Reserch On The Correlation Between NR Network Structure And Fatigue Microcosmic Mechanism

In this paper,the correlation between network structure of vulcanized rubber and fatigue microscopic mechanism was studied,with the help of rubber processing analyzer(RPA),nuclear magnetic cross-linking densitometer,scanning electron microscope(SEM),Fourier transform infrared spectrometer(FTIR),and conventional dynamic and static force performance tests.First,the different network structures were designed by changing the composition system.Through the use of conventional sulfur vulcanization systems(CV),semi-effective vulcanization systems(SEV),effective vulcanization systems(EV),peroxide curing systems,and sulfur/peroxide composite vulcanization system,maintaining the sulfur-promoting ratio unchanged,increasing the amount of sulfur and accelerator,changing the amount of zinc oxide to design the different cross-linked network structure.Different filler network structures were designed by varying the carbon black loading and the ratio of silica/carbon black in the composite filler.Then through a variety of performance tests to investigate the effect of different mating systems on the dynamic and static mechanical properties and flexion fatigue properties of rubber.The microscopic morphology of fatigue profiles of vulcanizates with different network structures was described and analyzed in detail.The model of crack development was obtained.The correlation between the network structure and the microscopic mechanism of flex fatigue was established eventually.Studies have shown that flex fatigue performance of CV vulcanizate is best,which of EV vulcanizate is the worst.In the network structure,the cross-linking density and the type of cross-linking bond affect the flex fatigue resistance of the vulcanizate simultaneously.Reducing the cross-linking density and increasing the content of thepoly-sulfur bonds are beneficial to the improvement of the flex fatigue performance.In addition,the moving ability of-C-C-in the peroxide cure system is worse than the single sulfur bond,but it shows better fatigue performance than EV which presumed that the cross-link bond energy also affects the fatigue performance of the vulcanizate to some extent.The flexural fatigue properties of the vulcanizates show the best values within the range of 40 phr to 50 phr of carbon black loading.With the increase of the carbon black loading,the carbon black-carbon black and carbon black-macromolecular interactions in the rubber compound increase.The filler network in the rubber material develops from immature to stable to stability damaged.Therefore,the optimal fatigue performance occurs when the combined effects of reinforcement,Payne effect,and loss characteristics are optimal.In the filler-combined system,the flexural fatigue life of vulcanizate also shows the trend of increasing first and then decreasing with the increase of white carbon content.The combination of interactions between carbon black filler networks,silica white filler networks and carbon black-silica networks in filler-combined system is less than the interaction of either filler alone,so internal friction caused by filler breakage in the fatigue process of vulcanizates is lower.In addition,adding anti-aging agent can significantly improve the flex fatigue life of rubber.anti-aging agent RD/4020 has a good synergy.Scanning electron microscopy(SEM)and infrared spectroscopy analysis showed that the microscopic morphology of flexural fatigue sections of different network vulcanizates was significantly different.The fatigue failure of vulcanizates is caused by mechanical external forces and then progressed by force chemical reactions and thermal oxygen ageing.