Study On In Situ Ring Opening Polymerization Of Epoxy Monomer Filled Wood Fiber

Wood fiber, widely exists in nature, is a kind of renewable, biodegradable green material. Wood fiber as a reinforcing component is expected to replace synthetic fiber, glass fiber and other refractory fiber used in composite materials. However, wood fiber contains many hydrophilic hydroxyl groups, when used in polymer composites, the hydrophilic wood fiber and the hydrophobic polymer matrix have poor interface compatibility, leading to poor mechanical properties and poor water resistance of the composites. Therefore, the research of wood fiber hydrophobic modification has important significance.There are many ways to modify the surface of wood fiber, but some of the existing methods are complex, and make pollution in the process of modification, so it is difficult to promote large-scale application. Because the cellulose surface contains many hydroxyl groups, after alkali treatment (i.e., mercerizing) it can form a potassium or sodium alkoxide alcohol structure, which can effectively initiate ring opening polymerization of epoxy monomer. This study proposes a method that when pretreats wood fiber with alkali, then mixes fiber with epoxy monomers, then ring opening polymerization will occur on the surface of wood fiber. We establish a simple and easy way to modify the hydrophobic property of wood fiber. The main research work is as follows:First of all, we choose styrene oxide (STO) as a model of hydrophobic monomer, potassium alkoxides as initiators in anionic ring opening polymerization, and find the optimum conditions of polymerization process. The results show that, styrene oxide can be initiated by tert-butanolate through bulk polymerization, and the average number molecular weight of PSTO oligomer is about 2000. In this way we establish the formulation and process of epoxy monomer. The oligomerization process is expected to form a short chain of PSTO grafted on the surface of wood fiber, make fiber hydrophobic, and will not cause tangles.Secondly, we establish the method of the epoxy monomer grafting polymerization on the surface of wood fiber after mercerizing with potassium hydroxide. The results show that, when the concentration of potassium hydroxide is 10%, in 80℃ after 24 hours reaction, the grafting ratio of PSTO can be controlled between 10% and 15%, and the water contact angle of modified fiber significantly increases, effectively improving the hydrophobic of fibers. In addition, during the fiber surface grafting reaction we can add the epoxy monomer containing C=C double bond (allyl glycidyl ether (AGE) and glycidyl methacrylate (GMA)), then we can get hydrophobic modified fiber with double bond on the surface, and the double bond can take part in the curing process of UPR, forming a covalent bond between fiber and matrix, and improving the properties of composite materials.Finally, we use the hydrophobic modified wood fiber to fill unsaturated polyester resin (UPR) to make composite materials; we measure the shrinkage ratio, water and moisture absorption and mechanical properties of the samples. The results show that, when the fiber content is 5%-10%, the shrinkage ratios of hydrophobic modified wood fiber filled UPR composites are significantly lower than that of the unmodified fiber filled ones. The water and moisture absorption decrease significantly, which show that fiber-UPR matrix interface improves, to a certain extent, this will block water migration along interface. Through SEM observations, we can see that the interface of fiber and UPR matrix improves a lot, indicating that interface improvements between STO modified fiber and unsaturated polyester resin matrix.