Polyester degradation resistance

The flexural modulus and heat deflection temperature of these aryl polyesters are increased by the incorporation of reinforcing fillers. PET and related aryl polyesters are resistant to nonoxidizing acids, alkalis, and salts, as well as to polar and nonpolar solvents at room temperature. (Above room temperature some alkalis and acids begin to degrade polyesters.)... 

Despite its oxygen content, polyester (i.e., the aromatic polyethylene terephthalate) is degradation-resistant probably because of its rigid, rod-like chains. The same is true for polyamides in spite of their nitrogen content. 

Separator structures fall into four main categories microporous films, nonwovens, gel polymers, and solid polymers. Microporous films contain small pores (5 to 10 nm in diameter) and are often used for low temperature applications. They are made from nonwoven fibers such as cotton, polyester, glass, polyolefins (PP and PE), PTFE, and PVC. Microporous separators are commonly used with organic electrolytes and in acidic systems. Nonwovens are manufactured as mats of fibers and bind through frictional forces. They exhibit consistent weight, thickness, and degradation resistance but they show inadequate pore order and are difficult to make thinner than 25 pm. Nonwovens are generally made from cellulose, PTFE, PVC, PVdF, or a combination of polyolefins and receive preference in alkaline systems [114]. 

The persistent problem of conventional plastic waste disposal grows ever more severe as landfills approach capacity with these highly degradation-resistant substances (Section 12-15). Biodegradable plastics provide an option for nonre-usable items such as plastic bags, wraps, and bottles. A recently developed and commercialized biobased and biodegradable plastic is poly(jS-hydroxybutyrate-co-/3-hydroxyvalerate) (PHBV), a copolymer of 3-hydroxybutanoic acid and 3-hydroxypentanoic acid. PHBV is a polyester that is produced by bacterial fermentation of mixtures of acetic and propanoic acids. The ratio of the two hydroxy acids controls the properties of the plastic—it is more flexible with more... 

Thermoplastic polyurethane elastomers have now been available for many years (and were described in the first edition of this book). The adipate polyester-based materials have outstanding abrasion and tear resistance as well as very good resistance to oils and oxidative degradation. The polyether-based materials are more noted for their resistance to hydrolysis and fungal attack. Rather specialised polymers based on polycaprolactone (Section 25.11) may be considered as premium grade materials with good all round properties. 

Abrasion-resistant duties may involve abrasion in an aqueous phase or abrasion by dry particulate materials. The selection of the polyurethane type is most important to obtain the best results. Polyester-based polyurethanes perform best in dry abrasion due to their low hysteresis properties and excellent resistance to cut initiation and propagation. However, polyester polyurethanes are susceptible to hydrolytic degradation, and therefore polyether polyurethanes are normally used for aqueous abrasion duties. 

These materials, when exposed to continuous high humidity, especially in the presence of an electrical field, hydrolyze into the acid and alcohol precursors from which they are made. The acid plus water present make a conductive material that will cause the material to short the electrical circuit. The process by which the decomposition of the TS polyester takes place is very gradual at first and then accelerates so that extended testing of the material is necessary to be sure that the particular polyester composition used is resistant to hydrolytic degradation. 

The semicrystalline polyesters of the terephthalate and naphthalate family are resistant to a wide range of chemicals at room temperature, including water, alcohols, ketones, ethers, glycols, chlorinated solvents, aliphatic hydrocarbons, and oils. They are slowly hydrolyzed in boiling water and rapidly degraded in strongly basic or acidic medium. 

Although polymers in-service are required to be resistant toward hydrolysis and solar degradation, for polymer deformulation purposes hydrolysis is an asset. Highly crystalline materials such as compounded polyamides are difficult to extract. For such materials hydrolysis or other forms of chemolysis render additives accessible for analysis. Polymers, which may profitably be depolymerised into their monomers by hydrolysis include PET, PBT, PC, PU, PES, POM, PA and others. Hydrolysis occurs when moisture causes chain scissions to occur within the molecule. In polyesters, chain scissions take place at the ester linkages (R-CO-O-R ), which causes a reduction in molecular weight as well as in mechanical properties. Polyesters show their susceptibility to hydrolysis with dramatic shifts in molecular weight distribution. Apart from access to the additives fraction, hydrolysis also facilitates molecular characterisation of the polymer. In this context, it is noticed that condensation polymers (polyesters, -amides, -ethers, -carbonates, -urethanes) have also been studied much... 

Geotextiles are available as mats, textiles, webs, nets, grids, and sheets. When retention of the contained material is desired synthetic polymers such as polypropylenes, polyesters, nylons, PEs, and PVCs are used because they resist rapid degradation. When only shortterm retention is needed natural materials such as cotton are used. Geotextiles are not always made from fibers, but include film materials such as PE and polypropylene sheets used to retain moisture but retard weed growth in gardens. 

Hydrolytic degradation is especially important in polymers with hydrolyzable links between the CRUs. Thus, polyesters can be saponified to yield the starting materials from which they were formed. Acetal links in synthetic polymers such as polyoxymethylene, or in natural polymers such as cellulose, can be hydrolyzed with acids. However, the resistance to hydrolysis depends very much on the structure of the polymer for example, polyesters of terephthalic acid are very difficult to hydrolyze while aliphatic polyesters are generally easily hydro-... 

Amide urethane, and ester groups in the polymer chain, such as those present in nylons and polyesters may be hydrolyzed by acids to produce lower-molecular-weight products. Polyacetals are also degraded by acid hydrolysis, but ethers, such as polyphenylene oxide (PPO), are resistant to attack by acids. 

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