Research on Dynamic Wettability of Carbon Fibers and Its Surface Presoaking Sucrose Carbonizing Modification

Author:Qiu Si

Supervisor:zhang dong xing


Degree Year:2019





With the pursuit of lightweight and excellent performance of materials in various industries,carbon fiber and its composites are more and more widely used.The interface between carbon fiber and polymer matrix is one of the important factors to determine the properties of composites,and the interfacial strength between them is always the bottleneck to improve the properties of composites.Well wetting effect between fiber and matrix is the premise of forming good interface,good mechanical meshing,chemical bonding and other interactions are the guarantee of improving the interfacial strength of composite materials.At present,the measurement of contact angle is the main method to evaluate the wettability of carbon fiber.However,because the size of carbon fiber is very small,the surface tension is very small when the contact angle is measured,there is a deviation between the measured contact angle of carbon fiber monofilament and the real value.At the same time,although there are many modification methods of carbon fiber surface aimed at improving the interfacial properties of composite materials and the interface properties are improved to a certain extent,there are some defects such as complex technology,high energy consumption and environmental pollution.Therefore,this paper aimed at the above problems,carring out the relevant research work.Based on the analysis of the influence factors on the contact angle of single carbon fiber,the existing measurement methods are improved,and the dynamic wetting behavior of single carbon fiber in different tested liquids is analyzed.The static contact angle of carbon fiber is predicted by dynamic wetting theory,and the surface energy of carbon fiber is calculated.At the same time,At the same time,sucrose was pre-soaked and carbonized on the surface of carbon fiber to improve the interface and properties of carbon fiber reinforced epoxy resin composites.Based on Wilhelmy plate method,the influence of diameter and surface tension of carbon fiber monofilament on dynamic contact angle measurement is analyzed.The results show that when the fiber diameter changes,the dynamic contact angle also changes.When the contact angle is small,the force of the fiber will have a great impact on the measurement results of contact angle.The diameter of carbon fiber monofilament was accurately measured by SEM.In order to improve the existing method of measuring the contact Angle of carbon fiber monofilament,the force analysis is carried out when the dynamic contact Angle of carbon fiber monofilament and liquid is measured.The dynamic wetting behaviors of single carbon fiber in deionized water,ethylene glycol,diiodomethane and formamide at different test rates were studied.It is found that both the viscosity of the tested liquid and the adsorption of the tested liquid on the carbon fiber surface will affect the test results.The static contact angle of carbon fiber monofilament in each liquid was predicted by fitting the test results with MKT(Molecular Kinetic Theory)and HD(Hydrodynamic approach)theory.By analyzing the matrix condition number of different liquid combinations,it is concluded that the surface energy of single carbon fiber is the most accurate by using four liquid combination systems,and the surface energy of carbon fiber monofilament is 37.81 mJ/m~2±0.43 mJ/m~2,Polar componentγsab=5.70 mJ/m~2±0.30 mJ/m~2.The surface morphology and chemical composition of carbon fiber were studied by SEM,FTIR and XPS.The results showed that the main active groups on the surface of carbon fiber T300 were hydroxyl,amino and carboxyl group.By means of TG,DSC analysis research of sucrose in the carbonization behavior of air and nitrogen atmosphere,using FTIR and XPS analysis different atmosphere and temperature of the chemical structure of sucrose coking residue,results show that the carbonized sucrose above 230℃,air and nitrogen atmosphere coking residue in the same chemical composition,main is a mixture of ether and aldehyde compounds formed by,only group content is different.Using deionized water and ethyl acetate as solvent,the surface of carbon fiber was modified by sucrose preimpregnation carbonization.Through SEM observation,it was found that the sucrose carbonized residue formed a circular bulge on the surface of carbon fiber which could increase the roughness.Carbon fiber/epoxy resin composites were prepared from sucrose carbonized carbon fiber and tde-85 epoxy resin,and their mesoscopic and macroscopic mechanical properties were studied.The method of micro-debonding was used,and the results show that the carbon fiber modified by carbonization of sucrose at 290oC in air atmosphere has the highest interfacial shear strength,which reaches 60.2MPa±5.0 MPa,and increases 20.8%compared with the unmodified carbon fiber.The interlaminar shear strength of the modified carbon fiber composites increased to31.32 MPa,and increases 13.8%,and there was almost no fiber pull-out at the fracture surface of the carbon fiber composites modified by sucrose carbonization.The carbon fiber composite material after impact test was observed by means of ultra-depth of field three-dimensional microscope,and it was found that the pit depth was reduced by 33.9%,and the crack did not expand in a wide range,indicating that it had good impact resistance.AFM was used to observe the surface roughness of carbon fiber prepretreated with sucrose,the surface roughness of carbon fiber was increased by 126%;The contact angle of modified carbon fiber prepretreated with sucrose was measured by a modified carbon fiber monofilament contact angle measurement method.Its polar component has increased by 11.8%.Based on the carbonization behavior analysis,the interface model between sucrose carbonization residue and carbon fiber surface and epoxy resin was established.Through the differential charge density analysis of the two interfacial systems,it is found that there is electron transfer and loss between the sucrose carbonized residue and carbon fiber and epoxy resin,indicating that there is a weak intermolecular force between the two systems and the surface of carbon fiber.Fine wettability,rough surface structure of carbon fiber and the synergistic effect of weak intermolecular force can guarantee the interfacial properties of carbon fiber/epoxy composites.