Study of the effect of photooxidative processes on the surface morphology and physico-mechanical characteristics of biodegradable materials based on secondary polypropylene and chalk additives

When processing and operating polymer materials under the influence of environmental factors (ultraviolet radiation, moisture, oxygen, ozone, etc.), a change in their properties is often observed. This research is devoted to the study of the effect of chalk additives on morphology and topography, as well as the physical and mechanical properties of samples based on recycled polypropylene raw materials after exposure to UV radiation in air. In order to confirm the occurrence of photo oxidative processes, the data of two methods were used: modified iodometric analysis and IR spectroscopy. The physical and mechanical properties of polymer composites before and after photo aging were determined on standard 1 mm thick blades. To study the surface changes of experimental polymer composites under the influence of ultraviolet radiation, atomic force microscopy was used. The result of the experiment is the proof that the chalk additive interferes with the intensive course of photo-oxidative degradation. In general, the introduction of a chalk additive in a small amount (2 to 10 weight parts) allows maintaining the strength characteristics of composites based on recycled polypropylene raw materials after exposure to UV radiation in air, probably because of crosslinking of macromolecules due to the intermolecular interaction of hydro peroxide groups accumulated by the polymer, as well as involving only surface layers of composite samples in the photo oxidation process. Moreover, the analysis of AFM images of samples subjected to ultraviolet irradiation for 18 hours shows that the surface becomes smoother. This is confirmed by the calculation of the root mean square roughness and the maximum height of the roughness. Further irradiation for additional 18 hours leads to an increase in roughness, which indicates a change in the supra molecular structure in the surface layers of polypropylene as a result of photo oxidative transformations. Therefore, from the obtained composites, one can expect the maintenance of operational characteristics during the period of consumption, followed by decomposition under the influence of environmental factors.