Preparation Of Nanocellulose By Enzymatic Pretretment Combined With High-pressure Homogenization And Study Of Its Redispersibility

As the most abundant renewable resource on the earth,natural cellulose has many advantages,such as environment-friendly,non-toxic and biodegradable.Nanocellulose not only has the characteristics of cellulose,but also has many excellent properties,such as high Young’s modulus and crystallinity,good capability of water absorption,high degree of polymerization,which makes it very popular in various fields of application.The method of enzymatic hydrolysis combined with mechanical treatment of nanocellulose is relatively mature,but how enzyme treatment and mechanical treatment influence the nanocellulose needs to be further studied.The characteristic of large specific surface area of nanocellulose not only gives it high activity of chemical reaction,but also makes it easy to agglomerate in the drying process.Which hinders the development of its application.In this paper,the influences of enzymatic hydrolysis and high-pressure homogenization on nanocellulose were analyzed by the response surface method of Design-Expert.The redispersity of nanocellulose was studied,the cellulose nanocomposites were modified with EPTMAC.Then its properties after modification were studied.Hardwood pulp was treated with four kinds of cellulose endoglucanases,R-363,R-358,R-360,R-210.Then the length,width,coarseness,kinked fibers,curl index and fine fiber content of the enzyme-hydrolyzed fibers were analysed.The results showed that enzymatic treatment had significant influences on fiber length,width,kinked fibers,curl index and fine fiber content,but had no significant effect on fiber coarseness.And the pulp was treated best with R-363 endoglucanaseHardwood and softwood nanocellulose were prepared by enzymatic pretretment combined with high-pressure homogenization.The effects of time of pretreatment,dosage of cellulase,frequency of homogenization on the size of nanocellulose were analyzed by Design-Expert software.The properties of the nanocellulose prepared under the optimum parameters were analyzed systematically.The results showed that hardwood and softwood nanocellulose have the same law of influence.And the order of their influences on particle size was as follows: time of pretreatment ﹥ dosage of cellulase ﹥ frequency of homogenization.The morphology and transmittance of cellulose nanoparticles were analyzed.The results showed that hardwood cellulose nanoparticles were rod-shaped,the length was200 ~ 500 nm,the width was 20 ~ 40 nm.The softwood cellulose nanoparticles were interwoven into a reticulated structure with a length of 300~700 nm and a width of 5~20nm.The nanocellulose prepared from both raw materials were CNFs.Compared with hardwood CNFs,the surface of softwood CNFs was smoother,the agglomeration phenomenon was reduced.And the transmittance of softwood CNFs suspension was higher than that of hardwood CNFs.The effects of poly(ethylene oxide)(PEO)on the redispersibility of cellulose was studied on hardwood CNFs and softwood CNFs prepared under the optimum conditions.The results showed that: adding PEO into CNFs suspension before freeze-drying did not promote the redispersion of cellulose nanoparticles.On the contrary,it would prevent nanoparticles from redispersing in water due to self-agglomeration.Adding appropriate amount of PEO after freeze-drying could effectively promote the redispersion of cellulose.The optimal addition of PEO was 2.5%(w / w)when the hardwood CNFs was redispersed.The optimal addition of PEO was 1.5%(w / w)when the softwood CNFs was redispersed.Hardwood 、 softwood CNFs and CNFs suspension added PEO were modified with2,3-epoxypropyltrimethylammonium chloride(EPTMAC).The properties of the modified CNFs were characterized.The results showed that hardwood CNFs had higher grafting rate of quaternary ammonium than hardwood CNFs.Besides,CNFs suspension added with appropriate amount of PEO had higher grafting rate of quaternary ammonium than CNFs suspension without PEO addition.After being modified with quaternary ammonium,the surface of CNFs fiber became uneven and the structure between fibers became loose.Modified CNFs maintained the type I crystal structure of cellulose,but the crystallinity and the thermal stability decreased.The higher degree of the quaternization,the lower the crystallinity and thermal stability of the cellulose.