Evaluating Tensile Strength in Butt Fusion and Electrofusion Joints in Nanocomposite HDPE Pipes

In this paper, high-density polyethylene (HDPE) composite pipes, reinforced with glass fibers (GF) and carbon nanotubes (CNTs), are manufactured using a novel extruder and multiple molten reprocessing cycles in a screw cylinder barrel. Moreover, the study investigates the tensile strength of the junction of these composite pipes. The results indicate that the Young’s modulus and the ultimate tensile strength of the fabricated nanocomposite pipes increase by 150 and 163 %, compared to the conventional polyethylene pipes, respectively, using 2 wt% carbon nanotubes and two reprocessing iterations in the cylinder barrel. The effects of adding carbon nanotubes to HDPE and the number of reprocessing cycles on the fracture mechanism of the nanocomposite pipes have been explored based on SEM images and DSC testing. The pipes are joined using the two most common available methods; namely, butt fusion and electrofusion, and their respective tensile strengths are compared. The results demonstrate an 82 % and a 37 % decrease in the tensile strength for the welded pipes, compared to the non-welded pipes, using butt fusion and electrofusion, respectively. However, the tensile strength in the welding of the GFRP nanocomposite pipes can be enhanced by increasing the interconnection between the fibers at the junction. Nevertheless, butt fusion is not recommended for joining FRP composite pipes, while electrofusion can be utilized with some modifications.