Mechanical properties thermal degradation

Keywords polyoxymethylene, polyurethane, montmorillonite, nanocomposite, mechanical properties, thermal degradation. 

One of the main interests of the polymer chemist is to develop new polymers that have good mechanical properties at high temperature and to improve the thermal stability of existing polymers. Extensive studies of the mechanism of thermal degradation of the presently available macromolecules are very helpful in this field. 

Polyhydroxyalkanoates, Polyhydroxybutyrate, History, Bacterial synthesis. Chemical synthesis. Genetic engineering. Mechanical properties. Thermal transitions. Crystallization, Plasticizers, Thermal degradation. Processing, Applications... 

Carrasco, E., Pages, P., Gamez-Perez, J., Santana, O.O., Maspoch, M.L. Processing of poly (lactic acid) Characterization of chemical structure, thermal stability and mechanical properties. Polym. Degrad. Stab. 95, 116-125 (2010)... 

Nylon-6, thermal degradation of n. When exposed to elevated temperatures, immod-ified nylons undergo molecular weight degradation, which results in loss of mechanical properties. The degradation process is highly time-temperature dependent. 

Poly(phenylene oxide) (PPO) is a thermoplastic, linear, noncrystalline polyether commercially produced by the oxidative polymerization of 2,6-dimethylphenol in the presence of a copper-amine catalyst. PPO has become one of the most important engineering plastics widely used for a broad range of applications due to its unique combination of mechanical properties, low moisture absorption, excellent electrical insulation property, dimension stability and inherent flame resistance. This chapter describes the recent development of this polymer, particularly on the production, application, compounding, properties of its alloys and their general process conditions. The polymerization mechanism and thermal degradation pathways are reviewed and new potential applications driven by the increasing environmental concerns in battery industry, gas permeability and proton-conducting membranes are discussed. 

There is one characteristic that heavily limits the use of PLLA for commercial applications and that is the low crystallization rate. This results in a mostly amorphous product after processing. The minimum crystallization half time, t, for pure PLLA is of the order of several minutes, this is an extremely long time since the cooling time after the general processing methods is around 1 s. It has been described that the mechanical properties and degradation kinetics of the semi-crystalline PLLA are different from those of completely amorphous PDLLA. Mechanical and thermal properties of PLLA become almost constant when its molecular weight is above a threshold value of 70,000 Da (10). 

Structural concepts for tissue-compatible and biodegradable polymers, thermoplastic elastomers, and thermosets with shape memory capabilities will be introduced. Their thermal and mechanical properties and degradation behaviour will be explained. An important precondition for the shape memory effect of polymers is elasticity. An elastic polymeric material consists of flexible segments, so-called network chains, which are connected via netpoints or junctions. The permanent shape of such a polymer is determined by the netpoints. The network chains take a coil-like conformation in unloaded condition. If the polymer is stretched, the network chains become extended... 

Light radiation increases the brittleness of polyolefins and seriously lowers their physical properties, mainly mechanical properties. Such degradation is more pronounced in the presence of oxygen. All modifications produced by photo-oxidative degradation are similar to those produced by thermal degradation and, are accelerated by an increase in light intensity [19] and temperature [20]. 

The mechanism of thermal degradation is also directly related to the amount of oxygen present in the immediate environment as well as the presence of oils, chemicals or steam. When silicone elastomers are heated above 200 °C in close confinement, polymer reversion may result in softening and a loss of elastomeric properties. Usually this effect can be... 

The gel-based products have traditionally been the most expensive and highest performance activated alumina products. They have very good mechanical properties, high surface area, and their purity and ganima-aluniina stmcture make them somewhat resistant to thermal degradation. On the other hand, they are the most difficult to manufacture and disposal of by-product salts can present an environmental problem. 

---