water-soluble component was higher than alkali-soluble and DMSO soluble components when the pyrolysis comes to an end. The Coat-Redfern integral method was used to conduct dynamic analysis for the maximum weight loss range of the hemicelluloses components. The activation energy E and pre-exponential factor A of each component were obtained and compared.