– the toughness of the adhesive gets enhanced with addition of TEPs.
– the toughness improvement is obtained without any loss of stiffness (E) or ductility.
– a significant decrease in adhesive strength at yield with increasing wt% TEPs was found. This might be explained by the drastic change in the adhesive structure, by the volume occupied by the particles and by the fact that TEPs act as stress concentrators.
– the temperature where the particles show the maximum expansion varies inversely with TEPs wt%.
– TEPs-modified polyurethane adhesive should be used in products with controlled temperature between 90 and 120 degree centigrades, depending on the TEPs concentration to obtain the highest expansion ratio. Below this range of temperature, not all the particles will expand, and above it, the TEPs-modified adhesive will deteriorate.

References

1. Banea M. D., da Silva L.F.M., Carbas R.J.C., Campilho R.D.S.G.;Mechanical and thermal characterization of a structural polyurethaneadhesive modified with thermally expandable particles. International Journal of Adhesion & Adhesives; 2014.
2. Jayaraman, Krishnamoorthy;Studies on polyurethane adhesives and surfacemodification of hydrophobic substrates. University of Massachusetts Amherst; 2007
3. https://en.wikipedia.org/wiki/Scanning_electron_microscope
4. https://en.wikipedia.org/wiki/Fracture_mechanics
5. http://polyurethanes.org/en/where-is-it