Surface analysis of plasma grafted carbon fiber

The surface characteristics of carbon fibers were studied by X-ray photoelectron spectroscopy (XPS), atomic force microscopy (AFM), and wetting measurements. The surface of carbon fiber was modified by means of plasma graft silsesquioxane. The oxygen/carbon and silicon/carbon ratio increased rapidly after treatments. Fitting the C 1s, O 1s, and Si 2p spectra demonstrated that new photopeaks were emerged, which were indicated C-Si, Si-O groups, respectively. The degree of surface roughness and the wettability of carbon fiber surface were both increased by plasma graft silsesquioxane. The results may shed some light on the design of the appropriate surface structure, which could react with resin, and the manufacture of the carbon fiber reinforced composites.     

Surface and interfacial morphologies of PAN-CVI carbon–carbon composite

Scanning electron microscopy (SEM), polarized light microscopy (PLM), and transmission electron microscopy (TEM) techniques have been used to characterize the normal surface and flank surface microstructure of a polyacrylonitrile (PAN)-based carbon fiber reinforced chemical vapor infiltrated (CVI) matrix carbon–carbon composite. Optical and SEM results indicate that the CVI deposit consists of two structures: an isotropic phase is present in the fiber bundle-bundle junctions and a second highly oriented lamellar structure is present in the intrabundle matrix. TEM shows that matrix platelets are highly parallel to the fiber axis and the crystallites of the matrix near the fiber surface exhibit better alignment than those farther away from fibers.     

The effect of surface treatment of carbon fiber on the flexural property of thermoplastic polyimide composite

Rare earth solution (RES) surface modification and air-oxidation methods were used to improve the interfacial adhesion of the carbon fiber reinforced polyimide (CF/PI) composite. The flexural property of the PI composites reinforced by the carbon fibers treated with different surface modification methods was comparatively investigated. Results showed that the flexural strength of CF/PI composite was improved after RES treatment. The improvement of impact and flexural property of the CF/PI composite was mainly due to the improvement in interfacial adhesion after RES treatment. X-ray photoelectron spectroscopy (XPS) study of carbon fiber surface showed that the oxygen concentration was obviously increased after RES treatment. The increase in the amount of organic functional groups increased the interfacial adhesion between CF and PI matrix.     

XPS study of PBO fiber surface modified by incorporation of hydroxyl polar groups in main chains

Dihydroxy poly(p-phenylene benzobisoxazole) (DHPBO), a modified poly(p-phenylene benzoxazole) (PBO) polymer containing double hydroxyl groups in polymer chains, was synthesized by copolymerization of 4,6-diamino resorcinol dihydrochloride (DAR), purified terephthalic acid (TA) and 2,5-dihydroxyterephthalic acid (DHTA). DHPBO fibers were prepared by dry-jet wet-spinning method. The effects of hydroxyl polar groups on the surface elemental compositions of PBO fiber were investigated by X-ray photoelectron spectroscopy (XPS). The results show that the ratio of oxygen/carbon on the surface of DHPBO fibers is higher than that on the surface of PBO fibers, which indicates the content of polar groups on the surface of DHPBO fiber increase compared with PBO fiber.     

Effects of carbon fiber surface treatment on the tribological properties of 2D woven carbon fabric/polyimide composites

Polyacrylonitrile (PAN)-based carbon fabric (CF) was modified with strong HNO₃ oxidation and then introduced into polyimide (PI) composites. The friction and wear properties of the carbon fabric reinforced polyimide composites (CFRP), sliding against GCr15 stainless steel rings, were investigated on an M-2000 model ring-on-block test rig under dry sliding. Experimental results revealed that the carbon fiber surface treatment largely reduced the friction and wear of the CFRP. Compared with the untreated ones, the surface-modified CF can enhance the tribological properties of CFRP efficiently due to the improved adhesion between the CF and the PI matrix. Scanning electron microscope (SEM) and X-ray photoelectron spectroscopy (XPS) study of the carbon fiber surface showed that the fiber surface became rougher and the oxygen concentration increased greatly after surface treatment, which improved the adhesion between the fiber and the PI matrix and improved the friction-reduction and anti-wear properties of the CFRP. An erratum to this article can be found at     

Banana fiber strands–reinforced polymer matrix composites

Banana fiber (BF)-reinforced low-density polyethylene (LDPE) unidirectional composites were fabricated by the compression molding process with 40 wt% fiber loading. The fibers were modified with methylacrylate (MA) mixed with methanol (MeOH) along with 2% benzyl peroxide under thermal curing method at different temperatures (50–90 °C) for different curing times (10–50 min) in order to have better compatibility with the matrix. The effect of fiber surface modification on the mechanical properties (tensile and impact properties) of the composites were evaluated. Monomer concentration, curing temperature, and curing time were optimized in terms of polymer loading and mechanical properties. The mechanical properties were found to be improved based on the improved interaction between the reinforcement and the matrix. Optimized BFs were again treated with 2–5 wt% starch solutions and composites made of 4% starch treated BF showed the highest mechanical properties than that of MA treated composites. Scanning electron microscopy (SEM) was performed to get an insight into the morphology of the composites. Water uptake and soil degradation test of the composites were also investigated.     

