Four Canadian researchers make a case that lignin could become an important feedstock for bioplastics.
“Considering the current production of lignin from pulp and paper industries as well as potential future production from lingocellulosic ethanol industries, it is estimated that around 300 M ton/year of lignin will be produced in North America,” they said in an article presented at the Annual Technical Conference (Antec) of the Society of Plastics Engineers (SPE) held concurrently last month with NPE2012 in Orlando, FL. “Lignin is now considered as an inexpensive co-product and it is mainly used as a boiler fuel. The value of lignin can be better realized as a good source for new outlets such as renewable resource based materials.”
Lignin can be made into phenol, terephthalic acid, benzene, xylene, and toluene—important building blocks for aromatic plastics. Other potential uses are in the production of surfactants and UV stablizers. “However, all these new uses account for only 2% of the generated lignin and the remaining is mostly burnt for energy as low efficient fuel.”
That’s unfortunate because lignin has the advantages of low cost and a density about half of talc or calcium carbonate—common fillers in plastic compounds. As engineers take weight out of products, the density of talc and calcium carbonate is a problem. Lignin is a random amorphous polymer with various chemical functional groups including hydroxyl, methoxyl, carboxyl and carbonyl.
Here are some good things about lignin vis-à-vis plastics:
- It forms miscible blends with polyethylene terephthalate (PET) and polyethylene oxide,
- It forms hydrogen bonds with poly(vinyl 4-pyridine), boosting its mechanical properties,
- It can be used with other natural reinforcing materials (kenaf, bamboo) to create bio-composites, and
- It can even be used to produce carbon fibers.
Of course, the future of lignin as an important plastics resource will depend on the development of a biofuels industry, which is seemingly up in the air at the moment. The corn-to-ethanol industry was largely a political boondoggle in the United States. The economics of lingocellulosic ethanol may not be as upbeat as the Canadian authors suspect. We do have a pulp and paper industry, but the death of print media has made it a shadow of its former self.
The title of the study is “Improved Utilization Of Co-Products From Biofuel Industries In New Biomaterials Uses: A Move Towards Sustainable Biorefinery”. Authors are A. K. Mohanty, S. Vivekanandhan, N. Zarrinbakhsh, and M. Misra of the Bioproducts Discovery and Development Centre, Department of Plant Agriculture, Crop Science Building, University of Guelph, Guelph, Ontario.Mohanty is the corresponding author and he can be reached at firstname.lastname@example.org.
Interestingly, Amit K. Naskar (email@example.com ) of the Polymer Matrix Composite Group, Oak Ridge National Laboratory, Oak Ridge, TN, also made a presentation on lignin at Antec.
“Our recent efforts on synthesis of lignin-based bio-thermoplastics show significant promise,” he said in a summary of his talk provided by the SPE. “Compatibilization of blends of lignin with different polymeric matrices results good thermoplastic for certain lignin loadings. These routes would provide a low-cost alternative, recyclable resins for future composite applications.”
So it would appear clear that scientists like the technical potential for lignin. Note though that the research is being done by academics and governments. The economic availability of lignin as a large scale resource may be a long way off.