Lignin-derivable alternatives to petroleum-derived non-isocyanate polyurethane thermosets with enhanced toughness

Abstract

Lignin-derivable non-isocyanate polyurethane thermosets are highlighted as potential alternatives to petroleum-derived analogues with significant enhancement in toughness without compromising other application-specific thermomechanical properties.

Flexible and Heat-Resisting Lignin-Based Epoxy Resins by Hardwood Kraft Low-Molecular-Weight Lignin as a Sustainable Substitute for Bisphenol A

“…In view of the characteristics of the low-Mw lignin used in this study, it should be attributed to the much lower Mw and dispersity and higher phenolic hydroxyl groups. Based on the well-identified structures of low-Mw lignin, including lignin-derived monomers and dimers (Figure ), the possible enhancement mechanisms (Figures A–E and E) are proposed: (1) Stilbene (SB1) has the conjugated benzene ring and C–C double bond, which enhance the elongation at break and stress transfer; − (2) syringaresinol with furan rings reacts with the amine group to open the ring during curing; on the one hand, chemical cross-linking with long-chain amines in the branched chain enhances toughness, and on the other hand, the reaction sites are increased in both the backbone and branched chain, which promote three-dimensional (3D) cross-linked network formation and, as a result, improved stress–strain performance; − (3) aldoketones and amines can react to form Schiff bases, allowing monomers containing aldehydes and ketones to participate in the reaction at both ends of the curing stage, which results in a chain growth of epoxy resin and conjugate structures that increase elongation; (4) LKL is rich in methoxyl groups compared to BPA, which can provide additional hydrogen-bonding sites and enhance the ability to participate in hydrogen bonding and thus improve elongation; ,− (5) the decrease in T g is conducive to an increase in ductility; hence, the lower T g of the LEPs contributes to their high elongation; (6) in epoxy resins with different EEW and epoxy values, the lower the EEW, the higher is the epoxy value, the stronger is the reactivity, and the superior is the tensile strength . Considering that LKLGE-2 exhibited the highest epoxy value among all LKLGEs, it will have the smallest extent of polymerization and a maximal reaction with amine during curing, which result in its highest tensile strength.…”

A guide to modern methods for poly(thio)ether synthesis using Earth-abundant metals

“…Furthermore, epoxidebased polyethers and by extension episulfide-based polythioethers have the potential to be made completely from biorenewable resources. [222][223][224] Significant challenges remain, however, in the area of accessibility. As this article demonstrated, there are several techniques to synthesize poly(thio)ethers, but none of them are as facile, broadly applicable, and accessible as techniques like RAFT polymerization for vinyl-based monomers.…”

“…As mentioned above, epoxides can be sourced from fully biorenewable resources. [222][223][224] However, poly(thio)ether degradability is lacking; there is significant difficulty to place even some degradable units within a poly(thio)ether backbone, 89 let alone fully de-polymerize it. This is a problem not only from a plastic waste point of view, but also in the biomedical applications poly(thio)ethers are generally used in.…”

“…Furthermore, epoxide-based polyethers and by extension episulfide-based polythioethers have the potential to be made completely from biorenewable resources. 222–224…”

Lignin-derivable, thermoplastic, non-isocyanate polyurethanes with increased hydrogen-bonding content and toughness vs. petroleum-derived analogues

“…25,31,34,41 Recently, renewable bisguaiacols/bissyringols have been reported as potential alternatives to commercial bisphenols because of their structural similarity. These renewable alternatives have methoxy groups on their aromatic rings 30,[43][44][45][46] that have the potential to mitigate the toxicity concerns associated with commercial aromatics (e.g., estrogenic activity, genotoxicity, oxidative DNA damage). 28,47,48 Thermoplastic NIPUs have gained less attention in the literature in comparison to thermosetting NIPUs.…”