A study published in Advanced Optical Materials presents a scalable approach for enhancing both the visual and thermal properties of cellulose pulp using fluorescent materials.
Using plant-based pulp and commercial fluorescent paints, the researchers created vividly colored materials that also help reduce solar heat absorption, thus offering a dual benefit for energy-efficient applications.
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A New Take on Cellulose in Thermal Applications
Cellulose pulp is widely used across industries thanks to its abundance and renewability. However, its naturally brown hue (due to residual lignin) limits its suitability in visually driven or thermally demanding contexts like cool roofing or temperature-sensitive packaging.
While bleaching can improve whiteness and reflectivity, achieving vibrant colors without compromising thermal performance has remained a challenge.
This research introduces a fluorescence-based solution. Rather than relying solely on reflectance, the team incorporated fluorescent paints into bleached pulp to harness photoluminescence (PL). This light re-emission effect, known as Stokes shift, converts higher-energy sunlight into longer wavelengths, reducing heat buildup while enhancing color intensity.
Combining Structure and Function: A Two-Step Process
The research team developed a scalable, two-step method for producing fluorescent-colored cellulose pulp with improved thermal regulation. First, the pulp was bleached using a hydrogen peroxide spray to remove chromophoric lignin groups and enhance brightness. This step reduced the lignin content (as indicated by a lower Kappa number), while preserving the structural integrity of the fiber network.
In the second step, the bleached pulp was infiltrated with commercially available fluorescent paints in red, yellow, and blue (FP-R, FP-Y, FP-B). These were applied via spray-coating or brush-coating.
The pulp’s multiscale porous fiber network played a key role, enabling uniform distribution of fluorescent pigments and promoting strong interfacial bonding—likely through hydrogen or ionic interactions. The sheets were then air-dried under ambient conditions.
Measuring Optical and Thermal Performance
To characterize the material’s optical properties, the team used UV-Vis-NIR spectrophotometry, fluorometry, and infrared (IR) imaging. Reflectance spectra confirmed high solar reflectivity, while excitation and emission spectra validated the PL behavior of the fluorescent paints.
To separate the photoluminescent contribution from basic reflectance, the researchers implemented shortpass optical filters, which allowed them to isolate and quantify the true reflectance and re-emitted light. This step was essential for confirming that fluorescence, not just reflectivity, was responsible for the observed cooling benefits.
They also conducted thermal simulations based on a radiative heat balance model to predict steady-state surface temperatures and compute the cooling power saved by the fluorescent treatment.
These predictions were validated by 24-hour field tests conducted in West Lafayette, Indiana, where treated and untreated samples were exposed to real sunlight on a rooftop setup.
Key Findings and Insights: Fluorescence in Action
The results showed that integrating fluorescent paints into cellulose pulp significantly improved thermal regulation while preserving bright coloration. Under sunlight, fluorescent-treated samples remained 7 to 11 °C cooler than non-fluorescent controls. This temperature drop was attributed to both the PL effect and the pulp’s porous structure, which enhanced light scattering and solar reflectance.
Field tests confirmed these findings. During peak daylight hours, the treated samples showed average temperature reductions of 10.7 °C (FP-R), 6.9 °C (FP-Y), and 10.5 °C (FP-B) compared to their non-fluorescent counterparts. The estimated cooling power achieved ranged from 50 to 130 W m-2, depending on pigment type and spectral properties.
Significantly, the treatment did not compromise the material’s structural performance. The tensile strength of the fluorescent-treated pulp remained around 40 MPa, which is suitable for industrial applications. Additionally, the treatment altered the surface from hydrophilic to hydrophobic, improving water resistance and environmental durability.
Real-World Potential: Where Fluorescent Pulp Can Be Used
The dual benefits of thermal regulation and vivid color open up a range of applications for fluorescent-enhanced cellulose pulp:
- Construction: For cool roofs, wall panels, and sunshades to reduce heat absorption in buildings.
- Packaging: Particularly for cold chain logistics, where maintaining low temperatures is essential.
- Horticulture: In plant containers, where reduced soil temperature supports root health and growth.
- Outdoor Wear and Gear: Where both thermal comfort and design are key, especially in hot climates.
Because the process integrates with existing pulp and paper manufacturing systems, it is cost-effective and scalable for commercial use. Minimal changes are required for implementation in standard production lines.
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Future Directions and Outlook
This study demonstrates that cellulose, traditionally considered a low-value, functional material, can be elevated into a high-performance, sustainable product by leveraging fluorescence and thoughtful material design. The work not only addresses current limitations in thermal and aesthetic performance but also broadens the role of bio-based materials in modern industry.
Looking ahead, further research could focus on optimizing fluorescent paint formulations, extending color variety, and tailoring optical properties for specific environmental conditions. This approach may also benefit new application areas such as smart packaging, wearable materials, or decorative outdoor architecture.
Journal Reference
Cheng, Q., et al. (2025). Fluorescent-Enhanced Radiative Cooling of Colored Cellulose Pulp for Thermal Management and Aesthetic Applications. Advanced Optical Materials. DOI: 10.1002/adom.202402827, https://advanced.onlinelibrary.wiley.com/doi/10.1002/adom.202402827
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