Effect Of Annealing On The Structure And Properties Of Polypropylene Membrane

Polypropylene was melt-extruded with experiencing elongation stress, so that the melt crystallized under stress field, and then annealed to obtain PP films. PP films’ s properties were mainly attributed to their row nucleated lamellar structure, in which comprise rows of crystalline lamellae arranged preferentially normal to draw direction. This hard elastic film was characterized by high modulus of elasticity, reversible deformation and easily form upon deformation was widely used in the preparation of microporous. The effect of traction rate, temperature of extrusion, annealing temperature and annealing time on crystallization behavior and hard elastic properties of PP films was investigated. Analysis and characterize the relation on the structure and hard elastic properties. The results were showed below:1. With the increase of the traction rate, the degree of crystallization and orientation degrees increased.Little of β form crystal could be observed in the films. When traciong rate up to 50 rpm, the film began to show hard elastic characteristics. With the improvement of traction rate, changes in tensile strength is unlikely, the elongation at break was decreased, the elastic recovery rate showed a significant increase from the 48.8% increase to 76.4%.2. Films prepared by different die temperatures were characterized and found that the affect of die temperature on crystallinity and orientation was not obvious, effect on tensile strength, elongation and elastic recovery rate was not large.3. Under the same film forming process conditions, with the increase of the annealing temperature, the crystallinity and degree of orientation were shown increasing trend. When the annealing temperature was 150 ℃, β form crystal disappear. When the annealing temperature was 140℃, the film started to show hard elastic characteristics. As the temperature increased from 25℃ to 150℃, elastic recovery rate increased from 21.2% to 78.4%, the elongation at break decreased obviously.4. Film under the same process conditions, with the annealing time increase, the crystallinity and degree of orientation were shown an increasing trend. When annealing time exceed 20 min, the film began to form hard elastic characteristics, with the increase of annealing time, the elastic recovery rate increased from 21.2% to 72.0%, the elongation at break showed a significant decreased trend.5. PP annealed film under 3% extension was examined. PP film annealed under extension compared with annealed under no extension, the peak of shoulder peak in DSC melting curve decreased to a lower temperature and the crystallinity decreased slightly. The tensile strength and elastic recovery rate of film annealed under extension were lower than film annealed under no extension.