The Effect Of Shear Flow On The Crystallization Behavior Of IPP/DMDBS Blends

The property of polymer product is strongly dependent on the crystal morphology structure, the crystal morphology structure is not only influenced by thermomechanical history, nucleating agents may also play an important role. One of sorbitol derivatives:(1,3:2,4)-Bis(3,4-dimethylbenzylidene)sorbitol or DMDBS has become widely used as a nucleating agent in terms of polypropylene, DMDBS can crystallize above the melting point of iPP and form fibrillar network structure. With the application of a shear flow the structure will pre-orientation, then induce the formation of iPP oriented HSK structure, in this way the property of iPP will be influenced. In this paper, by using the fusion index instrument to extrude samples, we mainly research the effect of nucleating agent content and shear flow on the crystallization behavior of iPP/DMDBS blends.1、By using iPP modified by DMDBS with different content, we have studied the effect of DMDBS on the crystallization behavior of iPP. The study found:(1) DSC tests show that when iPP non-isothermally crystallizes by adding DMDBS(cooling rate is 10oC/min), the crystallization temperature has increased by about 10oC, the melting point and crystallinity of iPP tend to increase with the increase of DMDBS concentration.(2) By using PLM we found that after adding DMDBS, the nucleation density of iPP significantly increases, and the crystal size gradually decreases with the increase of DMDBS concentration.WAXD tests show that when adding a certain concentration of DMDBS(0.3wt%-0.7wt%), iPP can generate a small amount of γ crystal, and γ crystal content decreases with the increase of DMDBS concentration. When the nucleating agent content is 1%, basically there is no generation of γ crystal.(3) Rheological tests show, DMDBS crystallization occurs above the melting point of iPP, and the crystallization temperature increases with the increase of its concentration. In summary, the addition of DMDBS is beneficial to the crystallization of iPP, and DMDBS crystallization occurs above the melting point of iPP,this leads to the phase separation of iPP/DMDBS system.2、To extrude iPP/DMDBS samples by using the fusion index instrument, we have studied the effect of extrusion conditions and shear flow on the crystallization behavior of iPP/DMDBS. The study found:(1) DSC tests show that the melting point and crystallinity of the extruded samples do not change with the extrusion conditions, and only the α crystal generates.(2) WAXD tests show that the iPP/DMDBS samples extruded at 165oC、25KPa generate orientation structure, and the degree of orientation increases with the increase of DMDBS concentration.(3) In situ tests(rheological tests) show, the application of a shear flow prior to the crystallization of DMDBS(205oC) can induce DMDBS to immediately crystallize. The application of a shear flow after the crystallization of DMDBS(175oC) causes the storage modulus of the sample drop, the decrease amplitude of storage modulus reaches 70% as the shear stress is 20 KPa,and the decrease amplitude of storage modulus increases with the increase of shear stress. In summary, when DMDBS crystallizes and forms fibrillar network structure, with the application of a shear flow the structure will pre-orientation, then induce the formation of iPP orientation structure.