Lignin as a Functional Green Coating on Carbon Fiber Surface to Improve Interfacial Adhesion in Carbon Fiber Reinforced Polymers

Abstract

While intensive efforts are made to prepare carbon fiber reinforced plastics from renewable sources, less emphasis is directed towards elaborating green approaches for carbon fiber surface modification to improve the interfacial adhesion in these composites. In this study, we covalently attach lignin, a renewable feedstock, to a graphitic surface for the first time. The covalent bond is established via aromatic anchoring groups with amine functions taking part in a nucleophilic displacement reaction with a tosylated lignin derivative. The successful grafting procedures were confirmed by cyclic voltammetry, X-ray photoelectron spectroscopy, and field emission scanning electron microscopy coupled with energy dispersive X-ray spectroscopy. Both fragmentation and microdroplet tests were conducted to evaluate the interfacial shear strength of lignin coated carbon fiber samples embedded in a green cellulose propionate matrix and in a commercially used epoxy resin. The microdroplet test showed ~27% and ~65% increases in interfacial shear strength for the epoxy and cellulose propionate matrix, respectively. For the epoxy matrix covalent bond, it is expected to form with lignin, while for the cellulosic matrix hydrogen bond formation might take place; furthermore, plastisizing effects are also considered. Our study opens the gates for utilizing lignin coating to improve the shear tolerance of innovative composites.

Structural Characterisation and Chemical Stability of Commercial Fibrous Carbons in Molten Lithium Salts

“…In this context, the presence of O, N and H in the CFs is associated with the existence of surface functional groups (-C-H; -C-OH; -C-O-C; -C=O; C=N; -COOH; etc. ), the number of which decreases with subsequent heat treatments at a higher temperature [33,43,45,[65][66][67][68][69]. Thus, the B-O results correlate well with the Raman analysis, where the carbonised CFs spectra showed broad and intense D 1 , D 4 and D 3 bands, indicating a significant number of heteroatoms and aliphatic side chains.…”

Short Carbon Fiber Reinforced Polymers: Utilizing Lignin to Engineer Potentially Sustainable Resource-Based Biocomposites

“…Recent advances achieved in our laboratory hold promise for deriving thermoplastic cellulose derivatives from biomasses (Kakuchi et al, 2017; Suzuki et al, 2018), and utilizing these materials for preparing short carbon fiber reinforced plastics (Szabó et al, 2019a). We have also shown that the adhesion between the cellulosic matrix and carbon fiber can be improved by modifying the carbon fiber surface (Szabó et al, 2018a,b, 2019b). It appeared that immobilizing lignin on carbon fiber surface leads to a great enhancement in interfacial properties due to secondary interactions between lignin and the polymer matrix (Szabó et al, 2019b).…”

“…We have also shown that the adhesion between the cellulosic matrix and carbon fiber can be improved by modifying the carbon fiber surface (Szabó et al, 2018a,b, 2019b). It appeared that immobilizing lignin on carbon fiber surface leads to a great enhancement in interfacial properties due to secondary interactions between lignin and the polymer matrix (Szabó et al, 2019b). It follows that lignin can serve as a functional material to improve the interfacial interactions in green biobased composites.…”

Mussel-Inspired Design of a Carbon Fiber–Cellulosic Polymer Interface toward Engineered Biobased Carbon Fiber-Reinforced Composites

“…Microdroplets on single CFs were prepared using polymer melts similar to others, 64 and in line with our previous report. 44 Briefly, CP was kept on a hot plate at 235 °C for 5 min, whereupon a single fiber was gently immersed into the melt and then transferred to another plate heated to 250 °C (3 min treatment time). Upon cooling to room temperature, the formation of separated microdroplets could be confirmed.…”