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New Nanocomposite Solar Absorber Paints With Improved Flame Retardancy

Polymeric solar absorbers are a low-cost method of harvesting solar energy that may significantly lower the cost of electricity for residential homes. However, they are very flammable.

flame retardant, coatings

Study: Effect of bridged DOPO/polyurethane nanocomposites on solar absorber coatings with reduced flammability. Image Credit: prapann/

A recent study published in the journal Solar Energy focuses on this problem by producing solar absorber paints with excellent flame-resistant characteristics using bridged DOPO derivatives in polyurethane nanocomposites.

Producing sustainable energy sources to minimize fossil fuel usage and carbon dioxide footprint is critical to a more sustainable society. Today, the majority of power produced sustains suitable living temperatures (20–25 degrees Celsius), owing to the inadequate thermal insulation of buildings' outer structures and the resulting substantial temperature variations.

As a result, a large proportion of the energy produced is wasted outside the living space. To reduce energy wastage, enhancing the building envelope's qualities is critical, not just for energy savings but also for power generation through the combination of solar systems and fuel cells.

Flammability Concerns of Polymeric Solar Absorbers

Recently, interest has shifted toward polymeric solar absorbers to address the problem of energy waste, mainly because they are composed of plastic and are relatively cost-effective. However, the usage of polymeric materials is restricted, owing to concerns about fire safety management due to their high flammability.

In the last few decades, considerable progress has been made in safety regulations and fire risk management in many sectors.

A particular focus has been placed on fire protection systems in the housing industry. Therefore, the application of contemporary polymeric solar absorbers necessitates technologies that effectively limit the danger of unintentional flame propagation.

Enhancing the flame-retardant characteristics of materials is one technique to solve fire safety problems. In modern environments, where eco-friendly and sustainable strategies are critical and often the only option, phosphorous-and nitrogen-based fire retardants have been widely explored.

A Novel Technique for Development of Flame-retardant Solar Absorbers

In this work, the researchers present a unique approach for developing a fire-retardant (FR) solar coating for use in thermoplastic absorbers. Using phosphorous and nitrogen as the base material, two bridging DOPO derivates (namely NED and PHED) were prepared and integrated into the polyurethane nanocomposite binder at the same time as the black pigment and other additives.

 In a vertical flame test, the impacts of various weight ratios of the embedded PHED and NED on the suitability of the polyurethane binder and polycondensation reaction rates of new fire-retardant solar absorber coatings were investigated. 

Research Findings

When DOPO derivatives are introduced to the PU binder at the same time as a black pigment, the result is a highly effective process for the preparation of fire-retardant absorption coatings. These coatings also have a long shelf life and no loss of optical characteristics when the absorption stagnation temperature is approached.

The vertical flammability test results determined that all of the compounds containing DOPO/PU nanocomposites had significantly increased flame-retardant characteristics. Apart from PU-NED-10%, all solutions containing 10 and 15% FR material demonstrated rapid flame-quenching capabilities after the initial ignition. After the 2nd ignition, only the PU-PHED-15 compound exhibited flame-quenching abilities and was classified as V2 as per the UL94 standards.

Solar absorber paints containing 15% FRs and 444 dark pigments were successfully applied to alumina and PPS substrates. The produced material exhibited excellent stability, as shown by the absence of detectable deterioration after 655 hours of testing at 150 degrees Celsius.

Future Perspectives

This study presents the synthesis of a multifunctional coating with a high solar absorption coefficient, low-temperature emittance, and good fire retardancy based on an environmentally friendly DOPO oxygen harvesting substrate at a cheap cost.

A novel 15% flame retardant polymer coating composite (PHED coating composite) was also developed and successfully deployed on alumina and PPS substrates. In the long run, PPS material can be used as a support material for the installation of thermoplastic solar absorbers on building surfaces. Depending on legal changes and the larger implications of polymeric solar absorbers, these sorts of applications may be in high demand in the near future.

Continue reading: Innovations in Nanocomposites: A Future Outlook.


Štirn, Ž. et al. (2021) Effect of bridged DOPO/polyurethane nanocomposites on solar absorber coatings with reduced flammability. Solar Energy, 231, 104-114. Available at:

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Hussain Ahmed

Written by

Hussain Ahmed

Hussain graduated from Institute of Space Technology, Islamabad with Bachelors in Aerospace Engineering. During his studies, he worked on several research projects related to Aerospace Materials & Structures, Computational Fluid Dynamics, Nano-technology & Robotics. After graduating, he has been working as a freelance Aerospace Engineering consultant. He developed an interest in technical writing during sophomore year of his B.S degree and has wrote several research articles in different publications. During his free time, he enjoys writing poetry, watching movies and playing Football.


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