Study On Cyanoethylation, Benzylation Of Wood Fiber Material And Their Utilization

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.