Effect of laser processing parameters and carbon black on morphological and mechanical properties of welded polypropylene

In the present work, laser process window and welding suitability of the neat isotactic polypropylene (iPP) and its carbon black (CB: 0–3 wt.%) composites was defined for laser transmission welding (LTW) with the help of thermal characterisation and thermal simulation. This novel approach of welding feasibility moves from trial and error to robust analytical methods. The non-contact spacer method is also a novel feature of this study, followed by X-ray diffraction of the laser-treated iPP composites. This study emphasises the importance of crystallinity in defining weld integrity and quality. The welding experiments were conducted with line energies of 0.06–0.12 J/mm using the Response Surface Methodology approach by varying laser power and welding speed. The composites with 0.5 wt.% and 1.0 wt.% of CB were welded successfully with neat iPP, but composites with CB (>1 wt.%) were difficult to weld due to degradation. Weld lap shear strength and apparent weld width measured during mechanical testing showed better weld quality for 1 wt.% CB welded at line energy 0.12 J/m. Mathematical models have been developed based on the experimental results of central composite design after backward elimination. The present study demonstrates that an increase in CB to an optimised value fulfils the requirements of high welding speed with improved crystallinity and weld strength. This study is of keen interest to industrialists and researchers.