Synthesis Of Cellulose Laurate By Mechanical Activation-strengthened Solid Phase Reaction

Cellulose,one of the most abundant natural resources,has the advantages of innocuity,renewability,biodegradability,environmentally friendly,etc.Cellulose ester is an important kind of cellulose-base materials.It has broad application prospect,especially that it may partly instead of the plastic based on petroleum products,which make it gradually attracted wide attentions.But,the shielding of lignin and hemicellulose,and particularly highly-crystalline supramolecular structure of natural cellulose make it difficult to react with esterification reagents.Therefore,in this thesis,the bagasse pulp was modified by mechanical activation(MA)-strengthened solid phase esterification.In the reaction process,the crystal structure of cellulose was damaged by mechanical force to enhance its chemical reactivity.The main research contents and results are as follows:Bagasse pulp was mechanically activated by a home-made stirring ball mill.The effect of MA time(tM)on the surface morphology,crystal structure,functional groups,surface characteristics,degree of polymerization(DP)and thermal stability of bagasse pulp was characterized by using scanning electron microscopy(SEM),fourier transform infrared spectroscopy(FTIR),X-ray diffraction(XRD),X-ray photoelectron spectroscopy(XPS),Contact angle tester and microcomputer differential thermal balance,respectively.The results showed that the link of hydrogen bonds between cellulose molecules was fractured and the fiber bundles were dispersed and refined by MA,leading to the decrease in crystallinity of cellulose.When tM was increased from 0 to 120 min,XRD crystallization index and infrared crystallization index decreased from 75.82%and 0.508 to 41.56%and 0.298,respectively,fiber surface carbon-oxygen ratio increased from 56.42 to 74.19,and the thermal stability and contact angle were both reduced.These results indicated that MA could enhance the reaction between cellulose and lauric acid.The crystalline form of cellulose gradually changed from cellulose I into cellulose II with the increase of tM.Cellulose laurate was synthesized by MA-strengthened solid phase reaction using a self-designed stirring ball mill as reactor.The effects of reaction temperature,reaction time,reagent molar ratio,dosages of auxiliary and catalyst,etc.were investigated respectively by using the degree of substitution(DS)of cellulose laurate as evaluating parameter.The results indicated that the optimized conditions for producing cellulose laurate by MA-strengthened solid phase reaction were:10.00 g of bagasse pulp,molar ratio of anhydro glucose unit(AGU)of cellulose:catalyst(NaH2PO2·H2O)of 1:0.30,molar ratio of AGU of cellulose:esterifying agent(lauric acid)of 1:4,molar ratio of AGU of cellulose:additive(ZnCl2)of 1:3.20,reaction temperature 45℃,reaction time 60 min.Under these reaction conditions,the DS of cellulose laurate was 1.94.The particle morphology,functional groups,crystal structure,thermal stability,DP and hydrophobic performance of the cellulose laurate were characterized by using SEM,FTIR,XRD,micro-computer differential thermal balance and contact angle tester,respectively.The results showed that after esterification,the compact and relatively smooth surfaces of bagasse pulp particles were eroded and destroyed,forming many gaps and holes.The absorption peaks of carbonyl group(C=O)and methylene(C-H)appeared at 1740cm-1 and 2852 cm-1 in the infrared spectra of products,which proved that the solid phase esterification had happened and cellulose laurate was successfully synthesized.XRD crystallization index of cellulose laurates with the DS values of 0.42,0.78 and 1.94 were determined to be 75.8%,66.5%,65.6%and 60.1%,respectively,attributing to intense milling and the introduction of laurate groups,but the crystalline form of cellulose laurate still kept cellulose I of native cellulose.The DP,thermal gravimetric starting temperature and thermal stability of cellulose laurate were all reduced,and the hot workability and contact angle were increased,which means that the hydrophobic performance was enhanced.