| Nowadays, the production and consumption of paper and paperboard in China has ranked first in the world. More than fifteen million tons of pulp was imported each year. In order to increase the proportion of wood pulp, the forest-paper integration has been developed and the fast-growing forest has been cultivated in China. Aspen has so many advantages in the production of chemimechanical pulp, thus it is considered as a promising fast-growing, high-yield hardwood species. About 30-70kg/t pulp of Dissolved and Colloidal Substances (DCS) will be released into the pulp suspension system during the mechanical pulping and bleaching processes. With the high recycling of white-water, the DCS will continue enriching, which will deteriorate the pulp and papermaking system and has negative impact on the paper properties. In this thesis, the dissolution rule of DCS and its biological control during chemical pretreatment, refining and bleaching processes are investigated.In this thesis, Populus×Euramericanacv ’Neva’was chosen as the raw material. The dissolution rule of DCS during chemical pretreatment process was studied. The composition of carbohydrates and MTBE extractives in DCS which released during the pretreatment process were determined by GC-MS. The contents of superficial lignin and extractives before and after chemical pretreatment were investigated by ESCA. The results showed that the physical characteristics and lignin content of DCS would change due to the different alkaline H2O2 pretreatment processes. Overall consideration, the optimized pretreatment process was 3% NaOH,3% H2O2,70＞,60 min. The turbidity, cationic demand and lignin content of DCS were 59.8NTU,1.19meq/L and 0.30mg/L under this condition. The carbohydrates in DCS were mainly composed of xylose, glucose, galactose, arabinose, mannose, galacturonic acid and glucuronic acid. The main components of MTBE extractives in DCS were benzoic acid which was the degradation product of lignin, and the second component was fatty acids which were mainly composed of succinic acid, tetracosanoic acid, hexadecanoic acid, eicosanoic acid and docosanoic acid, etc. After chemical pretreatment, the content of superficial lignin in fiber increased but the amount of extractives decreased.The effect of pulp consistency and disc gap on the dissolution of DCS and slurry properties during the third stage PFI refining process was discussed in this thesis. The change of carbohydrates and MTBE extractives in DCS before and after refining was studied by GC-MS. The contents of superficial lignin and extractives before and after refining were also determined by ESCA. The results showed that increasing pulp consistency and reducing disc gap could promote the dissolution of DCS which was supported by the increase of solid content, cationic demand and lignin content. Meanwhile, the tensile index of handsheet also increased. After a three-stage refining, the average particle size of DCS was reduced from 626.6 nm to 333.6 nm. Refining promoted the dissolution of carbohydrates, and the amount of galacturonic acid was more than that of glucuronic acid. Galacturonic acid was the dominating contribution to uronic acids before and after refining. The degradation product of lignin was the main component in MTBE extractives after refining. And the contents of fatty acids, sterol esters and monoglycerides increased to varying degrees after refining. The amyrin was also detected in the DCS after refining, but the resin acids were not found. After the three-stage refining, the content of superficial extractives in slurry fibre increased, but the superficial lignin content decreased.The effect of alkali treatment and alkaline H2O2 bleaching on the dissolution of DCS and slurry properties were also studied in this thesis. The changes of carbohydrates and MTBE extractives of DCS in aspen CTMP, ACTMP and BCTMP were analyzed. The content of superficial extractives and lignin in aspen CTMP and BCTMP were also determined. The results showed that the optimum condition of aspen CTMP bleaching was 3% NaOH,3% H2O2,75℃ and 90 min. The brightness and tensile index of handsheet was respectively 79.1% ISO and 33.7 N-m/g under this condition. The turbidity, cationic demand and lignin content of DCS were 60.2NTU,1.64meq/L and 0.23mg/L under this condition. Bleaching could promote the dissolution of DCS, which was reflected by the increase of solid content, cationic demand and lignin content, and the paper properties could also be improved. The dissolution of DCS was mainly determined by the NaOH rather than the H2O2. After alkali treatment, the average particle size of DCS in aspen CTMP dropped from 580.7nm to 159.6nm. After alkaline H2O2 bleaching, the average particle size of DCS decreased further to 97.03nm. The dissolution of carbohydrates increased dramaticlly during the alkali treatment. The content of carbohydrates increased further under the alkaline H2O2 bleaching. The point was that the dissolution of galacturonic acid was more than glucuronic acid after alkali treatment and alkaline H2O2 bleaching. The effect of NaOH on the dissolution of uronic acids was larger than H2O2. After alkali treatment and alkaline H2O2 bleaching, the contents of fatty acids and glycerides increased, but a decrease of sterol esters was found. The glycerides was 1,3-bis hexadecanoic acid glycerides, and the sterol esters were composed of cholesteryl esters and β-sitosterol ester. After alkaline H2O2 bleaching, the content of superficial extractives in slurry fibre increased but the lignin decreased.The treatment process of DCS with lipase and pectinase was optimized in this paper. And the influences of enzymatic treatment on DCS present in third stage PFI refined slurry, CTMP and BCTMP were investigated. The results showed that the optimum treatment process for lipase was pH 8.0, temperature 60℃, enzyme dosage 150u/g pulp, reaction time 120 min. The optimized treatment process for pectinase was pH 4.0, temperature 50℃, enzyme dosage 120u/g pulp, reaction time 150 min. The content of glycerol increased respectively by 7.86% and 9.73%, when the lipase was used to treat BCTMP and the residual DCS in third stage PFI refined slurry. The cationic demand of DCS decreased respectively by 71.48%,26.70% and 11.60%, when the pectinase was utilized to treat BCTMP, third stage PFI refined slurry and CTMP. |
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