Catalyst-Free Synthesis of Lignin Vitrimers with Tunable Mechanical Properties: Circular Polymers and Recoverable Adhesives

Abstract

Biobased circular materials are alternatives to fossil-based engineering plastics, but simple and material-efficient synthetic routes are needed for industrial scalability. Here, a series of lignin-based vitrimers built on dynamic acetal covalent networks with a gel content exceeding 95% were successfully prepared in a one-pot, thermally activated, and catalyst-free “click” addition of softwood kraft lignin (SKL) to poly­(ethylene glycol) divinyl ether (PDV). The variation of the content of lignin from 28 to 50 wt % was used to demonstrate that the mechanical properties of the vitrimers can be widely tuned in a facile way. The lowest lignin content (28 wt %) showed a tensile strength of 3.3 MPa with 35% elongation at break, while the corresponding values were 50.9 MPa and 1.0% for the vitrimer containing 50 wt % of lignin. These lignin-based vitrimers also exhibited excellent performance as recoverable adhesives for different substrates such as aluminum and wood, with a lap shear test strength of 6.0 and 2.6 MPa, respectively. In addition, recyclability of the vitrimer adhesives showed preservation of the adhesion performance exceeding 90%, indicating a promising potential for their use in sustainable circular materials.

Multifunctional lignin-poly (lactic acid) biocomposites for packaging applications

“…The 31 P NMR experiment was performed with a 90⁰ pulse angle, inversed gated proton decoupling, and a delay time of 10 s. For the analysis, 256 scans with a delay time of 10 s and a total runtime of 30 min for each sample were used. Two replicated experiments were conducted, and the mean value with one standard deviation is reported ( Moreno et al, 2021 ). Degree of substitution (DS) between was calculated using either phenolic hydroxyl content or similarly with carboxylic acids according to where the contents of phenolic OH or carboxylic acid groups are in units mmol/g.…”

Fully biomass-derived vitrimeric material with water-mediated recyclability and monomer recovery

“…14 A multitude of dynamic covalent bond exchanges have been investigated, including transesterification, 13,15,16 disulfide exchange, 17,18 imine exchange, [19][20][21] boronic ester exchange, 22,23 and transalkylation. 24,25 These new generation materials have been explored in many applications, including soft actuators, 26,27 3D printing, 28,29 recyclable adhesives, 30,31 and healable electronics. 32,33 Significant efforts have been devoted to improving the sustainability of CANs and vitrimers by following the principles of green chemistry.…”

“…In addition, subsequent work using bio-based feedstocks were still at least partially derived from fossil fuelbased starting materials. 31,48 These works inspired us to design fully recoverable acetal CANs from biomass sources, which is desirable for the development of sustainable and circular economy.…”

Stabilized lignin nanoparticles for templated assembly of silver nanoparticles and covalent functionalization in dispersion state

“…NMR spectroscopy: Quantitative analysis of hydroxyl groups of softwood Kraft lignin and hydroxymethylated lignin was conducted by 31 P NMR spectroscopy, [45] following adopted procedure previously reported by us. [46] Briefly, the dry lignin or hydroxymethylated lignin sample (30 mg) is phosphitylated with 2-chloro-4,4,5,5-tetramethyl-1,3,2-dioxaphospholane (0.9 mmol) in the presence of N-hydroxy-5-norbornene-2,3-dicarboxylic acid imine (0.010 mmol) as an internal standard and chromium(III) acetylacetonate as a relaxation agent. The 31 P NMR experiments (256 scans, 10 s relaxation delay) were performed with 90° pulse angle and inverse gated proton decoupling.…”