Example Calculation for a Typical Polyurethane Elastomer Synthesis

Example Calculation for a Typical Polyurethane Elastomer Synthesis 

Many suppliers of polyurethane systems provide them in the form of two components and advise on the actual weight of each component to be combined to form the polymer. This is the weight ratio, sometimes and confusingly called the index. Such a practice is to be decried as causing confusion with the chemical term isocyanate index . In many cases there is little difference in value between weight ratio and chemical equivalent weight ratio of index but it is important to understand the difference. Most suppliers supply an NCO-free system for one component and an NCO component (quoted in terms of the OH number) for the other side. 

Polyol alone. Consider the following arbitrary formulation  

Complete polyol system. As the individual ingredients in mix B will all contain minor quantities of OH active ingredients (e.g. trace amounts of free water, hydroxyl groups and bound water on filler particles), it is common for the hydroxyl number to be determined by analysis of the whole system when this calculation applies  

Batch weight increase over polyol weight = — = 134 

---