Effect of polyaniline loading, types of surface modifiers and secondary doping process on the properties of poly (vinyl chloride) / poly (ethylene oxide) / polyaniline conductive films

Abstract

The main objective of this research was to analyse the role of polyaniline (PAni) as conductive filler in the poly (vinyl chloride)(PVC) / poly (ethylene oxide)(PEO) matrix. The PVC/PEO/PAni conductive composite films were prepared via solution casting method. Based on the electrical conductivity test, the percolation threshold of the conductive films was obtained when 10wt% of PAni was used. Two different approaches were employed to enhance the PAni / matrix interactions in the conductive composite structure, thereby the electrical conductivity, tensile and thermal properties of the produced films. The first approach was to introduce surface modifiers where the efficiency of two types of surface modifiers; ethylene dimethacrylate (EDMA) and naphthalene in enhancing the PAni dispersion and PAni/matrix interactions was studied. Both surface modifiers have successfully increased the mechanical properties, electrical conductivity, thermal stability and filler dispersion of the conductive films. The SEM micrograph also indicated better filler dispersion with the addition of these surface modifiers. In the second approach, PAni was doped using ferric chloride, FeCl3 in order to raise the electrical conductivity of the conductive films. Unfortunately, the tensile and thermal properties of the resultant conductive composite films dropped significantly due to reduced quality of PAni dispersion inside the PVC/PEO matrix. Polyethylene glycol diglycidyl, (PEGDE) was then added into the PVC/PEO/PAni-FeCl3 conductive film as crosslinking agent to improve the PAni dispersion, and also the PAni/matrix interactions. As a result, the tensile and thermal properties were improved, but the electrical conductivity was seen to slightly decreased. Other than the PAni dispersion factor, the crystallinity factor also being examined to correlate between the structure and the electrical conductivity of all the conductive films containing different PAni content, surface modifiers, oxidant and crosslinking agent. The XRD results show that the crystallinity of the matrix reduced when greater amount of PAni was incorporated into the conductive films (with and without surface modifiers). Increased portion of amorphous phase in the matrix structure could also contribute to enhanced electrical conductivity of the conductive film by allowing higher mobility of ions. Lastly, PVC/PEO/PAni, PVC/PEO/PAni/EDMA, PVC/PEO/PAni/naphthalene, PVC/PEO/PAni- FeCl3 and PVC/PEO/PAni-FeCl3/PEGDE conductive films at 10 wt. % PAni loading were compared. The highest tensile properties were displayed by PVC/PEO/PAni/naphthalene conductive film. Moreover, PVC/PEO/PAni/naphthalene conductive film also exhibits the greatest electrical conductivity and thermal stability among all the conductive films. The capability of naphthalene in assisting dispersion of PAni filler inside the PVC/PEO matrix was the best among those surface modifiers, and this was thought to be the main cause of such properties enhancement. Furthermore, the naphthalene was seen to induce the greatest reduction in the matrix’s crystallinity. The amorphous portion in the PVC/PEO/PAni- 10/naphthalene conductive film was higher as compared to other conductive films, which is beneficial in inducing higher mobility of ions.