Study On The Morphology And PTC Effect Of The CB/MWNT Cofilled Polymer-Based Composites

Positive temperature coefficient (PTC) material is one of crucial functional materials. Polymer-based PTC materials with low cost, simple processing and excellent performances of polymers have been extensively studied. Because of the unique electronic, mechanical and other properties, the discovery of MWNT has brought a widespread research and their application as conductive fillers has been paid more attention. In this paper, the immiscible polymers, polyvinylidene fluoride (PVDF) and ultra high molecular weight polyethylene (UHMWPE) are used as the matrix and (CB-MWNT) co-filled the immiscible polymers. The PTC functional materials were prepared by melt blending method. The morphology, PTC properties and dielectric properties have been studied. In addition, the influences of the (CB-MWNT) co-filled network on the dynamic mechanical properties are also researched. The work is summarized in detail as follows:(1) Effect and mechanism of the surface modification of CB and MWNT conductive fillers by employing titanate coupling agent (NDZ-102) are investigated. The results are discussed in terms of the dispersion behaviors of the modified fillers and the rational electrical properties of the composites. The coupling agent can play a link role between the matrix and fillers and can effectively improve the adhesion. In particular, there is an interface between the matrix and fillers formed by the mono molecular layer of titanium coupling agent, so the interface strength is improved.(2) The morphology and electrical properties of the binary-matrix composite, CB-filled-(PVDF/UHMWPE), are studied. Results suggest that the percolation threshold is lower than the single matrix composite. The low percolation threshold is achieved when the volume ratio of two polymers is close to 1/1, which is attributed to the selective location of the fillers. The location of CB particles is analogized in terms of the microstructure and mechanism.(3) MWNT with high aspect ratio as the secondary fillers is added into the system and the CB-MWNT conductive network is formed, the influence of which on the conductive and PTC properties is studied. The better conductivity is achieved because of the long-range and short-range conductive paths respectively formed by MWNT and CB particles. Compared to CB, MWNT is considered as a rigid conductive chain composed of many arranged CB particles, so the re-congregation of MWNT becomes poor in the melting process. MWNT hinders the motion of polymer chains which result in higher viscosity of the system. Meantime, in order to destroy the long-range conductive paths formed by MWNT, a large volume expansion of the matrix is needed. Therefore, the addition of MWNT can improve intensity and stability of PTC characteristic. In addition, Negative Temperature Coefficient (NTC) is reduced after MWNT is added into the system. Meantime, thermal properties (DSC) of composites are researched to explain the resultant PTC properties.(4) The influence of CB-MWNT network structure on the dynamic mechanical thermal properties is studied. Results show that the viscosity is weakened with the addition of moderate MWNT, so the MWNT can intense the mechanical properties. And also, the value of loss factor (tanδ) becomes smaller and the softening temperature is improved. When the temperature is near to softening temperature, the loss modulus and storage modulus drop drastically.