Effect Of Pre-extraction On The Physicochemical Properties And Hemicellulose Composition Degradation Of Bamboo Chips

In this paper, the Pink Sheets bamboo in South China was investigated, treated by both Hot Water Pre-extraction (HWP) and Alkaline Hydrogen Peroxide Pre-extraction (AHPP) methods to extract hemicellulose from bamboo. The physico-chemical properties including chemical compositions, the content of functional groups on fibre surface, cellulose crystallinity, porosity, etc. were characterized before and after pre-extraction. Besides, the pulping properties including fiber morphology, refining energy, pulp yield, optical properties and physical strength of pulp were also analyzed so as to evaluate the impacts of different pre-extraction methods to the APMP process comprehensively. Moreover, the thermal degradation behavior of glucan and xylan under different conditions, based on high-performance liquid chromatography analysis technique, were investigated so as to unveil the degradation regularities of polysaccharides. It is expected, in this work, that improving sugar yield and minimizing the generation of toxic by-products could be achieved by controlling the pre-extraction conditions.The main conclusions are as follows:1. On the preparation of APMP process with bamboo as material, it was improved that, after HWP method, refiner energy consumption reduced whereas Bamboo chips color was deepened with significant decrease of the whiteness. Moreover, HWP method also has a negative effect on the most physical properties of the pulp relative to nonextracted. By contrast, APMP with AHPP increase the whiteness, keeping the performance of pulp bleaching significantly. The analysis of chemical composition indicates that the cellulose and extractives content of bamboo chips increased for various degrees after HWP. After AHPP, the cellulose content of bamboo chips increased slightly, but other chemical components declined inordinately.2. The porosity of bamboo rised after HWP. There are increasing proportion of damaged tissue and uncrystallized fibers found in the samples of electron micrographs. BET data elucidated, compared with non-extracted bamboo, bamboo, after HWP, both the pore volume and surface area had increased significantly, respectively. In terms of AHPP, the pore volume and specific surface area of treated bamboo had also increased significantly respectively, which were smaller than those of HWP. After both HWP and AHPP, cellulose crystallinity and X-ray crystallography indices of bamboo increased respectively.3. The spectra of FT-IR indicated that AHPP mainly led to the cleavage of lignin in the P-O-4, α-O-4, and C=C bonds and the degradation, even removal, partial lignin and extractives in the bamboo, which would be positive to the subsequent bleaching of the pulp. As for HWP, it tended to raise the contents of the C-C, C-C-O, C=O, C-H bond on the aromatic ring, the C=O bond on ester carbonyl group and H-benzene bonds on the guaiacyl, impeding the subsequent pulp bleaching via increasing the content of chromophore in the bamboo.4. XPS data demonstrated that bamboo fiber surface almost consisted of hydrogen, carbon, oxygen and a slight amount of nitrogen. The surface amino (-NH2) or an amide group (O=C-NH) of fibre was removed after HWP. According to the change of the O/C value, it was believed that HWP exposed more fiber surface cellulose than that of AHPP. Contrast with HWP, AHPP only removed partial amino (-NH2) or an amide group (O=C-NH, also known as peptide bonds) group on the surface of fibre. Besides, the contents of lignin and extractives were reduced significantly. However, a number of -C=O and O-C-O groups would generate on the surface of fibre.5. W (1), L (1) and Fines (1) were reduced after HWP. However the L (n) increased and the fiber aspect ratio decreased. A significant increase was observed in fines percentage by weight of APMP after HWP but the weight percentage of the fiber under all mesh class reduced to varying degrees, suggesting that the long fibers would be cut easily during pulping process after HWP. Compared with the former, AHPP long fiber content significantly increased. The distribution of fibre length in the bleaching APMP distribution changed a little with the addition of peroxide.6. In the HW process, the dextran started generating glucosamine monosaccharides at 190℃.Moreover monosaccharide glucosamine degraded of HMF speed became faster among with temperature and time riesd. At 170℃ with 1.5h, xylan started degradated to xylose. In the AHP process, temperature of xylan degradated to xylose started at 90℃, reaction rate accelerated within temperature increased, and the yield of xylose increased within same time. It was interesting that the generation of glucose, HMF and furfural did not observed during the entire AHP reaction process.