Author: [Bruce Zhou]
Affiliation: [Jota Machinery Composites Material Prepreg Solution]
Corresponding Author: [jotamachinery@gmail.com]
Published : December 09 , 2025

Abstract

Carbon fiber–reinforced thermosetting composites (CFRTCs) remain foundational materials in aerospace, automotive, energy, and infrastructure due to their exceptional stiffness, high strength-to-weight ratio, and thermal stability. However, the inherent chemical inertness and smooth surface morphology of carbon fibers often limit interfacial bonding with thermosetting matrices such as epoxy, phenolic, vinyl ester, and polyimide resins. This review consolidates current knowledge on carbon fiber surface modification—wet chemical oxidation, electrochemical activation, plasma functionalization, and tailored sizing—and evaluates their influence on composite interlaminar shear strength (ILSS), toughness, thermal behavior, and electrical performance. Preparation routes including hot-press curing, filament winding, autoclave consolidation, resin transfer molding (RTM), and emerging additive manufacturing workflows are summarized. The review further integrates post-2020 advancements, such as fiber recycling technologies and in-situ curing for 3D-printed thermosets, highlighting unresolved challenges in scalability, environmental impact, and damage evolution. Overall, surface engineering improves ILSS by 20–50% and can raise tensile performance by 10–30%, but aggressive treatments risk fiber degradation. Future progress requires integrated interface design incorporating plasma, nanoscale coatings, and bio-derived matrix chemistries.

carbon fiber reinforced thermosetting composites

Keywords

Carbon fiber; thermosetting composites; surface treatment; interfacial adhesion; epoxy; phenolic resin; plasma modification; recycling; ILSS; composite processing.

1. Introduction

Carbon fibers (CFs) possess high tensile strength, high modulus, low density, and excellent thermal and chemical stability, making them essential reinforcement in structural composites. When combined with thermosetting matrices—epoxy, phenolic, cyanate ester, vinyl ester, and high-temperature polyimide—CF composites achieve high stiffness and temperature resistance suitable for aircraft structures, rocket motor casings, automotive parts, and industrial tools.

Despite these advantages, CFs feature chemically inert graphitic surfaces with limited functional groups, resulting in poor fiber–matrix bonding. Weak interfaces lead to premature failure modes such as interfiber cracking, delamination, and reduced interlaminar shear strength (ILSS). Consequently, surface modification of CFs is a critical processing step in thermoset composite manufacturing.

This paper reviews major CF surface treatment strategies, thermoset composite preparation routes, and the resulting mechanical and electrical properties. It extends earlier studies by incorporating modern post-2020 research directions, including additive manufacturing of thermoset composites and fiber recycling, offering a holistic perspective on interface design for next-generation CFRTCs.

2. Literature Review

2.1 Surface Treatments for Carbon Fibers

Wet Chemical Oxidation

Nitric acid, sulfuric acid mixtures, and mild oxidants generate –OH, –COOH, and carbonyl groups, increasing surface polarity and wettability. ILSS improvements of 20–40% are commonly reported. However, excessive oxidation degrades tensile strength by etching graphitic layers.

Electrochemical Oxidation

Anodic oxidation in electrolytes such as ammonium carbonate and phosphoric acid introduces oxygen-containing groups uniformly across fiber surfaces. This method offers tunable current density and minimal fiber damage, with ILSS gains up to 50% in epoxy systems.

Plasma Functionalization

Low-pressure or atmospheric dielectric barrier discharge (DBD) plasmas use Ar/O₂ or air to roughen fiber surfaces and graft functional groups. Plasma treatment avoids chemical waste and minimizes fiber degradation. Reported improvements include 25–35% tensile interfacial strength without reducing intrinsic fiber modulus.

Dry Chemical Fluorination

Fluorine-containing gases react with fiber surfaces, increasing both polarity and chemical reactivity. Treated CF/epoxy composites show enhanced fracture toughness, although process control is critical due to potential over-reaction.

Sizing and Coating Technologies

Silane-based sizings introduce covalent bonding bridges between CF and matrix, while metallic (Ni, Cu) coatings improve conductivity and modify crack propagation. Modern sizings incorporate reactive oligomers compatible with epoxy or phenolic matrices.

2.2 Preparation Methods for Thermosetting CF Composites

Epoxy-Based Composites

Epoxy resins dominate structural applications due to high toughness and controlled cure kinetics. Key preparation approaches include:

  • Filament winding for cylindrical structures
  • Hot-pressing for unidirectional laminates
  • Resin transfer molding (RTM) for high-volume parts
  • Autoclave consolidation for aerospace-grade void levels

Phenolic Resin Composites

Phenolic matrices offer exceptional flame resistance and char formation, essential for thermal protection systems. Hot-pressing or vacuum-bag curing enables fiber-rich ablatives with high thermal stability.

