Abstract
Waterborne polyurethane (WPU) with high solid content (45%) was obtained by utilizing dimethylol propionic acid (DMPA) and ethoxylated capped polymeric diol as complex hydrophilic groups. Alkyl-grafted silica was incorporated into polymer matrix through in situ polymerization to improve the performance of coatings casted from WPU dispersions. The addition of alkyl-grafted silica enlarged the particle size distribution whilst increased emulsion viscosity, which showed little influence on attainment of high solid content for WPU. The properties of obtained WPU/Silica coatings were investigated. Results showed that the functionalized surface of silica provides good compatibility with the WPU matrix, which promoted the homogeneous dispersion of silica particles. This facilitated the formation of nanosized silica papillae on coatings, contributing to surface roughness and hydrophobicity. Solvent resistance of WPU was enhanced with existence of alkyl-grafted silica particles. The WPU/Silica coatings also displayed improved thermal stability due to the thermal insulation ability and tortuous path effect of silica. Besides this, valid interactions between silica and WPU resulted in hybrid microphase of which the synergistic effect imparted superior mechanical properties at relatively low loadings of silica (2%). The facile technique presented here will provide an effective and promising method for preparing WPU hybrids with enhanced performance.
Highlights
Compared with traditional solvent-based polyurethane, waterborne polyurethane (WPU) has the advantages of being non-toxic, non-flammable, and non-polluting to the environment [1]
The results indicate the difference in the dispersive γd and the polar component γp of the WPU/Silica coatings (Table 1)
After addition of alkyl-grafted silica, the average particle size of waterborne polyurethane (WPU) dispersions enlarged whilst the particle size distribution broadened
Summary
Compared with traditional solvent-based polyurethane, waterborne polyurethane (WPU) has the advantages of being non-toxic, non-flammable, and non-polluting to the environment [1]. They have been widely used in leather finishing, automotive painting, fiber processing, coatings, and adhesives [2]. As high viscosity will lead to more burden of production and product handling equipment, conventional WPU usually has a low solid content in the range of 20% to 40%. The low solid content results in inferior drying rates and slower development of adhesion. These shortcomings can be largely overcome by increasing the solid content of WPU [3]. Kim et al [7] have found that high solid content (45%) of WPU can be obtained at a low ionic content (2%) by incorporating the ionic groups to the soft segments
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