Synthesis and Characterization of Lignin-graft-poly(ethylene brassylate): a Biomass-Based Polyester with High Mechanical Properties

Abstract

Lignin is an important biopolymer that can be used as a raw material to produce functional polymers due to its abundance, low price, sustainability, and high concentration of aromaticity. However, lignin modification is not well understood or characterized, limiting its potential as a new sustainable raw material. The biopolymer lignin can be integrated with aliphatic polyesters to produce new biomass-based biodegradable polymers. Among various aliphatic polyesters, poly­(ethylene brassylate) (PEB) is a relatively unexplored polymer with many advantages. PEB is low in cost and made from castor oil, making it a sustainable resource. In this work, we have synthesized a new lignin-containing copolymer, lignin-graft-PEB. The biopolymer lignin was chemically modified by sebacic acid to introduce a carboxylic acid functionality. Lignin’s abundant hydroxyl groups were used for its modification. Another precursor of the copolymer, PEB, was prepared by ring-opening polymerization of ethylene brassylate in the presence of the catalyst 1,5,7-triazabicyclo[4.4.0]­dec-5-ene (TBD). The condensation copolymerization of the modified lignin and PEB occurred by reactions between the TBD terminus of the PEB and the carboxylic acid of the modified lignin. A decent melting temperature (78 °C) of the new polymer enables thermal processing. The mechanical properties of the new lignin-graft-PEB can be conveniently controlled by changing the mass ratio of lignin and PEB and the molecular weight of PEB. The highest modulus of lignin-graft-PEB is 471.99 MPa, which is 3-fold higher than that of homoPEB.

Highly stretchable, self-healable, and self-adhesive ionogels with efficient antibacterial performances for a highly sensitive wearable strain sensor

“…15 Furthermore, the results demonstrated that the mechanical properties have been enhanced after introducing lignin into the PU prepolymer. 16–18 The main reason is that lignin can act as hard segments and hard crosslinking points, leading to improved mechanical stiffness. Therefore, the mechanical properties of PU-based gels would be greatly enhanced via introducing crosslinking points.…”

Convenient Cross-Linking Control of Lignin-Based Polymers Influencing Structure–Property Relationships

“…To confirm the amount of reacted PEG in modified lignin-graft-PEG, the number of reactive sites (−COOH) on modified lignin was calculated based on 1 H NMR spectra (Figure b). The number of hydroxyl groups on lignin was reported previously. ,, According to the previously reported data, one gram of lignin possesses 4.48 mmol of hydroxyl groups. Thus, the number of reactive sites (−COOH) of uncapped lignin with 0% of acetic acid (UCL, entry 4 in Table S1) is 4.48 mmol per one gram of lignin.…”

“… a Acetic acid was used as a capping agent. b X CL- Y P Z , where X = mole % of the capping agent; Y = molecular weight of PEG; Z = mass ratio of modified lignin with PEG (6CL-2P13 (entry 13 in Table ) indicates a copolymer of modified lignin which capped 6 mol % and PEG of 2k g/mol with a 1:3 (lignin: PEG) weight ratio). c mmol of the reactive site (carboxylic acid) per one gram of lignin was determined by 1 H NMR of modified lignin (Figure b). There is 4.48 mmol of the hydroxyl groups in one gram of lignin. ,, d mmol of added PEG per one gram of lignin. …”

“… c mmol of the reactive site (carboxylic acid) per one gram of lignin was determined by 1 H NMR of modified lignin (Figure b). There is 4.48 mmol of the hydroxyl groups in one gram of lignin. ,, …”

“…The number of hydroxyl groups on lignin was reported previously. 56,63,64 According to the previously reported data, one gram of lignin possesses 4.48 mmol of hydroxyl groups. Thus, the number of reactive sites (−COOH) of uncapped lignin with 0% of acetic acid (UCL, entry 4 in Table S1) is 4.48 mmol per one gram of lignin.…”