The whitest paint was produced by university researchers in order to stimulate the cooling of buildings and address the climate crisis.
The new paint reflects 98% of sunlight, as well as infrared heat radiation through the atmosphere into space. In tests, it cooled surfaces by 4.5C below ambient temperature, even in bright sunlight. The researchers said the paint could be on the market in a year or two.
White-painted roofs have been used to cool buildings for centuries. As global warming rises, the technique is also used in modern city buildings, such as Ahmedabad in India and New York City in the United States.
Currently available white reflective paints are much better than dark roofing materials, but they reflect only 80-90% of sunlight and absorb UV light. This means that they cannot cool surfaces below ambient temperatures. The new paint does this, leading to a lower need for air conditioning and the carbon emissions they produce, which increase rapidly.
“Our paint can help fight global warming by helping to cool the Earth – that’s the cold spot,” said Prof. Xiulin Ruan of Purdue University in the United States. “Producing the whitest white means that the paint can reflect the maximum amount of sunlight back into space.”
Ruan said painting a 93-square-foot roof would provide 10 kilowatts of cooling power: “It’s stronger than the central air conditioners used by most homes.”
The new paint was revealed in a report in ACS Applied Materials & Interfaces magazine. Three factors are responsible for the cooling performance of the paint. First, barium sulfate was used as a pigment that, unlike conventional titanium dioxide pigment, does not absorb UV light. Second, a high concentration of pigment was used – 60%.
Third, the pigment particles were of various sizes. The amount of light scattered by a particle depends on its size, so the use of a range scatters more of the spectrum of sunlight. Ruan’s lab evaluated over 100 different materials and tested about 50 formulations for each of the most promising. Their previous white paint used calcium carbonate – chalk – and reflected 95.5% sunlight.
Barium sulfate paint allows surfaces to be below ambient air temperature, even in direct sunlight, because it reflects so much of the sunlight and also radiates infrared heat at a wavelength that is not absorbed by the air. . “Radiation can pass through the atmosphere, being lost directly into deep space, which is extremely cold,” Ruan said.
The researchers said the ultra-white paint uses a standard acrylic solvent and could be made like conventional paint. They claim that the paint would be similar in price to current paints, with barium sulphate actually cheaper than titanium dioxide. They also tested the paint’s abrasion resistance, but said long-term weathering is needed to assess its long-term durability.
Ruan said that the paint does not pose a risk to human view: “Our surface diffuses the sunlight so that the power that goes in a certain direction is not very strong. It just looks bright white, a little whiter than snow. ”
A patent for the paint was filed jointly by the university and the research team, which is now working with a large commercial corporation: “We believe that this paint will be widely available on the market in a year or two, I hope. if we do it fast. ”
Lukas Schertel, a light scattering expert at the University of Cambridge, UK, who was not part of the research team, said: “Using paint for cooling is not new, but it still has a high potential to improve our society because is widely used. This study takes a step towards commercially relevant solutions. If further improved, I am convinced that such technology can play a role in reducing carbon emissions and having an overall impact. ”
Schertel said the high concentration of pigment in the paint and the relatively thick layers used raised questions about cost: “Pigment is the main cost of paint.” Ruan said his team hopes to optimize the paint so it can be used in thinner layers, perhaps using new materials, so it will be easier to apply and lower in cost.
Andrew Parnell, who works on sustainable coatings at the University of Sheffield, UK, said: “The principle is very interesting and science [in the new study] is good. But I think there could be logistical problems that are not trivial. Millions of tons [of barium sulphate] would you need ”
Parnell said a comparison of carbon dioxide emitted by barium sulphate extraction with emissions saved from lower air conditioning use would be needed to fully evaluate the new paint. He also said that green roofs, on which plants grow, could be more durable where possible.
Project Drawdown, a charity that assesses climate solutions, estimates that white roofs and green roofs could avoid between 600m and 1.1 billion tonnes of carbon dioxide by 2050, roughly equivalent to two to three years of total annual emissions. of the United Kingdom.