铵盐电解质溶液中高模碳纤维的电化学氧化机制

Electrochemical oxidation mechanism of high modulus carbon fibers in ammonium electrolyte solution

聚丙烯腈基高模碳纤维(HMCFs)具有高比强度、高比模量、低热膨胀系数等优异性能,在航空航天、高端运动器材等领域应用广泛,但因其表面呈现极高惰性而难以与树脂基体有效结合,直接影响了复合材料性能。目前,电化学氧化是唯一实现在线配套的碳纤维表面改性工艺,而有关高模碳纤维表面的电化学氧化研究尤其是电解质溶液对HMCF表面的氧化机制尚缺乏系统研究。通过采用具有4种不同酸碱性特征的铵盐溶液对HMCF进行电化学氧化处理,表征并分析了处理前后纤维表面结构、力学性能及复合材料界面性能变化。结果表明:碳纤维经铵类电解质溶液处理后,表面发生氧化的同时引入N元素、产生含氮官能团,纤维表面无序化程度及含氧量随电解质溶液酸碱性的增强而增加;电化学处理后纤维模量都有不同程度地提高,而只有弱碱性的NH_(4)HCO_(3)和酸性的NH_(4)H_(2)PO_(4)电解质溶液处理后的纤维拉伸强度出现增加,分别从处理前的4.21 GPa提升到4.82 GPa和4.75 GPa,并且其复合材料界面剪切强度相对于从未处理碳纤维的复合材料分别提高了49.86%和49.02%,证明电化学氧化过程中适度的氧化刻蚀能够在纤维表面改性的同时提高纤维拉伸强度。

Polyacrylonitrile-based high-modulus carbon fibers(HMCFs)have excellent properties such as high specific strength,high specific modulus,and low coefficient of thermal expansion.So far,HMCFs have been widely used in aerospace and high-end sports equipment,etc.However,it is really difficult for HMCFs to effectively bond with the matrix owing to their extremely high surface inertness,which directly affects the performance of the corresponding composites.At present,electrochemical oxidation is one feasible surface modification process of carbon fiber which has been equipped online,whereas there is a lack of systematic research on the surface electrochemical oxidation of HMCFs,especially the oxidation mechanism of HMCF surface oxidized by different electrolyte solutions.In this paper,the electrochemical oxidation of HMCFs in four ammonium solutions with different acidbase characteristics was conducted.Changes in fiber surface structure,mechanical properties and composite interfacial properties before and after treatment were characterized and analyzed in detail.The results showed that after the treatment with ammonium electrolyte solutions,the fiber surface was oxidized together with the introduction of N elements and the generation of nitrogen-containing functional groups.Meantime,the degree of fiber surface disordering and the oxygen content also increased with the enhancement of the acidity and alkalinity of the electrolyte solutions.The fiber modulus increased to varying degrees after electrochemical treatment,while the fiber samples oxidized in NH_(4)HCO_(3) and NH_(4)H_(2)PO_(4) electrolyte solutions showed an increase in fiber tensile strength after treatment,from 4.21 GPa to 4.82 GPa and 4.75 GPa,respectively,and the interfacial shear strength of their composites also increased by 49.86%and 49.02%,respectively,compared with composites reinforced by untreated fibers.It is demonstrated that moderate oxidative etching during electrochemical oxidation can improve the tensile strength of fibers while modifying the fiber surface.