Oxazolidine Moisture Scavengers

The function of oxazolidine scavengers:
The function of oxazolidine moisture scavengers is to improve the coating appearance of PU systems through the elimination of carbon dioxide pinholes. Pinholing in PU films occur as a result of the reaction between moisture and isocyanate. However, this reaction can be reduced or eliminated by using an oxazolidine moisture scavenger, such as Incozol 2, which has a preferential reaction mechanism with moisture - effectively removing water from the system before it can react with the isocyanate.

Oxazolidine hardeners from Incorez use atmospheric moisture to trigger the curing process. This can offer greater cross-linking (faster through-cure), while minimising the carbon dioxide gas evolution that can cause bubbling, pinholing and down glossing. This allows the formulator to reduce the isocyanate level and the ­toxicity level without adversely affecting the cure rate.

 

How oxazolidines can be used in polyurethane cast systems (non-foaming systems):
Incorez is still developing their experience in using oxa­-
zolidines in cast PU systems. However, in theory, the general principles of using oxazolidines as a latent curing agents/cross-linkers can be applied to cast PU systems.  
Traditionally, polyurethane systems incorporate a high level of isocyanate to expedite the cure at an effective rate, often with the incorporation of toxic catalysts such as lead, mercury and more recently tin types. However, oxazolidine technology offers the opportunity of reducing the metal catalyst level in the PU system, while obtaining sufficient cure and also reducing/eliminating problems associated with CO2 formation and increasing tensile performance. All of these benefits are brought about by a so-called ‘moisture-triggered' mechanism.
On exposure to moisture, the heterocyclic oxazolidine ring effectively hydrolyzes, or is "triggered", to yield an amino alcohol functionality. The amino alcohol functionality reacts with the isocyanate functionality of the PU to effectively cross-link or network the system. This network formation means that the PU system reaches the gel-point (or gel-sol) phase much quicker, therefore reducing the need for metal catalysis, while simultaneously removing water.
Incorez is experiencing strong demand for 1K PU systems in flooring applications. The single pack system mitigates some of the problems associated with pot-life that affects 2K systems, as well as offering excellent gloss retention and good appearance over a long period of time. Other growing applications include the use of oxazolidine moisture scavengers in high build properties (waterproof balconies) and in wind turbine protective coatings.

Have Incorez done any research in cast systems?

Virtually all of the research has focused on PU films, elastomers and adhesives. Incorez have not researched specially cast systems like Adiprene or Vulkollan. However, in principle, oxazolidines could be used in applications in this area.

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