Healable azopolymer coatings with photoinduced reversible solid-to-liquid transitions for trenchless rehabilitation of pipelines

Abstract

The development of healable polymers is crucial for the maintenance of underground pipeline systems during trenchless rehabilitation. While photocurable resins are commercial materials for this purpose, we introduce an innovative option: azobenzene-containing polymers (azopolymers) with photoinduced reversible solid-to-liquid transitions. The newly developed azopolymer comprises a methacrylate backbone and side chains incorporating hexyl spacers, azobenzene moieties, and dodecyl tails. We compared the thermal stability, efficiency of photoinduced solid-to-liquid transition, and adhesive strength among azopolymers with varying molecular weights. Subsequently, we identified the most suitable azopolymer for PVC pipe lining. The robust trans azopolymer inner layer maintains a solid state at ambient temperatures. Upon pipe damage, UV irradiation triggers trans-to-cis isomerization, leading to the conversion of the solid trans azopolymer into a liquid cis state. This flowing cis azopolymer effectively repairs cracks and can be reverted to its trans isomer via visible light irradiation or thermal relaxation. Unlike commercial photocurable resins, the developed azopolymers offer the advantage of multiple repair cycles. This study highlights the potential of azopolymers with photoinduced reversible solid-to-liquid transitions as innovative healable materials in trenchless rehabilitation technology.