Y. Z. Wan

Influence of surface treatment of carbon fibers on interfacial adhesion strength and mechanical properties of PLA-based composites

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.

Effects of fiber volume fraction, hot pressing parameters and alloying elements on tensile strength of carbon fiber reinforced copper matrix composite prepared by continuous three-step electrodeposition

Abstract Carbon fiber reinforced copper matrix composites have been produced by continuous three-step electrodeposition plus hot pressing technique. Iron or nickel element was added to copper matrix to improve interfacial bonding of the composite. The effects of fiber volume fraction and hot pressing parameters (temperature, pressure and time) on the tensile strength of the composite were investigated. Emphasis was placed on the influence of alloying elements on the tensile strength of the composite. The composite was found to exhibit the highest strength at an optimum V f , hot pressing parameter temperature, pressure, or time by keeping other parameters constant. This optimum value was related to the alloying element incorporated in the copper matrix. It is observed that incorporation of alloying elements does not change the general trends, but changes the mechanism governing the decreasing trends of the tensile strength of the composites as the hot pressing temperature exceeds the optimum value. Further, the alloying elements affect the highest strength values ( σ max ). C/Cu(Ni) composite with the medium interfacial bonding strength exhibits the highest σ max . It is concluded from our experiments that a diffusion bonding is preferable since the fiber–matrix interaction can be easily controlled and the fiber degradation is limited during hot pressing process.

Carbon fiber-reinforced gelatin composites. I. Preparation and mechanical properties

Composites were made from carbon fibers and gelatin using a solvent-casting or solution-impregnation technique. Relationships between the fiber volume fraction (Vf), glycerol (plasticizer) content, gelatin content, fiber form, and mechanical properties (tensile strength and modulus, elongation at break, and shear strength) of the composites were investigated. In long carbon fiber gelatin composite (CL/Gel), tensile strength, modulus, and shear strength increased steadily with the Vf. In the case of a short carbon fiber gelatin composite (CS/Gel), an initial improvement in tensile strength and modulus was followed by a reduction, whereas the shear strength improved with the Vf and then reached a constant value. The elongation decreased with the Vf for both composites. It is shown that CL/Gel had higher values of strength, modulus, and elongation than did CS/Gel at any Vf level. The effects of glycerol and gelatin contents on the mechanical properties of the composites were found to be much less significant as compared to the Vf. According to scanning electron microscopic observation of the fracture surfaces, the fibers were uniformly distributed in the gelatin matrix, but the interfacial adhesion between the gelatin matrix and the carbon fibers was not very good for both composites. Fiber surface modification would be necessary to further improve the mechanical properties of the two composites.

Carbon fiber‐reinforced gelatin composites. II. Swelling behavior

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 (CL/Gel) and short carbon fiber-reinforced gelatin composite (CS/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 CS/Gel possesses a smaller swelling rate and maximum solvent uptake than that in CL/Gel. A mechanism governing these phenomena is discussed in this article.

Moisture absorption behavior of C3D/EP composite and effect of external stress

Abstract A three-dimensionally (3-D) braided carbon-fiber-reinforced epoxy (C 3D /EP) composite has been produced by vacuum impregnation technique by using a low-viscosity epoxy. The present study is carried out in order to determine the water absorption characteristics of this 3-D composite for internal fixation applications. Effect of external load on water uptake and changes in flexural, shear and impact strengths as a result of moisture absorption has been investigated considering the bone fixation devices are attacked by moisture and stress. The kinetics of moisture absorption by the stressed and unstressed 3-D composite samples has been determined for absorption at body temperature (37±0.5 °C). It has been shown that the water absorption characteristic of this C 3D /EP composite cannot be described by using Ficks law may be due to its high void content and/or its 3-D fiber structure. Results clearly demonstrate the contribution of external stress on water absorption behavior and changes in mechanical property. The external stress has been found to increase the moisture content and mechanical properties reduction at earlier stages. At later stages, a contrary trend is observed. Mechanisms are proposed to interpret our experimental results.

