LLDPE在挤出加工中的弹性现象研究

AN EXPERIMENTAL STUDY OF ELASTICITY ON THE PROCESSING OF LLDPE

使用Brabender PLD 651 挤塑仪配不同长径比、不同材质的毛细管流变口模,测定了几种LLDPE在一定温度下的挤出物胀大和熔体破裂的临界剪切应力,同时用Instron 3211毛细管流变仪做了对比实验。结果表明,毛细管口模的长径比达到一定值后,挤出物胀大随剪切速率的变化关系与长径比无关。这一长径比值又随毛细管口模材质而有所不同。对于一定长径比的毛细管流变口模,熔体破裂的临界剪切应力与挤出温度、口模材质无关。通过实验可知,采用提高口模温度、增加口模长径比或改变口模材质均能推迟熔体破裂现象的发生,从而提高了挤出加工的生产量。

The swell ratio of extrudates and the critical shear stress of melt fracture are (?)easuredon the Brabender PLD 651 plasticorder with the steel, copper and aluminium capillary dieof L/D =3, 16, 20, 30, 40 at a processing temperature respectively. It is found that theincreasing of swell ratio with the shear stress is independent with L/D when the values ofL/D is higher than a critical value, and at a capillary die with a constant L/D, the criticalshear stress of melt fracture is independant with temperature and capillary materials. Fromthe experimental study, we could predict that the onset of melt fracture on the processingof LLDPE may be controlled by raising temperature, increasing of L/D or changing thematerials of capillary die.