Hierarchical Design Of Composites Reinforcement And Study On Its Interfacial Enhancement Mechanism

With the rapid development of aerospace industry，the requirements for materials are more rigorous. In response to this demand, the composite has become the most important direction for new materials developing, as the most vitality branch of new materials. As an important branch of composites, polymer based composite materials play a important role in the aerospace industry. However, interface and dispersion of reinforcement in polymer become the performance bottleneck, in the further pursuing progress of properties for composites. In this paper, the physical and chemical micro structure of reinforcement were designed based on hierarchical design ideas, to improve properties of polymer based composites by overcoming the interface problem and dispersion problem. The poly(amido amine)(PAMAM)/carbon fiber(CF) hierarchical reinforcement, carbon nano/CF hierarchical reinforcement, nano carbon sponge hierarchical reinforcement were preparated characterised.The main research contents of this paper are as follows:Chemical self-assemble method is adopt to preparate PAMAM/CF hiararchical reinforcement for enhancing interfacial strength, which improves wettingbility and increases chemical bonds between CF and epoxy. The chemical bond between PAMAM and CF is identified by X-ray photoelectron spectroscopy(XPS), which provides opportunity to realize chemical bond between CF and epoxy. The test results and calculation of dynamic contact angle show that the surface free energy of CF increase30%-100%by introducing PAMAM, which improves wettingbility between CF and epoxy. The micro droplet bongding test shows that the interfacial shear strength(IFSS) between CF and epoxy shows69.3%increasement and controllability by adjusting PAMAM grafted density. Meanwhile, the “roof” trend of IFSS apears inflection point with increasing of PAMAM grafted density, when the PAMAM/DMF solution concentration is10-4mol/L. This is due to that the interfacial failure mode changes from weak adhesive failure between CF and epoxy to strong cohesive failure in epoxy. With the PAMAM grafted density further increasing, stacking PAMAM molecules change cohesive failure in epoxy to separation between PAMAM molecules by overcoming Van Der Waals.Chemical self-assemble method is adopt to graft nano carbon(carbon nanotube, graphene oxide) onto CF surface, to realize increasing mechanical interlock and uniform dispersion of nano carbon, thus enhance the interfacial strength. The XPS results confirm that nano carbon is grafted onto the CF surface with PAMAM as the media through chemical bond. The SEM results of carbon nanotube(CNT)/CF hierarchical reinforcement show that CNTs are grafted uniformly with high density on the CF surface. The CNTs grafted density is adjusted through controlling PAMAM grafted density. SEM results of graphene oxide(GO)/CF hierarchical reinforcement show that two kinds of grafting methods:(1) the graphene oxide edge connects with the CF surface;(2) the graphene oxide spreads partially on the CF surface, the other part extends out of the CF surface, supporting and lapping each other. Surface energy test and calculation results show that CF grafted nano carbon improves wettability for polymer. Due to introducing nano carbon, the wettability of CF gets improved. Because of effective mechanical interlock and good wettability by introducing CNT and GO, Nano carbon effectively prevents crack extending at the interface, the thus IFSS increases111%and69.2%respectively. At the same time, the IFSS could achieve controllability on the interfacial strength through the control of CNT grafted density onto CF surface.The graphene nanoribbon(GNR) sponge is in situ prepared by unzipping CNT sponge as template, which is prepared by chemical vapor deposition(CVD). The sponge structure realizes nano carbon dispersed well and increase the interfacial compatibility, which enhance the overall strength of nano carbon reinforced polymer composite. The SEM results of GNR sponge show that the CNTs has been transformed into GNRs. The specific surface area of sponge increases from62.8m2/g to113.1m2/g, which makes the specific capacitance increase from15.2F/g to92.6F/g. The GNR sponge after reduction makes specific capacitance further increase to114.9F/g, and exhibits good stability of charging-discharging cycles. Direct polymer infiltration can be used to prepare nano carbon sponge reinforced PDMS composite. Compared with pure PDMS, the strength, modulus and toughness of CNT-PDMS composites are increased by111.6%,460.9%,417%. The strength, modulus and toughness of GNR-PDMS composites are increased by143.8%,329.3%,962.2%. The interfacial enhancement mechanism was also explored in details.