Structure And Properties Of HDPE/POE Casting Film By Melt-Stretching Method

Due to the complex crystallization interaction of the crystal/crystal blend system,there was little research on this kind of blend system.If we can understand the crystallization interaction mechanism,it will be helpful for us to improve the performance of the system through the regulation of crystallization.In the melt-stretching flow field,the semi-crystalline polymer materials can form a parallel-arranged lamellar structure perpendicular to the stretching direction,which shows hard elastic properties.Due to the fast crystallization rate of HDPE in the process of melt-stretching,the orientation of HDPE was poor,which resulted in low elastic recovery value of extruded film and poor uniformity of pore structure of microporous membrane prepared by post-stretching.Polyolefin elastomer(POE)is a kind of material between rubber and plastic which has crystallinity and high elasticity.In this work,by introducing different types of POE elastomers,the crystallization and rheological properties of HDPE/POE blend system were investigated(Chapter 2),and on this basis,the structure and properties of melt-stretched HDPE/POE casting films at different melt-drawing ratios(MDRs)and different POE content were investigated(Chapter 3).The crystalline behavior of HDPE/POE blend system in the melt-stretching flow field was determined while the microstructure of HDPE film in the melt-stretching flow field was optimized.Through the experiment,the following conclusions are drawn:1.With the addition of POE elastomer,the storage modulus,loss modulus and complex viscosity of HDPE/POE blends decreased in order.The addition of POE changed the relaxation behavior of HDPE/POE blends,and the influence of different POE on the shear rheology of HDPE was quite different.In the test of melt-stretching rheology,POE1 elastomer with random copolymerization structure increased the melt strength of the blend system,but the addition of POE2 elastomer with block copolymerization made the molecular entangling and unentangling point of the blend system move back,which was beneficial to the processing of polymer.2.The non-isothermal crystallization test of HDPE/POE system was carried out by using differential calorimetry scanner.It was found that the addition of different contents of POE1 would accelerate the crystallization rate of HDPE,which indicated that POE1 played a role of heterogeneous nucleation.The addition of POE2 with different contents slowed down the crystallization rate of HDPE.3.The casting film of HDPE/POE at different melt-drawing ratios(MDRs)under 10%POE content was prepared by melt-stretching method.The DSC test showed that with the increase of MDR,the crystallinity of POE1 and POE2 systems decreased,and under the same MDR,the crystallinity of POE2 was lower than that of POE1,indicating that POE2 had a greater impact on the crystallization of HDPE.It could be seen from SEM that the addition of POE was beneficial to the crystal structure ordering for HDPE casting films.The FTIR test results showed that with the increase of MDR,the lamella orientation of the casting film increased,and the orientation of POE2 was higher than that of POE1 blend casting film under the same MDR,and the relaxation time of HDPE increased with the addition of 10% POE2.4.The HDPE/POE blend casting film with different POE2 content was prepared by meltstretching method under the same melt-drawing ratio(MDR=40).It was found that as the content of POE2 increased,its crystallinity decreased to a certain extent.In addition,XRD tests showed that the addition of POE2 had a certain effect on the crystallization of HDPE.With the increase of POE2 content,the crystal shape of HDPE changed to a certain extent,and the crystal growth of 110 crystal plane was weakened.The mechanical test showed that the elasticity of the film increased linearly with the increase of elastomer content,but the mechanical strength decreased to a certain extent,and the tear strength remained unchanged at 10% content.Excessive increase of POE content would lead to the decrease of mechanical properties of the film.