Novel waterborne poly(urethane‐urea)/silica nanocomposites

Abstract

A series of novel transparent mechanically strong waterborne poly(urethaneurea)/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.

Efficient Physical Mixing of Small Amounts of Nanosilica Dispersion and Waterborne Polyurethane by Using Mild Stirring Conditions

“…In order to allow an adequate dispersion into the PUD, the nanosilica particles in the aqueous dispersion should be separated and the most literature [ 30 , 31 , 32 , 41 ] have proposed severe mechanical stirring. However, in this study, a mild mechanical stirring of the aqueous nanosilica dispersion and the PUD was used, combined with the addition of small amounts (0.1–0.5 wt.%) of nanosilica.…”

“…The influence of the addition of the nanosilica dispersion to the waterborne polyurethane on its adhesion properties is not clear in the existing literature. Both increased adhesion [ 29 , 31 , 33 ] and decreased adhesion to different substrates [ 21 ] of silica–waterborne polyurethanes have been shown, the increased adhesion was related to the existence of interactions between the nanosilica and the polyurethane, and to the extent of the nanosilica agglomeration.…”

“…There are some previous studies dealing with the addition of different amounts of distinct nanosilica aqueous dispersions to PUDs by physical mixing [ 30 , 31 , 32 , 33 , 34 , 35 ]. Yang et al [ 30 ] added 20 and 50 wt.% colloidal nanosilica to a polyester-based PUD by mechanical stirring and they reported the agglomeration of the nanosilica particles caused by the interactions between their silanol groups.…”

“…However, improved thermal and mechanical properties of the PUD+nanosilica materials were found. Špírková et al [ 31 ] mixed a PUD with up to 50 wt.% aqueous nanosilica of 30 nm particle size by mechanical stirring, followed by treatment in an ultrasonic bath. Although the PUD properties were enhanced, the mixing method was not efficient for dispersing the nanosilica particles and micrometer-size silica aggregates appeared.…”

Effect of fillers on the microphase separation in polyurethane composites: A review

“…Among the commonly used inorganic fillers, SiO 2 nanoparticles have the advantages of small particle size, large specific surface area, high hardness, low refractive index, and commercial availability 29–31 . SiO 2 nanoparticles can improve PU's mechanical properties, thermal stability, shape memory behavior, and gas permeability 32–34 . Many studies have shown that the silanol (Si‐OH) groups on the SiO 2 surface affect the microphase separation of PU/SiO 2 composites because these groups may interact with HSs or SSs of PU matrix 10,13,29,31,35 …”