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Clever chemistry enhances buildings, streets, and pavements

Contributing Writer, C&EN BrandLab

They may appear to be humble substances, but the construction materials we use these days to build our homes, offices, and other spaces are anything but simple. Modern construction materials are high-performance items with cutting-edge chemical enhancements. These advanced materials can boost the appearance, longevity, and energy efficiency of our built spaces, with applications from road to roof.

1 Colorful solutions

Humankind has used iron oxide pigments for decorative purposes ever since the first artists used naturally occurring iron oxides for cave paintings. The range of colors available, including reds, yellows and black, and their longevity make iron oxide pigments just as appealing today. Industrially produced iron oxide adds color to many construction materials, including concrete paving.

Colored concrete can add aesthetic appeal to urban environments, and it can be a key safety element as well. Colored curbs for parking zones, bus lanes, crosswalks, and bicycle paths can be clearly marked with color. Unlike paint, it does not require maintenance - adding economic appeal as well.

Achieving specific color tones using iron oxide pigments in concrete is an art requiring fundamental expertise. “For concrete to have the desired hue when it dries, you have to first start with the right type of cement and also take into account the reactions of the pigments with the concrete aggregates,” says Michael Matheny, technical service manager construction for Lanxess Inorganic Pigments.

Lanxess Global Competence Centers for Construction provide this kind of expert support to concrete customers around the world with their use of iron oxide pigments through all stages of the production process.

2 Nature kept in check

Building materials will often need protection from microbes such as mildew, a risk in areas that are damp and have high humidity. “Wood is susceptible to mildew growth,” says Mojgan Nejad, who studies wood protection at Michigan State University. “It is important to use biocides for wood protection.”

Propiconazole is one of the azoles used in coatings for wood that protect the wood from fungus-induced rot.

As a fungus, mildew is susceptible to triazoles. These compounds contain a five-membered ring with two or three nitrogen atoms. Triazoles inhibit the fungal enzyme lanosterol demethylase. The enzyme is essential for the biosynthesis of ergosterol, a key component of the fungal plasma membrane, which leads to disruption of cell membranes. Besides triazoles, benzimidazoles, carbamates and isothiazolinones can be used to protect building materials such as wood, plaster, gypsum board, paint, and adhesives from fungal attack.

The latest trend is to encapsulate the biocide inside a water-soluble shell that slowly releases the active ingredient. “We are trying to reduce leaching of the biocide from the paint, for example, to have less impact on the environment and to have a longer lifetime for the paint film,” says Thomas Sames, the technical marketing manager biocides for the business unit Material Protection Products at Lanxess. The first biocides to feature this technology recently hit the market in Europe and Asia.

Nejad notes that the shift from organic solvent-based formulations of paints and other coatings to more environmentally friendly water-based formulations means biocides are also needed to protect the coating product itself from microbial spoilage. Spoiled coatings release a foul smell when the container is opened, and have impaired properties such as viscosity, spreadability and adhesion.

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.

4 Wrapped in a blanket

Polyurethanes are commonly used in construction as a foam, which makes an excellent insulation. One of the most useful formulation options is to produce ‘one-component’ polyurethane foams, which are applied in situ as a gap-filling sealant and adhesive, says Hüttl. “You can make a sprayable foam for surface insulation, or a sprayable construction foam to fix window or door frames and fill the gap between the wall and the door frame. One-component foams are even applied as adhesives to replace mortar for bricklaying which makes the construction of walls much faster, easier and cleaner.”

One-component foams typically come in a pressurized aerosol can. The can contains isocyanate and polyol that have been mixed together to form a partially polymerized, low-molecular-weight prepolymer. As the foam is sprayed, the prepolymer reacts exothermically with moisture in the air. The reaction produces gas bubbles that cause the foam to self-expand and seal a gap. The foam’s resulting cell-like structure sets hard, forming an excellent barrier to air drafts. The hard structure also offers sound insulation.

One-component foams are much more convenient to use than two-component foams in which the isocyanate and polyol are kept separately until foam is being sprayed. As well as being easy to use, the resulting foam has excellent longevity. “Once it is formed, it is very durable and stable. Also, in this application, prepolymers with reduced isocyanate content can be used for improved industrial hygiene during handling and processing,” Hüttl says.


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