The Study Of Vapor Sensing Behaviors Of PLA Basedconductive Polymer Composites

Conductive polymer composites are fabricated by adding one or several kinds of conductive filler into polymer, which have excellent electrical properties. It has aroused researchers’ wide concern due to its application in antistatic material, electromagnetic shielding material, self-controlled temperature material and environmental monitor sensor and so on. Percolation phenomenon is a special phase transition behavior of CPCs, it means that the sample conductivity will be changed sharply when the filler content changes a little, indicating the formation of conductive networks and the transition from insulator to conductor of CPCs. Based on the percolation behavior, the CPCs at percolation zone are more sensitive when they are exposed external stimuli, especially the temperature, tensile or organic solvent/vapor stimulation. At present, the sensing mechanism of conductive filler filled polymer composite to external stimulation is not clear yet, and this confines the application of CPCs in vapor leakage monitoring.In this paper, carbon black(CB) and carbon nanotubes(CNTs) were selected as conductive filler to mix with poly(lactic acid)(PLA), and the percolation behavior was investigated in detail. Samples at percolation zone were selected to testify the vapor sensing behavior towards different organic vapors. To discuss the influence of interface on the evaporation during the vapor sensing tests, ramie fiber(RF) was selected and fabricated as the same methods. By comparing the sensing results, the sensing mechanism of CPCs with different fillers were explained. At the same time, a schematic was proposed to describe the conductive network evolution of CB filled CPCs and CNTs filled CPCs. Results indicated that the addition of RF generated interfaces of fiber and polymer, which facilitated the permeation and evaporation of organic vapors. So the vapor sensing stablility was enhanced with the addition of RF.Then the CNTS/PLA/PP composites were manufactured by melt processing, the relationship between microstructure and electrical properties(vapor sensing) was investigated. To study the polymer component ratio on the microstructures of CPCs, a series CPCs with different component ratio were fabricated. When PLA/PP changed from 70/30 to 60/40, the microstructure of CPCs also suffered a transition from island-sea structure to cocontinuous structure, and the rheological measurement also verified the results. To investigated the CNTS distribution and conductive network construction on the electrical of CPCs, CNTS and PLA or PP were premixed and then mixed with another polymer, and the kinetics factor was discussed profoundly, and the CNTS location in polymer matrix was also analysed and predicted via Young’s equation. Afterwards, the vapor sensing behaviors of A7P3, A6P4, Pre-PLA and Pre-PP towards different organic vapors were carried out. Compared with single phase polymer CPCs, the multi-phase polymer CPCs can not only prolong its lifespan in good solvent, but also broaden the range because of the selective sensing of polymer towards vapors, and provided a new thought for functionalization and industrialization of CPCs.