Mechanical And Dielectric Properties Of Carbon Nanotubes Decorated Polyimide Fiber Reinforced Phosphoric Acid-based Geopolymers

Recent studies have shown that aluminosilicate material such as metakaolinite can be also activated by phosphoric acid to obtain a new type of geopolymers known as phosphoric acid-based geopolymers.Compared to alkali-based geopolymers,the phosphoric acid-based geopolymers show superior mechanical,thermal and dielectric properties.However,geopolymer has high brittleness and low shock resistance,and hence limits its use in many application fields.Polyimide(PI)fiber as a high strength,high thermal stability and low dielectric constant of the high performance fiber,its applied to enhanced phosphoric acid-based geopolymer can be prepared a new type of organic-inorganic composite materials.A new methodology to decorate the surface of PI fiber with carbon nanotubes(CNTs)has been developed in this study.This surface decoration was carried out through a surface alkali treatment,carboxylation modification,functionalization with acyl chloride groups and then with amino groups,and a surface graft of CNTs onto PI fiber.F ourier-transform infrared and X-ray photoelectron spectroscopic characterizations confirmed that CNTs were chemically grafted onto the surface of PI fiber,and scanning electron microscopic observation demonstrated the fiber surface was uniformly and densely covered with CNTs.The surface energy and wettability of PI fiber were improved in the presence of CNTs on the fiber surface,which makes a contribution to enhance the interfacial adhesion of PI fiber with other inorganic matrices when used as a reinforcing fiber.The application of CNTs-decorated PI fiber for the reinforcement of phosphoric acid-based geopolymers was investigated,and the results indicated that the geopolymeric composites gained a noticeable reinforcement,When the content of the fiber is 1.5 wt%,the compressive strength and the flexural strength are maximized.Compared to unreinforced geopolymer,the CNTs-decorated PI fiber reinforced geopolymeric composites achieved a remarkable increase in compressive strength by 91.3%and in flexural strength by 284%.While the compressive and flexural strength of the phosphate-based geopolymers using the pristine PI fibers were increased by only 61%and 174.4%.Fractography investigation demonstrated that the interaction adhesion between the fibers and matrix was enhanced due to the surface decoration of PI fiber with CNTs,which contributed to an improvement in fracture-energy dissipation by fiber pull-out and fiber debonding from the matrix.As a result,a significant reinforcement effect on geopolymeric composites was achieved through a fiber-bridging mechanism.This study provided an effective methodology to improve the interracial bonding force for PI fiber and also proves a high efficient application of CNTs-decorated PI fiber for the mechanical enhancement of geopolymeric composites.