Novel waterborne poly(urethane-urea)/silica nanocomposites

A series of novel transparent mechanically strong waterborne poly(urethane-urea)/silica nanocomposites were prepared by mixing a waterborne poly(urethane-urea) dispersion with aqueous nanosilica, followed by slow water evaporation. This procedure is simple, environmentally friendly and energetically undemanding. The silica content in the nanocomposite film varied from 0 to 50 wt%. Based on changes of tensile characteristics, for example, Young's modulus values, three types of behavior were observed: typical elastic (0-10 wt%), plastic (30 wt%) and ceramic-like (50 wt% silica) materials can be prepared. However, some films feature both elastic and plastic (material with 20 wt% silica) or plastic and ceramic-like characteristics (material with 40 wt% silica). The Young's modulus varied from 6 to 705 MPa, and the maximal tensile strength and elongation-at-break were 17.3 MPa and 1270%, respectively. The maximum energy-to-break, 60 mJ mm(-3), was achieved for the film containing 30 wt% silica. All these materials can potentially be used as soft-to-hard topcoats, depending on the specific demands.