硫酸体系下高模碳纤维在不同电场环境中的阳极氧化行为

Andic oxidation of high-modulus carbon fibers in sulfuric acid under different electric fields

高模量碳纤维的惰性表面导致其与树脂基体之间薄弱的界面结合,限制高模量碳纤维复合材料在众多应用场景中性能的发挥。阳极氧化作为目前唯一可与碳纤维生产线并线运行的表面处理技术,常用的以碳酸氢铵为代表的碱性电解质在氧化高模碳纤维时效果有限,氧化性更强的酸性电解质体系下的阳极氧化机制缺乏系统研究。采用稀硫酸对模量为371 GPa的碳纤维进行电化学阳极氧化处理,系统研究电流密度、电解质浓度等关键要素对高模量碳纤维表面极性结构的影响规律,继而研究表面处理效果对碳纤维/环氧树脂复合材料界面剪切强度的影响规律,建立表面处理要素与复合材料界面性能的关联性。结果表明:处理后的碳纤维在保持原有表面形貌和石墨化结构的基础上,在碳纤维的无定型碳和芳香环状结构区域发生氧化反应,反应后纤维表观石墨化程度降低,表面能增大,表面含氧官能团含量增加。在当硫酸浓度为1.0%(质量分数)、电流密度为0.26 mA/cm^(2)时,此时碳纤维的表面能最高,为57.7 mN/m,相比于未处理的碳纤维提高了62.08%,与环氧树脂的界面剪切强度达到80.9 MPa,相对于未处理对应的21.8 MPa提高了2.7倍,处理后碳纤维的单丝拉伸强度不受损。

The inert surface of high-modulus carbon fiber leads to the weak interface between it and the resin matrix,which limits the performance of high-modulus carbon fiber composite in many application scenarios.Anodic oxidation is the only surface treatment technology that can be combined with carbon fiber production lines until now,but the commonly used alkaline electrolytes represented by ammonium bicarbonate exhibit limited effect on the oxidation of high-modulus carbon fiber.The acidic electrolyte system has stronger oxidation ability,lacks systematic researches on anodizing mechanism.In this paper,dilute sulfuric acid was used for the anodic oxidation for carbon fiber with a modulus of 371 GPa.The effects of key factors such as current density,electrolyte concentration on the polar structure of the surface of high-modulus carbon fiber were systematically studied,and then the effects of surface treatment on the interfacial shear strength of carbon fiber/epoxy resin composites were investigated.The correlation between surface treatment factors and interfacial properties of composites was established.The results show that after the treatment,the surface morphology and graphitized structure of the carbon fiber are maintained,and oxidation reactions occur in the amorphous carbon and aromatic ring structure regions of the carbon fiber.After the reaction,the graphitization degree of the fiber decreases apparently,the surface energy increases,and the content of surface oxygen-containing functional groups increases.When sulfuric acid concentration is 1.0%(mass fraction)and current density is 0.26 mA/cm^(2),the surface energy of carbon fiber is the highest(57.7 mN/m),which is 62.08%higher than that of untreated carbon fiber.The interfacial shear strength between carbon fiber and epoxy resin reaches 80.9 MPa,which is 2.7 times higher than that of untreated one corresponding to 21.8 MPa.Furthermore,the single fiber tensile strength of the treated carbon fiber exhibits undamaged.