Characterisation of Hydroxyapatite/Bacterial Cellulose Nanocomposites

A novel nanocomposite material consisting of hydroxyapatite (HAp) deposited on a phosphorylated bacterial cellulose (BC) has been synthesised via a biomimetic route. X-ray photoelectron spectroscopy (XPS) showed that phosphate groups were successfully introduced to the hydroxyl groups of BC by phosphorylation reaction to promote the growth of calcium phosphate. Transmission electron microscopy (TEM) and the corresponding selected area electron diffraction (SAED) patterns of HAp/BC demonstrated that HAp crystals wrap the surfaces of BC fibres. In this work, HAp/BC nanocomposites were studied using thermo-gravimetric analysis (TGA) and differential scanning calorimetry (DSC). The TGA result suggested that HAp/BC nanocomposite, similar to natural bone in terms of composition, contained carbonate ions, in agreement with our previous Fourier transform infrared (FTIR) spectroscopy results. Thermal behaviour differences between BC and HAp/BC were observed by differential scanning calorimetry (DSC). The thermal stability of HAp/BC obtained from DSC showed an improvement when compared to that of a pure BC sample.

Effect of metal diffusion barrier on thermal stability of metal-coated carbon fibers

The thermal stability of carbon fibers coated with different metals was investigated. The fracture strength of metal-coated carbon fibers was measured at room temperature as a function of heat-treatment temperature. It was demonstrated that the fracture strength of the copper-coated carbon fibers (C/Cu) was not affected by heat-treatment at temperatures up to 900°C because of the inert of copper. However, the fracture strength of the carbon fibers coated with an active metal (nickel, iron and chromium) were found to decrease significantly after heat-treatment at temperatures >700°C, owing to graphitization (induced by nickel) of the carbon fibers or a chemical reaction (between fibers and iron or chromium) at the interface. A diffusion barrier layer between the active metal coating and the fibers can reduce the strength loss of the carbon fibers, but the effectiveness of a metal diffusion barrier differed depending significantly on the nature of the introduced metals. It was found that if the diffusing active metal had an adequate solubility in a metal, the latter can effectively hinder the diffusion of the former; if not, the latter can not effectively hinder the diffusion of the former.

ENHANCED CALCIUM PHOSPHATE PRECIPITATION ON THE SURFACE OF Mg-ION-IMPLANTED ZrO2 BIOCERAMIC

Modification of bioceramics by ion implantation of magnesium (Mg) is of interest as Mg is the fourth abundant cation in the human body. In this work, magnesium was ion-implanted into a ZrO2 based bioceramic stabilized with Y2O3 and Al2O3. Both Mg-implanted and unimplanted samples were soaked in a simulated body fluid (SBF) for a period of time. The deposits on the surface of various samples were characterized with scanning electron microscope (SEM), X-ray diffraction (XRD), and Fourier transform infrared spectroscopy (FTIR). We find that the Mg-implanted ZrO2 shows better bioactivity than the plain bioceramic. These results indicate that Mg-implantation can improve the bioactivity of the ZrO2 based bioceramic. Mechanisms governing the improvement are discussed in this paper.

FORMATION AND CHARACTERIZATION OF 3C-SIC BY CARBON-ION IMPLANTATION INTO SILICON WITH A MEVVA ION SOURCE

Crystalline cubic silicon carbide (3C-SiC) surface layers have been prepared by carbon-ion implantation into silicon (100) using a MEVVA ion source and subsequent annealing at 1250°C for 2 h. The obtained films have been characterized by SEM, XRD, and micro-Raman analysis. The effect of carbon-ion dose on the surface morphology of the ion-implanted samples has been investigated. Rectangular patterns are observed on the surfaces of carbon-ion-implanted silicon substrates. It is found that the amount of rectangular patterns increases with ion dose, suggesting the dependence of surface morphology on ion dose. The formation of rectangular patterns has been elucidated in this paper.