Study Of Natural Rubber In-situ Reinforced And Vulcanized By Double Bond Functionalized Nylon 66 Short Fiber

Short fiber reinforced rubber composites（SFRC）with excellent properties such as high modulus,high hardness,resistance to cutting,tearing,puncture and fatigue,low heat,low compression deformation,are widely used in the fields of tires,rubber hose,rubber shoes,seals and so on.The processing,structure and performance of SFRC are the important studying contents of material science.Nylon 66 short fiber（PSF）,as a kind of organic short fiber and an ideal reinforcement material for rubber,has many excellent properties,such as high strength,good toughness,good wear resistance and good rebound resilience.PSF is difficult to disperse in the non-polar rubber and easy to form the stress concentration point,due to the large surface polarity.To compound with rubber,PSF is usually chemically modified using vinyl monomers（acrylic acid,methacrylic acid and itaconic acid）through free radical reaction on the double bond.The graft product is difficult to form a co-vulcanization system with natural rubber in the vulcanization process,which is attributed to the disappearance of the double bond.In this paper,the PSF surface was grafted with organic molecules containing double bonds（methacrylic acid（MAA）,silane coupling agent（KH570）,Pentaerythritol triacrylate（PETA）,and Dipentaerythritol pentaacrylate（DPEPA））to realize the co-vulcanization between grafted fiber and natural rubber.Mechanical properties,interface interactions and rheological behaviors of the composite materials were studied in detail,which can provide theoretical guidance for the design,preparation and performance control of SFRC.Firstly,the surface of PSF was grafted with the organic molecules with only a double bond（MAA and KH570）.The effects of reactant concentration on surface functional groups,chemical bonds,crystallinity,surface morphology,graft rate and tensile properties of monofilament were studied by using FTIR,XPS,XRD,SEM,AFM,Raman,and NMR characterization methods.The mechanism of co-vulcanization between grafted fiber and natural rubber was detailedly discussed.NR/CB/PSF composites were prepared by adding grafted PSF to NR（containing50phr carbon black）through master batch milling.The effects of grafted PSF on curing properties,machining properties,mechanical properties,dynamic mechanical properties,fatigue behaviors and cutting resistance of composites were investigated.The results showed that MAA and KH570 had been successfully grafted on the surface of PSF fibers to form a graft platform containing C=C.The introduced C=C bond was transmitted into C-S in the co-vulcanization reaction.The curing time of the system was shortened with the addition of KH570 grafted PSF,while the curing process was delayed with the introduction of MAA grafted PSF.The adhesive force between the fiber and rubber interface,modulus at 100%and modulus at 300%were greatly increased with the graft of PSF.However,the dynamic mechanics loss factor of composites was reduced,due to the introducing C=C participating in the co-vulcanization reaction.Correspondingly,the cross-linking density and the fatigue property of the SFRC were improved by the co-vulcanization reaction.Secondly,in order to further increase the cross-linking points on PSF surface that play a role of"nailing",PSF was grafted with PETA and DPEPA that possess multi double bonds.The effects of grafted PSF fiber on the properties of NR/CB/m-PSF composite materials were studied.FTIR and XPS results confirmed that the PETA and DPEPA C=C double bond grafted on the surface of PSF participated in the co-vulcanization reaction.The curing time was shortened by the grafting modification.The adhesive force between fiber and rubber,modulus at 100%and modulus at 300%of the rubber composites were largely increased.Meanwhile,the crosslinking density,cutting resistance and fatigue performance were improved.However,the dynamic mechanics loss factor was decreased.Finally,the vulcanized rubbers prepared by adding MAA,KH570,PETA,DPEPA,or grafting modified PSF into NR or NR+CB were used as the research objects.The effect of the additives on the rheological behavior of NR vulcanized rubber was investigated.The results showed that the addition of carbon black into NR made the Payne effect more significant.And the Payne effect of the NR+CB vulcanized rubber could increase slightly with the increase of the concentration of grafted PSF.The important role of co-vulcanization reaction in NR reinforcing was further confirmed by studying the linear rheological behavior of the compound.The results showed that the rheological viscoelastic response of NR/single C=C grafted PSF and NR/multi C=C grafted PSF composites were similar.The Payne effect of the compounds was largely increased with the increasing fiber content（φ）.The curves of dynamic storage modulus（G’）,damping function（h（y））versus strain amplitude（y）for the filled rubber can be superposed on those of the unfilled NR,in good agreement with the Guth-gold relation.After graft modification,the reinforcing factor f₁（φ）of the compounds decreases,indicating that the fiber cannot play a reinforcing role in the compounds that had not experienced the process of co-vulcanization.