The Study Of Structural Chacteristics Of MWLs Prepared From Green Liquor Pretreated Poplar And Its Effect On The Adsorption Of Cellulase

Pretreatment is a key step in the process of bioconversion of lignocellulose. Green liquor(GL) is a mix of Na2CO3 and Na2 S. GL pretreatment can be used to improve the efficiency of enzymatic hydrolysis of biomass. In addition, the non-productive adsorption of enzyme on lignin was an important factor that may do effect on the enzymatic hydrolysis. It can be related with the changes of lignin structures and properties during the pretreatment process. In this work, MWL samples were prepared from wood meals and GL pretreated solids of poplar. Both wet chemistry and spectra analysis were used to investigate the changes of lignin structures during GL pretreatment. Besides, QCM technology was applied to evaluate the effect of changed lignin structures during GL pretreatment on the enzyme adsorption.1. Isolation and structural characterization of untreated and GL pretreated MWL of poplar. The purity of isolated MWL from GL pretreated solids(TTA charge 8% and 16% respectively) can be more than 96% while the purity of MWL from untreated poplar can just be 88.7%. Weight-average molecular weights(Mw) of GL pretreated MWL decreased from 9000 to 6000. The yield of NBO products decreased with the increase of TTA charge in GL pretreatment while the molar ratio of S/V exhibited a positive correlation with TTA charge. Ozonation analysis showed that the yield of ozonation products decreased with the increase of TTA charge while the E/T ratios increased with TTA charge, indicating that macromolecular fragmentation of lignin occurred and the condensation degree increased after GL pretreatment. Besides, the ether bonds of G-lignin and threo-lignin were more easily to be cleaved under mild alkaline conditions. From FT-IR spectra, it can be found that poplar lignin belongs to typical GS lignin. The S/G ratio increased with TTA charge. The results of 13 C and 2D HSQC-NMR spectral analysis both indicated that MWLs prepared from GL pretreated solids exhibited higher condensation degree and higher S/G ratio compared with MWL-P, which was in agreement with the results obtained by wet chemistry. The content of ?-O-4' structure occupied more than 50% in all the side chain structures, and it decreased with the increase of TTA charge while the amount of ?-?' and ?-5' increased slightly after GL pretreatment. The 1H-NMR spectra of acylated MWLs showed that the amount of methoxyl and aromatic hydroxyl groups of untreated MWL was 1.47/C9 and 0.22/C9 respectively, however, both of them increased after GL pretreatment.2. Preparation and characterization of MWL biosensor films. In order to prepare biosensor films, MWL solutions with different concentrations were prepared by dissolving MWL samples in dioxane solution. The MWL solutions were then spin-coated on the gold sensors using spinning coating technology. According to the observation of AFM images, the higher concentration of lignin solution, the smoother of MWL film surfaces would be under the same TTA charge; The Rq values of GL pretreated MWL films were smaller under the same concentration of MWL solution. The analysis of XPS indicated that the C-C% increased while the O/C ratio decreased simultaneously as the increase of TTA charge and MWL purity.3. The adsorption and desorption behaviors of cellulase on MWL films prepared from untreated and GL pretreated poplar. QCM-D was used to characterize the enzyme adsorption/desorption behaviors on lignin films at 4oC, which showed that all the adsorption processes can be divided into two phases, the rapid adsorption phrase and the slow adsorption phrase. The adsorbed and desorbed enzymes were proportional to the enzyme concentration. GL pretreated MWLs adsorbed more enzymes compared with the untreated MWL at different enzyme concentrations. From the ?D-?f plot, it can be seen that, the interactions between GL pretreated MWLs and cellulase were stronger when it was close to adsorption equilibrium. The MWL films were viscoelastic under low enzyme concentrations. And with the increase of adsorption amount, the adsorbed layers became looser and the conformation of adsorbed layers would change accordingly while the adsorbed layers were much compact and the conformation of adsorbed layers was stable under high enzyme concentrations. Furthermore, according to the analysis of QCM-D data, binding model of cellulase on MWL films was established to obtain the information of theoretical maximum binding value, adsorption rate etc. at different assumed conditions.