Scientists are seeking patent for ‘green’ method to treat main waste product from the paper industry

Acetic acid, a component of vinegar, was used by researchers in the state of São Paulo to fractionate kraft lignin. The method produces nanoparticles with different properties, including UV protection.

By Karina Ninni  |  Agência FAPESP – Researchers at São Paulo State University (UNESP) and the Federal University of São Carlos (UFSCar) in Brazil used acetic acid, the main component of vinegar, as a green solvent to promote the fractionation of kraft lignin, an abundant waste product from the Brazilian pulp and paper industry. This renewable, biodegradable option makes the process more sustainable.

Jessica Rodrigues, a chemical engineer with a Ph.D. in materials science from UFSCar and a postdoctoral researcher at UNESP’s Sorocaba campus, explained that lignin is a highly complex and heterogeneous molecule, which makes it difficult to use in various applications. Thus, the idea is to fractionate it and separate it into specific portions.

“There are several types of lignin: kraft, alkaline, organosolv, sulfonated, among others. These types vary according to the treatment of the raw material since the names refer to the lignin extraction process. When eucalyptus is treated by the kraft process to isolate cellulose, kraft lignin is generated as a by-product. We chose it because it’s the waste product obtained in the largest quantities in the paper industry in Brazil. We know that its phenolic structures are applicable in various fields, from advanced materials to nanotechnology. So we take the industry’s by-product and add value to it.”

The researcher explains that the idea came from the fact that acetic acid is already used for organosolv lignin extraction. “So we thought: why not use acetic acid to fractionate kraft lignin? It’s low cost compared to methanol, ethyl acetate, and other solvents used for this purpose, and it can be produced from waste. Not to mention that it’s safe, and in low concentrations, can be found in commercial products.”

The patent, filed with the National Institute of Industrial Property (INPI) under the number BR 10 2024 0201817, is called “Green process for obtaining specific fractions of kraft lignin and applications in nanotechnology.” Four other scientists, besides Rodrigues, are involved in the patent: Leonardo Fraceto, the Innovation Coordinator at the Center for Research on Biodiversity and Climate Change (CBioClima), one of FAPESP’s Research, Innovation and Dissemination Centers (RIDCs); Vagner Botaro; Amanda de Sousa Martinez de Freitas; and Marystela Ferreira.

The work is supported by FAPESP through five projects (23/06505-9, 22/03399-0, 17/21004-5, 23/00335-4 and 21/10639-5).

Rodrigues points out that there are several ways to fractionate kraft lignin. One method is precipitation with sulfuric acid, which reduces the pH. Another method is ultrafiltration, which separates by size. Fractionation can also be performed using sequential fractionation in organic solvents. “We were able to perform the fractionation with a single solvent, varying only the percentages of the solvent.”

UV protection

The group found that using 30%, 40%, or 50% acetic acid yielded more homogeneous lignin fractions with different properties. “Lignin fractionated with 30% acetic acid is rich in phenolic hydroxyl [OH] groups, while that fractionated with 50% of this solvent is rich in aliphatic OH.” These groups are indicators used to characterize lignin, which is not a well-defined molecule.

According to Rodrigues, one property of phenolic OH is its UV protection capacity. “It’s possible to produce UV protectors from this phenolic OH-rich lignin, which is what we ended up doing here: we obtained a nanoparticle from some fractions of this lignin and saw that that nanoparticle forms a capsule around the active ingredient to be protected. And the encapsulation efficiency was very good.”

She explains that the higher the percentage of aliphatic OH, the smaller the particle size. She also notes that a higher percentage of phenolic OH results in a larger nanoparticle size and greater UV protection.

The researchers are studying the biodegradation of nanoparticles in soil and water to reduce the emission of microplastics used in agriculture into the environment. When fertilizers, herbicides, and other agricultural products containing microplastic components are applied on a large scale, they generate environmental impacts due to the accumulation of this material in soil and water.

The group is interested in what it calls “structure-performance correlation.” “We hope, at some point, to be able to specify the areas of application for these nanoparticles when they have a higher percentage of phenolic OH and when they have a higher aliphatic OH content. We’re thinking in terms of biorefinery: to be able to show that each fraction of lignin is interesting for a specific area of application.”

In this regard, the researchers have produced several articles. The first, on the patent itself, has already been submitted to an international journal. “In a second article, we used lignin fractions as a stabilizer for another existing nanoparticle produced with synthetic biodegradable polymers. We tested these nanoparticles in controlling weeds such as black grass and caruru. And in the last article, we tested their efficiency in releasing NPK fertilizer into the soil. In other words, we’ve conducted research in several areas to prove the concept of the structure-performance relationship.”

Biodegradation

According to Rodrigues, the group is considering adding possible products derived from lignin fractions to the process patent already filed, given the diversity of applications. They are also trying to establish partnerships with industry. “We’ve already stabilized the nanoparticles and now we want to observe how they behave in biodegradation tests, checking whether they release microplastics in the process.”

The group wants to establish a relationship between stability and biodegradation and develop protocols to demonstrate biodegradability. “Due to the nanoscale size of the particles, proving this is challenging. We’re studying existing protocols and developing our own.”