Green Alginate Extraction from Macrocystis pyrifera for Bioplastic Applications: Physicochemical, Environmental Impact, and Chemical Hazard Analyses

To scale alginate production for widespread use, a focus on advancing sustainable extraction methods is needed. This study investigates greener extraction methods and their effect on alginate properties to advance sustainable methods suitable for bio-based plastic applications. Three alginate extraction protocols were selected by evaluating the hazard levels to human and environmental health of solvents and reagents used in 23 alginate extraction methods. The three methods were tested on samples of Macrocystis pyrifera algae and evaluated based on the efficiency of extraction, uronic acid composition (M/G ratio), molecular weight, and carbohydrate composition. Finally, the extraction methods were assessed using a partial life cycle assessment, assessing the water, chemical, and energy consumption and respective greenhouse gas emissions. The study found that the choice of extraction protocol significantly influenced the properties of the resulting alginate. Protocols 1 and 2, using operating conditions of high pH and temperature and short alkaline extraction times, produced alginates with a high M/G ratio (1.23 and 1.53, respectively) and comparable molecular weight to commercial alginate, but they had increased energy and water consumption and emissions (987 and 389 kg CO2-eq (CO2 equivalents), respectively) compared to the other protocol evaluated. Protocol 3, using ambient conditions and an alkaline chelating sodium citrate treatment, resulted in alginates with a decreased M/G ratio (0.63), reduced greenhouse gas emissions (177 kg CO2-eq), and high yield (26.7%) but produced alginates with lower molecular weight (59.5 kDa). This research highlights the adaptability of extraction protocols for achieving the desired alginate properties and evaluates the safety and environmental implications of the selected methods.