Co-curing of epoxy resins with aminated lignins: insights into the role of lignin homo crosslinking during lignin amination on the elastic properties

Abstract

To improve the reactivity of lignin for incorporation into high value polymers, the introduction of amines via Mannich reaction is a commonly used strategy. During this functionalization reaction, intra- as well as intermolecular lignin–lignin crosslinking occurs, which can vastly change the elastic properties of the lignin, and therefore, the properties of the resulting polymer. Therefore, the molecular structure of the amine that is used for such a lignin functionalization may be of great importance. However, the relationship between the molecular structure of the amine and the elastic properties of the lignin-based polymer that is generated thereof, has not been fully understood. Herein, this relationship was investigated in detail and it was observed that the molecular flexibility of the amines plays a predominant role: The use of more flexible amines results in an increase in elasticity and the use of less flexible amines yields more rigid resin material. In addition to the macroscopic 3-point bending flexural tests, the elastic modules of the resins were determined on the nanometer scale by using atomic force microscopy (AFM) in the PeakForce tapping modus. Thus, it could be demonstrated that the intrinsic elasticities of the lignin domains are the main reason for the observed tendency.

Solvent-Resistant Lignin-Epoxy Hybrid Nanoparticles for Covalent Surface Modification and High-Strength Particulate Adhesives

“…The presence of water in the formulation holds multiple benefits because it (1) enables easy spreading and penetration of the adhesive into wood due to a low viscosity and strong affinity toward wood and (2) reduces the curing temperature and/or time due to the catalytic effect at elevated temperature . Moreover, the use of unmodified SKL has strong environmental and economic advantages compared to other SKL-based adhesive systems where the prefractionation, degradation, or chemical modification is required, for example, amination of lignin as a hardener for epoxy resin or the solution state epoxidation of degraded/fractionated lignin for preparing lignin-based epoxy resins. − Furthermore, the hy-LNP-based waterborne adhesive presented herein is an one-component epoxy adhesive containing no volatile organic compound, which is relatively green and safe compared to formaldehyde-based adhesives that are criticized for their toxicity issues due to emission of formaldehyde during use or the commercial two-component epoxy adhesives that contain toxic hardeners ( e . g ., amines).…”

Lignin-based acrylate adhesive without organic solvent processing

“…This suggests that the introduction of LMA enhances the crosslinking density of ALMA, owing to LMA as a co-monomer, which has its long alkyl chains inserted into the polymer macromolecular chain segments, weakening the intermolecular forces of the polymer and increasing the mobility of the binder, thus enhancing the intermolecular crosslinking effect. 45 Fig. 5a shows the DSC curves for ALMA.…”

Lignin to value-added chemicals and advanced materials: extraction, degradation, and functionalization

“…Four amine reagents including diethylene triamine, propylene diamine, ethylene diamine and ammonia for the amination of kraft lignin were studied. 137 For ammonia, the amount of amine group introduced was the lowest (1.2 mmol g −1 ). Compared with other amine reagents, the benzoxazine produced by the Mannich reaction of lignin with ammonia was more likely to form a Mannich base.…”

“…For propylene diamine and ethylene diamine, due to the high steric hindrance of the aminated lignin, the degree of cross-linking was slightly lower, and thus the amount of amine group introduced was higher (1.8 and 2.0 mmol g −1 ). 137…”