| Under the circumstance of alternating stress or alternating strain,service life of rubber products is determined by the fatigue performance of materials.In this paper,the mechanical properties and fatigue behaviours of aramid fiber(AF)reinforced carbon black(CB)-filled butadiene styrene rubber(SBR)was studied.To activate its inert surface and increase the surface roughness,AF were treated using thermal oxidation treatment,complex processing with Ca Cl2,and etching by Na OH,respectively.Butadiene-vinylpyridine copylymer latex,domestic liquid rubber,and silane coupling agent were respectively applied as adhesive of the interface between SBR matrix and AF.The interfacial performances of the modified composites were analyzed via mechanical testing and fatigue behaviour characterization.The results are described as follow:(1)The mechanical properties of AF-CB/SBR composites can be obviously improved owing to the addition of AF with a small amount.The stress at definite elongation increases while elongation at break decreases with the increasing content of AF.When the dosage of AF is 2 phr,the overall performances of the composites are relatively superior.Under stress control condition,the fatigue life of composites notched specimens increases 25 times approximately due to the addition of AF.After fatiguing a certain cycle respectively under strain control and stress control condition,the stress at definite elongation of the composites increases firstly then falls with the increasing strain.Higher stress at definite elongation can be remained when the AF is added into the composites after fatiguing,however,the elongation at break declines with increasing the fatigue deformation.From the stress-strain curves,it can be observed that curves of the fatigued sample deviate from the straight line in the small strain region,which indicates that the fibers are degummed after the fatigue process and the composite interface suffers some damage.From the scanning electron microscope(SEM)photos,it can be found that the specimen fracture surface exhibits a shape of stripping,and the relaxations of matrix take place.The relative interface slip energy is calculated according to the stress-strain curves,and it is found that the values of relative interface slip energy decrease with the increase of fatigue deformation,which indicates that fatigue deformation makes a great influence on the interfacial failure of AF-CB/SBR composites.(2)The grease coating on the AF surface is disintegrated and the surface oxygen content increases after the thermal oxidation treatment,which enhances the interfacial interaction between AF and the SBR matrix,thus increasing the performances of the composites.Then,the treated fibers are infused into butadiene-vinylpyridine copylymer latex.The structure of butadiene-vinylpyridine copylymer latex is similar to that of SBR,and the pyridine structure on its molecular chain provides strong polarity as well as close-knit splice to AF.Thus,flexible interface can be established between fibers and rubber matrix and the adhesion can be improved.As a result,the mechanical properties and fatigue life of composites are enhanced greatly.After infusing,the tensile stress at 100% increases 13.6% and the fatigue life is 8.5 times compared with the uncoated AF.(3)CaCl2 solution was used to treat AF.The complex reaction between Ca2+ and the fiber is applied to break the hydrogen bond in order to decrease the surface crystallinity and roughen the fiber surface.It is found that surface crystallinity apparently decreases with the increasing concentration of Ca Cl2 solution,and the higher concentration does Ca Cl2 solution have,the severer surface destruction occurs.When the concentration of Ca Cl2 solution exceeds 10%,a sharp decline in intrinsic rigidity and strength of AF is achieved.The mechanical properties of composites are further enhanced owing to the addition of maleic anhydride grafted liquid poly(l,2-butadiene)oligomer rubber(MLPB)as compatilizer.Dynamic mechanical analysis(DMA)results show that the composite interfacial adhesion can be obviously improved due to the addition of compatilizer.MLPB in this system can co-vulcanize with the rubber matrix,which forms rigid interface between fiber and rubber matrix.During the stress-control fatigue process,the area of fatigue hysteresis loop decreases sharply,and lower deformation can be observed at the same stress condition compared with the sample without MLPB,which further indicates that MLPB can promote the interfacial adhesion.When the composite is under stress,the AF in the composite can transfer the stress and bear larger force,which decreases the deformation of the composites.(4)In this paper,silane coupling agent KH560 and KH570 were chosen to coat AF,and then the coated AF was used to prepare AF-CB/SBR composites.The performance test results show that AF coated with KH560 or KH570 can improve the interfacial adhesion of the composites compared with the uncoated sample,and meanwhile,the tensile stress at 100% increases 16.9% and 16.8%,respectively.Moreover,the fatigue life of the composites under stress control condition increased about 3 times.In Na OH/ CH3CH2 OH solution,amido bonds in AF are hydrolyzed and its surface is etched,which obviously increases the surficial roughness and the combination between AF and rubber matrix is enhanced.When AF is treated with Na OH and then coated with KH560,the interfacial adhesion of composites can be further enhanced.KH560 can interact with the rubber matrix and its epoxy group is compatible with the fiber,which is conducive to the dispersion of fillers and enhances the interfacial adhesion,thus the fatigue performance of the composites increases obviously.From the characterization of the fracture appearance,it can be found that interfacial adhesion between AF and rubber matrix is preferable when the AF was treated with Na OH and then coated with KH560,and the fiber is somewhat stripped with obviously fibrillation.After fatiguing,the interface remains relatively preferable adhesion. |
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