Isocyanate REACTION INDEX

For polyol and isocyanate blends, the total equivalents of isocyanate divided by file total equivalents of OH equals the reaction index. For more on urethane calculations, see refs. Id and lk. 

Isocyanate index (index number) = I (X)(actual amount of isocyanate used)/ (equivalent amount of isocyanate required). An excess of isocyanate groups is used in some applications like flexible foam. The analytical values required for isocyanate formulas are the isocyanate value, hydroxyl number, residual acid value (acid number), and water content. The last two parameters reflect the following reactions ... 

John et al. (70) studied and compared the properties of polyurethane foam obtained from soybean oil-based polyols and synthetic polyols and found that the soybean-based polyols showed enhanced reactivity and that the foaming reactions proceeded in a very similar way to synthetic polyols. It was also found that their properties were sensitive to several variables such as water content, isocyanate index, and catalysts. The reaction rate was mainly controlled by the water and isocyanate content. As the water content increased, the reaction was faster and the amount of the hard segment increased. In addition, MDl yielded more rigid foams than TDL... 

In all cases the prepolymer obtained from the reaction between macrodiol and diisocyanate, was reacted with EG in a quantity calculated so that there should remain theoretically no excess of unreacted NCO groups. This corresponds to an isocyanic index I = 100 where I = (lOOx [NCO])/([OH]m + [OHJce). The description of the poliadditon procedures are detailed elsewehere [127,207],... 

The equivalent weight of the mixture for reaction with an isocyanate is 105 20/0 46 equiv. = 228 g. That is, 228 g will react with 87 g of TDI on an equivalent basis (equivalent weight of TDI = 87). But in this case we wish to keep the total weight to that originally specified. Therefore, for the above weight 0 46 x 87 or 40 pbw of TDI should be used for a 100-index foam and 1 05 and MO times the amount for the 105 and 110 TDI-index foams. 

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