Effect of plasma treatment on the adhesion of carbon fibers with thermoset and thermoplastic matrices

• Main Author: Ang, Alson Da Wei
• Other Authors: Alfred Tok Iing Yoong
• Format: Final Year Project
• Language: English
• Published: 2019
• Subjects: DRNTU::Engineering::Materials
• Online Access: http://hdl.handle.net/10356/76741
• Institution: Nanyang Technological University

In various industries today, composites have become a popular material of choice with its desirable strength to weight ratio. However, the surface of carbon fibers are generally almost inert with low wettability and often do not have much bonding to the resin matrix. Studies have used plasma treatment to improve the performance of thermoset composites, while the exploration to thermoplastic composites is in absence. Thus, the effect of plasma treatment on thermoset and thermoplastic sized carbon fibers were investigated. The carbon fibers used in this project were non-crimp biaxial 22.5° 12k thermoset sized and thermoplastic sized carbon fibers. The resins used were Epolam 5015 epoxy and PMMA thermoplastic resins. As the amount of binder added increased, the permeability of both thermoset and thermoplastic sized carbon fiber decreased accordingly. The optimal binder weight percentage and plasma treatment parameters were determined by conducting permeability tests. Subsequently, using the optimal binder weight percentage and plasma treatment parameters, thermoset and thermoplastic composites with their respective plasma treated carbon fibers were made. Thermoset and thermoplastic composites with non-plasma treated carbon fibers were also manufactured to act as controls for comparison. The Mode I Interlaminar fracture toughness test was used to determine the effect of plasma treatment on the mechanical properties of the composites. The optimal plasma treatment parameters for thermoset sized carbon fibers with 5% binder weight percentage were 30 mm jet height, 80% reference voltage and 7m/min jet speed. The optimal plasma treatment parameters for thermoplastic sized carbon fibers with 5% binder weight percentage were 25 mm jet height, 80% reference voltage and 7m/min jet speed. Plasma treatment improved the infusion time for thermoset composites when comparing plasma and non-plasma treated thermoset composites while plasma treated thermoplastic composite samples have a 22% higher average critical fracture toughness (GIc) value than non-plasma treated thermoplastic composite samples. It was observed that non-plasma treated thermoset composite samples have higher mechanical properties than non-plasma treated thermoplastic composite samples. Since the binder is thermoset in nature, the phenomenon of non-plasma treated thermoset composite samples having better mechanical properties than non-plasma treated thermoplastic composite samples may be attributed to the addition of binder. The addition of binder may have affected the adhesion between thermoplastic sized carbon fiber and the thermoplastic resin. Therefore, for future work, it would be recommended to use lesser binder weight percentages such as 1% and 3% instead.