恒形变条件下硫磺用量对丁腈橡胶裂纹发展的影响

Effect of Sulfur Content on Crack Development of Nitrile-Butadiene Rubber Under Constant Strain

研究了恒形变条件下硫磺用量对丁腈橡胶(NBR)预置裂纹扩展发展的影响。利用疲劳试验机进行了疲劳试验,采用体视显微镜对裂纹的长度进行了测量,利用扫描电镜和轮廓仪观察了其断面形貌,利用溶胀法获得了其交联密度和交联键的类型。结果表明,随硫磺用量由0.5 phr增加到2.0 phr,NBR的拉伸强度增大,断裂伸长率减小,硫磺用量为1.5phr时撕裂强度出现最大值,且裂纹的扩展速度最慢;随硫磺用量增大,NBR的交联密度增大,交联键中的硫原子个数增多,1.5 phr时交联键主要为单、双硫键,且疲劳断面比较粗糙,这解释了硫磺用量为1.5 phr时NBR具有较好的耐疲劳性能的现象。硫磺用量为2 phr和2.5 phr时,NBR的交联键以多硫键为主,其键能较低,此时NBR的耐疲劳性能较差。

The effect of sulfur content on crack development of nitrile-butadiene rubber（ NBR） under a constant strain was investigated. The samples were tested by fatigue testing machine and the crack length was measured by stereoscopic microscope. The fatigue fraction surfaces were observed by scanning electron microscope and profilometry. The crosslink density and type of different NBR were studied through the swelling test. The results are presented as follows.When the sulfur content is increased from 0. 5 phr to 2 phr,the tensile strength is increased and elongation at break is decreased. When the sulfur content is 1. 5 phr,the tear strength reaches the highest value and the crack development rate is the lowest. With increase of the sulfur content,both the crosslink density and the sulfur atom number at every crosslink bond increase. The mono and dual sulfur crosslink bonds are dominant when the sulfur content is 1. 5 phr. At the same time,the fatigue fraction surfaces are rougher than others. These results explain why NBR with 1. 5 phr sulfur has good anti-fatigue properties. However,the crosslink bonds in NBR with 2 phr and 2. 5 phr sulfur are mainly multi sulfur bonds which possess relatively low energy. The anti-fatigue properties of these NBR are worse.