Fibers from Polyhdroxyalkanoates and Its Derivatives and Blends

Abstract

KeywordsBacterial polyester • Poly(3-hydroxybutyrate) • PLA • Core-sheath fiber • Knitted socksPolyhydroxyalkonates are a diverse family of biopolyester produced by bacteria as energy and carbon storage materials. Poly(3-hydroxybutyrate) (PHB) is the most common type of PHA that is commercially used. PHB is an thermoplastic material with a melting temperature of about 180 C and glass temperature that is below room temperature. Structure and properties of PHB are highly dependent on the conditions prevailing during fiber production. For instance, slow cooling from the melt produced large spherulites and rapid cooling results in amorphous state [01Yam]. It was suggested that PHB assumed orthorhombic or α-form or the β-zigzag form depending on the annealing conditions. PHB crystallized into orthorhombic form when annealed under high tension and into β-zigzag form when annealed under high tension [01Yam]. Based on X-ray diffraction patterns, it was found that the amorphous molecules transformed into orthorhombic crystal when annealed without tension and when annealed under tension, the amorphous regions were stretched and crystallized into the β-form [01Yam].Polyhydroxybutyrate-valerate (PHBV) is a copolymer of PHB that is less stiffer but tougher than PHB. However, the low crystallization rate of PHBV makes it difficult to produce fibers. To overcome this limitation, PHBV was blended with PLA to produce core-sheath fibers. PHBV with a viscosity average molecular weight of 490 kDa was extruded to obtain pellets with lower molecular weight of 260 kDa and PLA was reduced to a molecular weight of about 90 kDa, and the two polymers were blended and extruded into fibers. Table 65.1 lists the conditions used and the properties of the fibers obtained. As seen in the table, it was not possible to obtain fibers with PHBV as the sheath and PLA as the core due to poor processability of PHBV. Tensile properties of the fibers were dependent on the draw ratio and to the amount of PLA in the blend. Biocomponent fibers with PLA as the sheath and