Photooxidative Destruction of Composites Based on Polyethylene and Montmorillonites Modified with Transition-Metal Salts

Abstract

Metal-modified montmorillonites containing Ni2+, Co2+, Fe3+, Mn2+, and Cu2+ions are synthesized by interacting layered aluminosilicates Na+-montmorillonite and Cloisite 25A with transition-metal salts. The organomodified Cloisite 25A is saturated with ions of heavy metals Ni, Co, and Fe, retaining the organic modifier. The composition and structure of metal-modified aluminosilicates are studied by X-ray powder diffraction, X-ray fluorescence analysis, and FTIR spectroscopy. Montmorillonites of different degrees of intercalation are obtained depending on the particular transition-metal ion and silicate type. It is shown that metal-modified aluminosilicates being involved in the composition of LDPE-based composites considerably increase the rate of photooxidation of the polyethylene matrix. FTIR studies of the initial and irradiated films suggest that the photooxidation of polyethylene is accompanied by the formation of diverse oxygen-containing and unsaturated groups. According to the calculated carbonyl and vinyl indices, it is demonstrated that the efficiency of oxidation activation under UV irradiation depends on the particular transition metal and increases in the sequence Na < Co < Ni < Cu < Mn < Fe. The introduction of an iron-containing filler decreases the time of polyethylene matrix photooxidation by five to seven times. The irradiation of polyethylene films containing Fe-MMT and Mn-MMT for 250 h leads to the full loss of physicomechanical properties and destruction of the polymer. The activity of Cloisite 25A modified with transition-metal salts in sensitizing photochemical processes is higher than that of the fillers obtained by modification of Na+‑MMT; in this case, there is no destruction of the samples.