Oleochemical polyols are special polyfunctional alcohols based on natural vegetable oils. They offer alternatives to higher hydrophilicity petrochemical-based polyols.
Because they are derivatives of vegetable triglyceride oils, they retain the advantages of classical oil paints and alkyd resins. But because of their low viscosity, they offer a base for solvent-free, full solids coating systems. As so-called reactive diluents, they are additionally able to replace solvents in coatings by forming part of the polymer film after curing instead of evaporating as solvents do.
Building polyurethanes
Polyurethanes are built from the reaction orb polyfunctional hydroxide and isocyanate compound (1). Besides this fundamental reaction, a lot of other reactions with isocyanates (combining for example, an amine, acid, urea or water) are possible forming urea, amide or biurete. Isocyanates need an `active' hydrogen atom, which is present in alcohols or amines, to start the production of urethane or urea linkages. In addition, simply water can react with isocyanates to form urea and carbon dioxide. This carbon dioxide evolution is desired for polyurethane foam production, but may create a lot of undesirable effects and problems in coating application when the decorative surface is destroyed or disturbed by bubbles (Figure 1).As well as aromatic or aliphatic isocyanates, polyether and polyester polyols and also mixtures of both types are used in producing polyurethanes. Polyether or polyester polyols based on low-cost petrochemicals show disadvantages regarding sensitivity to moisture during the curing reaction of the hydroxide group with the isocyanate. This hydrophilic polyether or polyester chemical backbone increases the possibility of water disturbing the curing reaction and also the likelihood of obtaining surface defects in application, where foam (especially bubbles) must be avoided.
