• Macromolecular Research
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• v.11 no.1
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• pp.14-18
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• 2003

Grafting of glycidyl methacrylate (GMA) upon coralline hydroxyapatite in conjugation with demineralized bone matrix (CHA-DBM) using equal molar ratio of potassium persulfate/sodium metabisulfite redox initiating system was investigated in aqueous medium. The optimum reaction condition was standardized by varying the concentrations of backbone, monomer, initiator, temperature and time. The results obtained imply that the percent grafting was found to increase initially and then decrease in most of the cases. The optimum temperature and time were found to be 50 $^{\circ}C$ and 180 min, respectively, to obtain higher grafting yield. Fourier transform infrared (FT-IR) spectroscopy and X-ray powder diffraction (XRD) method were employed for the proof of grafting. The FT-IR spectrum of grafted CHA-DBM showed epoxy groups at 905 and 853 $cm^{-1}$ / and ester carbonyl group at 1731 $cm^{-1}$ / of poly(glycidyl methacrylate) (PGMA) in addition to the characteristic absorptions of CHA-DBM, which provides evidence of the grafting. The XRD results clearly indicated that the crystallographic structure of the grafted CHA-DBM has not changed due to the grafting reaction. Further, no phase transformation was detected by the XRD analysis, which suggests that the PGMA is grafted only on the surface of CHA-DBM backbone. The grafted CHA-DBM will have better functionality because of their surface modification and hence they may be more useful in coupling of therapeutic agents through epoxy groups apart from being used as osteogenic material.

• Journal of Radiation Industry
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• v.4 no.3
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• pp.259-263
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• 2010

Carbon fibers are used as a reinforcement material in an epoxy matrix in advanced composites due to their high mechanical strength, rigidity and low specific density. An important aspect of the mechanical properties of composites is associated to the adhesion between the surface of the carbon fiber and the epoxy matrix. This paper aimed to evaluate the effects of electron beam irradiation on the physicochemical properties of carbon fibers to obtain better adhesion properties in resultant composite. Chemical structure and surface elements of carbon fiber were determined by FT-IR, elemental analysis and X-ray photoelectron spectroscopy, which indicated that the oxygen content increased significantly with increasing the radiation dose. Thermal stability of the carbon fibers was studied via the thermalgravimetric analysis. Surface morphology of carbon fiber was analyzed by scanning electron microscope. It was found that the degree of surface roughness was increased by electron beam irradiation.

• Composites Research
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• v.24 no.5
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• pp.34-38
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• 2011

Carbon nanotubes (CNTs) have been widely investigated as reinforcements of CNT/polymer nanocomposites to enhance mechanical and electrical properties of polymer matrices since their discovery in the early 90's. Furthermore, the number of studies about incorporating CNTs into carbon fiber reinforced plastics (CFRP) to reinforce their polymer matrices is increasing recently. In this study, single-walled carbon nanotubes (SWNT) were dispersed in epoxy with 0.2 wt.% and 0.5 wt.%. Then, the SWNT/epoxy mixtures were processed to carbon fiber composites by a vacuum assisted resin transfer molding (VARTM) and a wet lay up method. The processed composite samples were tested for the interlaminar shear strength (ILSS). The relationship between the interlaminar shear strengths and processing, and the reinforcement mechanism of carbon nanotubes were investigated. CNT/epoxy nanocomposite specimens showed the increased tensile properties. However, the ILSS of carbon fiber composites was not enhanced by reinforcing the matrix with CNTs because of processing issues caused by increased viscosity of the matrix due to addition of CNTs particularly for a VARTM method.

