Maleated kraft lignin has been explored as a building block for degradable thermosets. The maleation procedure allows for a facile and atom-efficient way to install functional handles into the lignin structure, rendering the obtained lignin amenable for cross-linking via amine-Michael addition and thiol-ene coupling. Since lignin modification leads to the formation of an ester linkage, the final thermosets are susceptible to hydrolytic degradation, demonstrated under basic conditions (NaOH, 0.6 M, acetone/water (1/2.5, v/v) for 2.5 h at 75 °C). We also extended the study to biocomposite formulations with cellulose nanofibrils as reinforcing agents. The final biocomposites demonstrated strengths of 110-150 MPa and moduli of 4-5.5 GPa at 55-65 wt % of nanocellulose. This work offers a cradle-to-grave approach for biobased and degradable thermosets and composites from technical lignin.

Lignin is the largest source of renewable aromatics on earth. Despite numerous techniques for lignin depolymerization into mixtures of valuable monomers, methods for their upgrading into final products are scarce. The state of the art upgrading methods generally rely on catalytic funneling, requiring high temperatures, catalyst loadings and hydrogen pressure, and lead to the loss of functionality and bio-based carbon content. Here an alternative approach is presented, whereby the target monomers are selectively converted in unpurified mixtures into easily separable final products under mild conditions. We use reductive catalytic fractionation of wood to convert lignin into iso-eugenol and propenyl syringol enriched oil followed by an olefin metathesis to yield bisphenols and butene-2, thus, valorizing all bio-based carbons. To further demonstrate the synthetic utility of the obtained bisphenols we converted them into polyesters with a high glass transition temperature (Tg = 140.3 °C) and thermal stability (Td50% = 330 °C).

Cellulose nanofibril (CNF) materials are candidates for the sustainable development of high mechanical performance nanomaterials. Due to inherent hydrophilicity and limited functionality range, most applications require chemical modification of CNF. However, targeted transformations directly on CNF are cumbersome due to the propensity of CNF to aggregate in non-aqueous solvents at high concentrations, complicating the choice of suitable reagents and requiring tedious separations of the final product. This work addresses this challenge by developing a general, entirely water-based, and experimentally simple methodology for functionalizing CNF, providing aliphatic, allylic, propargylic, azobenzylic, and substituted benzylic functional groups. The first step is NaIO4 oxidation to dialdehyde-CNF in the wet cake state, followed by oxime ligation with O-substituted hydroxylamines. The increased hydrolytic stability of oximes removes the need for reductive stabilization as often required for the analogous imines where aldehyde groups react with amines in water. Overall, the process provides a tailored degree of nanofibril functionalization (2-4.5 mmol/g) with the possible reversible detachment of the functionality under mildly acidic conditions, resulting in the reformation of dialdehyde CNF. The modified CNF materials were assessed for potential applications in green electronics and triboelectric nanogenerators. Water is a standing challenge in the chemical modification of cellulose nanofibrils. Here, authors employ oxime-ligation to solve this by direct covalent chemistry on dialdehyde-CNF in water and assess the material for potential applications in green electronics and triboelectric nanogenerators.

Design of nanocellulose-based composite materials suitable for selective disintegration, recovery and recycling of individual components is of great scientific and technical interest. Cellulose nanofiber/epoxy (CNF/EP) composites are candidate bio-based substitutes for petroleum-based materials. However, chemical recovery of such intimately mixed nanocomposites has not been addressed, due to the limited chemical stability of nanocellulose and due to the covalently crosslinked epoxy network. In this work we develop CNF/EP composites designed for selective disintegration. Deconstruction is achieved by including two types of labile linkages to the polymer network; acetals and esters. Besides enabling recycling of the CNF reinforcement, the thermoset constituents were further depolymerized into valuable monomeric units in 63-95% yield. In addition, the preparation of both; epoxy monomers and final composite materials is performed using solely bio-derived materials and solvents. 

Coconut Coir Pith (CCP) is a relatively unexplored type of lignocellulosic waste from the coconut industry. As a feedstock that is highly enriched in lignin (Klason lignin content of 40.9 wt % found in this study), CCP is a potential source for renewable lignin-derived materials. We have performed a systematic study on the characterization and valorization of lignin from CCP. We have investigated two different valorization approaches: reductive catalytic fractionation (RCF) and soda pulping followed by catalytic hydrodeoxygenation. During RCF, the lignin was converted into monomeric products in 7.6 wt %. Using soda pulping conditions, we were able to isolate lignin from CCP in 74% yield. Subsequent hydrotreatment of the lignin over a Pt/MoO3/TiO2catalyst resulted in the formation of hydrogenated oil in 43 wt % yield, suitable for the production of biobased diesel fuels and lubricant base oils.