Modification Of Kaolin Surfaces And Its Application In The Polyolefin

Kaolin is a layered silicate clay, its application in polymer as a functional filler that not only reduce the cost of materials but also expected to improve the rigidity, thermal stability, flame resistance etc. Polyolefin is one of the most widely used thermoplastics in the world, which has rich source of raw materials, low price, easy molding and many varieties to meet different performance requirements. However, polyolefin chain do not contain polar groups, which is different from the polarity of kaolin interface, so that kaolin cannot be well dispersed in the polyolefin matrix, which makes the composite with less comprehensive performance.In this paper, kaolin surfaces were modified by silane coupling agent, titanium coupling agent and coupling agent compound process and used in preparation of the corresponding PP and LDPE composites. The influences of kaolin on polyolefin properties such as mechanical properties, thermal properties, electrical properties, crystal structure and micro dispersed morphology were studied. Main contents and conclusions are as follows.1. Coupling agent modification make kaolin surface properties from the hydrophilic to hydrophobe. FT-IR showed that silane coupling agent and titanate coupling agent organic modified kaolin surfaces commendably. SEM observation revealed that coupling agent treatment significantly attenuated kaolin agglomeration, the dispersion of kaolin in composite has been significantly improved, the crystal wafer became much finer than original kaolin.2. Compounded coupling agent modified kaolin (KST)/PP composites showed better comprehensive mechanical properties than single coupling agent treated kaolin (KS, KT)/PP composites and untreated kaolin (KU)/PP composites. The KST/PP composites can also obtained strengthen and toughening effect, and improved the rigidity of the composites. XRD indicated that grain size of KST/PP composites was reduced compared with that of pure PP. SEM images of the composites fracture surface showed KST had better dispersion in polypropylene matrix than KU. DSC indicated that KST played the role of heterogeneous nucleation in the process of crystallization of the composites. TGA illuminated that the addition of kaolin increased the heat resistance of PP composites. 3. KST/LDPE composites exhibited more comprehensive mechanical properties than KU/LDPE composites. DMA showed that the addition of kaolin improved the rigidity and glass transition temperature of the composites. XRD illuminated that KST formed intercalation structure in LDPE matrix, and its grain size also decreased compared with that of pure LDPE. SEM indicated that the KST well dispersed in LDPE matrix; the volume resistivity of KST/LDPE composites slightly improved, while the dielectric constant increased with kaolin content increasing.