【摘要】 通过溶胀硫化胶的溶剂冰点下降法研究了3种不同促进剂体系天然橡胶硫化胶交联网络结构对力学性能的影响.交联密度研究表明,加入TU或STU硫化胶的交联密度与单独使用CZ促进剂硫化胶的基本一致.溶胀硫化胶溶剂冰点DSC研究结果发现,添加了STU硫化胶的溶剂冰点下降幅度最小,而溶剂冰点下降峰的半峰宽(FWHM)值最大,表明了STU的加入有利于在硫化胶中形成了一个网格尺寸较大和更加不均匀交联键分布的结构.同时,XRD结果表明所有硫化胶的应变诱导结晶总结晶指数相同,即可以忽略其对力学性能的影响.力学性能结果表明添加了STU硫化胶的拉伸强度和断裂伸长达到了最大值,这主要是因为在外力作用下,较大网格尺寸和交联键稀疏区域有利于应力松弛,分散了应力集中,使得橡胶分子链和交联键稠密区的结晶束得到有效取向和松弛,提高了STU硫化胶的拉伸强度和断裂伸长.更多还原

【Abstract】 A novel testing approach,freezing point depression of solvent in the swollen vulcanizate,is acquired to estimate the effect of crosslinking network structure,i. e. mesh size and crosslinks dispersion,on the mechanical properties of natural rubber vulcanizates cured by three different accelerator systems in details. No evident discrepancy is found in the crosslinking densities of vulcanizates cured with TU or STU or CZ only,indicating thiourea only accelerates vulcanization process and the sulfur atom of thiourea does not contribute to the sulfur crosslinking in the matrix. Results from freezing point depression tested by DSC measurements show that for solvent trapped within the crosslinking network of vulcanizates cured by STU its freezing point depression is the lowest and its full width at half maximum( FWHM) is the highest among the testing samples,indicating that the incorporation of STU facilitates the formation of a larger network mesh size and a more heterogeneous network in the vulcanizates. Furthermore,the total crystal index( CI) of all vulcanizates induced by stretching is almost the same,i. e.,the effect of total CI on the mechanical properties of vulcanizates can be ignored. By eliminating the effect of crosslinking density and CI on the mechanical properties of vulcanizates,the tensile strength of vulcanizates cured by STU reaches the maximum values,which could be originated from a larger network mesh size and a more heterogeneous network that favors the relaxation of stress and orientation of rubber molecules and crystallization under stretching.更多还原