Page 97 - Biodegradable Polyesters

4.1 Introduction 75

As regards the aliphatic polyesters prepared from 1,3-propanediol (1,3-PD),
there has been considerable progress only in the last 15–20 years. Some of the
efforts reported will be presented in detail in this chapter. The preparation of
high-quality 1,3-PD in high quantity has also contributed to this progress.
4.1.2
Production of 1,3-Propanediol

Aliphatic polyesters prepared from 1,3-PD were not of high importance and it is
only during recent years that some of these polyesters have been prepared and
studied extensively. This is because 1,3-PD was not available in the market in high
purity even thought 1,3-PD is one of the oldest known fermentation products,
identified by August Freund as early as in 1881, in a glycerol fermentation
containing Clostridium pasteurianum [4]. However, till 15–20 years ago, its
industrial importance was limited in applications such as cosmetics, fragrances,
∘
medicines, detergents, and engine coolants. 1,3-PD has a melting point at −32 C,
∘
boiling point at 214 C, density of 1.053 g ml −1 and high solubility in water. The
production of high-purity 1,3-PD was the starting point to expand its applications
in polymer technology because owing to the presence of two hydroxyl groups
at 1 and 3 positions, it can be used for the production of linear polyesters,
polyethers, and polyurethanes. The alipharomatic polyester poly(propylene
terephthalate) (PPT) was the first studied polymer owing to its ability to form
fibers with better characteristics than those already in use by the familiar PET
®
polyester [5–7]. Sorona was the trade name of the first of such polyester fibers
based on 1,3-PD. It was commercialized by Dupont, offering better physical and
chemical properties. These characteristics are due to the different architecture
of macromolecular chains having a zigzag or coil-like shape. The prepared fibers
have higher hydrophobicity (low water absorption) which makes water to flow
from their surfaces, better dyeability in temperatures much lower than for the
PET fibers, superior stretching and stretch-recovery characteristics, higher
UV stability, and so on. Other alipharomatic polyesters such as poly(propylene
isophthalate) and poly(propylene naphthalate) with very interesting properties
have been also prepared and studied [8]. These applications probably initiated th
demand for high quantities of 1,3-PD on the market.
Completely biodegradable polyesters using different aliphatic acids and 1,3-PD
have been prepared and studied [9–11]. The properties of the prepared polyesters
are directly expanded from the methylene groups of aliphatic acids but the main
advantage of these are that they have high biodegradation rates, compared to the
traditional polyesters such as PLA, PLA, and PBSu.
In thermoplastic urethanes (TPUs), use of 1,3-PD can lead to improved ther-
mal and hydrolytic as well as thermal dimensional stability [12]. In engine coolant
formulations, 1,3-PD demonstrates improved heat stability, less corrosion (espe-
cially to lead solder), and lower toxicity than ethylene glycol coolants. Owing to
these advantages, the production of new PPT fibers and other applications has