Page 259 - Biodegradable Polyesters

10.1 Introduction 237

In some cases, a cradle-to-cradle approach about these renewable polymers
(i.e., from raw material extraction through materials processing, manufacturing,
distribution, use, repair and maintenance, and final disposal or recycling) can be
addressed by life-cycle assessment (LCA) [8].
As driven by the growing demand for durable bioplastics, the recent trend in
the market for renewable polymers is to now focus on their implementation into
important high-added-value sectors such as the electronics and automotive sec-
tors [9]. This will therefore boost both industrial and economic values of renew-
able polymers in the context of long-lasting applications. However, the main chal-
lenge faced by manufacturers of these renewable polymers is to impart them the
same performance and processing characteristics as the existing petropolymers at
affordable prices.

10.1.2
Polylactide and Its Industrial Production

One of the outstanding achievements in the realm of renewable polymers is
undoubtedly the rapid progress related to the research and development activities
for PLA [10], related to its high availability in the market and its low price [11].
PLA has been known since 1845, but was not commercialized at a high industrial
scale until the early 1990s [12]. At present, PLA is the most produced and used
biopolymer in the world; it is a commodity polymer with important applications,
particularly in packaging and fiber technology. The global production capacity
exceeds more than 250 kilotons per year with a steadily reducing price and
positive ecoprofile and related LCA [13–15]. Today, companies around the world
such as Mitsui Chemicals Inc. (Japan), NatureWorks Llc. (USA), or Futerro
(Belgium) produce PLA on a large scale.
PLA belongs to the family of aliphatic polyesters with the basic constitutional
unit of lactic acid. The monomer lactic acid is an α-hydroxy acid, which can be
obtained via chemical synthesis or via microbial carbohydrate fermentation from
renewable feedstocks (sugar beet, cornstarch, sugar cane, wheat, etc.) [16]. Chem-
ical synthesis of lactic acid is mainly based on the hydrolysis of lactonitrile pro-
moted by strong acids, which provides only the racemic mixture of D-lactic acid
and L-lactic acid [17]. The interest of the fermentation production of lactic acid is
its high product purity, producing a desired optically pure L-lactic acid or D-lactic
acid upon the microbial strain used during the fermentation process [18]. As it
is known, the optical purity of lactic acid is crucial for PLA production because
small amounts of enantiomeric impurities can drastically alter the properties of
the polymer. In this regard, corn has the advantage of providing a high-quality
feedstock for fermentation, that is, a high-purity L-lactic acid.
PLA can be produced by step-growth polymerization starting from lactic
acid or by ring-opening polymerization (ROP) of lactide (LA), that is, the
ring-formed dimer from lactic acid [19, 20]. LA is obtained by a condensa-
tion/depolymerization process, in which a low-molecular-weight LA oligomer
produced by step-growth polymerization is thermally degraded by the so-called