Study On Graft Modification Of Carbon Fiber Based On Ozone Oxidation And Its Mechanical Properties

Carbon fiber has excellent properties such as high temperature resistance,corrosion resistance,low coefficient of thermal expansion,good dimensional stability,high specific strength and high specific modulus,and its composite structural parts are often used in the fields of national defense technology,automotive tools and sports construction.However,while carbon fiber composites have excellent properties,they also have some defects that cannot be ignored,i.e.,they cannot form a good interface with the matrix,i.e.,carbon fibers cannot form a good interface with the matrix,and are prone to stress concentration leading to rapid failure of the composites,which limits the development of carbon fiber composites.In order to solve this problem,this paper will further introduce reactive groups to make them form good interfacial compatibility with the matrix and achieve the purpose of enhancing the interfacial bonding and mechanical properties.The main research contents are as follows:Firstly,ozone oxidation was used to improve the surface of carbon fiber and enhance the interfacial interaction between carbon fiber and resin through a green and pollution-free oxidation process.The changes of the surface morphology,elements contained and mechanical properties of carbon fibers treated at different temperatures and times were studied,and the mechanism of the interaction between ozone and carbon fibers was analyzed to optimize the oxidation process.The results show that ozone oxidation can make the longitudinal ridges on the surface of carbon fibers clearer,can introduce a large number of oxygen-containing functional groups,and produce some etching on the surface of carbon fibers;when oxidized at room temperature for 20 min,its tensile strength increases by 5.90 % without losing the strength of the fibers themselves,and the interlaminar shear strength(ILSS)and transverse fiber tensile strength(TFBT)of its composites can The interlaminar shear strength(ILSS)and transverse fiber tensile strength(TFBT)of the composites increased by 15.59 % and 22.00 %,respectively.Next,polyether amine(PEA)with different molecular weights was grafted on the surface of ozone-oxidized carbon fibers by chemical grafting method,and the surface morphology,surface elements,surface functional groups and wettability of modified carbon fibers were characterized to investigate the effect of PEA molecular weight variation on the mechanical properties of carbon fiber composites.The results showed that the carbon fiber grafted PEA could introduce amino active functional groups,significantly improve the surface energy of the fiber,and facilitate the carbon fiber to realize the chemical bonding with epoxy resin.Meanwhile,the molecular weight of grafted PEA affects the surface chemical structure and microscopic morphology of carbon fibers,which in turn affects the interfacial properties of the composites.As the molecular weight of PEA increases,the molecular chain grows,the mobility of polymer chain decreases,and the number of molecules grafted to the surface of carbon fiber decreases,resulting in weaker chemical bonding and mechanical engagement between the two phases of carbon fiber and resin,and lower interfacial properties of the composite.When the molecular weight of grafted PEA was 400,the highest ILSS and flexural strength of the prepared composites were obtained,with an increase of 29.35 % and 26.95 %,respectively,compared to the unmodified carbon fiber composites.Therefore,the modulation of the interfacial properties of the composites can be achieved by adjusting the molecular weight of the grafted polymer.Finally,by using PEA with different molecular weights as the connecting link and introducing dopamine(DA)with aromatic structure to give "rigidity" to the interface,and constructing polyetheramine/dopamine(PEA/PDA)"rigid-flexible" interface,OCF-D230-PDA,OCF-D400-PDA and OCF-D2000-PDA with different molecular weights were prepared.PDA,OCF-D400-PDA and OCF-D2000-PDA with different molecular weights were prepared.Comparing the mechanical properties of OCF-D230-PDA,OCF-D400-PDA and OCF-D2000-PDA,OCF-D400-PDA has the best ILSS and bending strength properties,which are 45.76 %and 47.63 % higher than those of unmodified carbon fibers,respectively;in addition,the impact resistance is significantly improved,and the damage of the modified samples under the same impact energy The damage area of the modified samples was smaller and could withstand larger impact loads at the same impact energy.The reason is that D400 has less molecular stacking structure,which can provide more amino groups to produce stronger covalent interactions with PDA,thus increasing the crosslinking density in the OCF-PEA-PDA/epoxy interphase region,while the higher the molecular weight,the lower the mobility of the polymer,and the molecular chain is prone to curl,which cannot provide more amino groups to interact with PDA.