Deterioration of polymers

Since most chemical reactions if carried to completion will result in deterioration of polymer properties, it is desirable to be able to ensure that all of the energy is dissipated in photophysical processes and to eliminate the photochemical reactions. However, in some cases, such as in the manufacture of photographic resists, it is desirable to maximize the photochemical effects. The polymer chemist is particularly concerned with the problem of how the relative efficiency of these various processes may be affected by the polymeric nature of the molecules he uses. 

The degree of polymer crystallinity, which characterizes the share of regularly packed molecules is estimated by the intensity of dispersion in maximum 1 m. Some differences connected with introduction of a dye are observed, namely intensity of dispersion is a bit lower both along the equator and meridian. This speaks about the fact that introduction of the additive leads to the decrease of a number of reflective planes (decrease of reflection centres), which, in its turn, is connected either with deterioration of polymer crystalline stmcture or with rotation of reflective planes. 

Deterioration of polymers, PO in particular, resulting from y- or other high-energy irradiation, takes place in diverse areas of their application. This includes controlled modification of polymers for industrial purposes, use of polymers in some radiation exposed parts of nuclear reactors and radiation sterilization of food packaging materials or of equipment and materials for medical uses. Radiation-induced primary free radicals result from either the scission of the main chain... 

This report deals with dynamic processes of the deterioration of polymers often used as paints and finishes in housing, and also refers to their influence as the reduction in protective performance on the durability of reinforced concrete. The deterioration processes of polymers by the simiiltaneous action of ultraviolet (UV) light and diffusive oxygen is explained theoretically based upon unsteady state dynamics. The parabolic law (/t" law) is derived for a typical path for the progress of the deterioration of polymers inwards from the surface (l), and compared with some experimental data. The same parabolic law involving a constant term was also derived for the carbonation of concrete, which well explains the retardation effects of finishes on the carbonation (2). 

Degradation of Polymers. From the results of dynamic analysis, the degree of the deterioration of polymers varies with time and the depth from the surface, and is influenced by the photochemical reaction constants (ki, k2) and diffusion coefficient (D.). Figure 9 shows the theoretical result of the influence of photo-oxidation on the distribution of oxygen in polymers. Deriving the time dependence of surface deterioration, we obtain equation 13. 

Electron spin resonance (ESR) spectroscopy has been used in polymer science for half a century. Two major areas have been investigated. One is the study of mechanisms of chemical reactions in polymerization and the effects of radiation. Intermediate species such as neutral and ionic radicals produced by exposure to ionizing radiation and ultraviolet light, mechanical fracture, deterioration of polymers and polymerization of monomers have been identified. Many kinds of reactions such as decay and conversion of the free radicals to different species, have also been observed. 

B-1) Assignment of unstable free radicals produced by irradiation of polymers with ionizing radiation and ultraviolet light, mechanical fracture, and deterioration of polymers and polymerization. 

Mechanism of deterioration of polymers by auto-oxidization (B-3) Mechanism of free radical type polymerization by grafting initiators (B-4) Diffusion controlled reaction of free radical decay in solid polymers... 

To date, various block copolymers have been produced using biological systems. This includes poly(3HB-fo-4HB) [17], P(3HB)-f>-poly(3-hydroxyvalerate-co-3-hydroxyheptanoate) [18], PHB-f -poly(hydroxyhexanoate) [19], poly 3HB-fc-poly(3-hydroxyheptanoate) [P(3HP)] [20], P(3HP)-f -poly(4-hydroxybutyrate) [P(4HB)] [21], poly(3-hydroxyhexanoate)-fe-poly(3-hydroxydecanoate)-co-[3-hydroxydodecanoate (3HDD)] [22] and poly[3-HDD-f -poly(3-hydroxy-9-decanoate)] [23]. These studies were motivated by the fact that although random copolymers, such as poly(3HB-co-3HV) and poly(3HB-co-4HB), exhibit useful mechanical and thermal properties they suffer from a deterioration of polymer properties due to the effect of ageing. It was found that all block copolymers exhibited improved properties compared with the two relative homopolymers, random and blend polymers. Various... 

The deterioration of polymer properties by ESC has been studied for several decades. But the actual mechanism is not certainly established (Hansen 2002). It is believed that in the presence of the stress, the active fluid causes local plasticization that generates crazes and eventually catastrophic cracks. The ultimate result in many cases is brittle fracture, even in normal ductile polymers like polyethylene, ABS, and polycarbonate. Since failure by ESC can be induced by environmental fluids like cleaning agents and lubricants and the mechanical stress can be the residual (molded-in) stresses, it was considered to be a silent killer (Sepe 1999). 

W.L. Hawkin in Environmental Deterioration of Polymers in Polymer Stabilization, Ed., W.L. Hawkin, Wiley Interscience, New York, NY, USA, 1971. 

Thermogravimetric Analysis - The thermogravimetric analysis of polyurethane microcapsules (without monomer) - Figure 13, presents a decreasing in weight (above 200°C) due to the deterioration of polymer. Therefore, this polymer is not a good candidate as well to encapsulate healed agent for aerospace applications. 

The additional chromophores, hydroperoxides or carbonyl groups are created during chain propagation in all types of HPD mechanisms proposed they may give rise to the initiation of new chain reactions upon prolonged irradiation and thus to rapid deterioration of polymers. 

Microorganisms are involved in the corrosion of metal and the degradation and deterioration of polymers, concrete, and stone under both aerobic and anaerobic conditions. They may influence the surface electrochemical properties, resulting in corrosion of metals under aerobic conditions, and induce hydrogen embrittlement by microbial production of hydrogen. Indirectly, degradation and deterioration of metals, stone, and concrete are... 

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