Surface properties (e.g., surface morphology and chemical moieties) are reported to affect shear strength of carbon fiber composites and influence their applications in aerospace, automotive industry, and wind energy.1 Plasma treatments are excellent methods to modify surfaces of composites for stronger bond line shear strengths.2 However, the relationship between surface properties and shear strength is still elusive. Here, oxygen plasma treatment (oxygen flowrate 25 sccm, pressure 220mTorr; March CS-1701, Nordson March) is investigated as an efficient and environmentally-benign surface preparation method for aerospace-utilized carbon fiber composites. After plasma-treated composites are cured with epoxy adhesive, an increase of 10% in in-plane shear strength (from 24.2 MPa to 26.6 MPa) is observed based on the lap shear test. Fracture surfaces of composites show mixed failure modes including adhesive, cohesive, and substrate failure. Surface profilometry and atomic force microscopy confirm that surface roughness of carbon fiber composite increases by two times after plasma treatment, suggesting stronger mechanical interlocking at composite-adhesive interfaces. X-ray photoelectron spectroscopy (XPS) shows an increase of nitrogen feature in N1s spectra centering from 400.6 eV to 400.8 eV, which is attributed to imide groups. These imide groups are further hydrolyzed into amines and bonded by Texas Red sulfonyl chloride dye that can be detected by confocal fluorescence microscopy. It turns out that more dyes are grafted onto carbon fiber composites after plasma treatment, suggesting more imide groups on plasma-treated surfaces. We propose that aniline derivatives (confirmed from both material data sheet and XPS) on composite surfaces are oxidized into imides during plasma treatment, which can subsequentially react with phenol derivatives and epoxy groups in adhesive and form stronger interfacial chemical bonding. Both stronger mechanical interlocking and interfacial chemical bonding can contribute to the enhancement of bonding of carbon fiber composite. These results suggest oxygen plasma treatment as a surface preparation method can be potentially incorporated into composite bonding processes to enhance structural capabilities.

Shear strength enhancement of carbon fiber composite via oxygen plasma treatment

Macromolecular Chemistry: The Second Century

[Author Benefits](https://scimeetings.acs.org/?utm_source=pubs_content_marketing&utm_medium=website&utm_campaign=0320_MCF_NPI_Launch_Spring_Homepage&ref=pubs_content_marketing)

[How to use SciMeetings](https://storage.googleapis.com/dl.morressier.com/acs/SciMeetings-ACSSpring2020-HowToGuide_M3020-Final.pdf)

[Frequently Asked Questions](https://storage.googleapis.com/dl.morressier.com/acs/SciMtng_ACSNMSp2020_FAQ_M3120_Final.pdf)

ACS Spring 2020 National Meeting & Expo

The official archive and repository for all ACS Meetings & Expositions abstracts and select posters or presentations.