Polyurethane adhesive is reactive adhesive, which means this product is applied on substrates as mixture of low molecular weight entitles (monomers and oligomers) and use chemical curing reaction to create a polymer, often cross-linked. Polyurethanes are formed by polyaddtion polymerisation. Among the reactive adhesives, polyurethanes are by far the most diverse group: they can be water-based adhesives, solvent-based adhesives or solvent-free adhesives purely moisture-curing or two-component adhesives. Reactive polyurethane contain polyurethane prepolymers with blocked NCO end groups. These prepolymers are solid at room temperature.
Polyurethane adhesives show very good adhesion to various substrates, high mechanical strength, as well as good flexibility and chemical resistance. Due to these properties, polyurethane adhesives are used in a wide range of applications.
And what is reaction of NCO with OH terminated?
Monomeric isocyanates are hazardous to human health and can be sensitising. Therefore, NCO terminated prepolymers are generally used, which reduces the content of free isocyanate monomers and accelerates the curing process. Next to diisocyanates, the second main ingredient in polyurethane adhesives are the diols or polyol components. Typical diols are for example ethylene glycol, diethylene glycol and propylene glycol. In addition to these glycols, OH-terminated oligomers based on polyethers or polyesters are also used for polyurethane adhesives. Among the polyether polyols, ethoxylated or propoxylated oligomers are mainly used. For polyester polyols dicarboxylic acids like adipic acid, ortho-phthalic acid or isophthalic acid react with polyols in excess so that OH terminated polyesters are formed. Castor oil is a polyol on natural base, which can also be used as an OH component in polyurethane adhesives.
