【作者】 曲保雪；

【导师】 储富祥； 秦特夫；

【作者基本信息】 中国林业科学研究院 ， 木基复合材料科学与工程， 2010， 博士

【摘要】 在全球能源和资源日益紧缺、环境不断恶化的压力下,生物质材料由于环保性和功能性,其开发应用越来越受到高度关注。将可再生资源转化为新材料以代替部分石油产品已成为一种重要的发展趋势。木质纤维材料可以通过酯化、醚化等手段进行改性,经过改性之后的木质纤维材料具有了热塑性,可用普通塑料加工成型的方法进行加工,制成各种高性能的功能性材料或复合材料,用以代替部分石油产品,或用于无胶人造板等的制造。这一方面有望部分缓解我们对石油产品的依赖,另一方面也是为木材在加工过程中产生的锯末、刨花等废料以及森林资源中大量劣等材和森林采伐剩余物的充分利用寻求新的途径。论文以木质纤维材料的氰乙基化和苄基化为研究方向,在前人工作基础上,通过系统研究温度、时间等因素对材料苄基化、氰乙基化的影响,确立纤维素苄基化和氰乙基化反应的动力学特性,揭示木质纤维苄基化和氰乙基化产物结构和性能间的关系,研究不同预处理条件对苄基化和氰乙基化的影响,探索苄基化、氰乙基化产物的应用途径,以便为我国废材进行资源化利用,为获得石油产品的替代物提供理论支持。丙烯腈的分子较小,反应活性高,可以在较低的温度下、较短的反应时间内取得较高的取代度。当反应在45℃以下进行时,温度越高纤维素氰乙基化反应速度越快,但反应温度超过50℃以上,反应物温度会急剧升高,反应过程不易控制。纤维素氰乙基化反应在开始阶段取代度会随着反应时间的延长而迅速增加,取代度超过2.6以后增加的趋势放缓,超过2.8以后基本不再增加,此时继续延长反应时间,由于副反应发生,取代度反而略有下降。和氰乙基化相比,苄基化反应需要更高的反应温度和更长的反应时间。在本文试验设定的反应温度和反应时间范围内,纸浆纤维素苄基化产物的取代度随反应温度的升高和反应时间的延长而增加。但液相反应中反应温度受反应混合物沸点的限制。纤维素的氰乙基化和苄基化反应均属于准一级反应。对于纤维素的氰乙基化反应,四个不同反应温度45℃、40℃、35℃、30℃下的反应速度常数分别为2.26、1.94、1.61、1.30,氰乙基化反应的表观活化能为29.8kJ/mol;对于纤维素的苄基化反应,在110℃、105℃、100℃、95℃下,反应速度常数分别为0.123、0.108、0.090、0.075,反应的表观活化能为36.95kJ/mol。微晶纤维素、纸浆、脱脂棉三种原料在同样条件下进行氰乙基化反应,反应后微晶纤维素的取代度略高于其它两种,脱脂棉最低,但三者间差别不显著。杨木(Populus)纤维和杨木刨花的氰乙基化反应产物增重率差别也不显著,杨木刨花略高。但上述三种纤维素类原料和两种木材类原料相比较,反应时间较长(如3h)时纤维素类原料氰乙基化后的增重率明显高于木材类原料。不同的纤维类原料同样条件下和氯化苄进行苄基化的反应后取代度有较大的差异,也是微晶纤维素最高,纸浆其次,脱脂棉最低。木纤维、木刨花等由于含有更易进行苄基化反应的木质素,所以同样条件下反应后的增重率高于纸浆和脱脂棉纤维。冷冻润胀、微波预处理等可以增加纤维素在碱性水溶液中的溶解性,溶解性的提高改善了纤维素的分散性,使氯化苄对纤维素的可及度增加,因而可以提高同等条件下所得产物的取代度或增重率。采用粉碎等方式降低原料的粒度对原料的苄基化也有促进作用。氰乙基化反应中,丙烯腈和羟基亲核取代反应速度较快,产物的溶解能够比较及时,丙烯腈向原料内部的渗透也比氯化苄容易,所以反应前原料的分散性或粒度对氰乙基化反应产物取代度或增重率影响很小。这样就导致了可以提高原料溶解性进而提高原料分散性的各种预处理手段如冷冻润胀、超声波预处理、微波预处理等对氰乙基化反应未表现出有利影响。X4熔点测定显微镜、维卡软化点、热变形测定仪、差示扫描量热仪的测试结果表明木质纤维原料经过氰乙基化或苄基化后所得的产物均可在一定温度下软化和熔融,具有热塑性,热塑性强弱和取代程度有关。氰乙基化产物软化点和熔融温度先随取代度的升高而下降,而后随取代度的升高而升高。纤维素氰乙基化产物拐点处的取代度为1.43。苄基化产物软化点和熔融温度都随其取代度的增加而下降。取代度较高的苄基化产物以及取代度适中的氰乙基化产物可以代替传统的胶粘剂用于胶合板生产,或者按比例和木纤维、秸秆混合后生产无胶纤维板、秸秆刨花板。上述人造板主要力学性能都能达到相应的国家标准,其甲醛释放量和原料木材本身的甲醛释放量相当。更多还原