• Proceedings of the KSME Conference
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• 2000.11a
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• pp.250-255
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• 2000

Damage induced by low velocity impact loading in aircraft composite laminates is the form of failure which is occurred frequently in aircraft. Low velocity impact can be caused either by maintenance accidents with tool drops or by in-flight impacts with debris. As the consequences of impact loading in composite laminates, matrix cracking, delamination and eventually fiber breakage for higher impact energies can be occurred. Even when no visible impact damage is observed, damage can exist inside of composite laminates and the carrying load of the composite laminates is considerably reduced. The reduction of strength and stiffness by impact loading occurs in compressive loading due to laminate buckling in the delaminated areas. The objective of this study is to determine inside damage of composite laminates by impact loading and to determine residual compressive strength and the damage growth mechanisms of impacted composite laminates. For this purpose a series of impact and compression after impact tests are carried out on composite laminates made of carbon fiber reinforced epoxy resin matrix with lay up pattern of $[({\pm}45)(0/90)_2]s$ and $[({\pm}45)(0)_3(90)(0)_3({\pm}45)]$. UT-C scan is used to determine impact damage characteristics and CAI(Compression After Impact) tests are carried out to evaluate quantitatively reduction of compressive strength by impact loading.

• Carbon letters
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• v.6 no.2
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• pp.106-110
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• 2005

In this work, the effects of atmospheric oxygen plasma treatment of carbon fibers on mechanical interfacial properties of carbon fibers-reinforced epoxy matrix composites was studied. The surface properties of the carbon fibers were determined by acid/base values, Fourier-transform infrared spectrometer (FT-IR), and X-ray photoelectron spectroscopy (XPS) analyses. Also, the crack resistance properties of the composites were investigated in critical stress intensity factor ($K_{IC}$), and critical strain energy release rate mode II ($G_{IIC}$) measurements. As experimental results, FT-IR of the carbon fibers showed that the carboxyl/ester groups (C=O) at 1632 $cm^{-1}$ and hydroxyl group (O-H) at 3450 $cm^{-1}$ were observed for the plasma treated carbon fibers, and the treated carbon fibers had the higher O-H peak intensity than that of the untreated ones. The XPS results also indicated that the $O_{1S}/C_{1S}$ ratio of the carbon fiber surfaces treated by the oxygen plasma led to development of oxygen-containing functional groups. The mechanical interfacial properties of the composites, including $K_{IC}$ (critical stress intensity factor) and $G_{IIC}$ (critical strain energy release rate mode II), were also improved for the oxygen plasma-treated carbon fibersreinforced composites. These results could be explained that the oxygen plasma treatment played an important role to increase interfacial adhesions between carbon fibers and epoxy matrix resins in our composite system.

• Composites Research
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• v.34 no.5
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• pp.305-310
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• 2021

Mechanical properties of fiber reinforced composites were affected to fiber volume fractions (FVF) and interfacial property by sizing agent conditions. An optimum interface can relieve stress concentration by transferring the mechanical stress from the matrix resin to the reinforcements effectively, and thus can result in the performance of the composites. The interfacial properties and wettability between the epoxy resin and glass fiber (GF) were evaluated for different sizing agent conditions and FVFs. The surface energies of epoxy resin and different sizing agent treated GFs were calculated using dynamic and static contact angle measurements. The work of adhesion, W_a was calculated by using surface energies of epoxy matrix and GFs. The wettability was evaluated via the GF tow capillary test. The interfacial shear strength (IFSS) was evaluated by microdroplet pull-out test. Finally, the optimized GFRP manufacturing conditions could be obtained by using wettability and interfacial property.

• Composites Research
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• v.36 no.6
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• pp.416-421
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• 2023

Multifunctional composite materials capable of both load-carrying and energy functions are promising innovative candidates for the advancement of contemporary technologies owing to their relative feasibility, cost-effectiveness, and optimized performance. Carbon fiber (CF)-based structural batteries utilize the graphitic inherent structure to enable the employment of carbon fibers as electrodes, current collectors, and reinforcement, while the matrix system is an ion-conduction and load transfer medium. Although it is possible to enhance performance through the modification of constituents, there remains a need for a systematic design methodology scheme to streamline the commercialization of structural batteries. In this work, a bi-phasic epoxy-based ionic liquid (IL) modified structural battery electrolyte (SBE) was developed via thermally initiated phase separation. The polymer's morphological, mechanical, and electrochemical characteristics were studied. In addition, the interfacial shear strength (IFSS) between CF/SBE was investigated via microdroplet tests. The results accentuated the significance of considering IFSS and matrix plasticity in designing composite structural batteries. This approach is expected to lay the foundation for realizing smart structures with optimized performance while minimizing the need for extensive trial and error, by paving the way for a streamlined computational design scheme in the future.

