The Supramolecular Structure Of Bamboo Cellulose And Its Effect On Hydrolysis Saccharification

Bamboo is a kind of sustainable natural resource with rapid growth and excellent mechanical properties.Bamboo fiber and parenchyma cells constitute the main body of bamboo.It is an important way to realize accurate value-added processing of bamboo to carry out directional utilization according to the structure and performance characteristics of different cell units.Cellulose is the main component in the cell walls of bamboo and parenchyma cells.It is an important direction of bamboo biorefinery to produce high value-added products by using bamboo fiber and parenchyma cell cellulose.It is an important direction of value-added processing to develop directional utilization according to the structural properties of different cell units.The previous research of the author’s team found that parenchyma cell cellulose is much easier to hydrolyze than bamboo fiber cellulose,but its internal scientific mechanism is still unclear,which may be related to the difference of supramolecular structure between fiber and parenchyma cell cellulose.This study focuses on the cellulose supramolecular structure in the fibers and parenchyma cells of Phyllostachys edulis(Carr.)H.de Lehaie,Bambusa longispiculata Gamble and Bambusa pervariabilis Mc Clure.Field emission scanning electron microscopy(FE-SEM),atomic force microscopy(AFM),solid state nuclear magnetic resonance(NMR)and X-ray diffraction(XRD)were used to characterize the arrangement and size of cellulose microfibril aggregates(CMFA),the orientation of microfibrils,the crystalline structure of cellulose elementary fibril and the effect of structural differences on the hydrolysis efficiency of cellulose.The main conclusions are as follows:(1)There was no significant difference in the intrinsic size of CMFA between fibers and parenchyma cells,ranging from 15 nm to 25 nm.The arrangement and size of cellulose microfibril aggregates(CMFA)in the cell wall of fibers and parenchyma could be clearly observed by FE-SEM and AFM.CMFA was randomly and irregularly arranged in the cross section of fiber cell wall and concentric lamellae arrangement in parenchyma cells.In addition,the orientation trend of broad and narrow lamellae between bamboo fiber and parenchyma cell was similar,that is,the microfibril angle of broad lamellae was smaller than that of narrow lamellae,which may be the reason why the CMFA apparent size of broad lamellae was significantly smaller than that of narrow lamellae.However,the average microfibril angle of the fibers was significantly smaller than that of the parenchyma cells.The average microfibril angle of fibers and parenchyma cells was about 10 ° and 60-70 ° respectively.(2)The two types of cells showed similar cellulose crystallinity index(Cr I).The cellulose from bamboo fibers and parenchyma cells also exhibited differences in crystallite sizes,with lateral sizes of ca.26.0-41.3 (?) and ca.22.7-39.3 (?) for bamboo fibers and parenchyma cells respectively.It was further found that cellulose chains in bamboo fibers were more closely packed,supported by its smaller d-spacing than that of parenchyma cell cellulose.The apparent length ca 123.8-137.4 (?) of crystalline cellulose in bamboo fiber was much shorter than that of parenchyma cell cellulose ca 261.3-299.1 (?),which might imply a much longer length of amorphous region for the latter if close Cr I between them was considered.In addition,FT-IR and NMR revealed that there was a higher Iβ content in fibers than parenchyma cells.These differences in the crystalline structure of cellulose should be related to the less recalcitrance to chemical degradation of parenchyma cells compared to bamboo fibers.(3)In the process of treating fiber and parenchyma cell cellulose with ionic liquid([C4mim]OAC),with the increase of temperature,both fiber and parenchyma cell undergo the transformation from cellulose I to cellulose II,but the conversion condition of parenchyma cell were milder.The structure of bamboo fiber cells was not obvious during the treatment,and the conversion efficiency of hydrolysate was low;In the process of treatment,with the increase of treatment temperature,the crystallinity decreased,the crystallite size decreased,and the dspacing increased,which improved the conversion efficiency of cellulose hydrolysis.The change of parenchyma cell cellulose structure leads to the change of the conversion efficiency of cellulose hydrolysis,which indicates that cellulose structure is one of the factors affecting the hydrolysis efficiency of cellulose,and further confirms the "low biodegradation barrier" characteristics of parenchyma cell cellulose.