BIODEGRADABLE FIBERS

Biodegradable polyesters comprise a diverse field, but the most well-developed fiber (monofil)
market is resorbable surgical sutures, which slowly disappear in vivo and do not need
subsequent surgical removal. The first commercial samples were introduced in the early
1970s by Ethicon Corporation [51]. These sutures were monofil fibers spun from a copolymer
of glycolic acid and D-lactic acid. Such aliphatic hydroxy acids are completely biocompatible
and harmless: in U.S. Food and Drug Administration (FDA) terms, these materials are
‘‘generally recognized as safe (GRAS).’’ The properties of polyglycolide and stereochemically
pure D- or L-polylactide polymers are quite good, and they form strong, highly crystalline
fibers by melt spinning. Other biodegradable polyester fibers have been explored. Synthetic
lactones such as e-caprolactone and 2-dioxanone have been copolymerized with glycolide and
lactide [52,53]. ICI began working on poly (3-hydroxybutyric acid) in the 1970s and later
developed a copolymer with 3-hydroxyvaleric acid. Both polyhydroxyacids are stereochemically
pure and give crystalline polymers, which can be processed into fibers and films. The
interesting feature of these polymers is that they are made in very high molecular weight form
by bacteria. Certain microorganisms, when cultivated and starved of nitrogen sources,
synthesize aliphatic polyesters instead of proteins. The number average molecular weight of
the as-harvested polymer can be several million daltons and it must be reduced to allow the
polymer to be processed and fabricated. ICI (now Astra-Zeneca) first developed ‘‘Biopol’’ as
one product and although others have been introduced by different companies, little has been
targeted towards fiber end-use [54]. All the polyhydroxyacids are unstable and degrade on
exposure or composting, but the degradation rate is very much governed by the ratio of
hydrophobic=hydrophilic properties. While hydrolysis is important, catalyzed degradation by
various lipases is also a factor.