Changes Of Cell Wall Chemical Components And Micromechanical Properties During Biodegradation Of Moso Bamboo

Cell walls of lignocellulosic biomass are mainly composed of polysaccharides and aromatic polymer lignin.These polymers have evolved into complex composites,which make the plant cell walls resistant to the use of lignocellulosic materials.Biological pretreatment as a more sustainable alternative to physical or chemical pretreatment is attracting more and more attention.However,the mechanism behind the biodegradation of cell walls is far from being fully understood.In this research,materials of the 4.5 years moso bamboo were decayed for 4-,8-,12-and 16 weeks by Coriolus versicolor and Gloeophyllum trabeum respectively.By observing the microscopic structure of bamboo,analyzing the microdistribution and quantitative characterization of chemical components,as well as measuring the mechanics of fiber cell walls,the response of micromechanical properties to the changes in chemical composition in the biodegradation process was clarified,and the mechanism of fungal degradation of bamboo was discussed.Thus it provides a theoretical basis for bamboo to be used as building material,pulping and papermaking,bionic material research and development,and bioethanol production.The degradation of bamboo by Coriolus versicolor and Gloeophyllum trabeum was not significantly different under the observation of SEM.In the same time of fungal degradation,the vessels were broken most seriously,followed by the parenchyma cells,while only a small number of mycelia perforation was found in the fiber cells in the later stage of degradation.Mycelia mainly spread between cells through pits,and at this time,the extracellular enzymes secreted by mycelia degrade the cell wall,resulting in the further enlargement of pits and the formation of perforation.The microdistribution changes of major components in the biodegradation process were studied by using confocal Raman and infrared microspectroscopy imaging techniques,and Raman average spectral were calculated for the SW regions.It was found that the degradation effect of C.versicolor in the fiber cells was significantly stronger than that of G.trabeum at 16 weeks of fungal treatment.However,in parenchyma cells,there was no significant difference in the degree of degradation.With the increase of treatment time by G.trabeum,carbohydrate concentration gradually decreased,which was especially prominent in parenchyma.By a series of chemical analysis,quantitative and semi-quantitative to characterize the biodegradation,we found in the biological treatment process,main ingredients are subject to different degrees of degradation.At the same time of pretreatment,C.versicolor to the degradation of lignin is a bit stronger than the G.trabeum,but not to the degradation of cellulose and hemicellulose showed obvious difference.The nanoindentation technique was used to test the mechanical properties of fiber cell wall before and after treatment.It was found that with the increase of fungal treatment time,the mechanical properties of fiber cells showed a nonlinear decreasing trend.After 16 weeks of degradation by G.trabeum and C.versicolor,NI modulus decreased from 20.99 GPa to18.47 GPa and 17.67 GPa,and NI hardness decreased from 477.75 MPa to 413.96 MPa and382.36 MPa,respectively.By calculating the coefficient of variation from the data in the group,it was found that the coefficient of variation increased with the increase of fungus treatment time.The correlation analysis showed that the micromechanical properties of bamboo fibers were negatively correlated with crystallinity after fungal treatment,but the correlation was not significant.The results of principal component analysis(PCA)of cell wall mechanics,crystallinity and each chemical component showed that the PC1 score gradually decreased with the increase of fungus time,and the PC1 score of G.trabeum was always higher than that of C.versicolor,while the PC1 and PC2 scores of untreated control group were the largest.The load diagram shows that the indentation modulus and hardness,lignin,xylem,glucose,95% ethanol extract,arabinose and galactose all have a strong positive load on PC1,while the crystallinity has a strong negative load.