Surface modification of carbon fiber by grafting gallic acid as a bridging model

Carbon fiber (CF) is often used in composites as it has superior high strength-to-weight ratio and temperature resistance. However, its smooth surface limits its wettability with polar matrices and results in poor interfacial interaction in CF reinforced composites. Thence, it is important to modify...

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Main Author: Sara Quake
Other Authors: Aravind Dasari
Format: Final Year Project
Language:English
Published: Nanyang Technological University 2021
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Online Access:https://hdl.handle.net/10356/147643
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spelling sg-ntu-dr.10356-1476432023-03-04T15:43:36Z Surface modification of carbon fiber by grafting gallic acid as a bridging model Sara Quake Aravind Dasari School of Materials Science and Engineering aravind@ntu.edu.sg Engineering::Materials Carbon fiber (CF) is often used in composites as it has superior high strength-to-weight ratio and temperature resistance. However, its smooth surface limits its wettability with polar matrices and results in poor interfacial interaction in CF reinforced composites. Thence, it is important to modify the fiber surface to maximise their full potential. In previous works, methods such as acid and dry treatment were reported to graft OH groups on the surface, but these treatments were also reported to lower the mechanical properties of the fiber or were difficult to conduct. In this report, although the fiber was not chemically grafted with hydroxyl (OH) groups, poly (vinyl alcohol) (PVA) was physically coated on them to simulate the modified fibers. This report focuses on using gallic acid (GA) as a bridging molecule to increase OH functionality between the modified CF and matrix. Two main methods of grafting GA onto the modified CF were attempted through esterification with activated gallic acid chloride and Steglich esterification with protected gallic acid. Protection of OH groups was required to esterificate and further epoxidize the GA ‘bridge’. Acetylation was selected due to the availability of chemical reagents and simplicity. But deacetylation or the deprotection could not be conducted as it potentially removes the ester bond formed at the fiber-matrix interface and breaks off the GA ‘bridge’. Alternatively, to deprotection and then epoxidation of GA, epoxidation of PVA coating on CF (PVA_CFE) was conducted to emulate a similar epoxidized chemical structure. Then, these chemical structures were characterized by Fourier-transform infrared spectroscopy and high performance liquid chromatography whilst their thermal properties were studied with differential scanning calorimetry and thermogravimetric analysis. To evaluate the interfacial fractures of the modified fibers-epoxy resin composites, an Izod impact test was performed to evaluate impact strength and optical microscope was used to observe the fracture. However, the 1%PVA_CFE composites had 18% lower impact strength as compared to untreated CF-epoxy composite. It is likely that the functionalised PVA coating on CF was removed and it formed a dense crack network at the interface. The lack of proper degassing the epoxy resin and small sample size could also improperly represent these observations. To evaluate GA as a bridging molecule more qualitatively, chemically modifying CF and using other protection methods such as silyl ethers are recommended. A higher fiber loading (~0.4wt%), better degassing and higher sample size should be taken to better represent the findings. Bachelor of Engineering (Materials Engineering) 2021-04-08T13:17:05Z 2021-04-08T13:17:05Z 2020 Final Year Project (FYP) Sara Quake (2020). Surface modification of carbon fiber by grafting gallic acid as a bridging model. Final Year Project (FYP), Nanyang Technological University, Singapore. https://hdl.handle.net/10356/147643 https://hdl.handle.net/10356/147643 en application/pdf Nanyang Technological University
institution Nanyang Technological University
building NTU Library
continent Asia
country Singapore
Singapore
content_provider NTU Library
collection DR-NTU
language English
topic Engineering::Materials
spellingShingle Engineering::Materials
Sara Quake
Surface modification of carbon fiber by grafting gallic acid as a bridging model
description Carbon fiber (CF) is often used in composites as it has superior high strength-to-weight ratio and temperature resistance. However, its smooth surface limits its wettability with polar matrices and results in poor interfacial interaction in CF reinforced composites. Thence, it is important to modify the fiber surface to maximise their full potential. In previous works, methods such as acid and dry treatment were reported to graft OH groups on the surface, but these treatments were also reported to lower the mechanical properties of the fiber or were difficult to conduct. In this report, although the fiber was not chemically grafted with hydroxyl (OH) groups, poly (vinyl alcohol) (PVA) was physically coated on them to simulate the modified fibers. This report focuses on using gallic acid (GA) as a bridging molecule to increase OH functionality between the modified CF and matrix. Two main methods of grafting GA onto the modified CF were attempted through esterification with activated gallic acid chloride and Steglich esterification with protected gallic acid. Protection of OH groups was required to esterificate and further epoxidize the GA ‘bridge’. Acetylation was selected due to the availability of chemical reagents and simplicity. But deacetylation or the deprotection could not be conducted as it potentially removes the ester bond formed at the fiber-matrix interface and breaks off the GA ‘bridge’. Alternatively, to deprotection and then epoxidation of GA, epoxidation of PVA coating on CF (PVA_CFE) was conducted to emulate a similar epoxidized chemical structure. Then, these chemical structures were characterized by Fourier-transform infrared spectroscopy and high performance liquid chromatography whilst their thermal properties were studied with differential scanning calorimetry and thermogravimetric analysis. To evaluate the interfacial fractures of the modified fibers-epoxy resin composites, an Izod impact test was performed to evaluate impact strength and optical microscope was used to observe the fracture. However, the 1%PVA_CFE composites had 18% lower impact strength as compared to untreated CF-epoxy composite. It is likely that the functionalised PVA coating on CF was removed and it formed a dense crack network at the interface. The lack of proper degassing the epoxy resin and small sample size could also improperly represent these observations. To evaluate GA as a bridging molecule more qualitatively, chemically modifying CF and using other protection methods such as silyl ethers are recommended. A higher fiber loading (~0.4wt%), better degassing and higher sample size should be taken to better represent the findings.
author2 Aravind Dasari
author_facet Aravind Dasari
Sara Quake
format Final Year Project
author Sara Quake
author_sort Sara Quake
title Surface modification of carbon fiber by grafting gallic acid as a bridging model
title_short Surface modification of carbon fiber by grafting gallic acid as a bridging model
title_full Surface modification of carbon fiber by grafting gallic acid as a bridging model
title_fullStr Surface modification of carbon fiber by grafting gallic acid as a bridging model
title_full_unstemmed Surface modification of carbon fiber by grafting gallic acid as a bridging model
title_sort surface modification of carbon fiber by grafting gallic acid as a bridging model
publisher Nanyang Technological University
publishDate 2021
url https://hdl.handle.net/10356/147643
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