Effect of the silica nanofiller on the properties of castor oil-based waterborne polyurethane hybrid dispersions based on recycled PET waste

Abstract

The paper describes the chemical depolymerization of the polyethylene terephthalate (PET) waste from postconsumer soft drink bottles and a search for the way to use this product. The depolymerized oligoester obtained from glycolysis of PET waste using tiethylene glycol was transesterified with castor oil which resulted in the formation of hydroxyl-functional polyester polyol, with hydroxyl value of 391 mg KOH g−1. In the presented paper, series of castor oil-based waterborne polyurethane (CPU)/silica hybrid dispersions were prepared using dimethylolpropionic acid as an ionic center. The polyurethane prepolymers with pendent castor oil groups were prepared first, and then different concentrations of hydrophilic fumed silicas (0, 0.5, 0.75, 1.0 and 2.0 wt%) were added. For waterborne polyurethane dispersions of hydrophilic fumed silica with the surface area (50 ± 15 m2/g) and a primary particle size of 40 nm in the polymer matrix, ultrasound waves were used. The hybrid dispersions were prepared by adding the required amount of triethylamine and water. The molecular structures and mass of glycolyzed PET oligoesters, castor oil-based polyol and castor oil-based polyurethane–silica hybrid dispersions were estimated by FTIR method and gel permeation chromatography.The incorporation effect of SiO2 nanoparticles into the PU matrix on the thermal and mechanical properties of resulting polyurethane films has been examined by Fourier transform infrared spectroscopy (FTIR), thermogravimetry analysis, differential scanning calorimetry (DSC), SEM microscope, and measurement of the coatings properties. The DSC data results suggest that hard segment glass temperature decreases, but mixed-phase glass transition temperature increases with increasing SiO2 content. The FTIR deconvolution result of the degree of phase separation between oxide nanoparticles and hard segment supports to the DSC analysis. The addition of silica oxide caused the increase in the thermal stability. The T10% and T50% of CPU films (the temperatures where 10 and 50% weight loss occurred) increased with increasing the SiO2 content. UV–Vis spectrophotometry showed that introduction of nanosilica particles into polyurethane enhanced the shielding property of obtained films for UV light. The hardness, adhesion, and gloss quality of the polyurethane films were also determined considering the effect of the phase separation and the SiO2 content, so this paper confirmed the suitability of using these castor oil-based waterborne polyurethane/silica hybrid dispersions as new materials with high-performance coatings materials.