Polyhydroxyalkanoate-based BB bullets as alternatives to ABS bullets based on muzzle velocity, penetrating power,...

Although extensive efforts have been made toward bulk plastic recycling and material development, relatively less attention has been paid to small quantities of plastics, such as BB bullets for toy guns, which are directly released into natural environments and found easily in playgrounds, yet are impossible to recover. In this study, BB bullets were fabricated via injection molding using acrylonitrile-butadiene-styrene (ABS), polylactic acid (PLA), poly(butylene adipate-co-terephthalate) (PBAT), and polyhydroxyalkanoate (PHA)-based polymers, and their processability, shooting performance, durability, and biodegradability were systematically compared. All the materials were successfully molded into spherical BB bullets with diameters of approximately 6 mm. Among these, B-PHBH, which is a copolymer of 3-hydroxybutyrate (3HB) and 3-hydroxyhexanoate (3HHx), exhibited a performance comparable to that of ABS and maintained relatively stable surface characteristics under repeated firing in the shooting tests. In the degradation experiments, while ABS and PLA showed negligible changes, B-PHBH exhibited approximately 42% weight loss after 14 days under microbial conditions, indicating significantly enhanced biodegradability. In addition, functional coatings using a fluorescent lacquer and phosphorescent powder to B-PHBH were comparable to known BB bullets, demonstrating the feasibility of further functionalization. Overall, the results suggest that 3HHx-based PHA is a promising biodegradable alternative for BB bullet applications, providing both practical performance and environmental advantages, and offering a potential strategy for reducing microplastic pollution.