• Korean Chemical Engineering Research
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• v.50 no.2
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• pp.371-378
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• 2012

Hydrophilic silica nanoparticles (SNPs) were treated by using 3-glycidoxypropyltrimethoxy silane (GPTMS) and then they were blended with polyurethane-urea (PUU) emulsions to obtain SNPs/PUU nanocomposite films. Thermo-mechanical properties of the nanocomposite films were investigated by varying the grafted amount of GPTMS onto SNPs and the contents of SNPs in the PUU matrix. The thermo-mechanical properties of the nanocomposite films were also compared in terms of the dispersibility of SNPs in the PUU matrix and thermal curing of the GPTMS-grafted SNPs. The maximum amount of grafted GPTMS was $1.99{\times}10^{-6}\;mol/m^2$, and which covered ca. 53% of the total SNP surface area. $^{29}Si$ CP/MAS NMR analyses with the deconvolution of peaks revealed the details of polycondensation degree and patterns of GPTMS in the surface modification of SNPs. The surface modification did not significantly affect colloidal stability of the SNPs in aqueous medium; however, the hydrophobic modification of SNPs offered a favorable effect on the dispersibility of SNPs in the PUU matrix as well as better thermal stability. XRD patterns revealed that GPTMS-grafted SNPs broadened the reduced the characteristic peak of polyol in PUU matrix. The composite films became rigid and less flexible as the SNP content increased from 5 wt.% to 20 wt.%. Particularly, Young's modulus and tensile modulus significantly increased after the thermal curing reaction of the epoxy groups in the SNPs.

• Journal of the Korean Society for Railway
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• v.11 no.4
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• pp.357-363
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• 2008

This study investigates the durability of carbon/epoxy composites for use on train car bodies under a salt water spray environment. Salt water solution with 5% NaCl, similar to natural salt water, was used for the salt water environmental tests. The specimens were obtained from a composite panel consisting of an epoxy matrix reinforced with T700 carbon fabric. The specimens were exposed to the salt water environment for up to 12 months. Mechanical tests were performed to obtain tensile properties, flexural properties, and shear properties. Dynamic mechanical analysis was used to measure such thermal properties as storage modulus, loss modulus, and tan $\delta$. Also FT/IR tests were conducted to investigate changes in chemical structure with exposure. The results revealed that fiber-dominated mechanical properties were not affected much by exposure time, but matrix-dominated mechanical properties decreased with increasing exposure time. Storage modulus was not very sensitive to exposure time, but glass transition temperature was affected, slightly decreasing with increasing exposure time. Although the peak intensity of FT/IR curves was affected slightly by exposure time, the peak shape and peak location of FT/IR curves were not noticeably changed. Carbon/epoxy composites used for this study were relatively stable to the salt water environment.

• Korean Chemical Engineering Research
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• v.43 no.3
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• pp.401-406
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• 2005

In this work, the effect of chemical treatment of multiwalled carbon nanotubes (MWNTs) on glass transition temperature (Tg), thermal stability, and dynamic viscoelastic behaviors of MWNTs-reinforced epoxy matrix composites has been studied by differencial scanning calorimeter (DSC), thermogravimetric analysis (TGA), and dynamic mechanical analysis (DMA) measurements. The MWNTs were chemically treated with 35 wt％ $H_3PO_4$ (A-MWNTs) or 35 wt％ KOH (B-MWNTs) solutions and the changes of surface properties of chemically treated MWNTs were examined by pH, acid and base values, Fourier transfer-infrared spectroscopy (FT-IR), and x-ray photoelectron spectroscopy (XPS) analyses. The chemical treatments based on acid and base reactions led to a significant change of surface characteristics and chemical compositions of the MWNTs, especially A-MWNTs/epoxy composites had higher thermal stability and dynamic viscoelastic properties than those of B-MWNTs and non-treated MWNTs/epoxy composites. These results were probably due to the improvement of interfacial bonding strength, resulting from the acid-base interaction and hydrogen bonding between the epoxy resins and the MWNT fillers.