Case Study 604 Carbon Fibre-Polymer Interaction
This case study, authored by Dan Burnett of Surface Measurement Systems Ltd., investigates how surface treatments of PAN‑based carbon fibres affect their thermodynamic interaction with three thermoplastic polymers (polysulfone, polycarbonate, polyetherimide). Using Inverse Gas Chromatography (IGC SEA), the dispersive and specific components of surface energy for each fibre and polymer are measured. Acid‑base numbers are derived via Gutmann and van Oss concepts (with Della Volpe scaling) to calculate total surface energies and work of adhesion (WAd). Single‑fibre pull‑out tests provide interfacial shear strength (ISS) as a practical adhesion metric. The study finds that oxidation of fibres raises dispersive surface energy, increases acidity, and generally improves both WAd and ISS across all polymers. Epoxy sizing, while increasing calculated WAd due to higher specific interactions, does not translate into higher ISS, likely because of incompatibility between the sizing layer and the polymer matrix. Detailed tables and figures illustrate surface energy components, acid/base parameters, and the correlation between WAd and ISS. The work concludes that oxidation is beneficial for fibre‑polymer adhesion, whereas sizing may be detrimental unless polymer‑sizing compatibility is ensured.
Topics
IGC SEA as a Thermodynamic Probe for Fibre and Polymer Surfaces
Explanation of the Inverse Gas Chromatography (IGC SEA) technique, its theoretical basis, and how it yields dispersive and specific surface energy components.
Acid‑Base Characterisation via Gutmann and van Oss Concepts
Derivation of acid (Ka) and base (Kb) numbers from specific free energies using Gutmann’s dimensionless approach and van Oss’s unit‑consistent formulation, with Della Volpe scaling to correct basicity overestimation.
Material Set‑up: Oxidised, Unsized, and Epoxy‑Sized Carbon Fibres
Description of the three carbon fibre variants (CA, AS4‑unsized, AS4‑sized) and the three thermoplastic polymers used, including their source and treatment conditions.
Surface Energy Findings: Oxidation Boosts Dispersive Energy, Sizing Dampens It
Presentation of measured dispersive and specific surface energy values, showing that oxidation raises dispersive energy and acidity, while epoxy sizing lowers dispersive contribution but raises specific (acidic) interaction.