Polycaprolactone-based biodegradable acrylated polyurethanes: Influence of nanosilica amount on functional properties

Abstract A series of nontoxic acrylated waterborne polyurethane/silica hybrid composites were synthesized from 1,6-hexamethylene diisocyanate (HDI), polycaprolactone diol (PCL), dimethylolpropionic acid (DMPA), a mixture of 3-aminopropyltriethoxysilane (APTES) and 2-hydroxyethyl methacrylate (HEMA) as chain extender. To control crosslink density the mono-functional HEMA was incorporated into the biodegradable polyurethanes. Different amounts of nanosilica were incorporated into acrylic-based polyurethanes to prepare polyurethane/silica hybrid composites. The structures of the acrylated waterborne polyurethane/silica hybrid composites were characterized by Fourier-transform infrared spectroscopy (FTIR), 1H NMR,13C NMR analysis and scanning electron microscopy (SEM). The effect of the amount of nanosilica on the thermal properties of polyurethane nanocomposite films was investigated by means of thermogravimetric analysis (TGA) and differential scanning calorimetry (DSC). Wide-angle X-ray scattering (WAXS) was used to investigate the degree of crystallinity of PCL as a soft segment into polyurethane hybrid composites. It is established that all samples containing PCL as a part soft segment with different silica loading are crystallisable polymers. The results from WAXS analysis have shown that the highest degree of crystallinity (37%) is reached in polyurethanes based on 1 wt% content of Aerosil OX50. The highest crystallization enthalpy (ΔHc) value for the sample with 1% nanosilica was 9.77 J/g confirmed by DSC analysis. The decrease of crystallinity of the PCL soft segment in polyurethanes indicates that the restriction of the crystallization of the PCL soft segment depends on the silica content. The incorporation of nanosilica into waterborne polyurethanes increases the thermal stability of the hybrid composite films. It was found that greater thermal and mechanical properties of waterborne polyurethane-silica hybrid composites were obtained due to a condensation process between triethoxysilane groups in the side chains of polyurethane molecules and silanols group on the surface of nanosilica.