Thermo-oxidation destruction

Thermo-oxidative destruction behaviour of the grafted rayon fabrics. 

We shall consider only some results of investigation of complex polymer systems by method of EPR-spectroscopy obtained recently (results obtained earlier were considered in details in works [2, 3]). We shall discuss possibilities of method of EPR-spectroscopy of spin marks and probes for determination of macromolecules conformation in solid state, and also the results of investigation of molecular dynamics and organization of micelle systems -complexes polyelectrolyte-SAS. We shall also discuss some results obtained with the use of method of EPR-spectroscopy and its modification - the method of EPR-tomography for revealing of particularities of spatial distribution of active sites resulted from process of thermo-oxidative destruction of solid polymers. 

Concentration profile of nitroxyl radicals resulted from thermo-oxidative destruction of other polymer - ethylene copolymer with propylene is presented in Figure 9b. In this case maximum concentration of nitroxyl radicals is observed not on the borders but in the center of sample the process of thermo-oxidative destruction proceeds mainly in sample depth [49],... 

Figure 9. Distribution of nitroxyl radicals concentration by thickness of sample underwent thermo-oxidative destruction at 120°C a - poly(acrylonitril-butadiene-styrene (ABS) copolymer), thickness of sample is 3,8mm b - polypropylene copolymer with polyethylene, thickness of sample is 3,4mm. The inset is the example of EPR-spectrum of nitroxyl radical in ABS-copolymer.

It is strongly advisable for formulations of inhibited plastics to make allowance for the effect the Cl exerts on the polymer binder properties during processing and service life of the final products. Some Cl may activate thermo-oxidative destruction and atmospheric aging of polymers, while others vice versa, are able to retard these adverse processes. 

Antioxidants improve the stability of plastics to oxygen. Such substances as oxygen acceptors (fine-dispersed metals and oxides of transient metals of lower valence) break the chains of radical reactions on thermo-oxidative destruction of pol miers or destroy intermediate products of these reactions. 

Aromatic polysulfone on the basis of bisphenylolpropane is relatively stable to thermo-oxidation destruction, because the sulfur is in its highest valence state in such polymers electrons of adjacent benzene nuclei shift, under the presence of sulfur, to the side of sulfogroups what causes the resistance to oxidation. 

At effective inhibition of the ester-t3pe plasticizers oxidation by oxygen of air the rate of PVC thermo-oxidative destruction in their concentrated solutions is getting closer to the rate of polymer s disintegration, what is characteristic for its thermal destruction at plasticizer s (solvent s) presence, i.e., slower, than PVC s desintegration without a solvent. This occurs due to a structural - physical stabilization. In these cases an inhibition of reaction of the solvent s oxidation at use of echo - type stabilizers - antioxidants causes PVC s stabilization (Fig. 5, curve 5). This fundamental phenomenon of PVC s stabilization in a solution at its thermo-oxidative destruction has received the name of an echo - stabilization of PVC [2, 15, 16],... 

In the conclusion it is possible to ascertain, that high efficiency synthesized phosphor organic compoimds in quality inhibitors thermo oxidation destruction aromatic the block-copolyesters is established - the appreciable effect is observed at the contents of these compounds in compositions in quantity up to 1,0 %. 

Fig. 26, Induction period of the thermo-oxidative destruction of polypropylene stabilized by mixtures of SAG-6 and pyro-catechol phosphite with ionol. Summary concentration of the stabilizers 0.015 mole/kg T = 200 C Pq = 200 mm Hg.

Hindered amine which formula is presented below is introduced into polymer. As a result of amine reaction with peroxide radicals formed during polymer oxidation process (Scheme 5) stable nitroxyl radicals are formed. Nitroxyl radicals may be formed only at those parts of polymers where there are peroxide radicals, i.e. process of thermo-oxidative (or photo-oxidative) destruction proceeds. Then one determines spatial distribution of nitroxyl radicals through the sample and so, it becomes possible to identify those regions of polymer in which oxidation reaction proceeds. 

The results of thermal destruction of polysulfone in vacuum have revealed that the first product of decomposition at 400°C was the sulfur dioxide there are also methane and bisphenylpropane in products of decomposition at temperatures below 500 °C. Therefore, the polysulfone is one of the most stable to thermo-oxidation thermoplasts. 

Figure 5. Echo -stabilization of PVC. Ebmination of HCl during thermo- (argon) (1,2) and thermo-oxidative (air) (3 - 5) destruction of PVC in solution of dioctyl sebacinate 1-4 unstabilized PVC, 5 - PVC, stabilized with diphenylpropane (0.02 wt. %) - echo stabilization 2,4 - PVC with no solvent 448 K.

Method of EPR-tomography developed in the Institute of Chemical Physics of RAS [46] allows both detecting of molecular mobility and its change at thermo- or photo-destruction of polymer in various points of sample and registration of the distribution of oxidation active sites through the sample. This method allows identification of polymers parts in which destruction process proceeds. Solution of this problem is of great importance for selection of conditions of polymer materials exploitation. 

---