A Swedish X-ray analysis has revealed for the first time how the internal molecular structure of different lignin products relates to the macroscopic properties of the materials they are ultimately used to produce.
As a by-product of papermaking, lignin has long been considered a promising, naturally occurring raw material for the manufacture of sustainable plastics. However, its quality has not always been as reliable or predictable as traditional petroleum-based alternatives.
New analysis — carried out at Deutsches Elektronen-Synchrotron DESY, and published in the journal Applied polymer materials — has uncovered an approach that offers a better understanding of the use of lignin as a raw material. These insights could facilitate the production of lignin-based bioplastics with properties that can be varied depending on the requirements of the application.
Lignin is responsible for the stiffness of plants. During paper production, it is separated from cellulose, before forming aromatic compounds which have been found to play a vital role in the manufacture of synthetic polymers or plastics.
A Professor at the Royal Institute of Technology (KTH) in Stockholm, Mats Johansson led the research project. He said lignin is the biggest source of these naturally occurring aromatic compounds, but until now has been viewed by the paper industry as merely a by-product.
“Millions of tonnes of it are produced every year, providing a steady stream of raw material for new potential products,” said Johansson.
While some lignin based plastics, or thermosets, already exist, their properties often vary and have proven difficult to control. The researchers were therefore keen to shed new light on the nanostructure of different types of lignin, by using DESY’s X-ray equipment, PETRA III.
The principle author of the study, Marcus Jawerth, also of KTH Royal Institute of Technology, said the team discovered lignin fractions with larger and smaller domains.
“This can offer certain advantages, depending on the particular application. It makes the lignin harder or softer by altering the so-called glass transition temperature at which the biopolymer adopts a viscous state,” said Jawerth.
Co-author of the paper, DESY’s Stephan Roth, explained the molecular structure impacts the macroscopic mechanical properties of the lignin.
“This is the first time this has been characterised. This is very important in order to be able to manufacture materials reproducibly, and in particular to predict their properties,” Roth said.
As a natural product, lignin comes in numerous different configurations. Further studies are required to develop an understanding of how different parameters affect its properties.
If you want to use a material industrially, you need to understand its molecular structure and know how this is correlated with the mechanical properties,” Roth said.
In light of the research, Jawerth estimated up to two thirds of lignin produced during paper production has the potential to be turned into polyesters, offering a natural raw material for the production of plastics.
“Lignin is one of the most ubiquitous organic compounds on Earth and offers enormous potential for replacing petroleum-based plastics. It’s far too valuable to simply burn it,” Jawerth concluded.
Source: Science Daily
