Solid-liquid Wetting Behavior of CNT/CF Multiscale Fibers and the Interfacial Properties of Their Thermoplastic Composites

Author:Wang Jian

Supervisor:zhang dong xing

Database:Doctor

Degree Year:2019

Download:42

Pages:130

Size:6705K

Keyword:

Carbon fiber and carbon nanotube reinforced polymer composites have been widely used in various fields due to their advantages of lightweight,high specific strength,high specific modulus and excellent electrical properties.However,their mechanical properties depend not only on the intrinsic properties of the reinforcement or the matrix,but also on the interfacial properties of the composites.At the same time,the wettability between the fiber and the polymer matrix plays a crucial role in determining the quality of the final composite interfacial physical bonding and the generation of pore defects at the interface during the processing.As a fiber reinforcement,from the carbon fiber tow to carbon fiber filament,from carbon nanotube fiber to carbon nanotube,the wetting behavior often occur simultaneously in multiscale due to their hierarchical structures.Therefore,in order to design and optimize the interfacial properties of polymer composites(especially the thermoplastic polymer composites),it is of great significance to precisely characterize the wettability of fiber material on multiscale.This study is aimed at the needs of development and application of highperformance polymer composites,carbon nanotube fibers were spun from multiwalled CNT arrays and carbon nanotube/carbon fiber multiscale fibers were prepared by using the continuous chemical vapor deposition method.The microstructure of carbon fiber tow,carbon nanotube fiber and carbon nanotube/carbon fiber multiscale fiber were characterized.According to their hierarchical structure,the multi-scale wetting theoretical models of carbon fiber tow,carbon nanotube fiber and carbon nanotube/carbon fiber multiscale fiber were developed based on the Cassie-Baxter theory.The contact angles of carbon fiber at meso-and microscales have been successfully linked by using the theoretical model.The relationship between the wettability of carbon fiber at meso-and microscales was discussed.How the surface microstructure of carbon fiber tow is effected on the wettability of carbon fiber tow at mesoscales was revealed.Additionally,the relationship between the wettability of multiscale fiber at microscales and carbon nanotubes sitting on the surface of them at nanoscale was described based on the multiscale wetting theoretical models.Aiming at the difficulties of high-precision characterization of wettability of carbon fiber tows,a new methodology,combining force method with synchronized in-situ optical observation is proposed and used to better characterize the wettability of carbon fiber at meso-and microscales.The methodology and the theoretical model are applied to evaluate the effect of sizing on the wettability of carbon fiber at mesoand microscales.The measured contact angle results of carbon fiber at different scales were used to validate the theoretical model.The wetting behavior of carbon nanotube fiber and multiscale fiber were studied.The wettability of carbon nanotube at nanoscale were derived theoretically based on the theoretical model.The predicted contact angle of carbon nanotubes(sitting on the surface of carbon nanotube fiber)with water was close to the one of unsized carbon fiber.The similarity in contact angle values at the micro-and nanoscales with the same surface nature illustrated that the effect of diameter on the wettability of fibers is limited.In order to further investigate the wetting behavior of carbon nanotube/carbon fiber and the interfacial properties of their polymer composites,the surface energy of carbon nanotubes and their Lifshitz-van der Waals,acid and base components were calculated based on acid-base theory.The carbon nanotube fiber surface chemistry was analyzed via X-ray photoelectron spectroscopy(XPS),the B/A ratios analyzed by XPS for the carbon nanotubes are in agreement with the one obtained from contact angles,confirming the surface energy components calculation.The wettability and the interfacial properties between the carbon nanotubes and polymer matrix were predicted by using the surface energy values of both the carbon nanotubes and a series of polymers.Additionally,the wettability and the interfacial properties between the carbon nanotube/carbon fiber multiscale fiber and polypropylene were predicted based on their surface energy.Compared to the untreated carbon fiber,the molten polypropylene is more likely to spontaneously wet the surface of carbon nanotube/carbon fiber multiscale fiber,eventually formed stronger adhesion at the interface of their composite.The measured interfacial shear strength between multiscale fiber and polypropylene matrix was 11.20 ± 0.34 MPa,which was 53.4 % higher than the one of unsized carbon fiber.The measured interfacial shear strength and the predicted adhesion based on the wettability show the same trend,evidencing the role of wettability of carbon fiber on the interfacial shear strength of its composites.The effect of introducing carbon nanotube onto the surface of carbon fiber on the interfacial shear strength of its polypropylene composite and the interface enhancement mechanism are revealed.