By I.R. Clemitson
Castable Polyurethane Elastomers is a pragmatic advisor to the construction of castable polyurethane articles, from easy doorstops to advanced goods utilized in the army and nuclear industries. The publication indicates the development from uncooked fabrics to prepolymer construction, together with the chemistry and performance of the creation approaches. It presents a complete examine problem-solving and processing concepts, interpreting the choice of alternative varieties of structures on either the micro and macro degrees. It additionally discusses curing and post-curing operations, conveying the significance of utilizing the proper estate for the appliance.
Reorganized for greater movement, this Second Edition:
- Describes new tools within the processing of castable polyurethanes
- Expands insurance of future health and defense aspects
- Brings all criteria as much as date
Castable Polyurethane Elastomers, moment version explains the creation of polyurethane elements, filling the distance among natural chemistry and exchange information.
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Additional info for Castable Polyurethane Elastomers
Example text
Methylene diisocyanate (MDI) and a catalyst such as an organic tin or bismuth salt, provide the required rate of reaction. The size of the exotherm is such that the reaction proceeds to its full extent. 1 Urea and Urethane Reactions Introduction Compounds that contain the N-H group are all potentially reactive toward isocyanates. Simple primary amine groups are very reactive even at temperatures of between 0 ◦ C and 25 ◦ C, giving disubstituted ureas in high yields. Secondary aromatic amines are slightly less reactive.
The mercury catalysts are both toxic and caustic. Bismuth catalysts promote the isocyanate and OH reaction from the isocyanate side. This has the effect of reducing the water reaction and hence reduces the liberation of carbon dioxide gas. They are particularly useful in controlling the reactions when used in one-shot systems. General Catalysts are commonly used to control the pouring and gel times of polyurethane systems. As catalysts are used in small quantities, the addi- 44 Castable Polyurethane Elastomers tion must be carried out very carefully, otherwise very erratic results may be obtained.
Diisocyanates such as p-TMXDI do not form allophanates. This adds to their very stable storage life even at slightly elevated temperatures. The prepolymer has a shorter pot life and gel time compared to an equivalent prepolymer made with the aromatic MDI. Aliphatic polyurethanes with their non-yellowing also provide sufficient impact resistance so that they can be used in face shields (US Patent 3,866,242). Even with the non-yellowing properties, UV protection agents are often added to materials.