Preparation of aqueous dispersion of thermoplastic sizing agent for carbon fiber by emulsion/solvent evaporation

In this work, different sizing agent aqueous dispersions based on polyetherimide (PEI) were elaborated in order to improve the interface between carbon fibers and a thermoplastic matrix (PEEK). The dispersions were obtained by the emulsion/solvent evaporation technique. To optimize the stability and the film formation on the fibers, two surfactants were tested at different concentrations, with different concentrations of PEI. The dispersions obtained were characterized by dynamic light scattering (DLS) and the stability evaluated by analytical centrifugation (LUMiFuge). The selected dispersions were tested for film formation ability by scanning electron microscopy (SEM), and the sizing performance was assessed by observation of the fiber/matrix interface by SEM. The results revealed that an aqueous dispersion of PEI,stabilized by sodium dodecyl sulfate as the surfactant, led to very stable sizing agent aqueous dispersion with ideal film formation and better interface adhesion

생체재료용 Carbon/PEEK 복합재료의 기계적 특성의 향상에 관한 연구

The purpose of this study is to determine the correct estimation of the mechanical properties of carbon/PEEK composites and its validity has been tested with the alternative materials of the metal-based materials for artificial hip joint. This study evaluated the mechanical properties according to the temperature of heat treatments for the sizing removal of carbon fiber and the fiber ply orientation. First, the sizing removal of carbon fiber were conducted at 300℃ for 4 hours and 400℃ for 2 hours respectively. The fractured surface in the specimen of tensile test made from PEEK and epoxy resin was observed by SEM. The fracture surface of the tensile test specimen of the carbon/epoxy composites heat-treated to 400℃ showed that the resin did not adhere nearly in the fiber surface and pull out was observed. It is considered that 400℃ is suitable heat treatment temperature for the sizing removal of the carbon fiber. The mechanical test results represent that there was no significant differences in short beam strength. However, the tensile strength and compressive strength of the carbon/PEEK composites were higher than those of the carbon/epoxy composites in the case of the vacuum bag process. Furthermore, this result indicated that the sizing material did not have a significant effect on the strength of the carbon/PEEK composites. Second, the specimens for the carbon/PEEK and carbon/epoxy composites were manufactured based on the ASTM standard. The specimens were immersed in distilled water at 37℃ for 100 days and the coefficient of moisture was measured in accordance with Fick's law. Moreover, the fracture energy according to the fiber ply orientation was evaluated in this study. The result exhibited that the coefficient of moisture-absorption of carbon/PEEK composites was the lowest because the interface coherence between the fiber and resin are the strongest. As a result, the fracture energy of the carbon/PEEK composites was superior to the carbon/epoxy composites. Third, the effect of Carbon/PEEK composites on the tribological properties has been investigated. The unidirectional composites had higher friction coefficients than those multidirectional composites. This was caused by the debonding between the carbon fiber and the PEEK sheet, which was proportional to the contact area between the sliding surface and the carbon fiber. The friction test results showed that there was no significant differences in relation to the fiber ply orientation. However, the friction properties of the carbon/PEEK composites were higher than those of the carbon/epoxy composites. As a result, it seemed that when the carbon/PEEK composites slid in a direction normal to the prepreg lay-up direction, its friction coefficient may be represented a smaller value compared to sliding in a direction parallel to the prepreg lay-up direction. In a case where the speed was 2.5 m/s, the friction coefficient was relatively large for configuration I. The friction surface of the specimen was analyzed using an electron microscope. In all cases, the debonding of the fiber and PEEK could be confirmed. Finally, it is suggested that a new concept design of the stem and aims to determine the suitability of various carbon/PEEK composite should be designed for artificial hip joints. Shear stress and principal stress tested with alternative materials of the Ti-based stem for artificial hip joints. In addition, FEA is conducted according to the fiber ply orientation and the load condition for carbon/PEEK composites.Contents List of Tables List of Figures Abstract 1. Introduction 1 1.1 Background 1 1.1.1 Artificial joint surgery 8 1.1.2 Patient-customized artificial joint 11 1.2 Purpose of Study 13 2. Introduction of Artificial Joint 20 2.1 History 20 2.2 Manufacturing 23 2.3 Market Trends 26 3. Materials and Experiment Method 30 3.1 Preparation of the Materials 30 3.2 Removal of Sizing 34 3.3 Moisture Absorption Theory 37 3.4 Specimens 39 3.5 Experiment Method 43 4. Results and Discussion 49 4.1 Effect of Sizing Removal 49 4.1.1 Mechanical properties 49 4.1.2 Fracture surface 56 4.2 Behavior of Moisture Absorption 63 4.2.1 Mechanical properties 67 4.2.2 Fracture energy 68 4.2.3 Fracture surface 72 4.3 Friction and Wear Behavior 76 4.3.1 Tribological properties 76 4.3.2 Fracture surface 83 4.4 Finite Element Analysis 90 4.4.1 Design and modeling method 90 4.4.2 FEA models and load 96 4.4.3 Principal stress 98 4.4.4 Shear stress 104 5. Conclusion 107 References 11

Graphite fiber surface treatment to improve char retention and increase fiber clumping

