Alternative to Bisphenols Lignin Replaces Bisphenols in New Bio-Based Thermal Paper Formulation

Receipts and labels rely on heat-sensitive chemicals that can disrupt hormones and spread through recycling streams. New research demonstrates that lignin from wood can function as a low-toxicity developer in thermal paper, matching the performance of conventional materials.

Every day, millions of people use thermal paper without thinking about it. Receipts, shipping labels, tickets, and medical records all rely on heat‑sensitive coatings to make text appear. More specifically, heat triggers a reaction between a colorless dye and a “developer,” producing dark text where the paper is warmed.

Thermal paper is a small object with a large footprint. It is produced at scale, handled daily, and often recycled, which allows its chemicals to spread into water and soil. For decades, the most common developers have been bisphenol A (BPA) and, more recently, bisphenol S (BPS). Both can affect living organisms by disrupting hormone signaling, and both are detected in the environment and in people who handle receipts frequently.

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Finding safer alternatives to bisphenols is difficult because thermal paper must also be stable, printable, and cost-effective: in 2022, the global thermal paper market was valued at around 4 billion dollars and is expected to grow to about 6 billion dollars by 2030.

Regulators and manufacturers have looked for replacements, but progress has been slow, since any less toxic alternative must also react at the right temperature, stay stable during storage, mix well with other coating ingredients, and avoid background discoloration. And many proposed bio‑based materials fail on one or more of these.

A Solution from Wood

Scientists in the groups of Jeremy Luterbacher and Harm-Anton Klok at EPFL have now shown that wood‑derived materials can meet these requirements. In a study published in Science Advances, the researchers report thermal paper coatings that use lignin, a major component of wood, together with a sensitizer derived from plant sugars.

“We have developed thermal paper formulations — which are commonly found in daily products like cash receipts, package labels, airline tickets, etc. — made from plant-based molecules that have very low or no toxic signatures,” says Luterbacher, who became known in 2014 after developing a method for cheaply extracting lignin from plants, while avoiding its destruction (published in Science).

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The new study builds on the lab’s ongoing work with lignin. The researchers focused on it because it already contains chemical groups that can act as color developers.

But isolated lignin is usually dark and chemically messy, which makes it unsuitable for printing. To address this, the researchers used a controlled extraction method, called “sequential aldehyde‑assisted fractionation”, to produce light‑colored lignin polymers with fewer of the dark, color‑absorbing groups that can interfere with printing. Their chemistry also allowed it to be well mixed in the thermal layer — a key prerequisite to proper reactivity.

To make the lignin reactive at printing temperatures, the team added a “sensitizer,” a compound that melts when heated and helps the dye and developer interact. Instead of using conventional petroleum‑based sensitizers, they tested diformylxylose, a molecule made from xylan, a sugar found in plant cell walls. They then applied the resulting mixtures as thin coatings onto paper and tested them using controlled heating and commercial printers.

A Clear Advantage on Safety Tests

The lignin‑based coatings produced clear printed images when heated, with color density values in the same range needed for commercial thermal paper. The coatings stayed stable when stored near a window for months, and printed logos remained readable after a year. While image contrast was still lower than that of fully optimized commercial paper, the performance matched that of BPA-based thermal papers.

Safety tests also showed a clear advantage, as the lignin developers displayed estrogen‑like activity that was over two to four orders of magnitude lower than BPA. The sugar‑based sensitizer showed no estrogenic or toxicity profile under the tested conditions.

The study shows that safer thermal paper formulations can be made directly from non‑edible biomass using simple processing steps. While more work is needed to optimize print quality and scale‑up, the results point toward receipts and labels that do their job without relying on problematic chemicals.

Original Article: Sustainable Thermal Paper Formulation Using Lignocellulosic Biomass Fractions; Science Advances; DOI:10.1126/sciadv.adw9912

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