Fractionation And Characterization Of Main Components From Cell Wall Of Bamboo And Homogeneous Chemical Modification Of Whole Cell Wall Of Bamboo (Bambusa Rigida)

Based on the concept of biorefinery, the bamboo (Bambusa rigida) was chose as the research object. In this study, different alkalis were selected to isolate hemicelluloses and lignin fractions and their physical and chemical characteristics were investigated; the water-soluble and alkaline-soluble hemicellulosic fractions were extracted from the delignified and dewaxed bamboo culm, the detailed structure analysis were studied. The homogeneous lauroylation of ball-milled bamboo in ionic liquid were also investigated, and the structural features of these hydrophobic derivatives were also studied, this will provide theoretical basis for the industrial use of the bamboo. This thesis will summarize several main conclusions as follows,(1) This section investigated structural characterization of seven alkali-extractable lignin fractions by a two-step isolation method from bamboo (Bambusa rigida sp.). Different wet chemistry (sugar analysis of their associated hemicelluloses, composition of phenolic acids and aldehydes) and spectroscopy methods (UV, FT-IR, 1^H, (13)^C and HSQC NMR spectroscopy) as well as average molecular weight have been employed to assess the major structural features. The most striking characteristics of these lignin fractions are the almost absence of neutral sugars (1.12-2.21%) and their low average molecular weights (770-1890 g/mol). It also revealed that these lignin fractions contained considerable amounts of esterified p-coumaric acid, which cannot be completely hydrolyzed under the conditions given. Moreover, semi-quantitative HSQC-NMR showed that a dominant amount ofβ-O-4′linkages (about 82%) and resinol substructures (β-β′, 9%) together with small amounts of phenylcoumaran substructures (β-5′) were identified to be involved in the LiOH lignin fraction. However, a decrease ofβ-O-4′(about 70%) was found in NaOH lignin fraction. This indicated thatβ-O-4′units were subjected to more degradation under aqueous NaOH treatment. Furthermore, the results confirmed that these lignin fractions belonged to HGS-type lignin, and contained slightly more amounts of syringyl units than guaiacyl units. From S/G ratios, it also implied that non-condensed syringyl units were more liable to release than the guaiacyl units from the cell wall under the mildly alkaline condition.(2) Water and aqueous alkali sequential treatments of delignified bamboo particles were performed to extract hemicelluloses with a high yield and weight averaged molecular mass (M_w) in this section. The successively extractions together dissolved 42% of hemicelluloses based on dry holocellulose. GPC results showed that the alkali-extractable hemicelluloses have higher M_w (35000 and 44450 g mol^-1) than that of water-extractable ones (20100-28100 g mol^-1). Structural determination based on FT-IR, 1H, 13C and 2D-HSQC NMR analysis showed that both the water- and alkali-extractable hemicelluloses consist mainly of arabinoglucuronoxylans, and probably had a structure composed of the (1â†'4)-linkedβ-D-xylopyranosyl backbone with 4-O-methyl-α-D-glucuronic acid attached to O-2 of the xylose residues and L-arabinose attached to O-3 of the xylose residues. Moreover, it revealed that the water-extractable hemicelluloses retained original structure without cleaving chemical linkages. Furthermore, it was also found that the hemicelluloses with the highest yield and M_w were obtained by the aqueous alkali treatment from the delignified bamboo. Small amount of other minor hemicelluloses (β-glucans) including xylans in the the water-extractable hemicelluloses could be identified by NMR and other approaches.(3) This section investigated the physicochemical properties and structural characteristics of seven alkali-soluble hemicellulosic preparations extracted with 1M NaOH, KOH, LiOH, NH₃·H₂O, (CH₃CH₂)₃N, Ca(OH)₂, Ba(OH)₂ at 50°C for 3 h from bamboo (Bambusa rigida), respectively. The results of sugar analysis showed that these hemicelluloses contained D-xylose as major constituent, D-glucose and L-arabinose appeared in noticeable amounts. Uronic acids, principally 4-O-methyl-D-glucuronic acid occurred in a small amount. Furthermore, based on the results of the sugar analysis, FTIR, and NMR spectroscopy, it can be concluded that the hemicelluloses consist of a backbone ofβ-(1â†'4)-linked D-xylopyranosyl, having branches of arabinose and 4-O-methyl-D-glucuronic acid. Nitrobenzene oxidation results revealed that hemicelluloses obtained are mostly free of bound lignins. Moreover, it is noteworthy that hemicelluloses isolated with different alkaline solutions presented different chemical composition and slightly dissimilar structural features. These indicated that alkalinity played an important role in cleaving the chemical linkages between hemicelluloses and lignins.(4) Bamboo ball-milled meal was completely dissolved under constant conditions (130 oC, 6 h) in the ionic liquid 1-butyl-3-methylimidazolium chloride ([C₄mim]Cl) and then the lauroylation were carried out at different conditions in the last section. The various factors, such as molar ratio and temperature, were investigated to evaluate the effect of modification. The results showed that the molar ratio played a very important role for the lauroylation. The weight percent gain (WPG) ranged from 167% to 528% when the molar ratio increased from 1.0 to 2.0 at 100 oC for 2 h. It has been shown that highly substituted bamboo ester derivatives could be obtained by reacting wood dissolved in [C₄mim]Cl with lauroyl chloride as the molar ratio is 2.0. All reactions were performed under mild conditions, low excess of reagent and a short reaction time as compared to the heterogeneous chemical modification. The physicochemical properties of the esterified bamboo meal were also widely investigated. FTIR and NMR spectra determination of the derivatives confirmed that the esterified derivative was successfully synthesized in one step based on reaction of bamboo meal with diverse molar of lauroyl chloride and equimolar triethylamine as a neutralizer and catalyst. It was also found that thermal stability of the esterified derivatives is lower than that of the unmodified bamboo meal. Moreover, morphological properties of the esterified bamboo meal were significantly changed by chemical modification. The rough appearance of bamboo meal changed into a relatively homogeneous and smooth surface morphology after lauroylation. Furthermore, the lauroylation of bamboo had excellent solubility in chloroform, which provides feasibility to electrostatic spinning of modified bamboo ball-milled meal as biomaterials for industries.