Polyurea spray coatings: Tailoring material properties through chemical crosslinking

Abstract

Among the many desirable properties of polymeric coatings, the most important include ease of application, rapid cure time, adhesive properties and excellent mechanical properties. In this context, spray coated polyureas are finding increasing applications in niche areas that otherwise pose considerable challenge to the traditional coating chemistries. In this work, we demonstrate the effect of introducing chemical cross-linking on the mechanical, thermal and structural properties of spray coated polyurea. A long chain trifunctional amine was introduced as a co-reactant in the resin blend, the amount of crosslinker being varied from 0 to 3.5 mol % (crosslinking density 28–180 mol/m3, affine network model). The mechanical properties of spray coated polyurea films, both in quasi-static as well as dynamic conditions were determined. Physically crosslinked polyurea coatings (in the absence of chemical cross-linking) exhibited tensile strength ∼ 7.4 ± 0.7 MPa and elongation of 121 ± 3.7%. Introduction of long chain amine led to an improvement in these characteristic properties till maxima at 2.2 mol%, subsequent to which both strength and elongation decreased. Chemical cross-linking led to restraining of the segmental motions reflecting in terms of increased glass transition temperature, as evidenced by dynamic mechanical analysis and differential scanning calorimetry. The chemical resistance of polyurea also improved substantially due to crosslinking, which reflected in terms of decreased swelling ratio in different organic media.