Investigation into the Influence of UV Aging on Green Polyurethane/Nanosilica Composite Coatings Based on Transesterified Castor Oil and Palm Oil Isocyanate

Abstract

The current study aims to investigate the influence of UV aging on the properties of green polyurethane (MBPU) and polyurethane/nanosilica composite (MBPU/NS) coatings synthesized from transesterified castor oil and palm oil isocyanate for an exposure period of 1250 h. Changes in the mechanical properties, structural features, morphological and coating properties have been monitored at every 250 h by scanning electron microscopy (SEM), atomic force microscopy (AFM), Fourier transform infrared spectroscopy (FTIR), X-ray photoelectron spectroscopy (XPS) and colorimetry etc. MBPU/NS with 2.5 wt% of NS has been considered to be the optimum composition for a comparative UV aging analysis against neat MBPU. FTIR and XPS analysis revealed changes in chemical structure of MBPU and MBPU/NS-2.5 composite with reduction in –NHCO, C–C, C=O group concentrations. SEM and AFM micrographs indicated increase in roughness parameter with appearance of blisters and cracks on the exposed surface. Mechanical test results showed that UV aging decreases the tensile strength and elongation at break due to chain scission. The yellowness index (ΔYI) follows a systematic increasing trend with increment in irradiation time which indicates photodegradation of polyurethane. However, MBPU/NS-2.5 exhibited lower photo-oxidative degradation which can be due to its high UV absorption ability.