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5
Crystallization of Poly(lactic acid)
Maria Laura Di Lorenzo and René Androsch

5.1
Introduction

Poly(lactic acid) (PLA) is a renewable resource-based bioplastic with many advan-
tages, compared to other synthetic polymers. PLA is eco-friendly, because, apart
from being derived from renewable resources such as corn, wheat, or rice, it is
recyclable and compostable [1, 2]. PLA is biocompatible, as it has been approved
by the Food and Drug Administration (FDA) for direct contact with biological
fluids [3] and has better thermal processability compared to other biopolymers
such as poly(hydroxy alkanoate)s (PHAs), poly(ethylene glycol) (PEG), or poly(ε-
caprolactone) (PCL) [4]. Moreover, PLA requires 25–55% less energy to be pro-
duced than petroleum-based polymers, and estimations show that this can be
further reduced by 10% [5].
Unfortunately, PLA has also a few drawbacks, which limit its use in certain
applications. The limitations include poor mechanical properties and a low crys-
tallization rate. The latter causes difficulties in processing of end-use articles by
injection molding. PLA articles remain amorphous owing to the short cooling
cycle and the lack of stretching during the traditional injection molding processes.
For amorphous PLA, the heat deflection temperature is close to its glass transition
∘
temperature of about 60 C, above which a dramatic drop of strength and modu-
lus of elasticity occur. As a result, the heat resistance of amorphous PLA products
is poor, especially for industrial applications.
PLA was synthesized for the first time as early as in 1845 by Pelouze via con-
densation of lactic acid [6]. In 1932, Carothers et al. [7] developed a method to
polymerize lactide to produce PLA, which was later patented by DuPont in 1954.
Although PLA existed for several decades, but owing to its high cost, its use was
limited to biomedical applications such as biocompatible sutures, implants, or bio-
logically active controlled release devices. Advances in fermentation of glucose,
which turns the glucose into lactic acid, led to decreased costs of producing lac-
tic acid and significantly increased interest in this polymer [8]. The breakthrough
occurred in the early 1990s, with the development of large-scale operations for
the economic production of PLA using a commercially viable lactide ring-opening

Biodegradable Polyesters, First Edition. Edited by Stoyko Fakirov.
© 2015 Wiley-VCH Verlag GmbH & Co. KGaA. Published 2015 by Wiley-VCH Verlag GmbH & Co. KGaA.