Coloured polyhydroxyalkanoates: A review

Polyhydroxyalkanoates (PHAs) are a class of biopolymers produced by various microorganisms, with poly(3-hydroxybutyrate) being the most extensively studied. PHAs are widely studied as substitutes for conventional plastics due to their similar physicochemical properties. However, the production cost of PHAs remains high. In this context, the use of colours in biopolymers is a marketing tool that plays a significant role in influencing consumer purchasing behaviour. Therefore, the aim of this study was to review, analyse and compare different methodologies for colouring PHAs published to date. Studies reported various methods for colouring PHA films, which were classified into two main methodologies: (i) simultaneous synthesis and colouring of PHAs; and (ii) production and colouring of PHAs in different stages. The analysis revealed that the field of PHA colouring is still under-explored, with relatively few studies conducted to date. Further research is required to optimise the production processes for coloured biopolymers. Additionally, there is a need to investigate new classes of natural dyes for colouring PHA films and their application in innovative, environmentally sustainable products, such as intelligent and biodegradable packaging. This review article is the first to systematically assess the methodologies for colouring PHA films.