Processing of Poly(3-hydroxybutyrate-co-4-hydroxybutyrate) (P(3HB-co-4HB)) Using Acetic Acid: An Eco-friendly Alternative to Chloroform

Abstract The pervasive accumulation of plastic waste in terrestrial and aquatic environments has become a critical environmental issue, largely due to the resistance of petroleum-derived polymers to microbial degradation. This persistence leads to the long-term generation of microplastics and widespread ecosystem contamination. As a response, biodegradable and bio-based materials such as polyhydroxyalkanoates (PHA) have emerged as promising sustainable alternatives. Among them, poly(3-hydroxybutyrate-co-4-hydroxybutyrate) (P(3HB-co-4HB)) is a microbial polyester that exhibits excellent biodegradability, biocompatibility, and tunable mechanical properties. Owing to these characteristics, P(3HB-co-4HB) can be employed in a wide range of applications, from environmentally friendly packaging to biomedical devices. However, its processing has traditionally relied on toxic solvents such as chloroform. In this study, acetic acid is evaluated as a green alternative solvent for producing P(3HB-co-4HB) films and porous gels. Compared with chloroform, acetic acid caused moderate reductions in molecular weight (–12% for 10 mol% 4HB and − 5% for 34 mol% 4HB) and slight decreases in thermal stability, while degradation kinetics remained unaffected. DSC analyses revealed enhanced melting enthalpy for P(3HB-co-10 mol%4HB) films and the emergence of additional crystalline populations for P(3HB-co-34 mol%4HB). Mechanical tests showed moderate reductions in ductility and modulus at low 4HB content, whereas high 4HB content was unaffected. FTIR spectra confirmed the absence of solvent-induced chemical modifications. In addition, a simple thermally induced phase separation method produced highly porous (≈ 90%) gels. Overall, this study demonstrates that acetic acid offers a sustainable processing route for P(3HB-co-4HB), while preserving key material properties comparable to those obtained with chloroform.