Curing Process Simulation And Cross-Linked Network Structure Analysis For Peroxide-Cured EPDM

Ethylene propylene diene monomer (EPDM) rubbers are the most widely-used elastomer in non-tire products field today, which can be cured by sulfur, peroxide and resin. Peroxide-cured EPDM provides excellent resistance to high-temperature, and low compression set, which makes EPDM with peroxide curing a good choice in high-performance applications. The choice of co-agent, raw rubber structure and the utilization of extender oil directly affect the formation, development of cross-linked network and final curing conditions. The effect of peroxide/co-agent system, EPDM structural parameters and extender oil on the curing process of peroxide-cured EPDM and cross-linked structure of EPDM vulcanizates have been investigated by moving die rheometer, rubber process analyzer, magnetic resonance cross-link density spectrometer and other conventional test methods. Moreover, the evolution of vulcanization are studied by the phenomenological kinetic equation.Firstly, the influence of three different co-agents, such as triallyl isocyanurate (TAIC), trimethylol propane trimethacrylate (TMPTMA) and high vinyl poly(butadiene) (HVPBd)) on the curing characteristics, cure kinetics of the peroxide-cured EPDM compounds and the mechanical properties of EPDM vulcanizates have been studied. The addition of the co-agents are beneficial to improve the cross-linking density and suppress the thermal degradation of the EPDM vulcanizates. EPDM compounds containing TAIC or HVPBd have a good scorch safety. According to cure kinetics of the EPDM compounds by phenomenological approaches, it appears that the fitting results obtained for the Deng-Isayev model,1st order model and Hsich model were generally in good agreement with the experimental data. Due to the addition of the three co-agents, the activation energy of the curing reaction decreases respectively, with the EPDM compound with TAIC showing the lowest activation energy.In order to improve the effect of co-agent on the cure extent of peroxide-cured EPDM, the influence of different peroxide and co-agent levels on the curing behavior of EPDM, composition of cross-linked network and cross-linking efficiency of peroxide (a) have been studied. Increasing the BIPB content (No-o) and/or TAIC content, the total network density (Ctot) increases, and a linear relationship between and No-o is observed at certain TAIC concentration. Furthermore, the cross-linking efficiency of peroxide increases slightly with the increasing TAIC concentration. When the TAIC content increases, cross-link density increase, transverse relaxation time T2 of EPDM vulcanizates clearly decrease, which also makes the vulcanizates obtain a higher Tg and a lower tanδ peak value. The incorporation of TAIC into EPDM network makes the heterogeneity of network improved.Secondly, the influence of raw EPDM structure on the cure characteristics, cross-linked network and the molecular moviety of EPDM vulcanizates have been discussed. The results show that the increase of Mooney viscosity is beneficial for the improvement of the crosslinking density and curing rate. The EPDM with higher branching degree of long chain shows a slower curing rate and no effect on cure extent. The cure extent of EPDM vulcanizates is improved with the increasing of ethylene content, which has a stronger interaction between carbon black and rubber. The EPDM with higher ethylene content obtains a higher tensile strength.The network structure of peroxide-cured EPDM vulcanizates are related to chemical cross-links via combination reaction (Ccom), chemical cross-links via addition reaction (Cacid) as well as the contribution of entanglement density and network defects to the total cross-link density (CEN).The Ctot increases linearly with the peroxide content. The increase of ethylidene norbornene (ENB) concentration is beneficial for the improvement of cross-linking efficiency of peroxide, but it makes the diene conversion of EPDM decrease. CEN is dependent on the third monomer content, which also provides the dominant contribution to the Ctot at low peroxide contents.Thirdly, curing process simulation are performed by two first-order kinetic equations to describe the curing behavior of peroxide-cured EPDM. When the curing temperature increases, the cure extent and chain scission increase, both reaction rates increase. The differences in microstructure of EPDM vulcnizates affect the relaxation behavior of chains and dynamic mechanical properties. Furthermore, the raw rubber structure also affects both the reaction rates and activation energies of cross-linking reaction and ones of chain scission reaction.Finally, the effect of extender oils on the curing process of peroxide-cured EPDM, network structure and properties of vulcanizates have been studied. The increase of squalene content causes a decrease in crosslink density, which also makes cross-linking efficiency of peroxide and physical entanglement values decrease.The influences of extender oil on the total network density are individed into "dilution" which is followed as a linear function of squalene content and "chemical effect" which is followed as a exponential function of squalene content. According to MDR and DSC analysis, the squalene content shows minor effect on the Ea of the crosslinking reaction. Squalene can react with peroxide, forming dimer and trimer.According to the cure extent of EPDM vulcanizate filled by Sunpar2280, squalene, decalin and dodecane respectively, "Dilution" and "chemical effect" are related to the the structure of extender oil, which finally affects the cure extent of vulcanizates. The reaction rate decreases with the increase of extender oil content.