Coating of carbon fibers with adhesion-promoting thin poly(acrylic acid) and poly(hydroxyethylmethacrylate) layers using electrospray ionization

Abstract

Thin coatings of poly(acrylic acid) (PAA) and poly(hydroxyethylmethacrylate) (PHEMA) were deposited onto carbon fibers by means of the electrospray ionization (ESI) technique in ambient air. These high-molecular weight polymer layers were used as adhesion promoters in carbon fiber–epoxy resin composites. Within the ESI process, the carbon fibers were completely enwrapped with polymer in the upper 10 plies of a carbon fiber roving. As identified with scanning electron microscopy also shadowed fibers in a bundle as well as backsides of fiber rovings were pinhole-free coated with polymers (‘electrophoretic effect’). Under the conditions used, the layers have a granular structure. Residual solvent was absent in the deposit. PAA and PHEMA films did not show any changes in composition and structure in comparison with the original polymers as analyzed by X-ray photo-electron spectroscopy and matrix-assisted laser desorption/ionization time-of-flight mass spectrometry. Single-fiber pullout tests of coated fibers embedded in epoxy resin showed significantly increased interfacial shear strength. It is assumed that chemical bonds between carbon fiber poly(acrylic acid) and epoxy resin contribute significantly to the improved interactions.

Keywords:

• adhesion promotion
• thin polymer layers
• electrospray ionization (ESI)
• carbon fiber–epoxy resin laminates
• layer topography

Acknowledgments

The presented research was supported by the Deutsche Forschungsgemeinschaft (DFG) (Grant Award No: WE 4780/1-1). We would also like to thank Dr Rolf-Dieter Schulze for the construction of the ESI equipment (BAM, Germany). The running costs were paid by the PaCE (Polymer and Comosite Engineering) Group at the Department of Chemical Engineering at Imperial College in London and at the Institute of Materials Chemistry & Research, Faculty of Chemistry, University of Vienna, Währingerstr, 42, 1090 Vienna, Austria. We thank Professor Alexander Bismarck for his guidance and his significant scientific support.

Disclosure statement

No potential conflict of interest was reported by the authors.

Additional information

Funding

The presented research was supported by the Deutsche Forschungsgemeinschaft (DFG) [grant number WE 4780/1-1).