Isolation And Characterization Of Main Component Of Whole Cell Wall Of Pine Wood

Based on the concept of clean and effective separation of biomass components, Pinus yunnanensis was selected as the research object. In this study,(1) Pinus yunnanensis was subjected to extract lignin in aqueous alkaline solutions with different microwave heating time. The physicochemical features of lignins were comparatively characterized.(2) Fractionation of hemicelluloses from delignified Pinus yunnanensis was carried out with KOH/H3BO3solution followed by graded ethanol precipitation. Above research will provide theoretical basis for the industrial use of the pine. This thesis will summarize several main conclusions as follows:(1) LigninIn this section, Pinus yunnanensis was subjected to water-bath and microwave treatments in aqueous alkaline solutions to extract lignin. The physicochemical features of lignins were comparatively characterized by sugar analysis, GPC, FT-IR,13C and HSQC NMR, as well as thermogravimetric analysis (TGA). The results showed that the lignin fractions extracted with microwave heating (20-120min) had high molecular weights and polydispersities(Mw3150-5710g/mol, Mn2130-3020g/mol, Mw/Mn1.48-2.00) as compared to that prepared without microwave heating(Mw3080g/mol, Mn2080g/mol, Mw/Mn1.48). The most striking characteristic of all lignin fractions was the almost absence of associated sugars (0.16-3.25%). The TGA results indicated that the thermal stability of the lignin fraction increased with the increment of the molecular weight. FT-IR and NMR spectra suggested that the lignin fractions showed similar structures which were mainly composed of guaiacyl (G) and minor amounts of p-hydroxyphenyl (H) units. Moreover, HSQC NMR spectrum of a typical lignin fraction (prepared with microwave heating for120min) revealed that it contained dominant amounts of β-0-4’linkages (64.6%) and phenylcoumaran (β-5’) substructures (25.8%) together with small amounts of resinol (β-β’) substructures (6.7%) and coniferyl alcohol end groups (2.9%).(2) HemicellulosesFractionation of hemicelluloses from delignified Pinus yunnanensis was carried out with KOH/H3BO3solution followed by graded ethanol precipitation in this section. GPC results revealed that the hemicelluloses precipitated by low concentration of ethanol solutions had higher weight-average molecular mass (50090-79840g/mol) than those obtained in the high concentration of ethanol solutions (16500g/mol). The fraction precipitated by60%ethanol solution (H2) was composed of D-galactose, D-glucose and D-mannose in a ratio of approximately1:1:3.5. Structural determination indicated that the hemicellulosic fraction (H2) had a main structure of (1â†'4)-linked β-glucomannans backbone with (1â†'6)-linked a-D-galactose as a side chain attached to C-6of mannose units. In addition, this fraction also contained minor amounts of xylans.