Polyhydroxybutyrate (PHB): Critical Perspectives on Material Properties, Production Advances, and Challenges Toward Sustainable Commercialisation.

Polyhydroxybutyrate (PHB), a microbial polyester belonging to the polyhydroxyalkanoate (PHA) family, has emerged as one of the most promising biodegradable alternatives to conventional petroleum-derived plastics. Its inherent marine biodegradability (typically mineralizing within months depending on material geometry and ambient temperature), biocompatibility, and ability to be synthesised from renewable and waste-derived feedstocks position PHB as a key candidate for supporting the transition towards a circular bioeconomy. Despite these advantages, widespread commercial adoption remains limited by high production costs, processing challenges, and performance constraints relative to established commodity plastics and competing biopolymers. This review critically evaluates the current state of PHB development from the perspective of sustainable commercialisation. Key aspects discussed include microbial biosynthesis pathways, feedstock selection, upstream fermentation strategies, downstream recovery technologies, and technoeconomic considerations influencing industrial feasibility. The intrinsic thermal, mechanical, and degradation characteristics of PHB are examined alongside modification approaches such as copolymerisation, polymer blending, plasticisation, and composite reinforcement that have been developed to overcome certain inherent physical-mechanical properties, narrow processing windows, and limited functional performance. Furthermore, characterisation methodologies, environmental degradation behaviour, and emerging industrial applications are assessed within the context of market requirements and sustainability objectives. Particular emphasis is placed on identifying the interconnected technical and economic bottlenecks that continue to hinder large-scale deployment, including feedstock costs, fermentation scalability, downstream processing expenses, and material performance trade-offs. By integrating advances across the entire PHB value chain, this review highlights current opportunities, remaining challenges, and future priorities required to enable the sustainable and economically viable commercialisation of PHB-based materials.