Preparation,Composition,Structure And Performance Of Cryptocrystalline Graphite/Acrylonitrile-butadiene Rubber Composites

Cryptocrystalline graphite is widely distributed in China and has rich resources,but its high value-added functional utilization technology is backward.Under the support of the thirteenth fiveyear plan National Key Research and Development Plan "Preparation technology and Application Research of Environmental Friendly Non-metallic Mineral Functional Materials",the composition,phase,structure and structure-activity relationship of cryptocrystalline graphite were studied;and the purification,surface modification of graphite,preparation process and mechanical properties of rubber composites were carried out.At last,the effect of graphite on the mechanical and friction behavior of rubber composites was analyzed.The main achievements were as follows:(1)Cryptocrystalline graphite powders were successfully prepared by mechano-chemical force method.It was found that its aggregates were orderly arranged on grain scale but disorderly stacked between microcrystals.Defective structure,small size and high surface roughness were the physical and chemical basis for the functional properties as a rubber filler.(2)Acrylonitrile-butadiene rubber/carbon black/cryptocrystalline graphite composites were prepared by mechanical blending method and the optimized process parameters were obtained.It was found that the tensile strength,300% tensile stress and tear strength of rubber composites filled with 10 phr graphite were increased by 18.2%,11.0% and 10.0% respectively compared with the comparison sample.It was attributed to the improved dispersion and C-H interaction,physical entanglement,Van Der Waals force and electrostatic interaction between graphite and rubber molecules.(3)The results showed that the steady friction coefficient and specific wear rate of acrylonitrile-butadiene rubber/carbon black/cryptocrystalline graphite composites filled with 5 phr graphite decreased by 50.3% and 51.3% respectively under dry friction conditions,and the anti-wear properties were significantly improved.The results showed that the continuous lubrication film and transfer film with appropriate thickness forming on the friction interface reduced the direct contact between steel ring and rubber.It was the main reason for the significant reduction of friction coefficient and wear loss.It was also found that the excessive addition of CG would cause the large pieces of material to fall off and then increased the wear loss.(4)The interfacial compatibility,wettability and filler dispersion of graphite modified by liquid nitrile rubber could be improved,and thus the mechanical properties of the composites were improved.However,the friction coefficient and specific wear rate of the modified composites increased slightly under dry friction,which may be related to the increasing adhesion and decreasing inter-molecular force of rubber molecular chains.(5)Carboxynitrile rubber/graphite composites were prepared by different processes.When adding 20 phr graphite,the tensile strength,elongation at break,tear strength and fracture energy of the composites prepared by latex blending method increased by 17.1%,37.4%,30% and 60.9%respectively when compared with those prepared by mechanical blending method.Also,the friction coefficient and specific wear rate of the composites by latex blending process adding 5 phr graphite were decreased by 18.5% and 47.8% respectively compared with the mechanical blending products.It was speculated that the latex blending method improved the filler dispersion and decreased the friction heat generation,which was contributed to the formation of the lubricating film and transfer film.(6)The tensile strength and tear strength of carboxynitrile rubber/carbon black/graphite composites adding 8 phr acid-treated purified graphite were increased by 10.8% and 5.3%respectively.The unprocessed graphite could improve the friction and wear properties of the composites,but it showed a better wear resisting property after acid treatment.It was speculated that acid treatment could reduce the abrasive wear of hard large particles impurities,and made it easier to form a lubrication film and transfer film.The results of our research provided a new technical approach and theoretical basis for the high value-added functional utilization of cryptocrystalline graphite.