Study On The Clean Pulping Of Cotton Linters And The Properties Of Cotton Pulp

Cotton pulp has the characteristics of long fiber,good strength and high degree of polymerization,and is widely used in textile,paper and chemical industries.In the papermaking industry,the preparation of cotton pulp usually selects cotton linters as raw materials and have benn prepared by one-step alkaline hydrogen peroxide method.However,when preparing cotton pulp by many cotton pulp mills,there are problems of higher cooking temperature and higher alkali consumption,which is not conducive to the delignification of hydrogen peroxide,which can also damage the fibers and cause greater environmental pollution.Therefore,this study aimed at the problems in the preparation process of cotton pulp,and used the second type of cotton linters as raw materials for the purpose of clean pulping.Firstly,this research studied the preparation of cotton pulp by alkaline hydrogen peroxide cooking with lower alkali dosage and lower cooking temperature combined with element-free chlorine bleaching.On this basis,the effects of immobilized cellulase treatment on the subsequent bleaching of cotton pulp and the effects of the two beating methods of Valley and PFI on the physical properties of cotton pulp and paper were studied.Finally,aiming at the phenomenon of fluorescence in cotton pulp,the source and removal of fluorescent substances in cotton pulp were studied.The main research contents of the thesis are as follows:First,the chemical components of cotton linters were analyzed.The total cellulose content was 94.24%,and the Klason lignin content was 3.88%.Through single factor experiments and orthogonal experiments,we explored the alkalinity of lower temperature and lower alkali consumption.The effect of hydrogen peroxide pulping was better when the alkaline hydrogen peroxide pulping process was sodium hydroxide dosage 5%,cooking temperature 100°C,hydrogen peroxide dosage 3%,and cooking time 120 minutes.Compared with cotton linters,the kappa value of the pulp was reduced by 86.53%,and the brightness was increased by 2.28times.On this basis,the effects of elemental chlorine-free one-stage bleaching and three-stages bleaching of cotton pulp were compared,and the results showed that the alkaline hydrogen peroxide cooking combined with elemental chlorine-free three-stages bleaching pulp had higher brightness,less ash and dust.Immobilized cellulase treatment was added on the basis of optimized pulping process,and the effect of immobilized cellulase treatment on cotton pulp was studied.Through single factor experiments,the effect of immobilized cellulase treatment on the subsequent bleaching of cotton pulp was studied.With the increase of enzyme dosage and enzyme treatment time,the brightness of the subsequent bleached pulp also increased.Compared with the bleached pulp without enzyme treatment,after 1 hour of treatment with immobilized cellulase enzyme dosage of 3.375U/g and combined bleaching,the cotton pulp had a brightness increase of 4.31%ISO,a degree of polymerization increase of 157,a yield reduction of 2.24%,ash and alkali solubility S₁₀ and the extract content were lower.Using the cotton pulp prepared by the optimized pulping process as the raw material,on the basis of Valley heavy knife beating to cut the pulp to a certain weight average length,two beating methods of Valley beating and PFI refining were used to treat cotton pulp,and the effects of the two beating methods on the properties of cotton pulp were studied.When the freeness was 170m L,the pulp refined by PFI was better than the pulp beaten by Valley heavy knife.The folding resistance was increased by 140 times,the bursting index was increased by96.3%,the tearing index was increased by 119.9%,tensile index was increased by 66.0%.Finally,according to the fluorescence phenomenon in cotton pulp,the fluorescence source and chemical composition of cotton pulp were studied,and the removal of fluorescent substances was discussed.By analyzing the fluorescence spectra of cotton and its pulp,it could be known that the fluorescence in the cotton pulp comes from the raw material itself.On this basis,the cotton had been extracted and characterized,and the study showed that the fluorescent substances are derived from phenols and terpenoids.Combined with the fluorescence spectrum of the second type of cotton linters,it was found that the second type of cotton linters had the same composition of fluorescent substances as cotton.Because the alkaline hydrogen peroxide combined with element-free bleaching(chlorine dioxide as the main bleaching agent)processed the second type of cotton linters without fluorescence,and combined with the commonly used methods for preparing high-quality cotton pulp,alkaline hydrogen peroxide and alkaline hydrogen peroxide combined with a period of chlorine dioxide were used to treat cotton in the follow-up studies.Research showed that alkaline hydrogen peroxide combined with chlorine dioxide treatment can effectively remove the fluorescence in cotton.