Optimization Of Plant Fiber Permeability And Composite Molding Quality Under VARI Process

Plant fiber composite materials prepared by the vacuum assisted resin infusion(VARI)process utilize the characteristics of low price and environmental protection for plant fibers,which becomes a research hotspot in this field.However,the unique luminal structure of plant fiber and fiber-yarn-fabric multiscale structure of textile composite leads to the problems of resin penetration in the VARI process and unstable product quality of plant fiber composite materials.In order to improve the production efficiency and molding quality of plant fiber composite materials,the following researches have been carried out:The performance changes of ramie fabric before and after desizing and the chemical rheological properties of 191 unsaturated polyester resin were explored.The relationship model of resin viscosity changes with time and temperature was established.The results show that after desizing the impurities on the surface of ramie fiber are removed,which brings about increase of the roughness and the polar component of fiber.The constitutive relationship of the ramie yarn after desizing has changed,resulting in diversity of the tensile properties for the before and after ramie fabric in both warp and weft directions.The chemical rheological model could relative accurately predict the relationship between the viscosity of resin with time and temperature,which provides a theoretical guidance for the VARI process of composite materials.Based on Darcy's law,the formula of permeability is deduced to characterize the permeability of ramie fiber.The mould-filling experiments of 1,4,8,12 and 16 layers of ramie fabric were respectively used to explore the impregnation in different thickness reinforcements.The ramie fabric reinforced unsaturated polyester resin composite(RFUC)was prepared to investigate the way to control its molding quality.The results show that the layer thickness affects the compaction degree of the reinforcement,thus affects the size of the resin flow channel,which leads to a non-linear decline tendency in permeability with the increase of the layer thickness,and the accuracy of the resin flow simulation would be improved through the increase of layer thickness.Fiber volume fraction and internal defects have a synergistic impact on the mechanical properties of RFUC.When the fabric layers reach 16 layers,the lack of resin penetration results in poor mechanical properties of RFUC and more defects inside.In order to eliminate the infiltration defects of high-thickness RFUC,the three optimization schemes are put forward to,including glass fiber hybrid laminate structure design,controlling resin viscosity by styrene,and interface modification of KH550 silane coupling agent.The permeability and molding quality would be optimized and developed.The results show that the larger inter-bundle flow channel of the glass fiber fabric and the capillary force inside the fiber bundle are the main reasons for improving the permeability of the ramie reinforcement.The more dispersed in the reinforcement,the better the permeability.The mechanical properties of glass/ramie hybrid composites have different fracture failure modes due to the different hybrid modes.As for the viscosity of the resin,the permeability of the reinforcement decreases linearly with the increase of styrene and the decrease of viscosity.The mechanical properties of RFUC increase first and then decrease while the change of viscosity,which is related to the curing mechanism of styrene molecules.After RFUC modified by 3wt% silane coupling agent,the surface polarity of ramie is reduced,and the permeability and mechanical properties of RFUC are improved.