Cyanate Ester and Polyimide Composites

These high-temperature thermosets exhibit low dielectric loss and excellent oxidative stability. Processing requires elevated curing temperatures (170–380°C) and controlled volatiles management.

Vinyl Ester Composites

Vinyl ester resins provide corrosion resistance while maintaining moderate mechanical strength. They are widely used in marine and civil engineering sectors.

2.3 Mechanical and Electrical Properties

Mechanical Performance

Surface-treated CFRTCs exhibit:

  • 10–30% higher tensile strength due to improved stress transfer
  • 20–50% higher ILSS depending on treatment
  • Enhanced flexural strength and fracture toughness

Phenolic-based CF composites retain performance at elevated temperatures but show lower strain-to-failure than epoxy systems.

Electrical Performance

Aligned CF networks provide electrical conductivity from 10–100 S/cm, useful for EMI shielding. Metallic coatings further increase conductivity but require careful interfacial control to prevent galvanic coupling.

3. Methodology (Conceptual Framework)

The new paper adopts a comparative evaluation methodology:

  1. Classify surface treatments (wet, electrochemical, plasma, coating).
  2. Analyze how each treatment alters surface chemistry and topology using published XPS, FTIR, SEM, and AFM data.
  3. Map treatments to composite processing routes.
  4. Correlate interfacial modifications with mechanical and electrical property changes.
  5. Integrate post-2020 technologies such as:
    • Recyclable epoxy matrices
    • Additive manufacturing of CF-thermoset systems
    • Low-energy plasma treatments
    • Solvolysis-based fiber recovery

This framework synthesizes diverse literature while identifying consistent causation pathways between treatment, processing, and performance.

4. Results (Synthesized Findings)

4.1 Effectiveness of Fiber Surface Treatments

Across literature datasets:

  • Wet oxidation improves interfacial adhesion but risks reducing fiber tensile strength by 5–10%.
  • Plasma treatments consistently enhance ILSS by 25–40% with minimal mechanical degradation.
  • Electrochemical oxidation provides the most uniform activation; ILSS gains can reach 50% in optimized systems.
  • Silane sizing boosts epoxy compatibility, reducing void content and enhancing fatigue life.

4.2 Influence of Processing Techniques

RTM and autoclave curing yield lower void contents (<1%) compared to manual lay-up.
Filament winding improves fiber alignment, leading to tensile strengths near 2–3 GPa in optimized epoxy systems.

4.3 Emerging Post-2020 Innovations

  • Additive manufacturing (AM): New UV-assisted AM enables continuous fiber reinforcement within thermosetting matrices but struggles with cure gradients and interlaminar defects.
  • Recycling: Solvolysis and supercritical fluid extraction recover CFs with tensile strength retention of 80–95%.
  • Sustainable surface treatments: Atmospheric plasma and eco-friendly electrolytes reduce chemical waste.

5. Discussion

The compiled evidence clearly demonstrates that interfacial engineering is the dominant factor governing CFRTC performance. Treatments must balance increased surface functionality against risk of fiber over-etching. Plasma emerges as a promising industrial solution due to:

  • Fine control over functionalization
  • Absence of chemical effluents
  • Compatibility with automated production

However, thermosetting matrices themselves introduce constraints such as irreversible curing and environmental concerns. Emerging recyclable thermosets, including cleavable epoxies, offer routes to circular composite manufacturing.

Additive manufacturing is transforming the composite landscape but requires breakthroughs in cure kinetics, thermal management, and fiber placement accuracy.

Finally, economic and environmental considerations drive a shift toward sustainable surface treatments and bio-derived resin systems.

6. Conclusion

Carbon fiber–reinforced thermosetting composites achieve exceptional structural performance when fiber–matrix bonding is properly engineered. Surface treatments such as plasma functionalization, electrochemical oxidation, and optimized sizing significantly improve ILSS, toughness, and structural reliability. Preparation routes—including autoclave consolidation, RTM, and filament winding—determine fiber alignment and void content, influencing load transfer and fatigue behavior.

While traditional thermosets will remain critical for aerospace and high-temperature applications, advancements in additive manufacturing, recyclable matrices, and eco-friendly surface treatments will redefine next-generation composite manufacturing. Future research must integrate interface chemistry, process modeling, and sustainability to develop high-performance, cost-effective, and environmentally responsible CFRTCs.

References

  1. Jin, F.-L., Park, S.-J. Carbon Letters, 2015.
  2. Wang, Z. et al. Composites Part B, 2023.
  3. Zhang, X. et al. Frontiers in Materials, 2023.
  4. Ramesh, M. et al. Polymers, 2021.
  5. Dong, X. et al. ES General, 2023.
  6. Additional references from contemporary plasma, electrochemical, and sustainable composites studies (2020–2024).
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