Effects of electrochemical oxidation on surface and mechanical properties of dry-jet wet spun carbon fibers

The surface of dry-jet wet spun carbon fibers(CFs)is relatively smooth compared with those of wet spun CFs,which results in weak interfacial interactions between the fiber and the polymer resin.A surface functionalization treatment is particularly important to unleash the full potential of the superior mechanical properties of dry-jet wet spun CFs.In this study,the effects of electrochemical oxidation treatment time and current density on the surface structures and the mechanical properties of dry-jet wet spun CFs were investigated.The interlaminar shear strength of the CFs improves significantly from 69 to 84 MPa after 120 s of treatment.Further structural analysis reveals that the improvements are due to the addition of oxygen-containing functional groups and the optimization of the morphology on the surface of the CFs.

PAN干湿法纺丝工艺中原丝的表面沟槽形态

本文在研究了 PAN 溶液粘度特性的基础上，研究了纺丝液粘度特性与相关组成因素间的关系，初步探讨了不同纺丝工艺在纤维表面结构形成过程中的作用。实验表明，溶液粘度随 PAN 质量分数和相对分子质量的增加而增大，温度是调控体系粘度的有效方法；同时纺丝液中 PAN 质量分数的提高，有利于提高纤维的致密性并促使凝固牵伸倍数和总牵伸倍数增大。而干湿法纺丝技术在消除纤维表面沟槽方面有独特的作用。

Preparation and Characteristics of Novel Fibers Based on Cellulose Acetate and Soy Lecithin for Attracting and Binding POPs

Soy lecithin (SL)-modified cellulose acetate (L-CA) fibers for use as a novel biomimic material were prepared by a dry-jet wet spinning process from a solution of the polymer in dioxin. Characteristics of the L-CA fibers, such as structural properties, water absorbance, electrical conductivity and accumulation of trace persistent organic pollutants (POPs), were examined. Cross-sectional scanning electron microscopy (SEM) of L-CA unveiled a finger-like structure, along with a thin dense surface layer like that of CA. On the basis of X-ray photoelectron spectroscopic (XPS) observations, it was concluded that the enhancement of binding energy was optimum with 10% SL in the fiber, whereas superfluous SL led to self-assembly between the SL molecules, which weakened the binding between the SL and CA. Also, the L-CA fibers showed good water absorbance and a low charge conductivity in comparison to that of the non-modified CA fibers. Examination of the ability to accumulate POPs from water showed that L-CA is a effective candidate for the removal of micropollutants from aqueous solution.

Synthesis and AO Resistant Properties of Novel Polyimide Fibers Containing Phenylphosphine Oxide Groups in Main Chain

A series of co-polyimide(PI)fibers containing phenylphosphine oxide(PPO)group were synthesized by incorporating the bis(4-aminophenoxy)phenyl phosphine oxide(DAPOPPO)monomer into the PI molecular chain followed by dry-jet wet spinning.The effects of DAPOPPO molar content on the atomic oxygen(AO)resistance of the fibers were investigated systematically.When the AO fluence increased from 0to 3.2×1020the mass loss of the fibers showed the dependence on DAPOPPO molar content in co-PI fibers.The PI fiber containing 40%DAPOPPO showed lower mass loss compared to those containing 0%and 20%DAPOPPO.At higher AO fluence,the higher DAPOPPO content gave rise to dense carpet-like surface of fibers.XPS results indicated that the passivated phosphate layer was deposited on the fiber surface when exposed to AO,which effectively prevented fiber from AO erosion.With the DAPOPPO content increasing from 0%to 40%,the retentions of tensile strength and initial modulus for the fibers exhibited obvious growth from 44%to 68%,and 59%to 70%,after AO exposure with the fluence of 3.2×1020The excellent AO resistance benefits the fibers for application in low Earth orbit as flexible construction components.

Synthesis and Properties of Novel Polyimide Fibers Containing Phosphorus Groups in the Side Chain (DATPPO)

A series of polyamic acid copolymers(co-PAAs) containing phosphorous groups in the side chains were synthesized from [2,5-bis(4-aminophenoxy) phenyl] diphenylphosphine oxide(DATPPO) and 4,4′-oxydianiline(ODA) with 3,3′,4,4′-biphenyltetracarboxylic dianhydride(s-BPDA) through the polycondensation in N,N′-dimethyacetamide(DMAc). The co-PAA solutions were spun into fibers by a dry-jet wet spinning process followed by thermal imidization to obtain co-polyimide(co-PI) fibers. FTIR spectra and elemental analysis confirmed the chemical structure of PI fibers. SEM results indicated that the resulting PI fibers had a smooth and dense surface, a uniform and circle-shape diameter. The thermogravimetric measurements showed that with the increase of DATPPO content, the resulting PI fibers possessed high decomposition temperature and residual char yield, indicating that the PI fibers had good thermal stability. The corresponding limiting oxygen index(LOI) values from the experiment results showed that the co-PI fibers possessed good flame-retardant property. Furthermore, the mechanical properties of the co-PI fibers were investigated systematically. When the DATPPO content increased, the tensile strength and initial modulus of the co-PI fibers decreased. However, the mechanical properties were improved by increasing the draw ratio of the fibers. When the draw ratio was up to 2.5, the tensile strength and initial modulus of the co-PI fibers reached up to 0.64 and 10.02 GPa, respectively. The WAXD results showed that the order degree of amorphous matter increased with increased stretching. In addition, the SAXS results displayed that valuably drawing the fibers could eliminate the voids inside and lead to better mechanical property. WAXD revealed that the orientation of the amorphous polymer influenced the mechanical properties of the fibers.