Laser welding of HDPE/CNT to PP;an investigation on thermal and mechanical properties

The aim of this study is to develop a hybrid polymer structure based on polypropylene (PP) and high-density polyethylene (HDPE) using laser welding. To overcome the challenge posed by PP’s higher melting temperature, carbon nanotube (CNT) nanoparticles were incorporated into HDPE via 3D printing, aiming to enhance its thermal and mechanical properties and minimize the melting temperature differential between the two polymers. The resulting HDPE/CNT nanocomposite was then welded to PP using a pulsed laser. The performance of the nanocomposites and the welded joints was evaluated through tensile and bending testing, supplemented by SEM and DSC analyses. The effects of laser power, welding speed, and pulse frequency on weld bending strength and elastic modulus were modeled using Response Surface Methodology (RSM). The results indicated that an increase in the laser power from 30 to 40 W improved the elastic modulus by about 18%, though further raising it to 50 W caused a reduction of about 5%. At the same time, bending strength steadily increased across the 30–50 W range, achieving a total improvement of 24.5%. Moreover, increasing the laser power to 40 W along with raising the welding speed to 20 mm/s reduces microstructural defects, which correspondingly enhances the elastic modulus and bending strength to 720 MPa and 70 MPa, respectively. Optimal joint performance, maximizing both bending strength and elastic modulus simultaneously, was achieved at a laser power of 48 W, a welding speed of 20 mm/s, and a pulse frequency of 35 Hz.