Applications aromatic polyesters

For conventional technical applications aromatic polyesters such as polyethylene terephthalate (PET) and polybutylene terephthalate (PBT) are widely used. But these polymers are biologically inert and thus not directly applicable as biodegradable plastics. Combining both the excellent material properties of aromatic polyesters and the potential biodegradability of aliphatic polyesters has led to the development of a number of commercially available aliphatic-aromatic co-polyesters over the last decade or so. 

In 1977, Tokiwa and Suzuki reported that some lipases, which are extracellular enzymes that usually cleave esters in oils and fats, are also able to attack ester bonds in some aliphatic polyesters and can depolymerize such materials [38]. Aliphatic polyesters, however, exhibit only limited useful properties for many applications. Aromatic polyesters, such as PET and PBT, which are widely applied because of their excellent properties, are not attacked by hydrolytic enzymes. This led to the development of aliphatic-aromatic polyesters as biodegradable plastics that present a compromise between biodegradability and material properties [39]. Recently, however, Muller et al. [40] have isolated a hydrolase (TfH) from Thermofibida fusca which is able to depolymerize the aromatic polyester PET at a high rate in contrast to other hydrolases such as lipases. They have demonstrated for the first time that commercial PET can be effectively hydrolyzed by an enzyme at a rate that does not exclude a biological recycling of PET. The effective depolymerization of PET with the enzyme TfH will result in water... 

These copolyesters combine the biodegradability of aliphatic polyesters with the excellent properties imparted by aromatic polyesters. While aliphatic polyesters are easily biodegradable, they lack thermal stability and mechanical properties needed for many applications. Aromatic polyesters, on the other hand, provide excellent use properties but are resistant to mierobial attack under environmental conditions.Both BASF and Eastman Chemicals produce aliphatic-aromatic copolyesters from terephthaUc acid, adipic acid, and 1,4 butane diol. Witt et al. reported on a new group of copolyesters, which combine both biodegradability and excellent properties." These copolyesters are synthesized by conventional bulk condensation techniques from various ahphatic diols with a defined mixture of different aliphatic dicarboxyhc acids and terephthaUc acid. The key to biodegradability is the blocklength of the aromatic unit, which should preferably be no more than a trimer. 

Polymers with no pretence of high heat resistance but which complement the existing range of thermoplastics used mainly in light engineering application, e.g. phenoxies and aromatic polyesters. 

Over 4 billion PETP bottles will be available for colleetion across Europe in 1999. PUR Products has introduced technology into the UK which involves glycolysis of postconsumer PETP into materials for the manufacture of rigid urethane foams for building insulation. This application offers a substantial new market for aromatic polyester polyols derived from glycolised PETP recyclate. PUR(PRODUCTS)LTD. 

There is a significant gap of degradation rates and performance properties between the aliphatic and aromatic polyesters. However, taking some hints from nature can fill this gap. Mixtures of polyesters, molecular orientation, substitution of some functional groups, and macro structures have all been proposed as a means to provide a range of application performance properties versus degradation rates. 

The Ecovio patent portfolio covers the composition of compounds based on all aliphatic-aromatic polyesters and different compound partners (e.g., PLA) and branching agents, including different applications (EP-B 1656423, EP-B 1838784, EP-B 1204700, EP-A 2121838). 

Dyes with aromatic hydroxy compounds as coupling components, of which C.I. Disperse Yellow 3, 11855 [2832-40-8] is a representative example, have long been used to dye acetate fibers. Its use has been questioned for ecological reasons (see Chapter 8). For application to polyesters, sublimation fastness has been enhanced by increasing the size of the molecule. 

Polyester Polyols. Initially polyester polyols were the preferred raw materials for polyurethanes, but in the 1990s the less expensive polyether polyols dominate the polyurethane market. Inexpensive aromatic polyester polyols have been introduced for rigid foam applications. These are obtained from residues of terephthalic acid production or by transesterification of dimethyl terephthalate (DMT) or poly (ethylene terephthalate) (PET) scrap with glycols. 

Aliphatic polyesters like polycaprolactone (PCL) or polybutylene adipate (PBA) are readily biodegradable, but because of their melting points of 60 °C are unsuitable for many applications. On the other hand, aromatic polyesters like polyethylene terephthalate (PET) or polybutylene terephthalate (PBT) have high melting points above 200 °C and very good material properties, but are not biodegradable. 

Specialty polymers achieve very high performance and find limited but critical use in aerospace composites, in electronic industries, as membranes for gas and liquid separations, as fire-retardant textile fabrics for firefighters and race-car drivers, and for biomedical applications (as sutures and surgical implants). The most important class of specialty plastics is polyimides. Other specialty polymers include polyetherimide, poly(amide-imide), polybismaleimides, ionic polymers, polyphosphazenes, poly(aryl ether ketones), polyarylates and related aromatic polyesters, and ultrahigh-molecular-weight polyethylene (Fig. 14.9). 

The aromatic polyesters such as poly(ethylene terephthalate) (PET) were commercialized from about 1946 as fibres, but, because of the high processing temperatures, it was only some 20 years later that they appeared as engineering thermoplastics. The dominance of PET in beverage containers ensures the importance of the synthesis, processing and recycling of PET. Polyesterification is a suitable stepwise reaction to illustrate the principles of this industrially important polymerization. Applications in reactive processing will then be considered. 

Due to the low cost, the excellent physico-mechanical properties of the resulting urethane - isocyanuric foams, thermal and fire resistance and low level of smoke generation, the most important applications of aromatic polyester polyols are for rigid PU/PIR foams in the boardstock market (continuous rigid foam lamination) and for building insulation. 

Polyesters A broad class of polymers usually made by condensation of a diol with dicarboxylic acid or anhydride. Polyesters consist of chains with repeating carbonyloxy group and can be aliphatic or aromatic. There are thermosetting polyesters, such as alkyd resins and unsaturated polyesters, and thermoplastic polyesters such as PET. The properties, processing methods, and applications of polyesters vary widely. Also called Polyester Resins. 

For industrial applications, such as fibres, films and bottles, the chain length n should be between 700 and 1400. This is significantly higher than with partially aromatic polyesters like PET and PBT, where n is between 100 and 200. Therefore, the requirements on both raw material purity and technical effort are much higher. 

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