High-Shear-Strength Waterborne Polyurethane/Acrylic Soft Adhesives

International audienceUrethane/acrylic hybrid latex particles are prepared by miniemulsion polymerization for an application as soft adhesives. The polymerization of the acrylic monomers and grafting of an isocyanate functionalized PU on a hydroxyl functionalized monomer (HEMA) take place simultaneously, resulting in a complex PU/acrylic network while avoiding any macroscopic phase separation. Its structure can be tuned by changing the extent of grafting and a specific model is applied to analyze the final polymer microstructure. The resulting materials have a low level of adhesion but display an exceptionally high resistance to shear. Two parameters are varied: the fraction of HEMA in the monomer composition and the diol concentration

Influence of composition on the morphology of polyurethane/acrylic latex particles and adhesive films

International audiencePolyurethane (PU)/acrylic hybrid particles with different PU contents were synthesized by miniemulsion polymerization and subsequently dried to give solid adhesive films. The morphologies of the particles and the morphologies and mechanical properties of the resulting films were investigated by Transmission electron microscopy combined with selective staining of the PU and by uniaxial tension tests. Morphological investigations showed a clear change in the particle morphology as the PU weight fraction increased. While at 5 wt% and 25 wt%, PU (with respect to total organic content) the particles were relatively homogeneous and mechanical properties of the films could be readily interpreted with molecular arguments, at 50 wt% PU a core-shell structure was observed. This heterogeneous structure of the 50 wt% PU particles persisted in the films, resulting in a percolating network of the harder PU phase. The low deformability and strain at failure of the 50% PU films suggest that, unlike the adhesives with lower PU content, the relatively weak interfaces between the original latex particles dominate the mechanical properties. (C) 2014 Elsevier Ltd. All rights reserved