Study Of High-Temperature Natural Rubber Based Anti-Vibration Materials

The requirement of modern auto industry on hot-air aging resistance of rubber materials at elevated temperature goes even higher,the long term service temperature of engine mount for automobiles increases from 70-80 ? to 100 ? and even higher.From the viewpoint of vibration resistance of automobile engine,the most suitable material is nature rubber(NR).But it is well known that the hot-air resistance of NR is very poor,so it is really very important to improve the high temperature performance of NR.The effect of cure systems(conversional cure system CV,semi-effective cure system SEV,effective cure system EV),cure temperature(150,160 and 170 ?),antioxidants(4020 and RD)and on the processability,mechanical properties,hot-air aging properties at 100?,ratio of static stiffness and dynamic stiffness,and fatigue life of NR were systematically studied.The crosslink density and crosslink types of NR vulcanizates before and after aging were measured by means of chemical probe method.For cure systems CV,SEV and EV,NR with CR had the much lower cure rate and more obvious reversion.The mechanical properties,anti-vibration properties and fatigue life of NR with CV was much higher than SEV and EV,but the above mentioned properties of CV decreased dramatically after aged at 100 ? for 240 h,so it can't be used as anti-vibration materials at elevated temperature.By contrast,NR cure with EV had no reversion during cure procedure and superior hot-air resistance,and best anti-vibration properties and fatigue life after hot-air aging,it can be used as anti-vibration materials at elevated temperature.The performance of NR with SEV was between CV and EV,but its hot-air aging resistance is closer to CV.The fluidity and the cure rate of the NR compound were improved when the cure temperature was increased;but NR compounds had more obvious reversion and lower crosslink density.At 150 ?,NR with CV or SEV showed little reversion,but at 160 ?,there was obvious reversion for NR with CV or SEV;By contrast,NR with EV showed very good anti-reversion properties even at 170 ?.With increasing cure temperature,the hot-air aging resistance of NR cure with CV decreased,while the hot-air aging resistance of NR with EV increased,which means that NR with CV should be cured at lower temperature(150?),EV should be cured at higher cure temperature(160-170 ?)to improve its hot-air aging resistance.The addition of antioxidants also affected the properties of NR.Antioxidant RD prolonged the scorch time,shortened the processing optimum cure time,decreased the crosslink density and reversion,while antioxidant 4020 decreased the scorch time and optimal cure time,increased the crosslink density,lead to more serious reversion.During hot-air aging of NR at 100 ?,the tensile strength and elongation at break,anti-vibration properties and fatigue of NR vulcanizates decreased,the hardness of NR increased,and the modulus at 100%of NR reached a maximum after aged for 48 to 96 hours.The addition of antioxidant decreased the reduction of tensile strength and elongation at break to a certain extent,which meant that antioxidant improved the hot-air aging resistance of NR.But for NR with CV cure at any temperature and NR with EV cured at 150 ?,RD increased the change rate of modulus at 100%,while RD decreased the change rate of modulus at 100%of NR with EV cure at 160 ? and 170 ?.It was well known that,antioxidant could improve the hot-air aging resistance of NR,but from the viewpoint of mechanical properties,RD showed almost no any protective effect on NR with CV at 100 ? for240 h,by contrast RD improved the hot-air resistance obviously at 100 ? for 240 h.For NR with any cure systems cured at any temperature,the protective effect on hot air-aging of 4020 was worse than RD.The crosslinking network of the CV system is dominated by polysulfide bonds(Vp),and the content of the mono-sulfur bond(Vs)is very low;by contrast,the crosslinking network of the EV system is dominated by the Vs,and Vp is very low,the crosslink network of SEV consist of similar content of disulfide bond(Vd),Vp and Vs,Vd is a little bit higher than Vp and Vs.The bond energy of Vp is low and the flexibility of the network of Vp is high,so the above mention properties of NR with CV was the best,but its reversion resistance was the poorest,by contrast,the bond energy of Vs is high and the flexibility of the network of Vp is low,so the above mention properties of NR with EV was the poorest.After aging at 100 for prolonged time,the crosslinking network of CV was transformed into the structure with dominate Vs,very low content of Vp and rather constant content of Vd,which meant that the crosslink structure changed obviously,so the hot-air aging resistance of NR with CV was very poor,while the EV crosslink network didn't changed much,the content of Vs increased,the content of Vp reduced,and the Vd remained relatively stable,so the hot-air aging resistance of EV was very good.For NR with,both the content of Vd and Vp decreased,and changed to Vs,the crosslinking structure of NR with SEV changed obviously,so its hot-air aging resistance was very poor,and similar to CV.When EV was selected as cure system,RD and/or 4020 were selecte as antioxidant,160-170 ? was selected as cure temperature,the hot-air aging resistance at 100 ? and fatigue life of NR could be significantly improved,NR can be used in producing high performance anti-vibration products at elevated temperature.