Calculate polyurethane NCO/OH index, isocyanate mass, or polyol mass from %NCO and hydroxyl number or %OH, with equivalent weights, unit conversion, and stoichiometric balance.

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NCO/OH Ratio Formula

The following formula is used to calculate the NCO/OH ratio for a given amount of NCO and OH equivalents.

R = ENCO / EOH

Variables:

  • R is the NCO/OH ratio
  • ENCO is the NCO equivalents (eq)
  • EOH is the OH equivalents (eq)

To calculate the NCO/OH ratio, divide the NCO equivalents by the OH equivalents.

What is an NCO/OH Ratio?

The NCO/OH ratio is a measure used in polymer chemistry to describe the ratio of isocyanate groups (NCO) to hydroxyl groups (OH) in a chemical reaction. This ratio is crucial in determining the properties of the resulting polymer, such as its flexibility, hardness, and durability. By adjusting the NCO/OH ratio, chemists can tailor the characteristics of the polymer to suit specific applications, such as coatings, adhesives, foams, and elastomers.

How to Calculate NCO/OH Ratio?

The following steps outline how to calculate the NCO/OH ratio.

  1. First, determine the NCO equivalents (ENCO).
  2. Next, determine the OH equivalents (EOH).
  3. Finally, calculate the NCO/OH ratio using the formula R = ENCO / EOH.
  4. After inserting the values and calculating the result, check your answer with the calculator above.

Example Problem : 

Use the following variables as an example problem to test your knowledge.

NCO equivalents (ENCO) = 10

OH equivalents (EOH) = 5