corresponding to the polyurethane prepared with polyether show
marked changes in surface morphology caused by important
abrasion leading to a highly roughened surface. On the contrary,
the surfaces of the polyurethanes prepared with polycarbonate
diol and 50wt% polycarbonate diol + 50wt% polyether obtained
after abrasion show similar and lower roughness.
Shore A hardness values of the polyurethane films prepared
with different content of polyether (PTMEG) and polycarbonate
diol (PH50) increase by increasing the amount of PCD, i.e. the
higher is the content of PCD, the higher is the Shore A hardness
value of the polyurethane. Figure 8a shows the Shore A hardness
values as a function of the PCD content in the polyol mixtures
(for NCO/OH ratio of 1.20), and an almost linear increase of
hardness in the polyurethane as a function of the PCD content
in the polyol mixture is produced. On the other hand, by increasing the NCO/OH ratio in the polyurethane the Shore A hardness
value also increases (Figure 8b). Both, the increase in the NCO/
OH ratio and the polycarbonate diol content in the polyols mixture increases the Shore A hardness due likely to the increase in
the hard segments in the polyurethane; however, for high content
of PCD in the polyols mixture, the effect of the polycarbonate
diol on Shore A hardness values of the polyurethane is more important than the incidence of the NCO/OH ratio.
The mechanical properties of the polyurethanes were also obtained from stress-strain tests of polyurethanes prepared with polyether only and with 40wt% polyether + 60wt% polycarbonate
diol. Figure 9 shows that the polyurethane prepared with 40wt%
polyether + 60wt% polycarbonate diol has higher Young’s modulus and tensile strength than the one prepared with polyether only,
although the elongation-at-break is lower. The increase in tensile
strength in the polyurethane prepared with 40wt% polyether +
60wt% polycarbonate diol can be ascribed to higher cohesive forces between carbonate groups in the polyol chains in the soft segments of the polyurethane. On the other hand, a similar trend was
obtained in tear strength values of the polyurethanes (Figure 10).
Figure 8a. Variation of the Shore A hardness values of the polyurethanes as a
function of the PCD content in the polyols mixture. NCO/OH: 1.2.
Figure 8b. Variation of the Shore A hardness values of the polyurethanes as a
function of the NCO/OH ratio. Different PCD content in the polyols mixture.
Figure 9. Stress-strain curves of the polyurethanes prepared with PTMEG only
and with 40wt% PTMEG and 60wt% polycarbonate diol mixture.
Figure 10. Values of tear strength of the polyurethanes prepared with PTMEG
only and with 40wt% PTMEG and 60wt% polycarbonate diol mixture.
