CHARACTERIZATION OF SOLVENT-BASED POLYURETHANE ADHESIVES CONTAINING SEPIOLITE AS A FILLER - RHEOLOGICAL, MECHANICAL, SURFACE, AND ADHESION PROPERTIES

Different amounts (5-30 wt% with respect to the polyurethane content i n the adhesive) of a new filler, a partially defibrillated natural hyd rated magnesium silicate (sepiolite), were added to solvent-based poly urethane (PU) adhesive formulations. The rheological, mechanical, surf ace, and adhesion properties of the PU adhesives obtained were measure d. Increase in the amount of sepiolite added to PU adhesives led to an increase in viscosity and imparted thixotropy and pseudoplasticity to the adhesive solution. However, the addition of sepiolite produced an increase in storage and loss moduli and a decrease in the mechanical properties but did not affect the surface properties of the PU adhesiv e films. On the other hand, the immediate (measured 30 s after joint f ormation) T-peel strength of roughened or (roughened + chlorinated wit h 1 wt% trichloroisocyanuric acid solutions in 2-butanone) styrene-but adiene rubber/PU adhesive joints was greatly improved if the adhesive was filled with up to 10 wt% sepiolite. The T-peel strength measured 7 2 h after bond formation was similar for the joints prepared with PU a dhesives without and with up to 10 wt% sepiolite. The joint strength d ecreased if the amount of sepiolite in the PU adhesive was 20-30 wt%, due to the poor mechanical properties and too high moduli of the adhes ives. Some interactions between the sepiolite, the polyurethane, and/o r the solvent seemed to be responsible for the improved properties of filled PU adhesives. These interactions were responsible for the incre ased storage and loss moduli and the displacement of Tg Of the PU adhe sive films to higher temperature when it contained sepiolite. Furtherm ore, the addition of a high amount of sepiolite changed the rheologica l behaviour of the PU to a solid, giving rigidity to the structure, wh ich is responsible for the reduced adhesion in roughened rubber joints produced with polyurethanes containing 20-30 wt% sepiolite.