Thermoplastic polymers degradation resistance

Braun, U., Wachtendorf, V., Geburtig, A., Bahr, H., Schartel, B. Weathering resistance of halogen-free flame retardance in thermoplastics. Polym. Degrad. Stab. 95, 2421-2429... 

Thermoplastic polymers can be heated and cooled reversibly with no change to their chemical structure. Thermosets are processed or cured by a chemical reaction which is irreversible they can be softened by heating but do not return to their uncured state. The polymer type will dictate whether the compound is completely amorphous or partly crystalline at the operating temperature, and its intrinsic resistance to chemicals, mechanical stress and electrical stress. Degradation of the basic polymer, and, in particular, rupture of the main polymer chain or backbone, is the principal cause of reduction of tensile strength. 

Thermoplastic polymer with sir., toughness, and flexibilily resist. to oxidative degradation, electricity, acids, alkalis, oxidizers, halogens... 

Although starch is itself a thermoplastic polymer (thermoplastic starch, TPS) (Li et al, 2008) and can be processed via extrusion or molding with the aid of a plasticizer (Chuayuljit et al, 2009), this natural polymer is a rapidly degrading material with minimal moisture resistance. Application possibilities of TPS are as fillers or blends with other thermoplastics (Arvanitoyannis et al, 1997, 1998). Chemical modification of starch, on the other hand (Gandini, 2008 Lee et al, 2007), can be used to adjust degradation properties as well as the water stability of the resulting materials. 

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. 

Although the technological basis of all fluorine-containing plastics and most elastomers continues to be the free radical polymerization of fluoroolefins, which themselves are based on the vastly greater fluorocarbon refrigerant industry, important advances have been made in the past two decades These include primarily the production of polymers that are more resistant to degradation by heat, oxidation, bases, and solvents, as well as polymers that are more easily processable, that is, able to be converted mto their final forms for use, whether by thermoplastic or thermoset processes [1,2,3,4]... 

Acrylic Copolymers. A widely used method to modify the physical and chemical properties of polymers is to prepare copolymers that contain monomer units chosen to give the desired properties. For example, copolymers of MMA are used in thermoplastic coatings where improved flexibility or resistance to degradation are needed (15). 

As block copolymers are still rather expensive materials, it may be advantageous to use them as additives to important industrial polymers. In this domain, possibilities are extremely numerous and diverse. They include an improvement of chemical properties such as resistence to degradation agents, or rheological properties such as adhesion of vinylic paints, high impact properties of conventional thermoplastics, or a compatibilization of polyolefins, polystyrene and poly(vinyl chloride) allowing the reuse of polymeric waste products. The above examples illustrate the great intrinsic potential of block copolymers in the quest of new materials with specific properties. 

In general, there is a paucity of information on the relationship between polymer structure and degradation kinetics. This becomes especially critical in multiphase polymers like heterophasic copolymers, thermoplastic elastomers and blends. This review should stimulate research in this important area, which could ultimately lead to polymers with better photo-thermal and radiation resistance as well as more effective stabilizers. 

The mechanisms of the thermal and photochemical degradation of poly(vinyl chloride) (PVC) continue to be active areas of research in polymer chemistry mainly because its high chemical resistance, comparatively low cost and wide variety of application m e PVC one of the most widely used thermoplastic materials. The wide variety of forms which the material can take includes pastes, lattices, solutions, films, boards and moulded and extruded pieces and depends to a very large extent on the good electrical and mechanical properties of the polymer. In spite of these advantages the even wider application of the material has been restricted by its low thermal and photochemical stability. Thermal instability is a problem since processing of the polymer is carried out at about 200 C and the photochemical instability places a limit on the extent of the outdoor applications which can be developed. 

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