A more sustainable and less toxic form of paper used in tickets is being developed using wood derivatives

The study conducted by Professor Luterbacher and Professor Klok's groups is a step forward in replacing non-renewable products with more sustainable equivalents produced from biomass, with the added advantage of reduced toxicity. Often, everyday products that appear to be harmless contain additives that may be toxic or carcinogenic. This is the case with thermal paper, where letters and images appear when heated instead of using ink. This makes it a widely used paper, for example, in receipts, shipping labels, tickets and, in general, devices where avoiding the use of ink is an advantage. Although its use does not pose a health problem, as it is not perceived as toxic waste, it is often discarded and the toxic additives are released into the environment, potentially causing unexpected problems.

The use of renewable products, although possible, has always been complicated because current products derived from non-renewable sources such as petroleum are usually cheaper. Biomass fractionation has been carried out for decades in the paper industry, with good results obtained with cellulose but little innovation regarding the use of lignin and hemicellulose. The work of Professor Luterbacher's group and the company Bloom Biorenewables in developing assisted fractionation has been one of the greatest innovations in this field, opening up new possibilities. This process, unlike any previously studied, combines the fractionation of biomass into cellulose, hemicellulose and lignin with the protection of lignin and hemicellulose. This allows for the production of a different type of lignin than that obtained through other processes, which has now been shown to be usable for synthesising products equivalent to BPA, which is carcinogenic. Professor Luterbacher's process prevents the condensation of lignin that occurs in other processes, which makes it unusable as a chemical product and only usable as an energy source. This is the case with the Kraft process (the main process used in the paper industry). In addition, this protection, which can be achieved with various chemical compounds, gives lignin new functionalities that allow it to be used as a raw material in processes that were not previously considered possible, such as the one described in this article. Similarly, a new use has emerged for hemicellulose, diformylxylose, a sugar compound with properties very different from those of the original sugar (xylose) or other compounds derived from it, such as furfural or xylitol. This new natural compound obtained in Professor Luterbacher's laboratory also opens up many new possibilities and has resulted in one of the greatest innovations in the area of pentose (five-carbon sugar) valorisation, which is set to be very successful in the future.

It is true that thermal paper obtained using these compounds does not have as good properties as commercial paper, and that is a limitation, but the research is in its early stages and still needs optimisation, especially considering that the leading researchers in this work are not dedicated to the production of this type of paper but to developing more sustainable chemistry. The authors of the work also discuss the economic issue, acknowledging that it may not be as economical as the paper used today, but the values presented are not far from the cost of the chemicals used today. If we take into account the reduced toxicity of the new products, a small additional cost may be acceptable, especially since this difference can be reduced with the scaling and optimisation of the process. In addition, this work may encourage the use of these new chemicals obtained from biomass in other applications that were not previously considered possible.

The article is not only of interest to scientists and companies specialising in the field. The authors describe the product, the related chemistry and the problems that can be encountered in the production and use of thermal paper in a simple and easy-to-follow way for non-experts, so it may also be of interest to the general public.

The study looks promising and fits in with existing evidence, because it is a small step forward from previously published studies on the use of lignin. Lignin is one of the two main components of wood. On the one hand, there is cellulose, which is used to make paper, and on the other, there is lignin, which is normally discarded, although research is now being conducted into its possible applications.

As I say, it seems incremental because even the authors themselves refer to a previous study by the same group. In that article, they had studied this type of lignin use for similar applications and also used a process for manufacturing inks and receipts that was described. So I understand that it is not such a novel study.

What the authors have achieved is to develop, from lignin, several components that could be used to print receipts such as those from supermarkets, motorway tolls, car parks, etc., in a slightly more sustainable way. Sustainable because they are compounds obtained from one of the main components of wood, which is reused instead of being discarded. But it is also more sustainable because one of the ingredients currently used to make these types of receipts work is bisphenols, especially bisphenol A, which has been linked to hormonal problems (endocrine disruptors).

The receipts do not contain large amounts, but according to the article, they sometimes use more bisphenols than light-sensitive inks. The authors also cite other studies showing that these lignin-derived substances are not as dangerous as petroleum-derived bisphenols.