Surface and core modification of carbon fibers

Thermal and thermochemical treatments with amines have been shown to improve both the mechanical strengths of carbon fibers and their interfacial bonding forces with polymer matrix. In this report, the wettabilities of the surface-treated carbon fibers were studied by dynamic contact angles with epoxy resin. Two mechanisms occur during the fiber modification processes, namely, the fiber core restructuring and surface etching. The former occurs at elevated temperature and increases the fiber strength significantly. When surface reaction occurs, the number of surface oxides increases to improve the surface wettabilities, which may be observed by the decreased dynamic contact angles. Accompanying the etch-cleaning effects, the fiber strength would also increase initially. Deeper penetration of amine would destroy the graphite crystallinity on fiber surfaces and lower the fiber strength.     

Surface treatment of single sisal fibers with bacterial cellulose and its enhancement in fiber-polymer adhesion properties

In this work, a simple and effective method to modify the surface of single sisal fibers with G. xylinum was described. Single fiber tensile strength test, single fiber fragmentation test, thermal gravimetric analyses were conducted to assess the effects of different modification methods (unmodified, NaOH treatment and BC treatment). Fourier transform infrared spectroscopy, scanning electron microscopy and water uptake experiments were employed to characterize the resulting interfacial adhesion. It was shown that BC treatment produced better reinforced polymer composites with improved mechanical and long-term properties. The results also elucidated that BC nanofibrils formed a dense three dimensional network on single sisal fibers covering the roughened surface and filling the grooves and other surface ‘defects’ caused by NaOH modification in addition to its exposed hydroxyl groups to form hydrogen bonds with sisal fiber, all contributed to enhanced mechanical properties of sisal fibers as well as the better binding between sisal fibers and resin matrix. Moreover, this work also confirmed that internal geometrical and morphological differences exist in sisal fibers and this result is insightful for future natural fiber research about the importance of careful selection of fibers for consistent comparisons.     

Dynamic mechanical characterization of PMR polyimide/carbon fiber composites modified by fiber coating with silicones

Viscous and elastomeric silicones have been applied as interlayers to carbon fibers in order to develop a tougher, micro-crack resistant, thermally stable polyimide (PMR-15) composite. Carbon fiber is continuously coated with very high molecular weight polydimethylsiloxane (PDMS) and polyvinyl-methylsiloxane (PVMS). Dynamic mechanical properties of the composites have been determined and compared with uncoated carbon fiber reinforced PMR-15 polyimide composites. The presence of the interlayer is shown by the appearance of a new relaxation peak. The peak temperature is found to be a good indication of the degree of the cure of the silicone elastomer. Comparison of the storage moduli of uncoated and coated carbon fiber composites at the service temperature range of the composites indicates that the presence of the silicone interlayer affects the shear moduli of the composites. Apparent activation energy of the α transition of the matrix in the modified composites varies with the amount of interlayer and composition in concert with the impact strength.     

Interphase formation and fiber matrix adhesion in carbon fiber reinforced epoxy resin: influence of carbon fiber surface chemistry

The chemistry and morphology of the carbon fiber surface are important parameters which govern the properties of the interfacial region and the adhesion between carbon fibers and polymeric matrix in carbon fiber reinforced polymers. In the presented paper the surface chemistry of the fibers is varied while the surface morphology is left unchanged. We analyze chemical functionality and morphology of carbon fiber surfaces showing different degrees of activation, together with the adhesion of these fibers to an epoxy matrix and the width of the interfacial region between fiber and matrix. An increase of the oxygen and nitrogen concentration of the fiber surface, in particular in form of carboxyl functional groups, results in a significant increase of interfacial shear strength. Also the width of the interphase, as determined by scanning force microscopy in nanomechanical mode, depends on the activation degree of the carbon fibers. However, no direct correlation between interphase width, surface chemistry and fiber matrix adhesion is found, suggesting no direct influence of interphase width on adhesion properties.