Polymer degradation ozone

Antiozonants (qv) prevent or reduce polymer degradation by the active ozone molecule. Some antioxidant compounds, such as the /)i7n7-phenylenediamines, are excellent as antiozonants (36). The protection by these compounds is thought to be either a reaction with the ozone before it can react with the surface of the mbber or an aid in reuniting chains severed by ozone (37). 

This reaction is very exothermic (A// —180 to —200kJ mol-1) and, therefore, seems to be very probable from the thermochemical point of estimation. The pre-exponential factor is expected to be low due to the concentration of the energy on three bonds at the moment of TS formation (see Chapter 3). To demonstrate that this reaction is responsible for the oxidative destruction of polymers, PP and PE were oxidized in chlorobenzene with an initiator and analyzed for the rates of oxidation, destruction (viscosimetrically), and double bond formation (by the reaction with ozone) [131]. It was found that (i) polymer degradation and formation of double bonds occur concurrently with oxidation (ii) the rates of all three processes are proportional to v 1/2, (iii) independent of p02, and (iv) vs = vdbf in PE and vs = 1.6vdbf in PP (vdbf is the rate of double bond formation). Thus, the rates of destruction and formation of double bonds, as well as the kinetic parameters of these reactions, are close, which corroborates with the proposed mechanism of polymer destruction. Therefore, the rate of peroxyl macromolecules degradation obeys the kinetic equation ... 

Some authors took advantage of the reactivity of polymers with ozone to recycle some peculiar plastic wastes coming from different origins. In this way, Fargere [155, 156] succeeded in degradation of cross-linked ethylene-vinyl acetate copolymers used in the production of sport shoes. This operation was achieved on grinded industrial wastes in suspension in CC14. In a second... 

BQDI 53 is the principal product of both sacrificial and depleting transformations of PD in model hydrocarbons, PO and rubbers and is formed via oxidation with ROO , oxygen, ozone, ozonides, organic peroxides or ions of transition metals. BQDI have therefore been found in PD doped polymers degraded under various conditions [3-5,58]. They are formed in high preparative yield by oxidation with femcyanide and also result in interactions of PD with some rubber chemicals, e.g, with benzothiazolyl-2-sulfenemorpholide. 

In the presence of oxygen or ozone, as soon as free radicals form, oxygenation of the radicals gives rise to peroxy radicals, which through a complex series of reactions result in polymer degradation. Oxidative degradation may occur at moderate temperature (thermal oxidation) or under the influence of ultraviolet radiation (photooxidation). Unsaturated polyolefins are particularly susceptible to attack by oxygen or ozone (Equation 9.6). 

The study of the polymer degradation is complicated by their structural peculiarities on molecular and supramolecular level and diffusion effects. It is difficult to find simple model reactions for clarification of particular properties and for the express examination of the proposed assumptions. An exception, in this respect, is the ozone reaction with C=C bonds, whose mechanism has been intensively studied and could be successfully applied upon ozonolysis of polymeric materials [28]. 

While this type of experiment has never been reported, it can provide unique and useful information. For instance, it can be useful in determining the effects of slightly increased levels of UV radiation in sunlight on its potential for increased polymer photodegradation. Levels of UV-B in terrestrial sunlight are expected to increase as a result of the partial depletion of the stratospheric ozone layer. The effect of this spectrally altered, UV-B-rich sunlight on polymer degradation can also be ascertained from activation spectra, subject to several assumptions mentioned earlier. 

Radhakrishnan, C., Alex, R., Unnikrishnan, G., Thermal, ozone and gamma ageing of styrene butadiene rubber and poly(ethylene-co-vinyl acetate) blends. Polymer Degradation and Stability 2006,91,902-910. 

Golczak, S., Kanciurzewska, A., Langer, J.J., and Fahlman, M. (2009) Degradation of microporous polyaniline film by UV-ozone treatment. Polym. Degrad. Stab., 94 (3), 350-354. 

W. Czerwinski, J. Nowaczyk and K. Kania. Ozonization of electronic conducting polymers. I. Copolymers based on poly[3-nonylthiophene]. Polym. Degrad. Stab. 80(1), 93-101 (2003). 

Anachkov, MP, Rakovsky, SK, Stefanova, RV and Shopov, DM, Kinetics and mechanism of the ozone degradation of nitrile rubbers in solution. Polymer Degradation and Stability, 19, 293-305 (1987). 

Basiuk, V. A. Organic reactions on silica surface Synthetic applications. Uspekhi Khimll, 1995, 64(11), 1073-1090 Cataldo, R. Rosati, A. Lilia, E. Ursini, O. On the action of ozone at high concentration on various grades of polyethylene and certain straight chain paraffins. Polymer Degradation and Stability, 2011, 96(5), 955-964. 

Razumovskii SD, Zaikov GY (1982) Effect of ozone on saturated polymers. Polymer Sci USSR 24(10) 2305-2325 Roy PK, Surekha P, Rajagopal C, Chatterjee SN, Choudhary V (2005) Effect of benzil and cobalt stearate on the aging of low density polyethylene films. Polym Degrad Stabil 90(3) 577-585 Scott G (1981) Mechanism of polymer stabilization. In Scott G (ed) Developments in polymer stabilization, 4th edn. Applied Science, London, pp 276-289... 

An examination of the stability of the model 1,2,4-trioxolane 107 pointed to the crucial role of ozone in promoting polymer degradation (13PCCP16428). Trithiole-fused phthalocyanines 108 and related compounds have been synthesized (13H(87)245). 

The performance of polymer artifacts is adversely affected if degradation occurs during the various stages of polymer manufacture, fabrication, and subsequent exposure to the environment. Molecular oxygen is the major cause of polymer degradation and is responsible for the ultimate mechanical failure of polymer artifacts. The deleterious effect of molecular oxygen is accelerated by many other factors sunlight heat ozone atmospheric pollutants water mechanical stress adventitious metal and metal ion contaminants. 

Gugumus F. Novel role for tropospheric ozone in initiation of autoxidation. Polym Degrad Stab 1998 62 403-6. 

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