Isocyanates 290 INDEX

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... 

Isocyanate index for all formulations was 105 Samples were hardened for 3 days before testing... 

This method, however, did not result in improved flame retardance because the isocyanurate content was too low. In recent years, however, high-functionality and low-viscosity polyether polyols have become available, and therefore the above method has become less important. Even so, the method was sometimes used to make foams having increased crosslink density to improve dimensional stability or chemical resistance. Therefore, a higher isocyanate index, e.g., 150 to 200, was used to incorporate isocyanurate linkages in rigid urethane foams. 

Figure 34 shows a comparison of temperature stability in terms of TGA at different isocyanate indices (16). The results indicate that the higher the isocyanate index, the higher the temperature resistance. 

Figure 34. Dependence of thermal resistance on isocyanate index (16).

In this paper, the hard segment content is defined as the percent by weight of the isocyanate and extender in the polymer at a fixed stochiometry or isocyanate index. 

Infrared Measurements. In Figure 12, the infrared spectra of two foam formulations are shown which have been quenched on cold salt plates 20-30 seconds after the end-of-mixing. The first formulation is "A" the second,a similar formulation also at 105 isocyanate index but with 4 phr water. In each, the strong... 

Elastomers were made from B-625 at various initial mixing temperatures, using an isocyanate index of 1.05. 

In order to achieve the desired balance of hydroxyl to isocyanate groups in a formulation, the isocyanate index is specified ... 

The isocyanate index is quoted as 100 to give conditions essentially producing urethance and urea group only. 

The high isocyanate index of catalyst system will promote the formation of isocyanate structures. 

With the use of ABA, both the available densities and the available foam hardnesses were lowered in comparison to the purely water blown foams, as in these cases gas volume was produced without generation of urea. Softening of foam was also achieved chemically, either with the use of an additive to change the urea morphology [13] or with the use of crosslinkers in combination with a low isocyanate index [14]. 

Price and workers [31] studied the flame retardancy of rigid PU foams with various isocyanate indexes using the laser pyrolysis-mass spectrometry technique. 

Equal in volume to component A and to give an isocyanate index near to 100... 

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],... 

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