The Study Of Isolation And Structural Characterization Of Lignin From Valonea Of Quercus Variabilis

As one of three main components of Lignocellulosic biomass, lignin is a natural phenolic polymer with great significance. The lignin has some character, for examples, complex structure, mass molecular weight, great difference of structure in different plants and so on, which lead to great hinder on the comprehensive usage of lignin. As an important bio-energy tree species, Quercus variabilis were cultivated about 133×104-160×104 hm2. There were large of valonea waste were produced per year, which pollute the environment and waste the resources. It was found that the valonea of Quercus variabilis contained about 31.21% lignin after a preliminary experiment. However, there was never study about the lignin from valonea of Quercus variabilis. In order to provide some theoretical basis for the usage of valonea, this paper studied the isolation methods, isolation process, physicochemical property and structure character of lignin from valonea of Quercus variabilis. The results showed that:1. The chemical composition of valonea was cellulose(28.03%), hemicellulose(20.95%) and lignin(31.21%).2. Alkali lignin(AL), milled wood lignin(MWL) and enzymatic hydrolysis lignin(EHL) were isolated from valonea of Quercus variabilis. Meanwhile, alkali isolation process was optimized with response surface method(RSM). The results showed that the highest isolation rate of AL was 22.67% under its optimum isolation process: liquid/solid(12.21), isolation time(4.21h), isolation temperature(42.21℃) and alkali concentration(0.85mol/L), which was higher than that of MWL(10.33%) and EHL(8.38%).3. The physico-chemical properties(TG, GPC and SEM) of three lignin samples were studied. The results showed that the MWL had the poorest thermal stability(onset degradation temperature=111℃; the fast degradation rate temperature=268℃) and the lowest molecular weight(Mw=1100 g/mol; Mn=640.26 g/mol). The results of SEM showed that the alkali and enzymatic broken the surface structure of AL and EHL.4. The structure features of three lignin samples(AL, MWL and EHL) were characterized by UV-Vis, FT-IR, 1H-NMR, 13C-NMR and 2D-HSQC techniques. The UV-Vis showed the structure of three lignin samples were similar; The FT-IR and 1D-NMR indicated that the three lignin samples were all GSH type; The 1H-NMR showed the AL contained the most functional groups; The results of HSQC showed that the relative content of main linkage β-O-4’ in the three lignin samples were 89.75%, 60.21% and 75% respectively. The MWL had the lowest content due to more β-O-4’ were destroyed in the isolation process; the relative content of β-β’ in AL, MWL and EHL were 8.26%, 9.30% and 12.45% respectively. In addition, it can be found the existence of phenylcoumarane, ferulic acid, p-coumarates and p-hydroxycinnamyl alcohol end groups; the S/G ratio calculated from 2D-HSQC were 8.27, 1.30 and 0.96 in AL, MWL and EHL respectively, which provide some theoretical basis for the further study.