Preparation Technology, Interfacial Characteristic And Properties Of Aramid Fiber Reinforced Soluble Poly(Aryl Ether) Composites

This work was financially supported by National Natural Science Foundation of China (No. 50743012) and Liaoning Excellent Talents in University (No. RC2005-14). One kind of novel thermoplastic resin with excellent thermal resistance and solubility-Poly (phthalazinone ether sulfone ketone)(PPESK) was chosen as resin matrix in composite system in our paper. The fiber soakage, preparation method, interfacial structure characteriztion and properties relationship during twisting and molding procedure of continuous aramid fibers reinforced PPESK composite were investigated. Due to the problems of fiber surface with few polar functional groups, smooth surface and low surface energy, low temperature plasma treatment on fiber surface modification was used. The composite interfacial adhesion was optimized design. In addition, the aging behavior of plasma treatment on fiber surface was at the primary stage discussed.In our work, two kinds of organic aramid fibers including Twaron and Armos were modified by oxygen plasma treatment. The fibers reinforced PPESK composite before and after plasma treatment were prepared through solution impregnating process and high temperature molding technique. The changes of fiber surface chemical structure, element composition, surface morphology, surface roughness and surface wettability before and after plasma treatment were characterized by FT-IR spectra, X-ray photoelectron spectroscopy (XPS), scanning electronic microscopy (SEM), atomic force microscopy (AFM) and dynamic contact angle analysis (DCAA) system, respectively. The composite interfacial adhesion property was evaluated by interlaminar shear strength (ILSS), and indirectly illustrated by the water absorption measurements and composite fracture mechanism was analyzed by the morphology of interlaminar shear ruptures of composite observed by SEM.The effects of oxygen plasma treatment on Twaron aramid fiber surface and its composite interfacial properties were first studied in this paper. The results showed a new oxygen-containing functional group -COO- was introduced onto the fiber surface, the fiber surface roughness increased and the fiber surface wettability was improved obviously after oxygen plasma treatment. Composite interlaminar shear strength increased from 39.2MPa for untreated sample to 52.0MPa for plasma treated for 15min under discharge power at 200 W, with an increase of 32.6%. Secondly, the influence of plasma treatment condition such as time and discharge power on Armos fiber surface and its composite interfacial properties were studied. It was found that oxygen plasma could introduce a lot of oxygen-containing functional groups onto the fiber surface, the fiber surface was etched obviously and the fiber surface wettability was improved consequently. Composite interlaminar shear strength increased from 59.5MPa for untreated sample to 68.8MPa for plasma treated for 10min under discharge power at 200 W, with an increase of 15.6%. The water absorption of composite decreasing also indirectly showed that oxygen plasma treatment improved composite interfacial adhesion. However, long time and large discharge power would make the fiber surface melting. Then, the fiber surface polar functional group decreased, surface roughness declined and surface wettability degraded. Finally, the composite interfacial properties turned to be weak.In addition, compared with the morphology of composite interlaminar shear ruptures before and after plasma treatment, it was found that the fibers were smooth with low amount of resin adhered to surface for the untreated specimen, the rupture took place near the interface between the fiber and matrix; However, a large proportion of fibers stuck tightly to matrix, the primary failure mode varied from interface failure to matrix or fiber failure for the oxygen plasma-treated specimen. It suggested that the interfacial bond strengths between the fiber and the matrix were well improved by oxygen plasma treatment. The relationship between the fiber surface characteristics and composite interfacial properties indicated that both the chemical bonding between the fiber and the matrix in composite system and the mechanical interaction contributed for increasing composite interfacial properties.Finally, the aging behavior of plasma-treated fiber surface was studied. The fiber surface properties such as polar functional groups, surface morphology, surface roughness and surface wettability as a function of storage time in air after plasma treatment were measured. The fiber surface aging behavior could be detected obviously in chemical composition and surface wettability, whereas the surface morphology and roughness remained nearly stable after storing in air as long as 10 days after oxygen plasma treatment. The polar functional groups on fiber surface reorientated or reversaled may be responsible for the weak interfacial strength between the fiber and the matrix in composite system.