Preparation And The PTC Properties Of Modified Graphene/Polymer Composites

The dispersion of conductive filler in the polymer matrix play an important role in performance of PTC (positive temperature coefficient) material and influence the development and application of PTC material. Coupling agent modified carbon black and carbon fiber are a common means for the surface treatment of conductive filler. However, graphene as conductive fillers and the study on it is very little. The modified graphene/polymer PTC material prepared by the solution method has not been reported in the literature. In this paper, to improve the dispersion of conductive filler in the polymer matrix, eliminate NTC (negative temperature coefficient) effect and improve the stability of the PTC material, we studied the PTC properties and electrical properties of the modified graphene/polymer conductive composites.Firstly,we selected polyaniline (PANI), which has high conductivity and also has excellent dispersibility an organic solvent, as a modifier on the graphene surface. Unlike conventional routes for preparing graphene/Polyanilinecomposites coupled by van der Waals forces, a novel approach to graft polyaniline (PANI) particles onto graphene to acquire a polyaniline-graphene hybrid connected by amide groups is described in this paper.Secondly, graphene modified by polyaniline and polymethyl methacrylate (PMMA) were mixed to prepare a modified graphene/PMMA composite systems by the solution method. It was found that the modified graphene can uniformly distribute in PMMA matrix. PTC intensity of modified graphene/PMMA composite system is 0.725, which is higher than PTC intensity of unmodified graphene/PMMA system. But there is NTC phenomenon in the two systems.Finally, modified graphene were mixed with PMMA in solution, and then a solution of low density polyethylene (LDPE) was added into it. Modified graphene/PMMA/LDPE composites were prepared. By electron microscopy, modified graphene/PMMA/LDPE system showed a clear "island " structure. Island type LDPE was distributed among PMMA, and modified graphene completely uniformly dispersed in PMMA. PTC intensity of modified graphene/PMMA/LDPE system increase 54.5% than the modified graphene/PMMA system. And the system has excellent stability of PTC effect. NTC phenomenon of modified graphene/ PMMA/LDPE system disappeared.