Polyurethane Coatings
December 2014 www.coatingsworld.com Coatings World | 39
Properties of the polyurethanes after hydrolytic degradation
The resistance to hydrolysis of the polyurethanes was determined by measuring their mechanical properties before and after immersion in water at 70ºC for 15 days. Noticeable changes in the polyurethane structure are found (Figure 11). After immersion in
hot water the color of the polyurethane was clearer in the polyurethane prepared with polyether only although it becomes soft and
has gum-like appearance.
Figure 12 (next page) shows the TGA thermograms of the polyurethanes prepared with PTMEG only and with a mixture of PTMEG and PH50 (PU- 40wt% PTMEG + 60wt% PH50). The TGA thermograms of the polyurethanes are quite
similar before and after hydrolysis, although in the polyurethane prepared with PTMEG only no residue is obtained at the
end of the experiment (2wt% remained in the polyurethane before hydrolysis). For the polyurethane prepared with 40wt%
PTMEG + 60wt% polycarbonate diol mixture similar residue is obtained ( 4. 7-5.1 wt%). There are fewer residues because
the structure of the PCD is more compact than the polyether one; and the variation of the residue after degradation is more
notable for the PTMEG PU (no residue left) due to the defragmentation of the backbone polymer chains produced by polyether hydrolysis.
Figure 11. Photos of the polyurethanes before and after water immersion at 70ºC for 15 days. [Photos by José A. Jofre-Reche, Andrés J. Yáñez-Pacios and José
Miguel Martín-Martínez - Adhesion and Adhesives Laboratory – University of Alicante]
