The whitest paint ever was produced by academic researchers, with the aim of promoting the cooling of buildings and overcoming the climate crisis.
The new paint reflects 98% of the sunlight as well as the emission of infrared heat through the atmosphere to space. In tests, it cooled surfaces by 4.5 C below ambient temperature, even in strong sunlight. According to the researchers, the paint may be on the market in a year or two.
Whitewashed roofs have been used for centuries to cool buildings. As global warming raises the temperature, the technique is also used in modern city buildings, such as in Ahmedabad in India and the city of New York in the USA.
Currently available reflective white paint is much better than dark roofing material, but reflects only 80-90% of sunlight and absorbs UV light. This means that they cannot cool surfaces below ambient temperature. The new paint does this, leading to less need for air conditioning and the carbon emissions it produces, which is rising rapidly.
“Our paint can help fight global warming by helping the earth cool down – that’s the coolest point,” said Prof Xiulin Ruan at Purdue University in the US. “The production of the whitest white means that the paint can reflect the maximum amount of sunlight in the space.”
Ruan said the paint from a 93-square-foot roof would provide a cooling of 10 kilowatts: “It is more powerful than the central air conditioners used in most homes.”
The new paint was unveiled in a report in the journal ACS Applied Materials & Interfaces. Three factors are responsible for the cooling of the paint. First, barium sulfate was used as the 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 different sizes. The amount of light scattered by a particle depends on its size, so if you are using a series, scatter more of the light spectrum of the sun. Ruan’s laboratory evaluated more than 100 different materials and tested approximately 50 formulations for each of the most promising. Their previous whitest paint uses calcium carbonate – chalk – and reflects 95.5% sunlight.
With the barium sulphate paint, surfaces, even in direct sunlight, can be below ambient temperature because they reflect so much of the sun’s light and also emit infrared heat at a wavelength that is not absorbed by air. “The radiation can pass through the atmosphere and be lost directly to the deep space, which is very cold,” Ruan said.
The researchers said the ultra-white paint uses a standard acrylic solvent and can be manufactured like regular paint. They claim that the paint would be similar to the current paint, with barium sulfate actually being cheaper than titanium dioxide. They also tested the paint’s resistance to abrasion, but said long – term wear tests are needed to determine its long – term durability.
Ruan said the paint is not a danger to sight: ‘Our surface reflects sunlight diffusely, so the force going in a specific direction is not very strong. It just looks bright white, a little whiter than snow. ‘
A patent for the paint has been filed jointly by the university and research team, working closely with a large corporation to do commercialization: ‘We think this paint will be widely available within a year or two, if we do it quickly. ”
Lukas Schertel, an expert in light distribution at the University of Cambridge, UK, who was not part of the research team, said: ‘The use of paint for cooling is not new, but still has great potential around us. improve society because it 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 a global impact. ‘
Schertel said the high concentration of pigment in the paint and the relatively thick layers used raised cost questions: “Pigment is the most important cost for paint.” Ruan said his team hopes to optimize the paint so that it can be used in thinner layers, perhaps by using new materials so that it will be easier to apply and lower cost.
Andrew Parnell, who works on sustainable painting at the University of Sheffield, UK, said: ‘The principle is very exciting and the science [in the new study] is good. But I think there may be logistical problems that are not insignificant. How many million tons [of barium sulphate] would you need? ”
Parnell says a comparison of the carbon dioxide released by barium sulphate extraction with the emissions saved by lower air conditioning is necessary to fully assess the new paint. He also said that green roofs on which plants grow can be more sustainable where practical.
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 equal to two to three years of the UK’s total annual emissions.