| As the working load,internal pressure and speed of modern large aircraft tires are getting higher and higher,putting forward higher requirements on the performance of skeleton materials and their adhesion to rubber.The polyimide fibers,a new type of high-performance fiber,have the basic properties of ideal framework material and are expected to be used as cords in rubber.However,the smooth surface and chemical inertness of polyimide cords hinder its application in rubber.Therefore,this paper mainly focuses on the surface modification of the polyimide cords.(1)Dopamine was used to treat the surface of polyimide cord,and the introduction of hydroxyl and amino groups improved the surface roughness and surface activity of polyimide cord.Silane coupling agent was selected for subsequent functionalization treatment.The effects of the codeposition of dopamine and silane coupling agent and the types of silane coupling agent on the interfacial adhesion of polyimide/natural rubber composite were studied.The experimental results showed that the tensile strength of polyimide cord before and after dopamine treatment increased from 3.3GPa to 3.72GPa,and the elastic modulus increased from 108.73GPa to 109.11GPa,indicating that the attachment of dopamine made up the structural defects on the surface of polyimide cord to some extent.The adhesive layer on the surface of polyimide cord obtained by co-deposition method of adding silane coupling agent into dopamine solution has better adhesion effect,and the extraction curve shows that the adhesive layer has better capability of transferring shear stress,resisting deformation and resisting external force.Dopamine and silane coupling agents KH550,KH560,KH570 and Si69 are co-deposited on the surface of the polyimide cord,so that the surface roughness is obviously increased;and the introduced active groups such as amino,epoxy,carbon-carbon double bond and polysulfide bond can be co-vulcanized with rubber,thereby improving the interfacial adhesion performance of the polyimide cord and natural rubber,wherein the combination of dopamine and Si69 has the best adhesion effect on the polyimide cord.The interfacial properties of polyimide cord and natural rubber were improved by 92.8%,while when dopamine was combined with KH550,KH560 and KH570,the interfacial adhesion properties of polyimide cord and natural rubber were improved by 60.9%,57.6%and 50.8%,respectively.(2)The surface of polyimide cord was treated by RFL process.The effects of the molar ratio of resorcinol to formaldehyde,the dry weight ratio of phenolic resin to latex,the types of latex,curing conditions and other important influencing factors on the interfacial properties between polyimide cord and natural rubber were studied.The experimental results showed that when the molar ratio of resorcinol to formaldehyde was 1/1,the dry weight ratio of phenolic resin to latex was 0.22.The latex type was butyl pyridine latex,and the best curing condition was curing at 180? for 2min.At this time,the adhesive force between polyimide cord and natural rubber,that was,H pull-out force,reached the maximum value of 149.4N,which was 424.2%higher than the adhesive force between original polyimide cord and natural rubber.(3)Polyimide cord was treated by two-step method,silane coupling agent,sorbitol glycidyl ether and caprolactam blocked isocyanate were selected as one-bath treatment,and optimized RFL system was selected as two-step treatment.The effects of functional groups of silane coupling agent,one-step process of sorbitol glycidyl ether and caprolactam blocked isocyanate,and mass fraction of sorbitol glycidyl ether on interfacial adhesion between polyimide cord and natural rubber were studied.The experimental results showed that KH560 containing epoxy group had the best compatibility with RFL system,and its adhesion between polyimide cord treated by two-step method and natural rubber was 10.1%higher than that of RFL system alone.When sorbitol glycidyl ether and caprolactam blocked isocyanate were used together as one-bath RFL system as two-step treated polyimide cord and natural rubber composite,the adhesive force of RFL system treatment was increased by 29.3%,and the adhesive force of 9wt%sorbitol glycidyl ether and RFL system treated polyimide cord and natural rubber composite was increased by 35.9%compared with pure RFL system treatment.(4)The properties of natural rubber composites reinforced by polyimide and PPTA cord were compared and studied.The experimental results showed that the breaking strength(770.4N)of polyimide cord was 45.7%higher than that of para-aramid cord(528.9N),and the adhesion performance between polyimide cord and natural rubber-H pull-out force(193.9N)was 2.4%higher than that of para-aramid cord(189.3N).Single peeling force(11.3N)was 5.6%higher than that of para-aramid cord(10.7N),aging resistance(93.2%higher than 89.7%higher than that of para-aramid cord after aging at 100?for 96h),and fatigue resistance(4mm tensile displacement,93%higher than that of PPTA cord after 300,000 fatigue cycles).To sum up,polyimide cords have great potential for application in tire industry. |
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