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

•This paper describes the issues faced in defining the process window and the suitability of the polymer and its composites for the Laser Transmission Welding process.•The importance of carbon black and thermal properties are emphasised in the LTW process.•The non-contact spacer method was used to study the morphological changes in laser-treated material.•Weld quality is defined in terms of apparent weld width and weld lap shear strength.•Optimisation and regression modelling was carried out using the Response Surface Methodology.