Flexibility in Adjustments to Formula

Polyurethanes based on MDI have the greatest flexibility in the choice of curatives and blends of curatives that can be used to obtained the desired properties. In cast elastomers, the hygroscopic nature of the curatives must be taken into account and proper handling and storage used otherwise, there may be a very high reject rate. Catalysts are also more readily used with the MDI materials. Organic acids such as adipic or oleic acids work better with TDI materials than MDI systems. 

TDI-based materials are normally cured with a range of amine-based curatives. The current most popular are Ethacure 300, followed by MOCA. MOCA is still popular despite the carcinogenic concerns associated with it. 

For soft materials, extension with either a reactive or nonreactive plasticizer is best with an ester-based material. The toughness of the ester helps keep the properties usable at lower hardness. 

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