Influence of oxygen plasma treatment parameters on the properties of carbon fiber

This study is focused on the impact of oxygen plasma treatment on properties of carbon fibers and interfacial adhesion behavior between the carbon fibers and epoxy resin. The influences of the main parameters of plasma treatment process, including duration, power, and flow rate of oxygen gas were studied in detail using interlaminar shear strength (ILSS) of carbon fiber composites. The ILSS of composites made of carbon fibers treated by oxygen plasma for 1 min, at power of 125 W, and oxygen flow rate of 100 sccm presented a maximum increase of 28% compared to composites made of untreated carbon fibers. Furthermore, carbon fibers were characterized by scanning electron microscopy (SEM), tensile strength test, attenuated total reflectance Fourier transform infrared (ATR-FTIR), and Raman spectroscopy analyses. It was found that the concentration of reactive functional groups on the fiber surface was increased after the plasma modification, as well the surface roughness, which finally improved the interfacial adhesion between carbon fibers and epoxy resin. However, high power and long exposure times could partly damage the surface of carbon fibers and decrease the tensile strength of filaments and ILSS of treated fiber composites.     

Mechanical properties of carbon fiber composites modified with nano-SiO2 in the interphase

The performance of carbon fibers-reinforced composites is dependent to a great extent on the properties of fiber–matrix interface. To improve the interfacial properties in carbon fibers/epoxy composites, nano-SiO₂ particles were introduced to the surface of carbon fibers by sizing treatment. Atomic force microscope (AFM) results showed that nano-SiO₂ particles had been introduced on the surface of carbon fibers and increase the surface roughness of carbon fibers. X-ray photoelectron spectroscopy (XPS) showed that nano-SiO₂ particles increased the content of oxygen-containing groups on carbon fibers surface. Single fiber pull-out test (IFSS) and short-beam bending test (ILSS) results showed that the IFSS and ILSS of carbon fibers/epoxy composites could obtain 30.8 and 10.6% improvement compared with the composites without nano-SiO₂, respectively, when the nano-SiO₂ content was 1 wt % in sizing agents. Impact test of carbon fibers/epoxy composites treated by nano-SiO₂ containing sizing showed higher absorption energy than that of carbon fibers/epoxy composites treated by sizing agent without nano-SiO₂. Scanning electron microscopy (SEM) of impact fracture surface showed that the interfacial adhesion between fibers and matrix was improved after nano-SiO₂-modified sizing treatment. Dynamic mechanical thermal analysis (DMTA) showed that the introduction of nano-SiO₂ to carbon fibers surface effectively improved the storage modulus of carbon fibers/epoxy.     

A study of the effect of oxygen plasma treatment on the interfacial properties of carbon fiber/epoxy composites

In this work, effects of the interface modification on the carbon fiber‐reinforced epoxy composites were studied. For this purpose, the surface of carbon fibers were modified by oxygen plasma treatment. The surface characteristics of carbon fibers were studied by X‐ray photoelectron spectroscopy (XPS), atomic force microscopy (AFM), dynamic contact angle analysis (DCAA), and dynamic mechanical thermal analysis (DMTA), respectively. The interlaminar shear strength (ILSS) was also measured. XPS and AFM analyses indicated that the oxygen plasma treatment successfully increased some oxygen‐containing functional groups concentration on the carbon fiber surfaces, the surface roughness of carbon fibers was enhanced by plasma etching and oxidative reactions. DCAA and DMTA analyses show that the surface energy of carbon fibers increased 44.9% after plasma treatment for 3 min and the interfacial bonding intensities A and α also reached minimum and maximum value respectively. The composites exhibited the highest value of ILSS after oxgen plasma treated for 3 min. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

Mechanical properties of carbon nanotube/carbon fiber reinforced thermoplastic polymer composite

