Effect Of Pretreatment Of Hot Water And Biological Enzyme On The Properties Of Hardwood Chemimechanical Pulp

High yield pulp had good physical strength and excellent optical properties,which improved the proportion of high yield pulp in the paper market.So as to improve optical properties and physical strength of high yield pulp,the study mainly focused on the several aspects:optimization of treatment methods and process parameters in alkali impregnation and bleaching stage,the influence of hot water and biological enzyme pretreatment on the chemical composition,morphology and structure of wood chips and pulp properties and the optimization of hot water and biological enzyme treatment process.In the process of alkaline hydrogen peroxide treatment,when the temperature was lower(70-80?),most of the bleaching liquor would react with wood chips,and the bleaching efficiency was high,while when the temperature was higher(90-95?),hydrogen peroxide would release a lot of oxygen and the bleaching efficiency was lower.Contrary to the law of bleaching reaction,high temperature and high alkali dosage was beneficial to increase the tensile strength and tear index of the pulp.Based on the mechanism of hydrogen peroxide bleaching,the kinetic model of temperature,alkali dosage,and hydrogen peroxide dosage was established.It was found that when the alkali dosage was 6%,the calculated value of the model of hydrogen peroxide concentration had little difference with the actual measured value.The model was as follows:(?)In order to keep the decomposition of hydrogen peroxide steadily,a new treatment method of alkaline hydrogen peroxide was put forward in this study,that is,segmented alkali and hydrogen peroxide treatment(A-P),and explored the effect of different alkali dosage and hydrogen peroxide dosage on the brightness and physical strength of pulp.Firstly,alkali liquor was used to swell wood chips,then hydrogen peroxide bleaching liquor was used to treat wood chips.The results showed that the pulp brightness of A-P treatment was significantly higher than the AP treatment,and the tensile strength of A-P treatment was much higher than the AP treatment and A treatment.When the dosage of hydrogen peroxide was 4%,the tensile strength of A-P treated pulp was 3.33 k N/m,which was super than the highest tensile strength of AP treatment and P treatment.When the alkali dosage was 6%and the hydrogen peroxide dosage was 6%,the tensile strength of A-P,AP,and A treated pulp was 3.62 k N/m,3.16 k N/m and 2.17 k N/m respectively.Comparing the morphology structure,component content and pulp properties of the wood chips after high-temperature hot water treatment and heat resistant xylanase treatment,it was found that the chemical components in the wood chips were removed in different conditions.The specific surface area of the wood chips increased with increasing temperature,and the porosity first increased and then decreased.Moreover,as the degree of pretreatment intensifies,the amount of pseudo-lignin and microfibril fragments in the pores of the wood chips increased,which blocked the pores of the wood chips and hindered the subsequent penetration of the alkali liquid into the wood chips.With the treatment of heat-resistant xylanase,the pulp physical properties have improved.Especially,when the temperature was 90?and the enzyme dosage was 20 U/g,the heat resistant xylanase could be more effective in removing hemicellulose,and the specific surface area and porosity were also the maximum at the condition.Combined with the figures,the pores of the wood chips treated with heat resistant xylanase were transparent and clear.It showed that the effect of heat resistant xylanase pretreatment was remarkable,which not only removed hemicellulose efficiently,increased specific surface area and porosity,but also removed impurities in the pores of wood chips.By analyzing the properties of the pulp after high-temperature hot water pretreatment,it was found that with the increase of the temperature of hot water pretreatment,the brightness of the pulp gradually decreased,and the strength properties of the pulp were better,however,when the temperature was higher than160°C,the strength properties of the pulp dropped rapidly.As the temperature of the enzyme treatment increased or the dosage of the enzyme increased,the physical properties of the pulp first increased and then decreased.In particular,when the enzyme treatment temperature was 90°C and the dosage of the enzyme was 20 U/g,the strength properties and brightness of the pulp were better.The tear index of the pulp was 3.73 m N·m~2/g,the tensile strength was 3.77 k N/m,and the brightness was70.3%ISO respectively.The pulp treated with heat resistant xylanase had excellent properties,and the enzyme treatment saved energy consumption and reduced the difficulty of industrial production.