Branched vinyl esters copolymers for high-performance intumescent emulsion coatings

 
Intumescent coatings serve as passive fire protection systems. When exposed to high temperatures, they expand significantly, creating a thermally insulating foam preventing the spread of fire and protecting underlying structures. The viscoelastic properties of polymeric binders significantly impact the foam expansion in intumescent coatings. These organic resins also contribute to char formation. Their chemical structure, that governs their thermal decomposition mechanism, directly influences char formation and efficiency. At elevated temperatures, polyvinyl acetate copolymers undergo an autocatalytic deacetylation reaction, resulting in unsaturated polymer backbones (polyenes) with conjugated carbon-carbon double bonds. These polyenes then experience slower allylic chain scission reactions compared to non-conjugated polymers found in other thermoplastic materials like polyacrylates. Subsequently, slower complete degradation occurs. Kinetics of this process lead to optimal intumescent properties in the case of polyvinyl acetate. To enhance coating performance, co-monomers like ethylene or acrylates can be introduced into the polyvinyl acetate backbone. However, these co-monomers interfere with deacetylation and subsequent allylic chain scission. Research indicates that ethylene negatively impacts the deacetylation process, especially at higher concentrations. Branched vinyl ester comonomers, such as vinyl neodecanoate, however, have been found to efficiently improve overall coating performance. Paint formulations containing these copolymers exhibit excellent intumescence development. Notably, vinyl neodecanoate significantly enhances intumescent properties by improving foam expansion and stability, as demonstrated in our comparative study with waterborne binders of different chemical compositions (vinyl-ethylene, acrylics, and styrene-acrylics). The benefits of vinyl neodecanoate extend beyond its intumescent properties. This highly branched monomer enhances the water repellence of the polymer due to its elevated carbon content. Consequently, the resulting coating exhibits improved weather resistance, and the in-can stability of the paint is increased, leading to a longer product shelf-life.