Correlating microstructure and performance of PU/(meth)acrylic hybrids as hardwood floor coating

In this work chemically grafted PU/(meth)acrylic hybrid dispersions for wood floor coating applications were synthesized using functional monomers containing hydroxyl groups as well as different vinyl functionalities (acrylic, allylic and methacrylic) to graft the polyurethane and acrylic polymer phases. A complete study of the effect of the type of functional monomer and polymerization mode of (meth)acrylic monomers (batch and semibatch) on the polymer characteristics, particle and film morphology and final properties of the films as wood floor coatings is presented. It is shown that using monomers with lower reactivity during the acrylic polymerization, such as glycidyl mono-allyl ether, limits the formation of a gel fraction, whilst more reactive double bonds, such as the of glycidyl methacrylate, leads to high gel content and significantly higher molar mass of the gel fraction. Using TEM analysis it is demonstrated that more homogeneous particle and film morphologies were obtained in the case of grafted hybrids. The impact of these features on the properties of the coating is discussed. It is shown that grafted polymer films had higher Young´s modulus and strain hardening than the non-grafted ones and this effect is more pronounced in the case of functional monomers that led to hybrids with higher gel content. Finally, it is shown that the wood floor coatings prepared with these PU/(meth)acrylic hybrid dispersions had final properties comparable to a commercially available reference coating.