Preparation Of Cellulose Nanofibrils From Hardwood Pulp And Improvement Of Its Redispersibility

Cellulose nanofibril(CNF)has mechanical and colloidal properties,barrier properties,low density,regeneration and biodegradability.These characteristics make CNF has broad application prospects in the fields of papermaking,composite materials,packaging,coatings,biomedicine and automobiles.However,CNF has some defects,such as high energy consumption in the preparation process,poor dispersion and stability of the prepared CNF,and low solid content.Moreover,the hydrophilicity of CNF easily leads to hornification in the drying process,and CNF can only exist in the form of water suspension,which is unfavorable for the storage,transportation and expanded application.In view of the above defects of CNF,this paper prepared pulp fiber-based CNF with poplar bleached kraft pulp as raw material by choline chloride-urea deep eutectic solvent(DES)pretreatment combined with nano-homogenization mechanical treatment,and discussed the effects of different drying methods and different hydrogen bond blockers on the dispersion performance of CNF,so as to prepare CNF with low energy consumption and high dispersion.The research results can provide theoretical guidance for the preparation and drying of high-performance CNF.The main research contents and results of this paper are as follows:Pulp fiber-based CNF was prepared by pretreatment of choline chloride-urea deep eutectic solvents system combined with nano-homogenization mechanical treatment.The results showed that DES pretreatment could promote the swelling of pulp fibers,which was beneficial to the fibrillation of fibers in the process of nano-homogenization.Under the same homogenization treatment for 15 passes,compared with the energy consumption of fiber raw materials without DES pretreatment(4.35×10~7 KWh/ton),the energy consumption of fiber raw materials after DES pretreatment(2.44×10~7KWh/ton)decreased by 43.91%.DES pretreatment can reduce the crystallinity of fiber raw materials.After homogenization for 15 passes,the crystallinity of CNF prepared without and after DES treatment was 54%and 44%,respectively.DES pretreatment had no obvious effect on the polymerization degree of fiber raw materials.The effects of vacuum drying and freeze drying combined with sodium chloride pretreatment on the redispersibility of CNF were investigated.The results showed that vacuum drying(55°C)could promote hydrogen bond retardation of sodium chloride.After pretreatment with sodium chloride,the crystallinity of CNF obtained by vacuum drying was 64.7%,which was 2%lower than that of CNF treated by freeze drying(-84°C,66.7%).The redispersibility of CNF aqueous solution obtained by vacuum drying was higher,and the stability index of CNF aqueous solution after redispersion after vacuum drying was between 0 and 0.1,which was smaller than that after freeze drying(0 to 0.3).Pretreatment with sodium chloride can improve the stability of CNF redispersed suspension.The effects of pretreatment with sodium chloride and potassium chloride combined with spray drying on the redispersibility of CNF were investigated.The results showed that KCl pretreatment was more suitable for spray drying to prepare CNF,and could play a strong role as hydrogen bond blocker.The non-complex index of dried CNF after sodium chloride pretreatment was 0.20,while that of dried CNF after potassium chloride pretreatment was 0.15.Compared with the redispersibility value of CNF after sodium chloride pretreatment of 21.10,the redispersibility value of CNF after potassium chloride pretreatment was smaller(8.06).Potassium chloride pretreatment was beneficial to improve the redispersibility of CNF.