Investigation Of Evolution Of Micro-and Meso-structures In NR Vulcanizates Filled With Modified Pyrolysis Carbon Black During Tension Fatigue Process

At present,research on rubber fatigue mainly focuses on fatigue failure,fatigue crack growth,and fatigue life prediction,while there is little research on the fatigue process before fatigue failure.At the same time,it has not effectively addressed social hotspots and proposed methods to improve the fatigue life of rubber materials.The evolution of micro-and meso-structures and properties of NR vulcanizates filled with modified pyrolysis carbon black during uniaxial stretching fatigue process was investigated by means of Malvern laser particle size analyzer,X-ray photoelectron spectrometer（XPS）,dynamic mechanical analyzer（DMA）,transmission electron microscope（TEM）,atomic force microscope（AFM）characterization methods and so on.The results were shown as follows:As for the modification methods of the CBp,the Ar plasma had obvious etching and polarized effect,and the collaborative modification of CBp by air classifier and plasma had the smallest everage particle size and the strongest surface activity.The NR/AM-CBp had the longest fatigue life.In the aspect of meso-structure,the surface roughness of the composites increased with increase of fatigue degree.In the aspect of micro-structure,the total and chemical cross-linking densities increased at the first fatigue stage（0-20%）,and then decreased with increase of fatigue degree.The physical network density decreased drasticly at the first fatigue stage,and then kept constantly with increase of fatigue degree.The E’_stdecreased gradually when the fatigue degree from 0%to 60%,and the E’₁ decreased obviously when the fatigue degree got to 20%.As for the plasma modification power,the specific surface area of CBp-200W was the largest.The fatigue life of NR/CBp-200W composite was the longest.In the aspect of meso-structure,the surface roughness of the sample increased with increase of fatigue degree for the sample filled with the modified CBp,whose modification power was not higher than 400W.In the aspect of micro-structure,the total and chemical cross-linking densities of the samples increased and then decreased with increase of fatigue degree.Nevertheless,the physical network densities of all the samples decreased obviously when the fatigue degree reached 20%of the fatigue lives,and then kept constantly.The E’_stdecreased gradually when the fatigue degree from 0%to 40%,and the E’₁ decreased obviously when the fatigue degree got to 20%.As for the NR filled with CBp（AM-CBp）/N330 blends,the fatigue lives of the NR filled with N330/AM-CBp composite was longer than that filled with N330/CBp composite when the filler blending ratios were the same.With increase of the blending ratios between the CBp（AM-CBp）and N330,in the aspect of meso-structure,the surface roughness of the samples increased with increase of fatigue degree.In the aspect of micro-structure,the total cross-linking density of filled NR composites decreased.The total and chemical cross-linking densities increased and then decreased with increase of fatigue degree.However,the physical network densities decreased at the first fatigue stage obviously.The E’_stdecreased gradually when the fatigue degree from 0%to 40%,and the E’₁ decreased obviously when the fatigue degree got to 20%.In summary,the enhanced interaction between filler-rubber is beneficial for extending the uniaxial tensile fatigue life of filled rubber composites,and it is mainly attributed to the synergistic effect of strong and weak filler-rubber interactions.This work establishes the correlation between the physical network density and uniaxial tensile fatigue life of filled rubber composites.