Composites containing carbon and graphite fibers can release fibers into the atmosphere during a fire. This release can potentially cause failure in some types of electrical equipment. Reduced fiber dispersion during and after combustion will reduce risks. Epoxidized char forming systems were synthesized which will react with commercially available surface treated carbon fiber. Fibers modified with these char formers retained adhesion in a specific epoxy matrix resin. Small scale combustion testing indicates that using these char former modified fibers in laminates will help to reduce the dispersement of fibers resulting from exposure to fire without sacrificing resin to fiber adhesion

Effects of fiber/matrix interactions on the properties of graphite/epoxy composites

A state-of-the-art literature review of the interactions between fibers and resin within graphite epoxy composite materials was performed. Emphasis centered on: adhesion theory; wetting characteristics of carbon fiber; load transfer mechanisms; methods to evaluate and measure interfacial bond strengths; environmental influence at the interface; and the effect of the interface/interphase on composite performance, with particular attention to impact toughness. In conjunction with the literature review, efforts were made to design experiments to study the wetting behavior of carbon fibers with various finish variants and their effect on adhesion joint strength. The properties of composites with various fiber finishes were measured and compared to the base-line properties of a control. It was shown that by tailoring the interphase properties, a 30% increase in impact toughness was achieved without loss of mechanical properties at both room and elevated temperatures

Characterization of low thermal conductivity PAN-based carbon fibers

The microstructure and surface chemistry of eight low thermal conductivity (LTC) PAN-based carbon fibers were determined and compared with PAN-based fibers heat treated to higher temperatures. Based on wide-angle x ray diffraction, the LTC PAN fibers all appear to have a similar turbostratic structure with large 002 d-spacings, small crystallite sizes, and moderate preferred orientation. Limited small-angle x ray scattering (SAXS) results indicate that, with the exception of LTC fibers made by BASF, the LTC fibers do not have well developed pores. Transmission electron microscopy shows that the texture of the two LTC PAN-based fibers studied (Amoco T350/23X and /25X) consists of multiple sets of parallel, wavy, bent layers that interweave with each other forming a complex three dimensional network oriented randomly around the fiber axis. X ray photoelectron spectroscopy (XPS) analysis finds correlations between heat treated temperatures and the surface composition chemistry of the carbon fiber samples

Interfaces and interfacial effects in glass reinforced thermoplastics - Keynote Presentation

Optimization of the fibre-matrix interphase region is critical to achieving the required performance level in thermoplastic matrix composites. Due to its initial location on the fibre surface, the sizing layer is an important component in the formation and properties of the composite interphase. Consequently, any attempt to understand the science of the composite interphase must encompass an understanding of the science of sizing. In this paper the role of sizings from fibre manufacture through to performance of composite parts is reviewed. In particular the role of organosilane coupling agents and how the formation of a polysiloxane interphase is influenced by the surface properties of the fibre is examined. The influence of the sizing film former in terms of its level of interaction with the silane coupling agent is also examined. The importance of residual stresses in thermoplastic composites in the values obtained for the apparent adhesion levels in these systems is highlighted. These residual stresses are shown to play a significant role in determining the level of interfacial strength in thermoplastic composites and in particular in polyolefin matrices. By applying some of the available models for this phenomenon this analysis is extended to explore the effect of the anisotropic fibre microstructure of carbon, aramid and natural fibres on the apparent interfacial strength in thermoplastic composites

Composite Flexible Blanket Insulation

Composite flexible multilayer insulation systems (MLI) were evaluated for thermal performance and compared with the currently used fibrous silica (baseline) insulation system. The systems described are multilayer insulations consisting of alternating layers of metal foil and scrim ceramic cloth or vacuum metallized polymeric films quilted together using ceramic thread. A silicon carbide thread for use in the quilting and the method of making it are also described. These systems are useful in providing lightweight insulation for a variety of uses, particularly on the surface of aerospace vehicles subject to very high temperatures during flight

Basalt short fibers dispersion and fabric impregnation with Magnesium alloy (AZ63). First results

Magnesium is one of the lightest structural metals used in different industrial sectors and many works in the literature have studied its reinforcement by filler addition. Basalt fibers are natural fillers that have good mechanical properties, excellent resistance to high temperatures, and lower cost than carbon fibers. Considering this, in recent years, they have been increasingly used in the production of composite materials with polymericmatrices. However, very little information is available in the literature about the use of basalt fibers as reinforcement inmetalmatrix compositematerials. It is well known that the impregnation of fiber reinforcement affects the mechanical behavior of the composite materials. The aim of this study was to investigate the impregnation and the behavior of basalt fibers in a magnesium alloy composite material manufactured by a centrifugal casting technique

Development of an improved toughness hyperpure silica reflective heat shield

High purity three dimensionally woven silica-silica materials were evaluated for use as a tough reflective heat shield for planetary entry probes. A special weave design was selected to minimize light piping effects through the heat shield thickness. Various weave spacings were evaluated for densification efficiency with an 0.7 micron particle size high purity silica. Spectral hemispherical reflectance was measured from 0.2 to 2.5 microns at room temperature. Reflectance increases due to densification and purity of material were measured. Reflectance of 3D hyperpure silica was higher than 3D astroquartz silica for all wavelengths. Mechanical properties were measured in beam flexure and beam shear tests. Results indicated strengths lower than reported for slip cast fused silica. Low strengths were attributed to low densities achieved through vacuum impregnation