退火对剪切改性的长链支化聚丙烯流变性能回复的影响

Effect of Annealing on the Recovery of Rheological Properties of Shear Modified Long Chain Branched Polypropylene

利用密炼机对长链支化聚丙烯(LCB-PP)施加一定的剪切历程,随后利用真空退火和高压二氧化碳(CO_2)饱和退火对剪切改性的样品作后处理。通过熔体流动速率(MFR)、挤出胀大比(SR)以及动态流变数据等表征方法,研究了退火工艺对剪切改性样品流变性能的回复作用。结果表明,退火使流变性能得到一定回复,包括MFR减小,SR增大,低频下的储能模量和复数黏度增大。MFR和SR的结果表明,CO_2的存在使得解缠结的支链能更快恢复缠结状态,因此高压CO_2饱和退火法加速了流变性能的回复。通过分析损耗角正切、Cole-Cole曲线,也证明了高压CO_2饱和退火法对剪切改性样品流变性能回复的作用比真空退火法更显著。

Shear history was applied to long chain branched PP（ LCB-PP） by an internal batch mixer. Then vacuum annealing and high-pressure CO_2 saturation annealing were performed on samples after shear modification. The effects of annealing process on the recovery of rheological properties of shear modified LCB-PP were characterized by melt flow rate（ MFR）,swelling ratio（ SR） and dynamic rheological data. The results indicate that the rheological properties of shear modified LCB-PP can be recovered partially after annealing,including lower MFR,higher SR and larger storage modulus and complex viscosity at low frequency. The results of MFR and SR demonstrate that the presence of CO_2 makes disentangled branched chains recover to entanglement state more quickly,so the recovery of rheological properties is speeded by high pressure CO_2 saturation annealing. As for the recovery of rheological property of shear modified LCB-PP,the analyses of tanδ and Cole-Cole plot also verify that high-pressure CO_2 saturation annealing is much more effective than vacuum annealing.