Figure 13 shows the stress-strain curves of the polyurethanes
prepared with PTMEG only and with 40wt% PTMEG and
60wt% polycarbonate diol mixture, before and after immersion in water at 70ºC for 15 days. After hydrolysis a decrease
in stress and an increase in elongation-at-break are obtained
in the polyurethanes, the changes in the mechanical properties are more pronounced in the polyurethane prepared with
polyether only. On the other hand, the mechanical properties
of the polyurethanes prepared with 40wt% PTMEG + 60wt%
polycarbonate diol mixture after water immersion are higher
than in the polyurethane prepared with polyether only before
hydrolytic degradation.
Table 2 shows the values and the percentages of variation
of different mechanical properties in the polyurethanes before
and after water immersion at 70ºC during 15 days; for sake
of clarity, the percentage of variation for each mechanical
property is given in Figure 14 (red bars: polyurethane pre-
pared with polyether only; blue bars: polyurethane prepared
with 40wt% polyether + 60wt% polycarbonate diol). In gen-
eral, the decrease in the Young’s modulus, elastic limit, tough-
ness and resilience values is more important (up to 70% lower)
in the polyurethane prepared with polyether only (except for
the yield point); however, for the polyurethane prepared with
40wt% polyether + 60wt% polycarbonate diol the reduction
in mechanical properties is lower than 40%. It is interesting
that after water immersion an increase in elongation-at-break
is produced in both polyurethanes.
Conclusions
Polyurethane coatings prepared with polycarbonate diol shows
noticeable improvement in abrasion resistance, Shore A hardness, mechanical properties and hydrolytic resistance than in the
Figure 12. Variation of the weight loss as a function of the temperature of the PU films prepared with PTMEG only and with 40wt% PTMEG + 60wt% polycarbonate diol mixture, before and after water immersion at 70ºC for 15 days.
Figure 13. Stress-strain curves of the polyurethanes before and after water
immersion at 70ºC for 15 days.
Figure 14. Percentage of variation of the mechanical properties of the polyurethanes prepared with PTMEG only and 40wt% polyether + 60wt% polycarbonate diol mixture after immersion water at 70ºC for 15 days.
