Non-Reactive Compatibilizers for Laser-Welded Immiscible Polymer Interfaces: Strengthening Effects and Molecular Mechanisms

Laser welding enables precise, energy-efficient joining of polymer components via localized interfacial heating, yet achieving strong joints remain difficult for dissimilar, immiscible polymer pairs. In this study, the effect of a nonreactive compatibilizer, chlorinated polyethylene (CPE), on adhesion in laser-welded joints between a polyvinyl chloride (PVC) substrate and a transparent polyethylene (PE) film is examined by combining welding experiments with all-atom molecular dynamics (MD) simulations. Joints fabricated without CPE showed limited adhesion: weld strength and fracture energy exhibited little dependence on laser irradiation energy. In contrast, applying CPE solutions at concentrations of 25 g/L or higher prior to welding produced systematic improvements with increasing irradiation energy, giving enhancements of more than 2.7-fold in weld strength and more than 4.5-fold in fracture energy relative to CPE-free joints. MD simulations clarified the molecular origins of these improvements. Introducing CPE formed a thicker mixed interfacial region, with CPE penetrating into both PVC and PE phases and increasing molecular-level proximity between dissimilar species. Tensile deformation simulations further indicated that the interfacial fracture energy increased by approximately 1.5–2 times upon CPE incorporation, capturing the same qualitative strengthening trend observed experimentally. Analysis of void evolution and nonbonded interaction energies showed that fracture is governed by the nucleation of microscopic voids and their coalescence into critical nuclei. CPE suppresses void nucleation and growth mainly through enhanced interfacial mixing and molecular connectivity, while electrostatic interactions contribute secondarily by delaying void growth at large strains. These findings provide a mechanistic basis for compatibilizer-assisted laser welding of immiscible polymers.