Qrganic Molecular Chain Modification Of Carbon Nanot-ubes And Their Application For The Epoxy Resin

Because of its unique structure and transfer characteristic, carbon nanotubes (CNTs) have excellent mechanical, electrical, thermal, optical and magnetic properties. Applications of CNTs in reinforced materials of special polymer matrix have received extensive attention from researchers in all walks of life. Nanocomposite can greatly enhance performance of polymer materials and make them apply more broadly. However, in polymer matrix, CNTs are easy to form serious entanglement and reunion, and their dispersion and interfacial adhesion is poor, which seriously restricted the application fields of CNTs in polymer matrix applications. Epoxy resin (EP) is one of commonly used thermosetting resins and has a wide range of applications in industry. High-performance CNTs/EP composite materials can be prepared by EP enhanced with CNTs, which makes the application of EP broader.The purpose of this work was to resolve the fundamental problems existed in the preparation process of CNTs/ EP composite, thus to prepare high-performance composite materials. The research contents of this work were divided into three parts. This work, primarily from the perspective of the dispersion and interface of CNTs in EP matrix, investigated preparation and characterization of CNTs/EP composites. The effect mechanism of CNTs in EP was analyzed and achieved through microstructure, thermal properties, electrical properties and mechanical properties of composites. In the first part of the research, surface hydroxylation modification of CNTs was mainly studied. After purification of CNTs with dilute nitric acid, CNTs were modified in order to introduce hydroxyl groups on their surface with mixed acid, strong alkali, mixture reagent of concentrated sulfuric acid/ hydrogen peroxide and Fenton reagent, respectively. Subsequently, the CNTs were modified by oxygen-propyl glycidyl silane coupling agent (KH560) and characterized using SEM, FTIR, TGA and other methods.The results showed that, amorphous carbon, catalyst and impurities on the surface of the purified CNTs were removed. Due to the relatively mild reaction conditions, purification with dilute nitric acid plays a small role on damaging the surface of CNTs, and do not introduce carboxyl and hydroxyl groups. In the four kinds of methods, Fenton reagent method is the best to prepare surface hydroxylation CNTs. After the Fenton reagent treatment, the surface of CNTs achieves a large number of hydroxyl groups, and further epoxy groups with the coupling agent (KH560) modification.After the silane coupling agent and Fenton reagent treatment, CNTs have the best dispersion and stability in acetone, and their surface weight loss rate is 8.11%. Hydroxyl groups are not introduced on surface of the original and other reagent-modified CNTs. Further modification with the silane coupling agent (KH560) do not improve dispersion and stability of the original and other reagent-modified CNTs in acetone, and the surface weight loss rate of those CNTs is low.In the second part of the study, the hydroxylation of CNTs modified with four kinds of coupling agents and EP composites have been mainly investigated. To improve the dispersion and achieve different interface characteristics, hydroxylation CNTs were further modification with silane coupling agent KH550, KH560, KH570 and titanium coupling agent NDZ201, respectively. Different kinds of CNTs/EP composite materials were prepared by a processing of (ultrasonic + high-speed mixing) dispersing - exhaust - casting - curing. Effect of different coupling agents-modified CNTs on micro-structure, thermal properties, electrical properties and mechanical properties of the composites was studied. The results showed that, when 1:1of mass ratio of CNTs and silane coupling agent KH560 is used to treat CNTs, the according the EP composite have the best thermal properties, electrical properties and mechanical properties. The main reason is that silane coupling agent KH560 modification introduces the epoxy groups on surface of CNTs, which improved the dispersion of CNTs and interfacial interaction in EP. When the content of CNTs is 0.25%, impact strength, bending strength, flexural modulus and fracture toughness of the composites, in relation to pure EP, were increased by 108%, 32.8%, 8.7% and 20%. In comparison, the properties of the other coupling agent modified CNTs/ EP composites are poor.In the third part of the research, graft polymerization modification of CNTs and properties of their EP composites were mainly studied. The graft polymerization monomer was glycidyl methacrylate (GMA), a kind of multi-functional acrylate glycidyl derivatives. Dispersion of GMA modified CNTs with three kinds of grafting rate in EP matrix and effect of the CNTs on glass transition temperature (Tg), electrical properties, mechanical properties of composites were studied. Moreover, effect of the contents of CNTs modified by GMA and other methods on electrical and mechanical properties of composites was investigated. The results show that, the grafting rate is the highest when mass ratio of GMA/CNTs is 15:1, and the according CNTs have the best dispersion and stability in acetone. GMA modified CNTs increase Tg of EP more significantly than coupling agent KH570 modified CNTs, and GMA-modified CNTs with grafting rate of 30.16% is the most effective for increasing Tg of EP. When the grafting rate of GMA-modified CNTs is 5.12%, the conductivity of CNTs/ EP composites is the best. The dielectric properties of GMA-modified CNTs/ EP composites significantly change compared with pure EP, and the dielectric constant and dielectric loss decrease ten times. When the mass ratio of GMA and CNTs is 15:1, the best is the comprehensive mechanical property of the CNTs/ EP composite. Compared to pure EP, its impact strength, bending strength, flexural modulus and fracture toughness are increased by 90%, 30%, 10 % and 20%, respectively.