COMPARISON OF THE PROPERTIES OF POLYURETHANE ADHESIVES CONTAINING FUMED SILICA OR SEPIOLITE AS FILLER

Fumed silica is a well-known mineral filler of epoxy and polyurethane adhesives. Although effective, the small particle size and the relativ e high cost of fumed silicas suggest the need for an alternative fille r. In this study, the usefulness of adding a natural hydrated magnesiu m silicate (sepiolite) as a new filler in solvent-based polyurethane ( PU) adhesive formulations has been demonstrated. The rheological and a dhesion performance of the sepiolite-filled PU adhesive was compared w ith that in PU adhesives containing fumed silicas. The addition of a f iller to PU adhesives provided an increase in viscosity, imparted thix otropy and pseudoplasticity to the adhesive solution, produced an incr ease in storage and loss moduli, and improved the rheology of the PU. The mechanical properties of adhesive films were increased by adding f iller, mainly with fumed silica. On the other hand. the immediate T-pe el strength of roughened or (roughened + chlorinated) styrene-butadien e rubber/PU adhesive joints was greatly improved in filled PU adhesive s. The effects produced by adding sepiolite or fumed silica to the adh esives were very similar, although in general more noticeable in fumed silica filled PU due to the formation of hydrogen bonds between the f iller and the solvent and/or the polyurethane (in sepiolite-filled adh esives, van der Waals forces seemed to be responsible for the interact ions between the filler and the solvent and/or polyurethane).