Surface oxidation of polyhydroxyalkanoate films with different molecular structure via photo-activated chlorine dioxide radical and comparison of the influence on the properties

Polyhydroxyalkanoates (PHAs) are novel candidates for biodegradable plastics, and hydrophobic surfaces have been modified to improve their dyeability and adhesion to other materials. In this study, surface oxidation by photoactivated chlorine dioxide radicals was carried out on four types of PHA films with different molecular structures to investigate whether the number of introduced functional groups changes. Whether the mechanical properties, crystallinity, enzymatic degradability, and biodegradability in seawater were changed by oxidation was also investigated. It was found that the number of functional groups decreased in the polymer having monomer units without side chains, indicating that the reactivity of the oxidation is affected by the presence of the side chain. No significant changes in mechanical properties and crystallinity were observed. The enzymatic degradability of some of the oxidized PHA films was significantly reduced because it did not match the substrate specificity of the catalytic domain of a PHA depolymerase due to changes in the molecular structure caused by oxidation. In a biodegradation test using seawater, the initial biodegradation rate of the oxidized films was slightly reduced, suggesting that the oxidation may affect the biodegradation of microorganisms in the environment.