Biodegradable polyester thin films and coatings in the line of fire: the time of polyhydroxyalkanoate (PHA)?

From sustainability standpoint, bio-based resins are of crucial importance nowadays rather than fossil-based resins, but the former suffers from low flame retardancy. Bio-based thin films and coatings are in their early stage of development; hence, a long way must be paved to make them resistant against flame/fire. Polylactic acid (PLA)-based biocompatible (times and some biodegradable) coatings have been in the core of attention, but even among available works one can rarely find a comprehensive report on flame retardancy of PLA thin films and coatings. Attention should also be paid to the fact that first-generation biodegradable polyesters, PLAs, are not fully biodegradable. Moreover, synthesis of PLAs is hooked on crop consumption. On the other hand, poly-hydroxyalkanoates (PHAs) with more or less similar structure, but different physical properties due to their lower glass transition temperature compared with PLAs, are known as the second-generation of bio-polyester. Overall, we highlight here that PHAs might be a better candidate for thin film manufacturing thanks to their synthesis by microorganism as well as significant variability of their microstructure that provides a wide range of properties, and notably their full biodegradability compared with PLAs. Though mass production of PHAs is not cost-effective these days and their market just entered into the growth phase, we suggest study on flame retardancy of PHA-based resins, thin films, and coatings for near future. This short communication deals with the current status and future ahead of PHA-based flame retardant thin films and coatings.