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. 2023 Sep 16;15(18):3784.
doi: 10.3390/polym15183784.

Enhanced Interfacial Properties of Carbon Fiber/Maleic Anhydride-Grafted Polypropylene Composites via Two-Step Surface Treatment: Electrochemical Oxidation and Silane Treatment

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Enhanced Interfacial Properties of Carbon Fiber/Maleic Anhydride-Grafted Polypropylene Composites via Two-Step Surface Treatment: Electrochemical Oxidation and Silane Treatment

Dong-Kyu Kim et al. Polymers (Basel). .

Abstract

The interfacial adhesion between carbon fibers (CFs) and a thermoplastic matrix is an important aspect that should be improved in manufacturing CF-reinforced thermoplastics with high strength and rigidity. In this study, the effects of a two-step surface treatment comprising electrochemical oxidation and silane treatment of the CF surface on the mechanical properties of CF/maleic anhydride-grafted polypropylene (MAPP) composites were confirmed. The surface characteristics of the treated CFs were analyzed via scanning electron microscopy, atomic force microscopy, Fourier transform infrared spectroscopy, and X-ray photoelectron spectroscopy. The tensile testing of a single CF and interfacial adhesion of the samples before and after the surface treatment were analyzed using a single-fiber testing machine and a universal testing machine. After the silane treatment, the roughness of the CF surface increased due to the formation of a siloxane network. In addition, the interfacial shear strength increased by ∼450% compared to that of the untreated CFs due to the covalent bond between the -NH2 end group of siloxane and MAPP. This two-step surface treatment, which can be performed continuously, is considered an effective method for improving the mechanical interface strength between the CF and polymer matrix.

Keywords: carbon fiber; composites; electrochemical oxidation; interfacial shear strength; silane treatment.

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Conflict of interest statement

The authors declare no conflict of interest.

Figures

Figure 1
Figure 1
Schematic of the microbond test: (a) sample preparation and (b) debonding process.
Figure 2
Figure 2
Scanning electron microscopy images of the surface of the untreated, electrochemical-oxidation-treated, and electrochemical-oxidation/silane-treated carbon fiber; (a) AS-CF, (b) EO-CF, and (c) EOS3-CF.
Figure 3
Figure 3
Atomic force microscopy images of the surface of the untreated, electrochemical-oxidation-treated, and electrochemical-oxidation/silane-treated carbon fiber; (a) AS-CF, (b) EO-CF, and (c) EOS3-CF.
Figure 4
Figure 4
Fourier transform infrared spectra of the untreated, electrochemical-oxidation-treated, and electrochemical-oxidation/silane-treated carbon fibers.
Figure 5
Figure 5
Chemical reaction of silane on the oxidized carbon fiber surfaces.
Figure 6
Figure 6
X-ray photoelectron spectra of the carbon fiber samples; (a) wide-scan survey, (b) surface element concentration of the carbon fiber samples, (c) fitting curve of the Si2p peaks of EOS3-CF, (d) N1s spectra of the carbon fiber samples subjected to different treatments.
Figure 7
Figure 7
Interfacial shear strength and tensile test results of the untreated and surface-treated carbon fiber samples subjected to different conditions.
Figure 8
Figure 8
Schematic of the interfacial adhesion enhancement mechanism between the silane-treated carbon fiber and maleic anhydride-grafted polypropylene; (a) carbon fiber and maleic anhydride-grafted polypropylene covalent bonding mechanism, (b) mechanism of interpenetrating polymer network formation.

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