ABSTRACT
There are two main methods of polymers thermooxidative degradation inhibition by antioxidants [1]. First of them assumes desactivation of oxidation intermediate products accelerating the chain process of polymer degradation (chain inhibition): R • +JnH —» RH + Jn • , (4.1)
where R* are active centers, JnH is nonchain antioxidant.The second stabilization method is connected with desactivations of substances participating in any reaction resulting to polymer degradation (nonchain inhibition): A + Z - » inert product, (4.2)
where A is chemical agent causing degradation, Z is nonchain antioxidant (acceptor of A).The successful usage as nonchain antioxidant (inhibitor) of highly-dispersed mixture Fe/FeO, obtained at thermal decomposition of iron oxalate, predetermines detail research of stabilization mechanisms [2]. At the same time it was ascertained, that the mixture Fe/FeO (Z) is an effective modificator of polymer structure, that defines to a considerable extent stabilization efficiency. Below these structural effects will be considered more detailed. 4.1. THE STRUCTURAL CHANGES CAUSED BY INTRODUCTION OF THE HIGHLY-DISPERSED MIXTURE Fe/FeO
The introduction in semicrystalline polymers of highly-dispersed mixture Fe/FeO (Z) small contents results to essential changes of these polymers structure and properties [2-5]. Table 4.1 illustrates these changes of compositions HDPE+Z properties on the example of impact toughness Ap, stability to the cracking in aggressive environments and coefficient of gas permeability under nitrogen PN . It is quite obvious, that such consider able changes of the mentioned (and the number of other) properties [6] assume corresponding structural changes of compositions HDPE+Z in com
As can be seen, to extreme properties change, pointed in Table 4.1, the minimum values of AH and Tm at Cz=0.05 mass. % correspond. This observation assumes crystallites size decrease at pointed Z concentration [8]. The data of electron microscopy confirm this conclusion. In Fig. 4.2 the electron micrographs of samples of initial HDPE and compositions HDPE+Z, subjected to chemical etching, are adducted which clearly illustrate the studied samples of morphology change.
