In the present study C/PLA composites with different fiber surface conditions (untreated and with nitric acid oxidation for 4 h and 8 h) were prepared to determine the influence of surface treatment on the interfacial adhesion strength and mechanical properties of the composites. A chemical reaction at the fiber–matrix interfaces was confirmed by XPS studies. Nitric acid treatment was found to improve the amount of oxygen‐containing functional groups (particularly the carboxylic group, —COOH) on carbon fiber surfaces and to increase the surface roughness because of the formation of longitudinal crevices. The treated composites exhibited stronger interface adhesion and better mechanical properties in comparison to their untreated counterparts. There was a greater percentage of improvement in interfacial adhesion strength than in the mechanical properties. The strengthened interfaces and improved mechanical performance have been mainly attributed to the greater extent of the chemical reaction between the PLA matrix and the carbon fibers. The increased surface roughness also has had a slight contribution. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 80: 367–376, 2001

ABSTRACT:In the present study, carbon fiber-reinforced polylactide (C/PLA) composites with different interfacial conditions were prepared to determine the influence of interfacial adhesion strength (IAS) on in vitro degradation behavior of the C/PLA composites. Pure PLA and untreated and treated C/PLA composite samples were immersed in phosphate buffered saline (PBS; pH 7.4, 37 Ϯ 0.5°C) for predetermined time periods. These samples were removed at each degradation time, measured to analyze molecular weight loss, weighed to assess water uptake and mass loss, and mechanically tested to obtain bending strength, modulus, and IAS. The matrixes in the C/PLA composites showed higher water uptake and lower mass loss in comparison with the pure PLA. Further, the PLA matrix in the treated composite absorbed less water and lost less mass and molecular weight than its counterpart in the untreated composite. Mechanical tests confirmed that the treated C/PLA composite exhibited a slower rate of decrease in bending strength, modulus, and IAS than the untreated one. The differences in degradation behavior between two composites can only be attributed to the difference in interfacial conditions because all other parameters were kept constant. The loss of bending strength and modulus was mainly caused by the interface degradation of the C/PLA composites. It can be concluded from our in vitro observations that the IAS had an obvious influence on the degradation characteristics of the C/PLA composites.

Carbon fiber-reinforced gelatin composites have been prepared in our laboratory to obtain a novel biomaterial of improved mechanical properties. The swelling behavior (swelling rate, swelling kinetics, maximum solvent uptake, etc.) for both continuous carbon fiber-reinforced gelatin composite (C L /Gel) and short carbon fiberreinforced gelatin composite (C S /Gel) are investigated. Experimental data show that the swelling process of the original gelatin and gelatin matrixes in both composites follows a second-order kinetics. The swelling of the gelatin matrixes in both composites proceeds slower than that of the pristine gelatin, and depends on fiber form and fiber volume fraction (Vf). Results indicate that the presence of carbon fibers suppresses the swelling of the gelatin matrixes in both composites. It is found that the gelatin matrix in C S /Gel possesses a smaller swelling rate and maximum solvent uptake than that in C L /Gel. A mechanism governing these phenomena is discussed in this article.

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ABSTRACT:Interfacial adhesion between carbon fiber and epoxy resin plays an important role in determining performance of carbon-epoxy composites. The objective of this research is to determine the effect of fiber surface treatment (oxidization in air) on the mechanical properties (flexural strength and modulus, shear and impact strengths) of three-dimensionally (3D) braided carbon-fiber-reinforced epoxy (C 3D /EP) composites. Carbon fibers were air-treated under various conditions to improve fiber-matrix adhesion. It is found that excessive oxidation will cause formation of micropits. These micropits are preferably formed in crevices of fiber surfaces. The micropits formed on fiber surfaces produce strengthened fiber-matrix bond, but cause great loss of fiber strength and is probably harmful to the overall performance of the corresponding composites. A trade-off between the fiber-matrix bond and fiber strength loss should be considered. The effectiveness of fiber surface treatment on performance improvement of the C 3D /EP composites was compared with that of the unidirectional carbon fiberepoxy composites. In addition, the effects of fiber volume fraction (V f ) and braiding angle on relative performance improvements were determined. Results reveal obvious effects of V f and braiding angle. A mechanism was proposed to explain the experimental phenomena.