热老化对丁苯胶乳体系机械稳定性的影响

研究了热老化处理对丁苯胶乳体系机械稳定性的影响.发现丁苯胶乳在高温老化过程中,胶粒容易团聚并形成凝胶,老化处理温度越高,凝胶出现时间越短,但是它的机械稳定性却随着老化处理时间的延长和老化处理温度的升高反而不断提高.为了阐明这种异常现象,测试了不同老化处理温度下胶乳的粒子尺寸、剪切作用下的凝胶比率、丁苯分子的结构与分子量分布,以及胶粒的力学强度随老化时间的变化规律,分析了影响机械稳定性的可能因素.结果表明,胶乳体系中丁苯分子在高温老化过程中发生了轻度的交联反应,导致胶乳干膜的300%定伸模量提高.进一步研究还发现,这个定伸模量与胶乳的机械稳定性具有对应关系,胶乳干膜的定伸模量越大,胶乳的机械稳定性越高,因此造成机械稳定性大幅上升的主要原因很可能是热老化交联后刚性较大的胶粒在高速剪切碰撞时难以及时融合.

INFULENCE OF THERMAL AGING ON MACHENICAL STABILITY OF STYRENE BUTADIENE LATEX

The influence of thermal aging on dispersion stability and mechanical stability of styrene butadiene latex(SBL) was studied.It was found that with increasing the aging temperature,the SBL particles are easy to coagulate together and to form a solid gel within a short time period.However,the gelation ratio determined by Maron test showed that the mechanical stability remarkably increased for the thermal aged samples.To clarify the mechanism of the abnormal phenomenon,FTIR,GPC,as well as stress-strain behavior of the thermal aged SBL system were investigated.It is found that the reduction of dispersion stability is mainly due to lowering the barrier energy between the latex particles,and thermal degradation of poly(styrene-butadiene) in the colloid state is not oxidized into carbonyl group at the double-bond site,but turns into cross-linking between the macromolecules,resulting in an increase of mechanical strength of the SBL film.Correlation of the tensile modulus at 300% strain to the gelation ratio demonstrated that the improvement of the mechanical stability was originated from crosslink-induced high tensile modulus of the SBL particles.