Question 1

What is the formula for equivalent weight from OH value?

Accepted Answer

For polyurethane polyols, equivalent weight is commonly calculated as 56100 divided by hydroxyl value. This converts OHV into the weight per equivalent of reactive hydroxyl functionality.

Question 2

Why is water included in equivalent calculations?

Accepted Answer

Water reacts with isocyanate and consumes NCO groups while generating carbon dioxide. Because of its low equivalent weight, even a small amount of water can significantly increase the isocyanate requirement.

Question 3

Can this equivalent weight calculator be used for TDI and MDI?

Accepted Answer

Yes. Enter the correct %NCO for TDI, MDI, polymeric MDI or a prepolymer. The calculator uses %NCO to calculate isocyanate equivalent weight and required isocyanate parts.

Question 4

What is blended system equivalent weight?

Accepted Answer

Blended system equivalent weight is the total formulation parts divided by the total reactive equivalents. It helps compare the overall reactive demand of a mixed polyurethane formulation.

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