66. Polylactic Acid (PLA) Fibers

Poly(lactic acid) commonly known as PLA is produced by condensation polymerization from lactic acid which is derived by fermentation of sugars from carbohydrate sources including corn and sugar cane. Commercial production of PLA is through the conversion of the lactide to PLA through ring opening polymerization catalyzed by a Sn(II)-based catalyst [10Gro]. The processing, properties, and potential applications of PLA are mainly dependent on the ratio of the l- and d-isomers of lactic acid. Among the different forms of PLA that can be derived, stereo-complex type polylactides that consist of both enantiomeric poly(lactic acid) and poly(d-lactic acid) are high performance polymers with melting temperature of 230 °C, higher (50 °C) than that of PLLA or PDLA. Some of the properties of the stereo-complex PLA and PLLA are provided in Table 66.1 in comparison to poly(glycolic acid) (PGA) and poly(3-hydroxybutyrate) (PHB) [10Hir]. PLA and its isomers have been blended with various other synthetic and natural biopolymers to produce blends. PLA can be solution spun or melt spun into fibers, but generally, the latter is more economical and environmentally friendly and also produces fibers with better properties [10Aga]. However, melt spinning of PLA can cause significant hydrolytic degradation and, therefore, solution spinning of PLA is used to obtain fibers with high performance properties. Some of the fiber production conditions and the properties of the fibers obtained are listed in Table 66.2.