The WVP and waterproof properties of waterborne PU-coated
fabrics were measured and the results are shown in Table 2. In general,
the WVP of PU-coated fabric is a function of the hydrophilic
content at a given temperature, due to the increase in the interactions
between water vapors and polymer chains. As expected, all of
the WVP values obtained in this study were similar to one another
(910–990 g/m2 × 24 h) due to the similar amounts of PEO in the PUs.
On the other hand, the waterproof properties of PU-coated
fabrics are closely related to the hydrophobic segments in the
polymer main chains. The most important achievement in the
present study is the significant increase in the waterproof ability
of PU-coated fabrics (greater than 10,000 mm H2O), as compared
to PU*-coated fabrics (2 000 mm H2O), where the waterborne PU*
was prepared using a mixture of PEG, PPG, and PTMEG at the
same molar ratio as PU-21. The main reason for the improvement
in the waterproof capability of the PU-coated fabrics may
be due to the more even distribution of hydrophobic segments in
PPG2050-based PU because PPG2050 itself has both hydrophobic
and hydrophilic segments. In other words, the improved waterproof
capability of the PPG2050/PTMEG-based PU-coated fabrics
probably resulted from the much smaller hydrophilic domains