Facile Catalyst‐Free Approach toward Fully Biobased Reprocessable Lignin Thermosets

Abstract

Reprocessable and biobased thermosets are prepared from two renewable feedstocks, lignin and polyamine (Priamine 1071). Lignin is oxidized to produce polycarbonyl and further reacts with polyamine to form a crosslinked network of imines. The thermoset materials are formed under heat and pressure in the absence of any catalysts. The mechanical strength and thermal properties of thermosets are tunable by changing feedstock ratios. The dynamic imine crosslinks can be associatively reformed.

Mechanically Tunable and Reconstructable Lignin Thermosets via “Click” Chemistry and Surface Functionalization

“…Furthermore, the decrease in peak intensity for the δ = 100−140 ppm and the formation of a new chemical shift around δ = 60 ppm indicate the conversion of alkenes to thioethers via the thiol-ene reaction. Further studies using 29 Si NMR confirmed the presence of Si in the material at δ = 100 ppm, which corresponds to the chemical shift of the cross-linker (Figure S6).…”

“…Since the thiol-ene reaction proceeded via thermal initiation, the thermosets could be used directly for testing after curing. 36 The incorporation of silyl ether crosslinkers into the thermosets was qualitatively measured using FTIR and solid state 13 C and 29 Si NMR (Figure 3 and Figure S6) and ICP-MS (Table S1).…”

“…To ensure that the silyl ethers could be chemically degraded, in a model reaction TBAF was added to a solution of crosslinker using DSE-6. The reaction was tracked via 1 H, 13 C, and 1 H− 29 Si HMBC NMR (Figures S3−S5). Disappearance of the alpha protons to the silyl ether confirms its degradation while the correlation between the Si and the methine proton in isopropyl remains intact.…”

“…The high hydroxyl content of lignin makes it appealing for undergoing cross-linking reactions. Previous work used different chemistries to cross-link lignin, including epoxide opening, esterification, Diels–Alder, thiol-ene, and many others. − Three factors were considered when designing cross-linkers: ease of synthesis, strong bonding, and degradability. The strength of a Si–O bond is comparable to a C–C bond, which affords its stability during usage .…”

Covalent Adaptable Networks with Tailorable Material Properties Based on Divanillin Polyimines

“…Also, due to the fast kinetics of the exchange reactions taking place in the network, self-healing behavior and fast stress relaxation has been observed in this class of CANs . In addition, the biobased pool of aldehydes is rather extensive, and includes vanillin, − syringaldehyde, , furfural, − and functionalized lignin. − Imine formation is a well-known reaction in which a primary amine reacts with an aldehyde, yielding a CN moiety, with water as the sole byproduct . Taken together, imine-based CANs represent a promising platform as a substituent for nonrenewable materials since dynamic covalent chemistries allow closed-loop recyclability .…”