【作者】 刘文；

【导师】 蒲俊文；

【作者基本信息】 北京林业大学 ， 林产化学加工工程， 2014， 博士

【摘要】 我国年产醋酸纤维素近30万吨,其中90%是用来生产醋酸纤维丝束,年消耗溶解浆20万吨左右。醋化级溶解浆的α-纤维素含量和聚合度等指标的要求均比一般的粘胶级溶解浆高,目前我国还不能生产,全部依靠进口。本文以蓝桉、桦木、棉短绒为原料,分别采用不同的制浆和漂白方法,研究了其制造醋酸纤维用溶解浆的理论和技术,并对其应用性能进行了较全面的分析评价,以期为国内溶解浆厂开发出高附加值的新产品。蓝桉采用预水解硫酸盐法制浆,预处理试验结果表明,预水解处理去除聚戊糖的效果明显优于碱预处理,二者聚戊糖去除率相差17%左右。在用碱量(Na2O计)15%条件下,所得未漂浆卡伯价为13.4,聚合度1742,白度45.8%,细浆得率41.9%。经二段氧脱木素处理,XD0ED1ETD2漂白,在总ClO2用量1.4%的情况下,所得溶解浆α-纤维素含量达到97.63%,聚合度为1086,漂白得率为88.7%。桦木创新性采用预水解亚硫酸盐法制浆,在总酸用量6.5%,化合酸用量1.5%的条件下,所得未漂浆卡伯价为24.2,聚合度为1545,白度72.1%,细浆得率为40.6%。结合企业现有生产条件,采用CEHETD漂白,所得溶解浆白度可达93.0%,聚合度为1032,α-纤维素含量为98.24%,漂白得率为87.9%。棉短绒分别采用烧碱、Soda-H2O2、氧碱法等三种不同的制浆方法进行蒸煮。结果表明,Soda-H2O2法蒸煮工艺条件最为缓和,所得浆料白度也最高,优化的较佳蒸煮工艺条件为用碱量6%,过氧化氢用量3%。未漂浆得率在88%以上,α-纤维素含量在96%以上,聚合度在1900左右,白度72-73%。结合我国棉短绒制浆企业现有生产条件,Soda-H2O2未漂浆采用二段次氯酸盐漂白,在总用氯量5.0%时,白度能够达到90.2%,漂白得率为92.1%。如采用CEH三段漂白后,在总用氯量4.0%条件下,白度可以达到90.2%以上,经次氯酸盐或过氧化氢的补充漂白,白度可提高到93%以上。采用HED漂白,在次氯酸盐漂白用氯量3%,ClO2用量1.5%的条件下,可将其白度漂白至93.8%。不同蒸煮方法的漂白浆的α-纤维素含量均在98%以上,部分甚至达到99%以上,这说明棉浆粕比较容易提纯。试制的浆粕物化性质分析表明,预水解桉木KP漂白浆、预水解桦木SP漂白浆、Soda-H2O2法蒸煮结合二段次氯酸盐漂白棉浆的性能,均能达到用户进货标准的要求,除个别指标略有差距外,总体与进口产品相差不大。SEM分析表明,预水解桉木浆粕的纤维表面较光滑,纤维结构显得较致密,但有较多的凹凸不平的破坏痕迹,与进口产品相比,表面破坏稍显剧烈。预水解亚硫酸盐桦木浆的纤维表面破坏非常剧烈,超过了进口的针叶木亚硫酸盐浆。棉浆粕的表面也有部分破坏的痕迹,但纤维较细且致密光滑。其形态特性预示了其反应性能差别。醋化试验分析表明,桉木浆粕醋化过程的峰值温度最高48.8℃,温升时间最短为34min,平均温升速率最大为1.64℃/min,桦木浆粕醋化过程的平均温升速率(1.50℃/min)也快于进口木浆粕(1.46℃/min),均表现出了较好的反应性能。而棉浆粕在制浆过程中去除的物质较少,纤维较致密,纤维素的含量高,因而导致其醋化过程温升速率(1.42℃/min)低于进口木浆粕。与进口产品相比,桉木浆粕、棉浆粕的醋酸纤维素分子量分布范围宽,在丙酮溶液中的溶解性差,而桦木浆粕的醋酸纤维素分子量分布较均匀,溶解性能也优于进口产品。更多还原

