Original Investigation into the Molecular Mechanisms of Photodegradation of Polyolefin Films Under Nigerian Solar Irradiance Conditions and Development of Stabilisation Strategies

Nigerian agricultural and packaging industries deploy large volumes of polyolefin films in environments characterised by high solar irradiance values significantly exceeding those of temperate regions for which most commercial stabilisation systems are designed. This research conducts an original investigation into the molecular mechanisms of photodegradation of low-density polyethylene and polypropylene films under Nigerian solar irradiance conditions, establishing structure-reactivity relationships and developing optimised stabilisation strategies for tropical deployment. Solar irradiance and UV spectral distribution were measured at six sites across Nigeria's geopolitical zones over 24 months, providing irradiance input data for accelerated photodegradation protocol design. Photodegradation mechanisms were investigated using ESR spectroscopy to track radical species formation and evolution, FTIR spectroscopy for carbonyl and hydroxyl group development, and gel permeation chromatography for molecular weight distribution changes as functions of irradiance dose. Quantum yield for chain scission and crosslinking reactions were determined from kinetic analysis of molecular weight data. Stabilisation strategies investigated include hindered amine light stabiliser concentration optimisation, UV absorber combinations, antioxidant synergist pairs, and novel nano-TiO2 UV screening incorporation. Outdoor weathering data at Lagos and Maiduguri sites validated accelerated laboratory protocols and stabilisation performance. Results demonstrate that Nigerian solar irradiance produces polyolefin photodegradation rates 2.3 to 3.1 times higher than equivalent irradiance doses from Northern European standard weatherometers due to higher UV-B proportion in tropical solar spectra. Quantum yield for chain scission averaged 1.8 times 10^-6 mol/einstein for low-density polyethylene under Nigerian spectral conditions. Optimal stabilisation was achieved by ternary hindered amine light stabiliser/UV absorber/antioxidant systems, extending service life by 340 percent relative to unstabilised films. The research provides a scientific basis for reformulating polyolefin film stabilisation packages for Nigerian climatic service conditions. Keywords: polyolefin photodegradation, UV stabilisation, solar irradiance, tropical climate, Nigeria