Bio-based non-isocyanate polyurethane(urea) waterborne dispersions for water resistant textile coatings

Abstract

Currently, the resins used in industrial polyurethane coatings are made from petro-based polyols and isocyanate building blocks. In traditional coating formulations, polyurethane resins can be solubilized in solvents for their application on substrates, thus releasing possibly volatile organic compounds (VOCs) upon drying. To circumvent these issues, polyurethanes synthesized from non-isocyanate and bio-based building blocks are receiving more interest. However, only few references describe the development of waterborne non-isocyanate dispersions with a direct application.In this study, non-isocyanate polyurethane(urea)s of very high bio-based contents (>80 wt%) and having controlled amount of reactive hydroxyl ends were synthesized via transcarbamoylation. The obtained resins were used as cationic waterborne dispersions in a sustainable coating system. The influence of the functionality and hydrophobicity of the neutralization agent used to protonate the non-isocyanate polyurethane(urea) backbones, as well as the dicarbamate monomer structures were assessed. It was found that the combination of monofunctional and hydrophilic dl-lactic acid neutralization agent (for electrostatic repulsion) led to stable dispersions with better properties (particle size and zeta potential) than the commercial waterborne polyurethane dispersion reference. Those dispersions were cross-linked through their reactive hydroxyl end groups with tetramethylol acetylene diurea into freestanding films and adhesive layers for textile coatings. The freestanding films exhibited high cross-linking efficiency (gel content >90 %), low water uptake (down to 2 %) and high water and methyl ethyl ketone (MEK) resistance (≥200 rubs) as well as good mechanical properties (Young's modulus between 1.5 MPa and 3.1 MPa and elongation at break up to 300 %) to resist the deformation of the fabrics when applied on them. Finally, when used as an adhesive layer on textiles, good resistance to hydrolysis and heat aging were ensured by the coating system, thus potentially replacing isocyanate based adhesive layers.