Laser-induced blackening on surfaces of thermoplastic polyurethane/BiOCl composites

Using Bismuth Oxychloride (BiOCl) as a laser-sensitive component, and thermoplastic polyurethane (TPU) as the matrix, the TPU/BiOCl composite capable of laser marking can easily be produced by melt blending of TPU with various proportions of BiOCl. The TPU/BiOCl composite samples showed high contrast black markings on the surface after laser treatment, depending on the BiOCl loading and laser fluence in terms of visual and microscopic analysis. The laser-induced blackening on material surfaces was examined by XPS, XRD, and Raman spectroscopy. The results revealed that the laser-induced blackening on the composite surface entails laser absorption of the BiOCl particles and local heating of the surrounding TPU chains. This led to the generation of amorphous black carbonised materials and the reduction of BiOCl into black bismuth metal. The carbonisation of TPU chains and the photo-thermal conversion of BiOCl particles synergistically contributed to the formation of the black-coloured marking on composite surfaces.