According to typical structural mod

According to typical structural model of high tensile strength CFsdeveloped by Guigon et al. [58], the carbonaceous materials were madeof the same basic structural units (BSU), and the BSU were stacks of twoor three fringes less than 1 nm in diameter associated edge to edge in azigzag, thus forming larger crumpled and entangled transversallywrinkled layers. When two crumpled sheets of layers become closeenough, the bonding occurs in the faulty areas as a result of crosslinks,tetrahedral bonds, etc. at the boundaries, which gave lateral cohesion tothe fiber [59]. In HMCFs, the wrinkled layers made of small BSU associated edge to edge were dewrinkled, and they were also easily to beunfolded by mild chemical treatment [60]. In the process of electrochemical surface oxidation, an in-depth modification possibly resultedin chemical crosslinks in the form –O– between the unfolded graphitelayers of UMHCFs (Fig. 9). The chemical crosslinks most likely happened between the outmost layer and the secondary layers, and aboveXRD analysis also confirmed that the surface oxidation couldn't affectthe internal graphite structure. The cross-linked structure was similarwith the turbostratic structure which could give longitudinal or lateralcohesion to the fiber. As a result, a further increase in the value of thetensile strength of UHMCFs occurred as the current density more than 1.0 A/m2 (Fig. 8). As for the tensile modulus of UHMCFs, either chemical etching and oxidation or chemical crosslink could both destroythe ordered graphite structure. Therefore, their values gradually decreased in the process of electrochemical surface oxidation (Fig. 8)