Mechanical and functional properties of nano-structured polyvinylidene fluoride and its carbon nanotube composites
Date of Issue2016
School of Materials Science and Engineering
Polyvinylidene Fluoride (PVDF) is one type of semicrystalline fluoropolymers that has been widely used in automotive and chemical industries, semiconductor, biomedical and sensor applications; owing to its superior chemical resistance, excellent mechanical properties and unique electronic properties. Polymeric composites containing nanoscale fillers, such as graphene, carbon nanotube (CNTs) or nanoclay often render polymers with interesting mechanical, structural, electrical, optical and many other functional properties. The objective of this work is to improve mechanical and functional properties of PVDF by the advantageous introduction of CNTs. Studies will focus on the preparation methodology of PVDF/CNTs composites with uniform morphology, the interaction between CNTs and polymer matrix and surface treatment of CNTs. The surface properties of CNTs often play an important role in determining the performance of polymer/CNTs composites. Therefore, in the first study, we focused on studying the surface functionalization of CNTs. Controlled thermal annealing in air was employed in order to oxidize CNTs. It was found that longer time/higher temperature can effectively increase the oxygen content in CNTs. Shorter duration/higher temperature annealing results in more C-O-C groups than longer duration/lower temperature annealing, while the latter yields more C=O groups. The mechanism of CNT surface functionalization by air annealing was proposed. In the following work, PVDF/CNTs composites with well dispersed and distributed CNTs were fabricated using both solution mixing and melt extrusion strategies. The introduction of low content of CNTs lead to an unusual observation of large enhancement in ductility; while marginal increase were observed for Young’s modulus and tensile strength. Systematic characterizations lead to the conclusion that the unexpected phenomenon is correlated with the change of polymorphs because of the existence of CNTs. Mechanism of phase transformation and pinning effect are proposed to further elucidate the phenomenon. In the third study, we explore the possibility using PVDF and its CNTs composites for oil/water separation applications. PVDF and PVDF/CNTs aerogel were fabricated through a vapor induced phase inversion process. Contributed by the hierarchical micro-nano structure that is tailorable by PVDF concentration, both surfactant-free and surfactant-stabilized oil-in-water emulsion could be effectively separated by the fabricated PVDF aerogel simply under gravity, with good flux and high filtrate purity up to 99.99%. PVDF aerogel also exhibited moderate oil absorption capacity and almost instantaneous oil up-taking when tested using various types of oil. Furthermore, PVDF aerogel is highly stable towards concentrated alkaline solution owing to its superhydrophobicity, and shows good reusability in both oil/water separation and oil absorption. The influence of introduction of CNT on the mechanical and porous microstructure was examined. With 0.1 wt. % CNTs, the mechanical performance could be improved without impairing the surface properties of aerogel. In the last part of this thesis, the findings are summarized and potential future works are suggested.