Millions of people touch thermal paper daily, whether it's receipts, shipping labels, or medical reports. This paper almost always contains bisphenols like BPA or BPS, substances that can disrupt hormone balance. Researchers at EPFL in Switzerland have developed a sustainable alternative that uses lignin and wood sugars as the basis for safe printing.
Thermal paper works through a chemical reaction between a dye and a developer. As soon as the print head of a cash register heats the paper, the text becomes visible. Bisphenol A (BPA) or its successor, bisphenol S (BPS), is typically used for this reaction. Because these substances can be absorbed through the skin and end up in the environment, they are subject to strict supervision by European regulators. Finding a safe alternative has proven complex so far, as a replacement must not only be less toxic but also remain stable under varying environmental conditions.
Lignin as a natural foundation
Scientists from the groups of Jeremy Luterbacher and Harm-Anton Klok at EPFL have demonstrated that lignin can offer an effective solution. Lignin is a main component of wood and is often considered a byproduct in the paper industry, but it naturally contains chemical groups suitable for use as a color developer. The biggest challenge for the researchers was the material's color; unpurified lignin is dark, which is undesirable for white paper.
By using a specialized extraction method, the sequential aldehyde-assisted fractionationThe team succeeded in producing light-colored lignin polymers. This material mixes well into the thermal coating layer, creating a smooth and printable surface. To achieve the necessary reactivity at the right temperature, the researchers also added a plant-based substance derived from wood sugars (xylan).
Verified safety and performance
The results of the new formulation show that the prints on the lignin paper are sharp and, according to the researchers, remain legible for at least a year. The color intensity of the prints is therefore comparable to current commercial standards for thermal paper.
In terms of safety, the gains are significant. Extensive testing shows that the estrogenic activity of the wood-based developer is up to ten thousand times lower than that of BPA. The sugars used showed no toxic signals in the study. Although further steps are needed to reproduce the process on an industrial scale, this research proves that an everyday product like a cash register receipt can be completely transformed using biochemistry from woody waste streams.
Source: EPFL News
Photos: Basic Sciences | SB
