Welding and Disassembly of Microwave Welded HDPE Bars

Microwave welding of polymers is performed by placing an electromagnetic absorbent material (polyaniline) at the interface. The absorbent polyaniline converts electromagnetic energy into heat which is conducted into the bulk materials forming molten layers. Pressure, which is applied after the heating stage squeezes the molten layers to form the welded joint. However, if sufficient conductive polymer is retained at the interface, then the welded samples can be placed in the microwave, reheated, and disassembly for recycling and reuse purposes can be performed. Controlling the amount of remaining conductive polymer at the joint interface is the key for achieving disassembly of a microwave welded joint. For this purpose the total displacement was used to characterize both the welding and the disassembly processes. The effect of displacement on joint strength was analyzed. It was found that if the total displacement exceeded 2.7 mm, regardless of the polyaniline concentration (30, 40, 50, 60%) and welding parameters employed, a joint strength of at least 90% the bulk strength is obtained. Disassembly of butt welded joints was then performed. It was found that ajoint with a tensile strength of approximately 60% of the bulk strength can be disassembled with a relatively low force of 27 N. However, a long reheating time of 120 seconds and a high power level of 2000 W is required for disassembly to occur. In order to increase the disassembly capability a tuned single-mode microwave system was used. Thus, while the reheating time and power level decreased to 30 seconds, and 1000 W respectively, the maximum joint strength which can be disassembled increased to 80% of the bulk strength. The maximum displacement which can be disassembled was found to be 1 mm regardless of the concentration of PANI used. After disassembly the 60% PANI samples were welded once more with the same parameters as the original welds. The rewelded samples exhibited a maximum loss of 15% in tensile strength.