Tunable Thermosetting Epoxies Based on Fractionated and Well-Characterized Lignins

Abstract

Here we report the synthesis of thermosetting resins from low molar mass Kraft lignin fractions of high functionality, refined by solvent extraction. Such fractions were fully characterized by P NMR, 2D-HSQC NMR, SEC, and DSC in order to obtain a detailed description of the structures. Reactive oxirane moieties were introduced on the lignin backbone under mild reaction conditions and quantified by simpleH NMR analysis. The modified fractions were chemically cross-linked with a flexible polyether diamine ( M ≈ 2000), in order to obtain epoxy thermosets. Epoxies from different lignin fractions, studied by DSC, DMA, tensile tests, and SEM, demonstrated substantial differences in terms of thermo-mechanical properties. For the first time, strong relationships between lignin structures and epoxy properties could be demonstrated. The suggested approach provides unprecedented possibilities to tune network structure and properties of thermosets based on real lignin fractions, rather than model compounds.

Future opportunities for bio-based adhesives – advantages beyond renewability

“…Decrease susceptibility to hydrolytic degradation 111,[113][114][115][116] Statistical design, 117 enzyme layer deposition, 119 amphiphilic battery binder, 121 seaweed 120,122 Lignin Increase reactivity to condensation reactions, 123,124 improve reproducibility and definition of structure 125 Vitrimer with reversible bonding 126…”

Using Fractionation and Diffusion Ordered Spectroscopy to Study Lignin Molecular Weight.

“…[11,12] For example, low molecular weight (MW) Kraft lignin fractions were shown to form thermosets with more optimal properties. [13] This was determined by first fractionating the bulk material taken directly from the industrial process using a selective dissolution protocol (see Figure 1D). Subsequent conversion of the selected fractions into the corresponding thermosets identified the best fraction to use.…”

Lignin for polymer and nanoparticle production: Current status and challenges

“…Due to its high hydrophobicity, OL has been incorporated into different thermoplastic polymers, such as polyurethane and poly(ester‐amine) by crosslinking or grafting . It was found that the polyurethane foams produced with OL demonstrated a higher crosslinking density and thus better mechanical properties compared to that incorporated with KL, probably due to the better miscibility of OL in the polyol . Table also shows that lignosulphonate is considered to be a potential candidate for polymerization attributing to its larger amount of functional groups.…”

“…[65,77] It was found that the polyurethane foams produced with OL demonstrated a higher crosslinking density and thus better mechanical properties compared to that incorporated with KL, probably due to the better miscibility of OL in the polyol. [78,79] Table 5 also shows that lignosulphonate is considered to be a potential candidate for polymerization attributing to its larger amount of functional groups. As expected, few studies on the polymerization of HL have been reported due to its low reactivity.…”