Co-authors​ :

 Pejman HEIDARIAN (FRANCE), Peter HALLEY , Tony MCNALLY , Ton PEIJS (UNITED KINGDOM), Luigi VANDI , Russell J. VARLEY (AUSTRALIA) 

In recent years, there has been growing concern about the impact of petroleum-based plastic waste on the environment, leading to an urgent need for sustainable and biodegradable alternatives. Among the diverse array of bio-based polymers, bacterial aliphatic polyester polyhydroxyalkanoates (PHAs) have emerged as promising alternatives to traditional petroleum-based plastics due to their biodegradability, biocompatibility, and similar hydrophobicity and mechanical properties to most common polyolefins, such as polyethylene and polypropylene. Among PHAs family, polyhydroxybutyrate-co-valerate (PHBV) stands out as a highly promising biodegradable polymer in many applications, such as food packaging materials. Nevertheless, PHBV faces limitations due to its relatively low mechanical strength, restricting its widespread use. One approach to improve the mechanical performance of PHVB is to fabricate fully biodegradable PHVB composites either using sustainable fillers, such as natural fibers, agricultural wastes, cellulose-derived fibers, wood-derived fibers, or utilize a self-reinforcing approach. The self-reinforcing effect relates to the reinforcement of polymers with highly oriented films, fibers, or particles from the same polymer. Of particular interest is the ability of PHBV to crystallize into ɑ and β phases, with the β phase standing out for its highly ordered crystalline structure. The β phase in PHBV is formed from the orientation of free chains between the ɑ-form lamellar crystals, exhibiting a twisted planar zigzag conformation with a high crystal lattice modulus. The β phase in PHBV demonstrates a highly ordered crystalline structure and superior mechanical properties, with high potential self-reinforcing effects, but compared to the ɑ phase, preserving the β phase is challenging due to its lower melting temperature. In this study, we explore an approach to improve the mechanical performance of PHBV by harnessing the self-reinforcing effect of β-phase induced PHBV electrospun nanofibers, followed by synergizing this self-reinforcing effect using a low-temperature post-spun vapor solvent interfiber welding. The orientation of polymer chains along the fiber axis and the formation of ɑ and β crystalline phases were confirmed through XRD diffraction and FTIR spectra analyses confirming that the vapor solvent welding allowed for the preservation of the β-phase. DSC experiments provided insights into the thermal behaviour of the fibers, and tensile and DMA tests were conducted to comprehensively evaluate their mechanical performances. Results demonstrated that higher polymer chain orientation, in conjunction with the preservation of the β -phase through vapor solvent bonding, led to enhanced mechanical properties, making the self-reinforced fibers suitable for applications requiring improved strength.