Investigation of microwave welding of thermoplastics using intrinsically conductive polyaniline

ntrinsically conducting polymer, such as polyaniline, absorbs microwave energy which offers the opportunity to develop new joining techniques. The main objective of this work is to develop a novel joining technique which combines microwave energy and intrinsically conducting polymers. The effect of welding parameters such as heating time, pressuring method, and polyaniline concentration on joint strength were studied and an equivalent circuit heating model was also constructed to predict the power absorption of the conducting composites. The finite element method was also used to calculate the internal heat generation rate during welding process. Multi-mode microwave welding of HDPE was successfully demonstrated by placing the conducting composite at joint interface. It was found that increasing the gasket thickness results in higher joint strength using constant pressuring method. Also, increasing the polyaniline concentration in the gasket results in higher joint strength. It was also found that increasing the welding pressure results in higher joint strength. However, the constant pressuring method squeezes out the heating composite in the middle of the heating stage; thus, less heating occurs. The maximum joint strength was 86% of the HDPE strength for both 50%, 1mm thick gasket and 60%, 0.5mm thick gasket. A modified multi-mode microwave welding method, post heating pressure, was also demonstrated to improve the joint quality. The maximum joint strength was equal to the bulk strength of HDPE. It was found that post heating pressure method not only increases the maximum joint strength but also reduces the heating time to reach a specific joint strength. The FEM calculation of the heat generation rate shows that 60%, 0.5mm gasket provides faster heating rates and higher temperatures than the 50%, 1mm which reveals that gasket heating ability depends on the gasket composition and not the amount of the conducting powder in the gasket. Single mode microwave welding of HDPE was also successful and it reduced the heating time from 80 seconds in multi-mode to 15 seconds in single mode due to a higher power source and better energy transfer efficiency. The maximum heat generation rate using 1800 watts and 60%, 0.5mm PANI composite was...