Study On Preparation And Properties Of Thermally Stimulated Shape Memory Of LLDPE/PP Blends

Thermally stimulated shape memory polymer is a new type of functional materials which has attracted great interest in recently years. In this paper, moderated cross-linked blend (LLDPE-PP) of linear low-density polyethylene (LLDPE) and polypropylene (PP) were prepared by the reactive melt mixing, and a novel thermo-stimulative shape memory blends of LLDPE/PP were prepared by melt blending with LLDPE-PP as compatibilizer. Effects of LLDPE-PP content on the shape memory effect, mechanical, rhelolgical and thermal properties of LLDPE/PP blends were investigated using scanning electron microscopy (SEM), dynamic mechanical analyzer (DMA), wide-angle X-ray diffraction (WAXD), polarized optical microscopy (POM), differential scanning calorimetry (DSC), mechanical testing machines, HAAKE torque rheometer and capillary rheometer. And the relationships between phase morphology and properties of the blends were also discussed.In the moderated cross-linked LLDPE/PP blends (LLDPE-PP), some chemical bonds were formed between LLDPE and PP, and the two-side structures of LLDPE-PP were same to that of LLDPE and PP respectively. Thus, LLDPE-PP could improve the compatibility of LLDPE/PP blends. It was found that when the blend ratio of LLDPE/PP was70/30and the content of BPO was0.4phr. LLDPE-PP exhibited the best compatibilization efficiency for LLDPE/PP blends.In the system of LLDPE/PP/LLDPE-PP blends, LLDPE-PP not only enhanced the interfacial adhesion between LLDPE and PP, but also enhanced the melt strengths of the blends. So the shape memory effect and combined mechanical properties of the blends were improved. Furthermore, the blends possessed good thermal property. The experimental results showed that when the blend ratio of LLDPE/PP/LLDPE-PP was87/13/2, the blend possessed the best mechanical and thermal properties. Meanwhile, when the blend ratio was87/13/6, the LLDPE/PP/LLDPE-PP blend exhibited the best shape memory effect at stretch ratio of80%, stretch rate of25mm/min. and recovery temperature of135℃. Moreover, from the shape memory investigation results, a new shape memory mechanism for this type of SMP system was concluded. In this SMP blends, dispersed PP acted as fixed phase whereas continuous LLDPE phase acted as reversible or switch phase. During the deformation process, the droplets of fixed phase were unchanged to keep the original shape, whereas the molecular orientation occurred in reversible phase and internal stress was kept in the system. Consequently, heating up the material and releasing the stress would deform the shape back to the original shape.