An overview on microalgal polyhydroxybutyrate (PHB) production and improvement of mechanical properties

Polyhydroxybutyrate (PHB) is fully biodegradable under home-composting conditions, but its low yield and brittleness hinder widespread adoption. Microalgae have gained attention for PHB production due to their photoautotrophic nature, which enables the use of light and carbon dioxide as primary energy and carbon sources. This characteristic offers a low-cost and environmentally sustainable alternative for biopolymer synthesis. This review consolidates recent research on optimizing PHB productivity from microalgae, including strain selection, cultivation methods and growth media conditions. Chlorella pyrenoidosa achieved the highest PHB productivity when cultured mixotrophically in cheese whey wastewater under conditions of nitrogen and phosphorus limitation. Eco-friendly solvents like dimethyl carbonate (DMC), can achieve high recovery rates and produce PHB of good quality. This review also examines strategies to enhance the mechanical properties of microalgae-derived PHB through plasticization and biopolymer blending. The effects of plasticizers on PHB's glass transition temperature, crystallinity, tensile strength, and elongation are discussed, along with the synergistic impact of blending PHB with biodegradable polymers such as polycaprolactone (PCL), polybutylene succinate (PBS), and polybutylene adipate-co-terephthalate (PBAT). In conclusion, this review provides valuable insights into optimizing PHB production and improving its mechanical properties for sustainable packaging applications.