Study On Extraction And Performance Of High Purity Cellulose

At present,some paper-making factories pretreat fast-growing poplar wood with high-temperature hot water in order to extract hemicellulose and lignin which prepare high value-added chemicals such as functional sugar.After that,the wood was cooked and bleached to produce dissolving pulp,high-purity cellulose or used in papermaking.In this project,the combined severity factor?CSF?was used as a key parameter to measure the high-temperature hot water pretreatment of poplar wood chips.And its influence on the subsequent kraft cooking and ECF-bleaching or TCF-bleaching was researched.At the same time,the process conditions and reaction mechanism of using deep eutectic solvent?DES?to separate kraft pulp fibers was also studied.High-temperature hot water pretreatment had influence on the content of the three major components of poplar chips,it would mainly cause a large amount of hemicellulose degradation,a small amount of lignin dissolution and little impact on cellulose.The study determined that the critical number of CSF was 5.81.After the pre-hydrolysis critical point?CSF=5.81?,the size of pulp fibers would tend to be stable,and the paper physical properties would tend to stabilized.Based on the comprehensive economic benefits and treatment effects,the optimal pretreatment degree was determined when CSF was 6.61.Under this condition,the pulp yield was 45.27%,the content of?-cellulose was 86.65%,the degree of polymerization?DP?was 1290,the kappa number was 22.45,the brightness was 34.56%ISO,the average fiber length was0.725 mm,the average fiber width was 16.92?m,and the content of fine fiber was 9.12%Hot water pretreatment had a beneficial effect on ECF bleaching of poplar kraft pulp.When the wood chips reached the optimal pretreatment degree?CSF=6.61?,then the wood chips were pulped with Kraft cooking and bleached by D?EP?P process.After cooking and bleaching process,the brightness of the pulp would reach 85%ISO,the DP ws 930,and the?-cellulose content was 92.3%.In addition,the kappa number was 0.62 and the cellulose crystallinity was 75.39%.This research provides theoretical basis and technical support for producing of dissolving pulp and high purity cellulose by hot water pretreatment.This paper studied the influence of hot water pretreatment on TCF bleaching of poplar kraft pulp.It was found that the power function model could be used to simulate the kappa number of pulp after TCF bleaching.The model of the kappa number changing with CSF after OXH bleaching was obtained:K_t=K₀-CSF×?0.488+exp?-0.297×CSF???According to the data analysis and fitting function of pulp brightness and fiber viscosity,the viscosity,brightness and kappa number of bleached pretreatment Kraft poplar pulp with different CSF?other experimental conditions unchanged?can be predicted by referring to the delignification model.This subject also synthesized five different deep eutectic solvents?DES?of choline chloride system,and it was testified by Fourier Transform Infrared spectroscopy.Then made a simple analysis of its physical and chemical properties.The separation effects of five kinds of DES under microwave heating were investigated.The experimental results showed that the separation effect of formic acid/choline chloride?Fa Ch?solution was better and the damage of fiber was minimal under the condition of microwave heating at 100°C for 10 min.Under this condition,the content of cellulose in the solid part was 89.72%,the content of lignin was only 1.53%,and the crystallinity was 73.4%.The separation effect of oxalic acid/choline chloride?Oa Ch?solution was poor,the content of cellulose in the solid part was 83.68%,the content of lignin was 3.82%,and the crystallinity was 85.71%.Moreover,this solution severely damaged the fibers and had a great influence on the degree of polymerization of the fibers..According to the optimization results of Fa Ch separation of poplar kraft pulp,when the microwave reaction temperature was 110°C,the time was 15 min,the feeding amount was 10 g/g,the solid part cellulose content was 93.68%,the hemicellulose removal rate was78.25%,the removal rate of lignin was 74.25%.