Technological challenges and advances: From lactic acid to polylactate and copolymers

Abstract

Lactic acid is an organic acid that has been extensively used worldwide in a variety of industrial and biotechnological applications. Lactic acid can be obtained chemically or by microbial fermentation. Production by fermentation results in the formation of d(-) or l(+) lactic acid, or racemic mixture, depending on the microorganism used. Pure isomers present specific industrial applications from the polymerization of such monomers; different types of lactic acid polymers (PLA) are formed. The properties of PLA depend on the proportion of enantiomers, which enable the production of polymers with different characteristics directed to specific applications. There are three pathways for producing PLA from lactic acid; direct polymerization and polymerizations by lactide ring opening are the most widely used techniques. The degree of crystallinity and many other important properties, such as strength and melting point, are controlled by the ratio of enantiomers used in the polymers. l(+) lactic acid is used for the synthesis of poly(l-lactic acid) (PLLA), a semicrystalline, biodegradable polymer, with potential application in the packaging industry and in medical products. Poly(d, l-lactic acid), a polymer consisting of two isomers, is degraded more rapidly due to its amorphous structure. PLA has been considered as one of the most promising biodegradable plastics due to it having physical characteristics similar to polymers derived from nonrenewable sources, such as elasticity, stiffness, transparency, thermoresistance, biocompatibility, and good moldability.