Abstract
Abstract The paper deals with surface properties modifications of cryogels based on poly(vinyl alcohol) and cellulose during exposure to several doses of ultraviolet (UV) irradiation. Significant color changes were observed during UV exposure. The cryogels exhibited a fading trend with irradiation dose increase. Structures accumulated instable red chromophores and exhibited a yellowing tendency. The ultraviolet–visible (UV–vis), X-ray photoelectron spectroscopy (XPS) and Fourier transform infrared (FTIR) spectra indicated important structural modifications during irradiation. The cryogels followed a complex photodecomposition mechanism through random macromolecular chain scissions accompanied by decarbonylation and photooxidation with carbonyl and carboxyl groups accumulation. Hydroperoxides, which were confirmed by an iodometric method, acted as important initiating sites. Cellulose chains were photochemically protected by poly(vinyl alcohol) up to a concentration of 70% in the cryogels, after which phase separation phenomena occurred as demonstrated by scanning electron microscopy technique (SEM), thus ending the protective effect of PVA. The major evolved volatile compounds during cryogels photodecomposition were identified by means of mass spectrometry (MS) and were the following: acetic acid, acetone, 2-propenal, propanoic acid, butanoic acid and ethyl methyl ketone.
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