Author's details: Marie-Pierre Laborie is full professor at the Faculty of Environment and Natural Resources at the University of Freiburg, where she leads the chair of Forest Biomaterials.   She obtained her PhD in Forest Products at Virginia Tech in 2002 and then joined the Department of Civil and Environment Engineering at Washington State Universiy as assistant Professor, where she received promotion to associate professor and tenure. She received her habilitation in Polymer Processing and Engineering from Grenoble Polytechnic Institute in 2009 and subsequently joined the University of Freiburg.  Since 2013, she is an elected Fellow of the International Academy of Wood Science.  She is the author of ca 90 peer-reviewed publications and co-inventor of several patents in the field of value-adding wood polymers in novel polymer materials and applications; Her team’ research work has been recognized with multiple awards including the German High Tech Champion Award 2013 for tannin-based foams and the Thinking Award 2020 for 3D printing with wood polymers.

Fields of Expertise:  lignin, condensed tannins, wood adhesives, 3D printing, polymer blends, tannin- and lignin-based thermosetting and thermoplastic blends

Abstract

Lignins and condensed tannins are the most abundant natural polyphenols.   Despite significant molecular differences, processability and reactivity, both renewable macromers exhibit attributes that make them attractive to design bio-based polymeric systems in both thermosetting adhesives and processable gels or thermoplastics applications.   As pioneered in the early 80s by Glasser’s group at Virginia Tech, one of the trick to impart process- ability and to design desirable properties in the final solidified material at once is to tune natural polyphenols in a molecularly controlled manner.  In this way, one can engineer their compatibility with other biopolymers as might be needed for flowable polymer blends; one can also engineer their reactivity and network formation kinetics for thermosetting polymer applications.  Expanding on the findings and research avenues explored in the early 80s, this overview presents the most significant findings our research group at the University of Freiburg has unravelled in the course of the past decade.  It is thereby demonstrated that flowability, network formation and end-use thermomecanical properties of natural polyphenolic systems can be molecularly designed through controled molecular derivatization.  Through fundamental model studies, light is further shed on the underlying thermodynamics of phase development, morphology and physico-mechanical properties.  For example, hydroxypropylation and bleaching-induced ring cleavage are both powerful to alter the polymer chain branching, stiffness and propensity for intermolecular interactions, thus enabling the fine-tuning of the end properties of polyphenolic polymer systems. Such strategy is highly meaningfull whether thermosetting or thermoplastic processes are to be employed for the polyphenolic material system.   Thus, applications of polyphenolic polymer systems as thermosetting wood adhesives and as processable inks for 3D printing might come one step closer to industrial reality.