Curing of polyurethane

The curing of polyurethane paints is a complex chemical and physical process therefore a mathematical model may be a valuable tool to describe the process and manage the data. 

The aim of our present Investigations has been the construction of a model for the curing of polyurethanes. 

The isocyanate concentration during curing of polyurethane paints has been quantified by tracing the infrared absorption of the isocyanate group (2272 cm- ) with a Perkin Elmer 983 spectrophotometer. 

With a minimum of analytical measurements, the effect of several parameters on the curing of polyurethane coatings can be studied using the presented model. 

In our opinion, the model has proved to be a valuable tool for the quantification of important phenomena occurring during the curing of polyurethane paints. 

Heat plays an important part in the curing of polyurethanes. The reaction itself gives out heat, so this must be taken into account in determining the temperature of the mold. The mold should be at the maximum temperature the curing prepolymer will reach. An MDI-based system will release heat more rapidly than a TDI-based system therefore the mold has to be hotter than when using a TDI-based material. 

This reaction has great significance in the preparation of polyurethane products as it causes chain extension and branching, provides the carbon dioxide necessary for foaming and forms the basis of air curing of polyurethane coatings. 

Figure 1.9 Equations for preparation, chain extension, and curing of polyurethanes.

Suitable plasticizers include phthalates, phosphates, partially hydrogenated terpenes, adipates, chloroparaffins, castor oil, etc. It is best that the plasticizer does not contain water since it will interfere with the cure of polyurethanes. 

Moisture-curing adhesives are formulated with resins that react with atmospheric moisture to form a curedpolymer. Most ofthese resins are one-part cyanoacrylates, silicones, or polyurethanes. The key advantage, of course, is their ability to cure without the use of heat or other external form of energy. However, in many cases, several days of ambient exposure are required to achieve full properties since the rate of curing is dependent on the relative humidity and the thickness of the adhesive. If there is too much moisture on the surface, curing of polyurethanes occurs so quickly that... 

From kinetic investigation of the curing of macro-triisocyanates (MTI) based on L-3003, P-2200, and their mixtures, kinetic curves of the polymerization process were obt uned at 298 K. Kinetic curves for the curing of polyurethane prepolymer mixtures obtained by reaction of TDI with L-3003, P-2200, and various mixtures with a double excess of NCO groups with respect to OH groups are linear. These dependences show that NCO group reactions continue until high fractional conversions comply with the second-order equation... 

Key words vegetable oil-based polyurethane, preparation of polyurethane, curing of polyurethane, stmcture-property relationships of polyurethane, application of polyurethane. 

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