| Polymer microporous membranes have lots advantages, such as low cost, highadded value. Has been widely used in Sewage purification, battery separator material,biomedical separation, et al. Isotactic polypropylene (iPP) is a kind of commonthermoplastic and a semi-crystalline polymer, which has prospects and greatadvantage in the application of microporous membrane. The primary factors affectingthe membrane performance was the structure of films, which were affected by MWand process conditions.In this paper, four types of different molecular weight iPP were selected to beextruded by Hakke extruder.The extruded stretching films were further heat-treatedby the small strain at140oCfor10min. WAXD, DSC and FTIR were used to identifiedthe effect of the size and distribution, pulling speed and small strain heat treatment oncrystallization behavior and orientation structure of extruded stretching iPP films,The work and main conclusions are as follows:(1) Under the same experimental conditions, molecular size and distribution ofthe resin had distinct effect on crystallization behavior and orientation structure of thesamples. DSC results shown that they almost had the same melting temperatures.According to DSC and WAXD results, the resin with a small molecular size could beadvantageous of crystallizing. In WAXD integral curves, we found a smallcharacteristic peak of β crystal, which might be induced by the shear during theprocess of crystallization. WAXD and FTIR results shown that the resin with a highmolecular size was conducive to the formation of orientation structure. Theamorphous phase almost has no orientation.(2) Under the same experimental conditions, DSC and WAXD results shown thatthe degree of crystalization of samples increased with the increase of the traction rate.with the increase of the traction rate, the diffraction arc of samples became smallergradually, which shown that the orientation degree of sample increased. Theamorphous phase without orientation. (3) The samples with small strain annealing appeared a "annealing peak" in140oC. The melting temperatures of the annealed samples almost had no change, butthe crystallinity were improved obviously. The annealing decreased the effect ofMolecular size and distribution on crystallinity. With the increase of the traction rate,the degree of crystallization of annealed samples increased, unannealed samples hadthe same trend. Which meant small strain annealing and draw rate had synergisticeffect in the improvement of crystallinity. The β crystal of annealed samples weredecreased or even disappeared.(4) After heat treatment, the orientations of crystallized and non-crystallizedphases were either improved. For unannealed samples, with the decrease of molecularweight, the orientations decreases, annealed sample showed the same change trend.Small strain annealing and drawing speed showed a synergistic effect in improvingthe degree of orientation. Before annealing, the amorphous phase almost had noorientation, after annealing the amorphous phase orientation degree were improvedsignificantly. |
