Study On Preparation And Properties Of Crop Straw Fiber / Desulfurization Gypsum Composite Material

Nowadays, the domestic discharge amount of desulfurization gypsum and crop straws increases year by year, but their comprehensive utilization ratio is still low. Most of desulfurization gypsum is stacked in storing yard, and a mass of crop straws is dealed samply with open burning. The sample disposal causes the occupancy of massive land resources and the environmental pollution. Desulfurization gypsum can be calcined into calcined gypsum from flue gas desulfurization (FGD) which possesses gelation property. Crop straws also can be made into fibers which possesses reinforcing effect. Aiming at the current situation of low utilization ratio of desulfurization gypsum and crop straws, the crop straw fiber/desulfurization gypsum composite material is prepared, and its properties are studied deeply in this issue. We hope that this composite material will be applied to the field of novel wall materials to realize the resource-oriented utilization of agricultural and industrial by-products.This issue mainly includes following several research contents: (1) Crop straws are pretreated to crop straw fibers, and the fibers'pretreatment technology is confirmed preliminarily. (2) The influence of different fibers'adding processes on fibers'dispersibility and composite materials'mechanical properties is studied. (3) The effect of fibers'size, dosage and type on composite materials'mechanical properties and waterproof properties is investigated. (4) Surfaces of crop straw fibers are modified by different modification projects, and the modification effect and modification mechanism are discussed. (5) The composite materials'matrix is modified with different admixtures, and their mechanism is analized. (6) The reinforcement mechanism of crop straw fibers on the composite material is discussed.Crop straw fibers'dispersibility is better, if the following adding process is used: Firstly, calcined gypsum from FGD mixes with water to make slurry; secondly, put crop straw fibers into the slurry and stir the mixture. The experimental study indicates that specimens'mechanical properties can increase by adding cotton straw fibers whose length is 5~8mm and dosage is 5%, or adding wheat straw fibers whose length is 4~8mm, width is 0.7~1mm and dosage is 3%.Crop straw fiber's surface is smart and it absorbs water easily, so the interface bonding between crop straw fibers and desulfurization gypsum is weak. Crop straw fibers'surfaces should be modified to improve specimens'strength, water absorption and softeningcoefficiency. Crop straw fibers are modified respectively by alkali treatment, alkali treatment & physical coating and alkali treatment & chemical coating. After modification, the roughness of fibers'surfaces increase markedly, and the interface bonding become compact.Desulfurization gypsum as the matrix materials has some disadvantages, such as low strength, high water absorption and poor softening coefficiency. By adding naphthalene superplasticizer, re-dispersible latex powder and hydraulic admixture respectively, the modification effect of different admixtures on specimens'properties is studied. The results show that the better dosage of naphthalene superplasticizer is 0.7~0.9%, while that of re-dispersible latex powder is 3%, and that the better component proportion of flyash is 20%.The reinforcement mechanism of crop straw fibers on the composite material is discussed. In specimens, crop straw fibers can reinforce the flexural strength and the compressive strength. The reinforcement effect of crop straw fibers depends on several factors, such as fibers'dispersibility, dosage, size, type and direction. Normally, better fibers'dispersibility, smaller fibers'size and better fibers'elasticity can make better reinforcement effect. Specimens'strength can increase by adding more crop straw fibers, but overmuch crop straw fibers can cause the fiber entanglement and local stress concentration which make specimens'strength decrease.