Study On Plasticizing Modification Of Lignocellulose In Aqueous Medium

Lignocellulose is the most abundant renewable resources in nature with excellent mechanical properties.The preparation of sustainable and environment friendly composite materials using lignocellulose as raw materials is very important.However,lignocellulose generally can't be processed as thermoplastic plastics due to the high crystallinity and melting temperature of cellulose.Traditional plasticizing modification of lignocellulose,such as esterification and etherification need large amounts of organic solvents that cause environmental pollution,as well as reduced the excellent inherent properties.In this thesis,we proposed to conducted the plasticizing modification method in aqueous medium combined with the pretreatment of lignocellulose and the peroxide /grafting process.These methods have the advantages of environment friendly,high utilization efficiency of lignocellulose and retains inherent properties of the fibers.Eucalyptus and sisal fiber was pretreated with different pretreatment method,such as acid(DA),alkaline(DB),hot-water(HW),organic solvent(OR),bleaching with sodium chlorite(SCB)and screw extrusion steam explosion(SESE).The effect of different pretreatment of lignocellulose on further modification were discussed.The results showed that there are different pretreatment efficiency of different pretreatment method on Eucalyptus and Sisal fibers.Alkaline pretreatment,organic solvent pretreatment and bleaching pretreatment could remove components partially,and disrupt the surface morphology structure of lignocellulose.Comparing with other pretreatment method,the SESE can improve the reactivity of lignocellulose preferably.Eucalyptus and Sisal fibers were divided into microfiber after the SESE pretreatment,and the fiber size reduced remarkably.,which results the increase of specific surface area and accessibility.Furthermore,the recovery of the pretreated lignocellulose was more than 95%,and the process does not require any chemical reagents.The plasticizing modification of Eucalyptus and Sisal fibers was conducted with the method combined with pretreatment and peroxide modification.The results showed that the glucose unit in the amorphous area of cellulose was destroyed due to the ring opening reaction in the peroxide process and obtained linear chain backbone containing ether linkage,which improved the process properties.Cellulose crystalline region was cladding by amorphous cellulose chain after peroxide modification,and formed core-shell structure.Partial hemicellulose and lignin was retained during the SESE pretreatment processing,which has an assisting role in coating efficiency.In addition,the properties of the peroxide treated lignocellulose grafting with different polymer monomers were discussed.The Eucalyptus and Sisal fibers after the SESE pretreatment were surface modified by free radical polymerization initiated with Ce4+ ions.We studied the effect of different monomers grafting on the lignocellulose,such as methyl methacrylate(MMA),glycidyl methacrylate(GMA),et al The grafting ratio was higher when monomers possessed high activity and low molecular weight,such as MMA and GMA monomers,which caused lignocellulose covered with grafted macromolecules completely.In addition,the sisal fibers after the SESE pretreatment has higher grafting ratio because of its high cellulose content and high reaction accessibility comparing to the other pretreatment methods.The lignocellulose modified with different pretreatment and oxidation/grafting was hot pressed molding and studied the property of plasticizing processing.The results indicated that the plasticizing processing properties of lignocellulose after treated with different pretreatments and peroxide or grafting were improved in different degrees.The Sisal fiber treated with the SESE pretreatment and peroxide modification has the most excellent comprehensive performance comparing to other pretreatments.MMA and GMA oligomers grafting on the lignocellulose surface melted and formed continuous phase in the process of hot pressed,which can significantly improve interfacial compatibility of composites.In summary,the lignocellulose treated with the SESE pretreatmentperoxide/graft-modified has very good thermal stability and thermoforming processability;and the lignocellulose utilization is improved,the modification process is environmentally friendly and able to open up new ways to the high value utilization of biomass.