A Comparative Study of Melt-Spun PHB Yarns: Processing-Dependent Biodegradation under Simulated Environmental Conditions

Poly(3-hydroxybutyrate) (PHB) is a fully biodegradable polymer with increasing potential for sustainable textile applications; however, biodegradation studies focusing on fiber-level structures remain limited. In this study, melt-spun PHB yarns produced under different processing conditions were investigated to explore processing–structure–biodegradation relationships. Mechanical testing showed that increasing draw ratio enhanced tensile strength while reducing elongation at break, indicating processing-induced molecular orientation. Structural analysis by XRD further revealed variations in hierarchical organization, including changes in crystalline reflections and oriented non-crystalline contributions. Samples were exposed to three simulated natural environments (soil, vermicompost, and treatment sludge) to evaluate environment-dependent degradation behavior. Mass loss measurements supported by SEM, FT-IR, and DSC analyses revealed processing-dependent surface erosion patterns and morphology-driven structural rearrangements without significant chemical modification. Distinct degradation responses emerged from the combined influence of processing-induced structural differences and environmental conditions. The results indicate that processing-induced structural variations modulate biodegradation behavior, while environmental conditions play a critical role in degradation progression. These findings provide insight into tailoring degradation performance of PHB-based textile fibers through controlled processing and application-specific environmental considerations.