| With the gradual exhaustion of non-renewable resources such as petroleum,coal,etc.,the development and utilization of renewable resources such as plant cellulose has attracted much attention.However,natural cellulose has the special structure such as long chain molecules,high crystallinity and degree of polymerization(DP),resulting to low accessibility and reactivity of cellulose because the reaction reagents are difficult to enter the crystallization region of cellulose but only reach the amorphous region,which extremely restrict the efficient utilization of natural cellulose.In this paper,the effect of mechanical activation(MA)time(tM)on the structure of natural cellulose was studied with using a homemade stirring ball mill as MA equipment,and bagasse pulp was used to produce long chain cellulose ester by MA-strengthened solid phase esterification with using the homemade stirring ball mill as solid phase reactor.The main research contents and results are as follows:Based on the research of the effect of MA on structure and properties of bagasse pulp in our previous works,pine bleached pulp and cotton wool,typical kinds of natural cellulose,were pretreatment by MA in this paper,and the effect of tM on the dissolving capacity and molecular chain structure of natural cellulose was investigated by the measurement of alkaline solubility(Sa)and DP,respectively.In addition,the effect of MA pretreatment on the surface morphology,crystal structure and functional groups of pine bleached pulp and cotton wool were characterized by scanning electron microscopy(SEM),X-ray diffraction(XRD),Fourier transform infrared spectroscopy(FTIR),respectively.The results showed that Sa of pine bleached pulp and cotton wool significantly increased with increasing tM.The crystal structure of cellulose was destroyed by MA,leading to the decrease of crystallinity index(CrI)and DP,the increase of amorphous region and specific surface area,the split of compact fiber bundles and the weaken in interaction of package between cellulose molecules,which obviously improved the accessibility and reactivity of cellulose,and thus increased its dissolving capacity in alkaline solution.Long chain cellulose ester was prepared by MA-strengthened solid phase esterification with co-reagent by using bagasse pulp as material,lauric acid as esterifying agent and acetic anhydride as co-reagent.The effects of dosages of co-reagent,esterifying agent and catalyst,reaction temperature,reaction time,pre-reaction temperature,pre-reaction time on the esterification reaction were investigated respectively by using the bound acid content(A)of modified products as evaluating parameter.The results indicated that the optimum conditions for esterification of cellulose were as follows:molar ratio of anhydro glucose unit(AGU)of cellulose:esterifying agents:co-reagent of 1:3:6,reaction temperature 80?,reaction time 90 min,pre-reaction temperature 90?,pre-reaction time 60 min,and dosages of catalyst 0.2 mL.The granule morphology,functional groups and crystal structure of esterification products were characterized by SEM,FTIR,XRD and 13C-NMR,respectively.The results showed that the compact and relatively smooth surfaces of cellulose were eroded and destroyed after chemical modification,forming many gaps and holes.It can be seen from the XRD patterns that the crystalline form of cellulose still belonged to cellulose I after chemical modification,but the crystal structure of cellulose was destroyed and the crystallinity reduced.The absorption peaks of carbonyl group(C=O)appeared at 1740 cm-1 in FTIR spectra of products,which proved that the solid phase esterification had took place and cellulose ester was successfully synthesized.The 13C-NMR spectra of modified products showed 5=170,30,20,which are assigned to the resonance region of carbonyl carbon,methylene carbon and methyl carbon,respectively,indicating that cellulose was successfully modified by esterification,and the modified products were mixed esters of cellulose laurate and cellulose acetate. |
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