Study On Structure Design And Enhancement Effects Of Ultra-high Molecular Weight Polyethylene /Wood Composite

To reinforce timber with high strength and high modulus fiber is a more effective way to improve its inadequate, such as low intensity and large deformation of wood. Ultra-high molecular weight polyethylene (UHMWPE) is the third generation hi-tech fiber materials following the carbon fiber and aramid fiber. It is widely used in military aerospace industry and reinforced fields. The bearing behavior and failure model of the timber can be changed by reinforced with UHMWPE. And the use of fast-growing wood and low-quality timber can be used effectively. In addition, there is a good market prospects for UHMWPE/wood composite in the field of anti-earthquake house and bulletproof structure housing. The only drawback for this kind composite is the weak adhesive force between UHMWPE fiber or fabrics and wood. This restricted its application. Currently the research of UHMWPE in the field of wood reinforcement is still blank. Therefore the study of this field has some positive significance. In order to explore the enhancement of UHMWPE-wood composite, this work designed to "Veneer -UHMWPE-Lumber "three-layers structure of wood composites, analyzed the strengthen mechanism of UHMWPE Using infrared spectroscopy (FTIR), scanning electron microscopy (SEM) and other means. The main work is as follows(1) As the large range of load fluctuation of the wood, and the small bearing capacity of the wood, the author proposed the research idea, which could give the wood an ideal material properties using UHMWPE to improve timber. In a comprehensive analysis of the pros and cons of various surface modification and matrix resins preparation, combining wood properties and application characteristics, it learned from "composite structure design" concept and combining applied "pre-stressed" approach, this work gave a solution for the weak bond performance. This work could greatly reduce the difficulty and cost of UHMWPE using for wood materials. Studies have shown that:the scientific design of composite structures is the method to solve the problem of poor adhesion properties following the modification of the fiber surface and matrix resin.(2) Using twill fabric manufactured by polyester filament and ultra-high molecular weight polyethylene (UHMWPE) fiber as the reinforcing material. The bonding performance of composites manufactured with wood lumber and the twill were studied, which was to explore the feasibility of UHMWPE in the field of wooden materials application. The twill widths in the structure of wood composites were designed, and the bonding mechanism was also analyzed. The results show that PUR adhesive could be used as twill/wood composite resin because of the lumber especially softwood lumber had low ILSS. The twill/wood composite had the best comprehensive performance in three kinds of forms of UHMWPE products. The ILSS of twill/wood composite could be significantly improved by decreasing the twill pavement width ratio. At last, the influence bonding mechanism was analyzed at the bond line thickness transition area.(3) As bending testing is convenient and efficient, so it is widely used in this field. It also used to evaluate the effect of UHMWPE/timber. In order to research whether Ultra high molecular weight polyethylene (UHMWPE) fiber could be used in wood-based composite, three layer structure of wood composite materials from planed timber-UHMWPE fiber-veneer was designed and prepared. The influences of UHMWPE fiber and veneer thickness composite with lumber on bending performance, ILSS, failure model and fracture energy of lumber were examined. The results showed that PUR could be used in UHMWPE/lumber composite; UHMWPE fiber obviously changed the wood failure process and failure morphology, and improved the bearing capacity of wood; the effect reinforced by UHMWPE fiber is closely related to the thickness of veneer. Reinforced effect of UHMWPE fiber much affects the shear performance of bonding interface, but method of structural design could reduce or even eliminate the impact on the shear properties.(4) For lack on the bearing capacity of finger-joined material, four kinds of same size specimens were prepared. Enhancement effect of UHMWPE fiber and effect of finger jointed on bending performance were evaluated by three kinds of indicators. Influence mechanism of fiber and finger jointed for bending performance was studied. The result shows that:the effect of finger jointed for bending performance and damage was attributed to stress concentration in the presence of finger area; UHMWPE fiber significantly improved the performance of finger-joined; the design of "finger jointed studs-veneer-UHMWPE fiber-veneer" multi-layer structure was proposed to further improve the performance of finger-jointed studs.(5) According to the characteristics of the composite structure, the concept of "effective pavement length" was proposed. The research shows that:when pavement length was less than "effective pavement length", UHMWPE fibers were pulled from the layer; when pavement length was higher than "effective pavement length", UHMWPE fibers were broken. Strain analysis shows that:in the tensile process twill presences stress concentration, which could effectively alleviated by pre-stressing. Prediction models of effective pavement length for UHMWPE fiber and twill were modeling to calculate the effective pavement length.(6) Enhancement mechanism was studied by SEM, FTIR and debonding simulation process. Enhancement mechanism of fiber was resulted to adhesive properties between PUR and fiber, inhibition of fracture in destruction process and the absorption of bending load. Enhancement mechanism of twill was attributed to good gluing properties of polyester and scientific structural design.