【Abstract】 Under the pressure of the increasing scarcity of global energy and resources, the exploitation and application of biomass materials have received more and more attention,predominantly owing to the needs of environmental protection and substitutes of petroleum. Wood fiber materials is the richest renewable resource in the world and can be modified by esterification, etherification or some other means. After the modification, the materials show thermoplastic properties and can be processed by the method of ordinary plastic processing and molding, and then be made into various kinds of high-performance functional or composite materials which can be used to replace some petroleum products or to manufacture non-gel based panels, etc. On the one hand, this can be expected to ease our dependence on oil products; on the other, it finds a new way of making full use of the sawdust, wood shavings and other wastes as well as a large number of low-grade timbers and logging slash of the forest resources.The central research direction of this paper is the cyanoethylation and benzylation of wood fiber materials. Based on the studies of predecessors, and by the systematic research of the influence of temperature, time and other factors on cyanoethylation and benzylation, the dissertation establishes the dynamic characteristics of the cellulose cyanoethylation and benzylation, reveals the relationships between the structures and the functions of the products of cyanoethylation and benzylation, studies the influences of different pre-treatment conditions on cyanoethylation and benzylation and provides theoretical supports for the comprehensive utilization of waste wood fiber materials, and the substitute for petroleum products.Molecules of acrylontrile are small, but have higher reaction activity and can obtain higher degree of substitution at lower temperature and in shorter reaction time during cellulose cyanoethylation. When the reaction is carried out at below 45℃, the higher the temperature, the faster the reaction of cellulose cyanoethylation will be. However, when the temperature of the reaction is over 50℃, the temperature of reactants increases rapidly, and the reaction becomes difficult to control. The degree of substitution of the cellulose cyanoethylation reaction increase rapidly with the reaction time at the beginning,, but when the degree is over 2.6, the tendency of the increase slows down, and it will no longer increase when the degree is over 2.8. At this time, due to the occurrence of side reactions, the degree will decrease slightly with the time. Compared to cyanoethylation, benzylation reaction requires higher temperature and longer time. In the range of the reaction temperature and time set in the test of this paper, the substitute degree of the products of benzyl cellulose pulp increases with the increasing of the temperature and time. However, in the liquid phase reaction, the reaction temperature is restricted by the boiling point of the mixture of reaction products.The cellulose cyanoethylation and benzylation reactions both belong to the quasi-first order reaction. Under four different reaction temperatures, say, 45℃, 40℃, 35℃, and 30℃, the reaction rate constants are 2.26, 1.94, 1.61, and 1.30, respectively. Cyanoethylation reaction’s apparent activation energy is 29.8kg/mol. As for cellulose benzylation reaction, under four different reaction temperatures, say, 110℃, 105℃, 100℃, and 95℃, the reaction rate constants are 0.123, 0.108, 0.090, and 0.075, and the reaction’s apparent activation energy is 36.9 kg/mol.When microcrystalline cellulose, pulp and absorbent cotton these three kinds of materials are taking cyanoethylation under the same condition respectively, the result will be that the degree of substitution of microcrystalline cellulose will be slightly higher than the other two, with the absorbent cotton lowest, but the distinction is not so obvious. The WPG of the poplar fiber and poplar parings after the cyanoethylation also makes little difference, with the poplar parings slightly higher. However, when the reaction takes longer time, for example, 3 hours, the WPG of fiber material is obviously higher than that of timber. When various fiber materials are taking benzylation with benzylchloride under the same condition, the degree of substitution will make a sharp distinction: microcrystalline cellulose the highest, and then pulp, the absorbent cotton lowest. Fiber and chips contain lignin that is more likely to take benzylation, so under the same condition the WPG is distinctively higher than pulp and absorbent cotton.Refrigeration swelling and microwave processing can improve the solubility of cellulose in the alkaline, which will enhance the disparity of cellulose and the accessibility of benzyl chloride to cellulose, thus the WPG or the degree of substitution will be increased. Lowering the granularity of material by grinding can also improve the benzylation. In cyanoethylation, acrylonitrile and hydroxy have nucleophilic substitution reaction more quickly, and the product can dissolve easily. Compared with benzyl chloride, acrylonitrile is more likely to permeate into the interior of material; therefore, in cyanoethylation the disparity and granularity of material before reaction have little influence on the degree of substitution and WPG of the product. As a result, all means such as refrigeration swelling, ultrasonic process and microwave process adopted in order to improve the solubility of the material and thus increase the disparity of material show no positive effect on cyanoethylation.The results of X4 melting point testing microscope, Vicat softening point, heat distortion analyzer, and differential scanning calorimeter, show that the products of wood fiber material after cyanoethylation and benzylation can be softened and melted at a certain temperature, and that means they have a thermoplastic, whose strength relates to the degree of substitution. The points of softening and melting of the products of cyanoethylation first decline with the increasing of the degree of substitution, and then increase with the increasing of the degree. The degree of substitution of the products of cellulose at the inflection point is 1.43. The points of softening and melting of the benzylation products both decline with the increasing of the degree of substitution.Benzylation products with a higher degree of substitution and cyanoethylation products with a moderate degree of substitution, can replace the traditional adhesive products for plywood production, or mix pro rata with wood fiber and straw to produce self-bonded fiber productions and straw particleboards. The main mechanical characteristics of the above mentioned wood-based boards all reach or exceed the corresponding national standards, and their formaldehyde emission amount is equal to the raw materials.更多还原