Lignin-containing cellulose nanofibril application in pMDI wood adhesives

Significance 

Recently, reinforced and functional polymers have attracted research attention owing to their application in numerous areas. Depending on the desired applications and material properties, different functional polymers have been developed. In particular, cellulose nanofibrils have been extensively used in the development of polymer materials owing to their excellent properties. Usually, production of the cellulose nanofibrils requires lignin removal to facilitate a thorough fibrillation of cellulose fibers to cellulose nanofibrils given that lignin acts as a binder between fibrils. Nonetheless, recent research shows that having some lignin component remain is advantageous in lowing the impact on the environment, cutting down the production cost and optimizing the performance efficiency (enhancing the thermal stability and increasing the compatibility with hydrophobic polymers). Therefore, lignin-containing cellulose nanofibrils (LCNF) without completely removing lignin have been developed in this context.

While a stringent regulation has been applied on the use of formaldehyde-based commercial wood adhesives taking into consideration of the potential harmful impact of formaldehyde, polymeric diphenylmethane diisocyanate (pMDI) is identified as a promising formaldehyde-free solution. Despite its advantages, several challenges especially during the manufacturing process, render pMDI wood adhesives unsuitable for applications that require a continuous bondline. Even though studies regarding enhancement of the mechanical performance of adhesives is well covered in existing literature, the effect of LCNF on pMDI wood adhesives remains a research area.

To this note, University of Toronto researchers: Heyu Chen (PhD candidate), Dr. Sandeep Nair, Dr. Prashant Chauhan and led by distinguished professor, Prof. Ning Yan, investigated the effect of LCNF on the reinforcing performance of pMDI wood adhesives. The authors tested either solvent-exchange or freeze-dried LCNF aqueous suspension before mixing with the pMDI. The solvent-exchange helped in replacing water with low polarity organic solvent while the freeze-drying helped in removing water from the aqueous solution without losing the original fibril structure. Specifically, 3wt% of solvent-exchanged LCNF and 3wt% of freeze-dried LCNF were added to the pMDI, respectively. Eventually, the performance of the two methods was compared based on the bonding performance of the resulting adhesives. The work is published in Chemical Engineering Journal.

For the solvent-exchanged and freeze-dried method, Prof. Ning Yan and her research team observed enhanced dry bonding strength by 109% and 69% and wet bonding strength by 119% and 84% respectively. This was attributed to the highly reactive nature and reaction accessibility of the lignin on the nanocellulose fibril. Furthermore, it was necessary to conduct curing kinetics analysis. Curing pMDI with LCNF required higher activation energy than that with the moisture in wood. The fact that neat pMDI performed poorly in applications require adhesive retention at the bonding interface was due to the inconsistent and partially starved bondline. However, this pMDI limitation was effectively solved with a small amount of LCNF addition by drastically enhancing the gap-filling properties thus forming continuous bondline. Therefore, sustainable LCNF from renewable biomass will advance the development of high-performance pMDI adhesives for wider practical applications.

Lignin-containing cellulose nanofibril application in pMDI wood adhesives for drastically improved gap-filling properties with robust bondline interfaces - Advances in Engineering

About the author

Heyu Chen is a PhD student in Faculty of Forestry at the University of Toronto. He received his Bachelor and Master’s degree at the Beijing Forestry University. His research focuses on the utilization of tree bark and bark components for polyurethane-related applications.

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About the author

Dr. Nair completed his PhD in Advanced Materials Research from the University of Tennessee, USA in 2012. He worked as a Postdoctoral Fellow for two years at the School of Chemistry and Biochemistry, Georgia Institute of Technology, Atlanta, Georgia. During this time, he also worked as a visiting scientist in the USDA’s Forest Products Lab, Fiber and Chemical Sciences Research unit in Madison, Wisconsin.

In 2014, Dr. Nair joined university of Toronto, Canada as a Post Doc and his current research focuses on the design, synthesis, and characterization of biomass derived polymers for high performance applications. His research areas include the development of advanced green barrier materials, sustainable green composites for various packaging, automotive and other applications.

Dr. Nair has played a significant role in the development of various novel bionanomaterials, such as high lignin containing nanocellulose, nanolignin particles, and nanosized fibrils from various allomorphs of cellulose. He has also been part of a team in developing various biobased smart materials using chemical and physical modifications of cellulose. Currently, his research also focuses on development of conductive composites and next generation green electronics.

About the author

Dr. Chauhan received his Bachelor (2008) and Master (2010) degrees in Organic Chemistry from University of Delhi, India. He completed his PhD degree (2013) from Department of Chemical Sciences, University of Padua, Italy. In 2014, he joined Rhodes University, South Africa for a brief postdoc research. Later, the same year he joined University of Toronto, Canada as postdoc and his present research focuses on nanocellulose derivatives for advanced applications.

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About the author

Dr. NING YAN holds a University of Toronto Distinguished Professorship in Forest Biomaterials Engineering at the Department of Chemical Engineering and Applied Chemistry. She was also an Endowed Chair in Value Added Wood and Composites. Dr. Yan is currently the Director of the Low Carbon Renewable Materials Centre in the Faculty of Applied Science and Engineering. Dr. Yan has more than150 peer-reviewed journal papers. She is an international expert on forest biomaterials science and bio-based products and has won numerous prestigious awards for her research excellence. She obtained her Ph.D. from the Department of Chemical Engineering and Applied Chemistry of the University of Toronto in 1997.

Reference

Chen, H., Nair, S., Chauhan, P., & Yan, N. (2019). Lignin containing cellulose nanofibril application in pMDI wood adhesives for drastically improved gap-filling properties with robust bonding line interfaces. Chemical Engineering Journal, 360, 393-401.

Go To Chemical Engineering Journal

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