3 Raincoat and sunscreen
Besides biological attack, construction materials are exposed to the rages of weather. Polyurethane coatings that are water resistant keep buildings watertight. Other types of polyurethane coatings can protect metal, wood, and other structures from the damage caused by too much rain or too much sun. For wooden structures, such as decks, the sun can be the biggest problem, says Nejad. “Most of the weathering deterioration that happens in wood is due to UV degradation of the lignin,” she says.
High performance polyurethane foams are typically made by combining a diisocyanate such as 4,4'-methylenediphenyl diisocyanate (top) with a polyester polyol (bottom).
Polyurethanes are typically low-molecular-weight polymers that have the potential to penetrate into wood cell walls and stabilize the wood, Nejad explains. They are a mixture of isocyanate and polyol monomers, and they generally have some free isocyanate in their formulation. As isocyanates can pose a potential risk to human health and the environment if not handled correctly, Lanxess has developed ‘low-free’ technology that minimizes free isocyanate content, says Matthias Hüttl, global strategic marketing manager for urethane coatings at Lanxess. “Our plants are equipped with technology that can remove the remaining residual isocyanate monomer content to below 0.1%,” Hüttl explains.
“Polyurethanes are known not only for their excellent mechanical properties but also for retention of those properties over time,” says Giulio Di Egidio, head of technical services and application development for surface coatings and polyurethane dispersions in Lanxess’s Urethane Systems business unit. “High-performance polyurethane coatings are particularly critical when the life expectancy of parts is supposed to be very long.”
As high-end coatings, polyurethane coatings tend to be used in high-demand applications, adds Hüttl. “For example, they can give very good abrasion resistance,” he says. These coatings are often used on wood or concrete floors or for balconies where their durability and waterproofing come into play.