Coatings World - December 2014

prepared with 50 wt% PTMEG + 50 wt% PH50 shows the differentiated thermal decompositions of both polyols.

Mechanical properties of the polyurethanes prepared with
PTMEG, PCD or PTMEG+PCD mixtures

Polyurethanes obtained with polyether diol only show poor abrasion properties (Table 1), as notable weight loss is obtained in the coatings by friction. However, in the polyurethanes with polycarbonate diol in the formulation, the abrasion resistance was highly improved, even when small amount of polycarbonate diol is added. Furthermore, when the polycarbonate diol content in the polyurethane was higher than 50wt%, the abrasion properties remain almost constant. The increase in abrasion in the polyurethanes can be ascribed likely to the higher interactions between polycarbonate chains with respect to these in the polyether chains (Figure 1).

Using lower values of NCO/OH ratio, a slight improvement in the wear resistance of the polyurethane films is obtained. This can be ascribed to higher stiffness of the polyurethanes containing higher number of hard segments, and thus when soft segments are dominant (such as for low NCO/OH ratios) better resistance to abrasion with low weight loss is produced. Figure 5 shows the values of weight loss after abrasion for the polyurethanes prepared with different NCO/OH ratios and different contents of polycarbonate diol in the polyol mixtures. The better wear resistances are obtained in the polyurethanes prepared with higher content of

Figure 3. DSC thermograms of the polyurethanes prepared with different contents of PCD in the polyols mixture. Second heating run.

Figure 4. Variation of the weight loss and the derivative of the weight loss (DTGA) as a function of the temperature of the polyurethanes with different weight content of PH50 PCD (NCO/OH ratio = 1.20).