Effect Of Flax Surface Modification And Carbon Fiber Hybrid On The Properties Of Flax Reinforced Polymer Composites

Fiber reinforced polymer composites(FRPs)are widely used in civil engineering because of their lightweight,high strength,and corrosion resista nce.The flax fiber reinforced polymer composite is used in the construction of engineering structures,which can reduce carbon emissions and reduce the consumption of non-renewable resources.However,compared with conventional manufactured fiber(carbon fiber,glass fiber,etc.),flax fiber has disadvantages such as lower mechanical properties and poor hygrothermal resistance.Therefore,studying the methods and principles of the high performance of flax fiber reinforced polymer composites(FFRPs)is the key to promoting its application in civil engineering.This paper proposes two methods to improve the performance of FFRPs,including grafting nano-clay on the surface of flax fiber and hybrid flax and carbon fiber.The improvement law and influence mechanism of two high-performance methods on mechanical properties and hygrothermal properties of FFRPs are studied,and an optimized design method for high-performance flax fiber composites is formed.The grafting method of nano-clay on the surface of flax fiber was studied,and the effect of nano-clay grafting on the interface bonding performance of flax/epoxy resin matrix and the mechanical properties of composite materials were studied.The study results show that nano-clay can be grafted to the surface of flax fiber through chemical bonds by the modification of a silane coupling agent.The grafting of nano-clay can effectively improve the surface roughness of flax fiber,promoting the physical and chemical bonding with epoxy resin,and obtaining an interface with higher stress transmission efficiency.Compared with the untreated flax fiber reinforced composite,the flexural strength of the nano-clay grafted flax reinforced composite is increased by 20.3%.The water absorption behavior,dimensional stability,and long-term thermal/mechanical properties evolution of FFRPs by nano-clay grafting in a humid and hot environment have been studied.The results showed that nano-clay grafting could effectively reduce the free hydroxyl groups on the surface of flax fibers,reduce binding water adsorption sites,and increase the diffusion path of water molecules on the fiber surface.The water absorption behavior of nano-clay grafted flax reinforced composite material conforms to Fick’s law.Compared with ungrafted flax composites,nano-clay grafting reduced the saturated water absorption of the composites by 27.7% and the diffusion rate of water molecules by 13.5%.Nano-clay grafting delays the deterioration of the mechanical properties of flax fiber composites by water molecules.A unidirectional thin-layered carbon fiber/flax hybrid composite was prepared by wet winding.The hybrid effect and pseudo ductility of the tensile properties of the carbon fiber/flax hybrid composite were studied,and the influence of carbon fiber volume fraction and hybridization method on the bending performance of hybrid composites.Studies have shown that the volume fraction,thickness,and hybridization of carbon fiber are the key factors that affect the hybridization effect of hybrid composites.If the modulus difference is too large and the failure strain difference is too small,the pseudo ductility of the carbon fiber/flax hybrid composite cannot occur.The tensile strength and modulus of the hybrid composite material optimized by the hybrid design are greatly improved under the low carbon fiber volume fraction,and the toughness loss is small at the same time.The higher the carbon volume fraction,the higher the apparent bending strength of the hybrid composite.The hybrid composite with carbon fiber on the compression side has the highest apparent strengthThe effects of carbon fiber volume fraction and mixing method on water absorption,long-term mechanical properties,and viscoelasticity of carbon fiber/flax hybrid composites under humid and hot environments,as well as the influence of damp heat aging on the hybrid effect of carbon fiber/flax hybrid composites,are studied.Studies have shown that the water absorption process of the hybrid composite material conforms to the two-stage water absorption model.The higher the carbon fiber content,the lower the equilibrium water absorption rate of the hybrid composite material.The considerable difference in wet expansion coefficient between carbon fiber and flax leads to a greater influence on the diffusion rate of water molecules by the number of interfaces between carbon fiber and flax fiber layers.The infiltration of water molecules affects the failure mode of hybrid composites,and the degradation of tensile properties is affected by th e hybrid effect.The diffusion of water molecules increases the toughness of the flax fiber layer,resulting in pseudo ductility during the stretching process of the thin-layered carbon/flax fiber hybrid composite material.The plasticization of water mole cules leads to a significant drop in the tensile modulus,flexural modulus,and glass transition temperature of hybrid composites.The low-velocity impact properties of carbon fiber volume fraction and hybrid method on unidirectional carbon fiber/flax hybrid composites were studied.Studies have shown that the brittleness of carbon fiber leads to a higher specific energy absorption rate of hybrid composites with a higher volume fraction of carbon fiber,and the high energy absorption comes from more severe fiber damage.The toughness of flax fiber makes the hybrid composite material with carbon fiber as the skin layer and flax as the core layer have excellent deformation and energy absorption capacity.The degree of impact damage affects the performance of hybrid composites after impact,and the compression strength retention rate of hybrid composites decreases with the increase of carbon fiber volume fraction.The main damage mode in the compression process of hybrid composites after impact is the further expansion of matrix cracks under impact load.