Investigating the physicochemical property changes of plastic packaging material exposed to UV radiation

Global plastic production is increasing, and as a consequence more waste is generated and released into the environment.Oceanic weathering factors such as ultraviolet (UV) radiation, temperature, and salinity result in the degradation of these plastics and subsequent formation of microplastics (MPs).These MPs in-turn pose a specific threat to ecosystems and their respective inhabitants.This study aimed to evaluate UV induced degradation of conventional packaging material made of polypropylene (PP) homopolymer and amorphous poly(ethylene terephthalate).Plastic sheets were prepared into four different shapes: small circles (6 mm dia.), large circles (12 mm dia.), small rectangles (8x4 mm), and large rectangles (40x10 mm).Sequential degradation was considered with samples initially degraded solely by UV radiation in air.The experiments were conducted in a UV chamber that offered two levels of irradiance exposure: 65 W/m 2 and 130 W/m 2 .After the initial degradation in air, samples were further exposed to either constant temperatures (25C or 60C) or cyclic UV conditions (65 W/m 2 or 130 W/m 2 ) while immersed in different aqueous solutions (demineralised water or seawater).Each experimental run commenced for six weeks, and samples were drawn and analysed fortnightly.The physicochemical properties monitored over time were mass, crystallinity, microhardness, and chemical functional groups (carbonyl and hydroxyl).These properties were measured via standard analytical techniques such as precision balance, differential scanning calorimetry (DSC), Vickers microhardness tester, and attenuated total reflectance-Fourier transform infrared (ATR-FTIR) spectroscopy.Results from the initial experiments indicated that UV irradiance proportionally instigated changes in plastic properties.Increased mass loss accompanied by considerable increases in carbonyl index was observed for the PPs.Shape did not significantly affect mass loss or functional group developments.Clear polypropylene (CPP) reflected the most severe degradation, resulting in the most considerable mass loss, increase in crystallinity, and highest carbonyl content.Overall PPs degraded more than PET; differences were mainly attributed to alternative compositions, with PP having high frequencies of tertiary carbon atoms whilst PET contained stabilising aromatic rings increasing its stability towards photo-oxidative degradation.The peak wavelength sensitivity of PP also almost exactly corresponded to the peak wavelength intensity of the UV lamps used in this investigation.Furthermore, it was suspected that black polypropylene (BPP) contained a UV absorbing additive (carbon black) responsible for shielding its interior from radiation by terminating free radical reactions and converting energy to heat.