Modification of polyvinyl alcohol by ozonated oxidation in an aqueous solution

Abstract

Currently, the task of obtaining polyvinyl alcohol oligomers (PVA) is urgent to create functional materials of a new generation with specified properties. One of the methods of modification of PVS is ozonolysis, which has a number of advantages over other methods of oxidative degradation of polymers. The aim of the work is to evaluate the structural changes and physico–mechanical characteristics of film samples of PVS modified by ozonated oxidation. To carry out the oxidation process, a 5% aqueous solution of PVA brand 1799 was prepared. The ozone-oxygen mixture was obtained using an ozonizer of a known design. The oxidation of PVS was carried out in a glass thermostatically controlled flask at 70 ° C, blowing an ozone-oxygen mixture through an aqueous solution of PVS for 40 minutes. Sampling was carried out after 10, 20 and 40 minutes of oxidation. The films were obtained by irrigation followed by air drying, after which they were subjected to IR spectrometric analysis and strength indicators were determined. As a result of the study, it was found that the modification of PVA brand 1799 by ozonated oxidation in an aqueous medium is accompanied by the following change in IR spectrograms: in the region of 1400 - 1600 cm-1, a sharp decrease in the intensity of the peak corresponding to hydroxyl groups forming hydrogen bonds is observed for ozone-oxidized PVA, in the region of 1650 – 1700 cm-1, a pattern of decrease in intensity is noted the peak with an increase in the oxidation time of PVA with ozone, which indicates a decrease in the MM of the polymer as a result of oxidative degradation, in the region of 3400 – 3600 cm-1 marked a change in the nature of the spectrogram, which also indicates a change in the structure of hydrogen bonds in oxidized PVS; the physico-mechanical properties of film samples subjected to 40-minute ozonated oxidation of PVS change towards a decrease in both strength and elongation at break by an average of 4 times, the Young's modulus decreases by more than 3 times, and the stretching diagram changes character in the zone of highly elastic deformation (the intensity of stress growth decreases by 1.5-2 times as the film elongates during stretching) and the fracture zone (the diagram acquires a stepwise character without a sharp break), which is associated with a decrease in the molecular weight of the PVS, the acquisition of new functional groups, a change in the stereoregularity of the hydroxyl groups of the main polymer chains, an increase in amorphousness and a change in their relaxation time.