【Abstract】 In China, the annual production rate of cellulose acetate is about300,000tons, of which90%is used to produce acetate fiber tow, and the annual consumption of dissolving pulp is about200,000tons. For acetate grade dissolving pulp, the requirements for some key parameters such as a-cellulose content and degree of polymerization (DP) are much higher than that for ordinary viscose grade dissolving pulp. As a matter of fact, there is still no domestic producer of acetate grade dissolving pulp and all of our domestic demands are currently met by importing. In this thesis, eucalyptus globules, birch and cotton linter were used as the raw materials to prepare acetate grade dissolving pulp through in-depth investigation of different pulping and bleaching techniques. New technologies for producing acetate grade dissolving pulps were developed. Important physical and chemical properties of the dissolving pulps produced were thoroughly analyzed and characterized, and their application performance was comprehensively evaluated. Through the work in this thesis the author wishes to offer valuable technical guidance for domestic dissolving pulp manufacturers in their efforts to develop acetate grade dissolving pulp, a high value-added new product.For eucalyptus globules, the prehydrolysis kraft pulping process was investigated. Pretreatment experiments indicated that the prehydrolysis treatment was more effective than alkali treatment in removing pentosan. The difference in their pentosan removal rates was about17%. Under the optimal condition at alkali dosage (in Na2O) of15%, the Kappa number of the unbleached pulp obtained was13.4, the DP was1742, the brightness was45.8%ISO, and the yield of the screened pulp was41.9%. After a two-stage oxygen delignification, followed by XD0ED1ETD2bleaching with total ClO2usage of1.4%, the dissolving pulp obtained had an a-cellulose content of97.6%and a DP of1086. The bleaching yield was88.7%.For birch, a novel prehydrolysis sulfite pulping process was experimented. Under the conditions of total acid dosage of6.5%and combined acid dosage of1.5%, the unbleached pulp produced had a Kappa number of24.2, a DP of1545, and a brightness of72.1%ISO. The yield of screened pulp was40.6%. Considering the existing mill production conditions, CEHETD2bleaching sequence was adopted. The dissolving pulp obtained had a brightness of93.0%ISO, a DP of1032, and an α-cellulose content of98.2%. The bleaching yield was87.9%.For cotton linter, three different cooking methods including Soda process, Soda-H202process and Alkali-oxygen process were investigated separately. The results showed that the Soda-H2O2process was the mildest one, and the unbleached pulp obtained had the highest brightness. The optimized cooking conditions were:alkali dosage at6%and H2O2dosage at3%. Under these conditions, the yield of unbleached pulp was above88%, and the pulp obtained had an a-cellulose content of above96%, a DP of about1900, and a brightness of72-73%ISO. Considering the existing production conditions of domestic cotton linter pulp mills, a two-stage hypochlorite bleaching process was adopted for Soda-H2O2unbleached pulp. When the total chlorine usage was at5.0%, the bleached pulp obtained had a brightness of90.2%ISO and the bleaching yield was92.1%. If a CEH three-stage bleaching process was adopted and when the total chlorine usage was at4.0%, the brightness of the bleached pulp could reach above90.2%ISO. After a supplemental bleaching with hypochlorite or H2O2, the brightness of the pulp could be further increased to93%ISO. When HED bleaching process was adopted and the chlorine dosage was3%during hypochlorite bleaching and the ClO2dosage was1.5%, the brightness of the bleached pulp could reach93.8%ISO. The bleached cotton pulps from all three cooking methods had an a-cellulose content of above98%, some even above99%, indicating that cotton pulp was easier to purify.Analysis of the chemical compositions of the above pulps showed that the properties of the bleached prehydrolysis KP eucalyptus pulp, bleached prehydrolysis SP birch pulp, and the bleached cotton linter pulp produced by Soda-H202cooking in combination with two-stage hypochlorite bleaching could all meet the purchasing specifications of users. The quality of the pulps obtained was generally very close to imported pulps except for some slight difference in a couple parameters.SEM analysis indicated that the surfaces of prehydrolysis KP eucalyptus dissolving pulp fibers was smooth, and the fiber structure appeared more compact, but there was some uneven damage observed and it seemed slightly more than the imported pulp. The surfaces of the prehydrolysis SP birch dissolving pulp fibers were however damaged very seriously, and much more so than that of the imported pulp. Some uneven damage was also observed on the surfaces of the cotton pulp fibers, but the fibers appeared finer, dense and smooth. These morphological characteristics are good indications of their performance differences during the acetification reactions.Results of acetification tests indicated that during the acetification reactions, the eucalyptus dissolving pulp had the highest peak temperature of48.8℃, the shortest heating time of only34min, and the highest rate of temperature increase (1.64℃/min). The rate of temperature increase for birch pulp was1.50℃/min, which was also higher than that for imported pulp (1.46℃/min). Both the eucalyptus and birch lab-made dissolving pulps demonstrated good performance in their acetification reactions. But the cotton dissolving pulp showed the lowest rate of temperature increase (only1.42℃/min) because of the lowest removal rate of impurities during pulping and its densest fiber structure. Compared to the imported pulp, the molecular weight distribution of cellulose acetates made from eucalyptus pulp and cotton pulp were wider, and their solubility in acetone was also poorer. However, the cellulose acetate made from birch pulp had more uniform molecular weight distribution and its solubility in acetone was also better than the imported pulp.更多还原