Sustainable two‐step functionalization of carbon fibers (CFs) with polyethyleneimine and investigation of curing kinetics in composite materials

Combining oxidative plasma pre-treatment of carbon fibers (CFs) with subsequent functionalization with branched polyethyleneimine (b-PEI) resulted in b-PEI-modified CFs. First, CFs were oxidized by plasma treatment, dipped into a water solution of b-PEI, and finally heated to promote reactions between the amine functionalities of b-PEI and carboxyl groups generated by plasma activation. By ajusting the operational parameters of the low-pressure oxygen plasma treatment, the b-PEI concentration, and the reaction time, we could modulate the content of grafted b-PEI. The extent of the modification was assessed by infrared and Raman spectroscopies, scanning electron microscopy, and thermogravimetric analyses. Interestingly, the described functionalization process is cost-effective and simple and offers a sustainable and environmentally friendly alternative to traditional industrial methods, as it does not require dangerous reactants and solvents. The latter part of the paper delves into the curing kinetics of an epoxy/anhydride system in the presence of 20 wt% of carbon fibers modified with b-PEI at two different concentrations, evidencing the role of grafted b-PEI in the curing process. Highlights: Oxidative plasma activation adds functional groups to the surface of CFs. A two-step cost-effective and tunable process to functionalize CFs with b-PEI was proposed. The kinetic analysis showed that b-PEI-modified CFs accelerate the resin curing.