Carbon nanotube (CNT)/carbon fiber (CF) hybrid fiber was fabricated by sizing unsized CF tow with a sizing agent containing CNT. The hybrid fiber was used to reinforce a thermoplastic polymer to prepare multiscale composite. The mechanical properties of the multiscale composite were characterized. Compared with the base composite (traditional commercial CF), the multiscale composite reinforced by the CNT/CF hybrid fiber shows increases in interlaminar shear strength (ILSS) and impact toughness. Laminate containing CNTs showed a 115.4% increase in ILSS and 27.0% increase in impact toughness. The reinforcing mechanism was also discussed by observing the impact fracture morphology. POLYM. COMPOS., 38:2001–2008, 2017. © 2015 Society of Plastics Engineers     

Effect of carbon nanotubes growth topology on the mechanical behavior of hybrid carbon nanotube/carbon fiber polymer composites

In this study, carbon nanotubes (CNTs) were incorporated into carbon fiber‐reinforced polymer composites (CFRPs) by growing them on the surface of PAN‐based carbon fibers utilizing a relatively low temperature technique. The effect of various surface treatments of the carbon fibers on the in‐plane and out‐of‐plane mechanical performance of the hybrid CFRPs (e.g., exposure to or shielding against elevated temperatures, patterned vs. unpatterned growth of the CNTs over the carbon fibers) were investigated. The in‐plane quasi‐static mechanical properties and out‐of‐plane dynamic properties of the hybrid CFRPs were examined utilizing tension and dynamic impact tests, respectively. To study the progressive damage mechanism of the hybrid CFRPs, spherical punch tests as well as X‐ray radiography of the impact damaged hybrid CFRPs were carried out. The results revealed that the strength and impact energy dissipation of the CFRPs improved by 11% and 127%, respectively, utilizing patterned growth of CNTs on the surface of the carbon fibers. POLYM. COMPOS., 37:2639–2648, 2016. © 2015 Society of Plastics Engineers     

Effects of polyhedral oligomeric silsesquioxane coatings on the interface and impact properties of carbon‐fiber/polyarylacetylene composites

Two kinds of polyhedral oligomeric silsesquioxane (POSS) coatings were used for the modification of the interface in carbon fiber (CF) reinforced polyarylacetylene (PAA) matrix composites. The effects of the organic–inorganic hybrid POSS coatings on the properties of the composites were studied with short‐beam‐bending, microdebonding, and impact tests. The interlaminar shear strength and interfacial shear strength showed that the POSS coatings resulted in an interfacial property improvement for the CF/PAA composites in comparison with the untreated ones. The impact‐test results implied that the impact properties of the POSS‐coating‐treated composites were improved. The stiffness of the interface created by the POSS coatings was larger than that of the fiber and matrix in the CF/PAA composites according to the force‐modulation‐mode atomic force microscopy test results. The rigid POSS interlayer in the composites enhanced the interfacial mechanical properties with a simultaneous improvement of the impact properties; this was an interesting phenomenon in the composite‐interface modification. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 102:5202–5211, 2006     

Effect of deposited carbon nanotubes on interlaminar properties of carbon fiber‐reinforced epoxy composites using a developed spraying processing

Carbon fiber‐reinforced epoxy composites, with incorporated carboxylic multiwall carbon nanotubes (CNTs), were prepared using vacuum‐assisted resin infusion (VARI) molding, and the in‐plane and out‐of‐plane properties, including mode‐I (G_Ic) and mode‐II (G_IIc) interlaminar fracture toughness, interlaminar shear strength (ILSS), tensile, and flexural properties were measured. A novel spraying technique, which sprays a kind of epoxy resin E20 with high viscosity after spraying the CNTs, was adopted to deposit the CNTs on the surface of carbon fiber fabric. The E20 was used to anchor CNTs on the fabric surface, avoiding that the deposited CNTs were removed by the infusing resin during VARI process. The spraying processing, including spraying amount and spraying sequence, was optimized based on the distribution of CNTs on the fibers. After that, three composite specimen groups were fabricated using different carbon fiber fabrics, including as‐received, CNT‐deposited with E20, and CNT‐deposited without E20. The effects of CNTs on the processing quality and mechanical properties of carbon fiber‐reinforced polymer composites were studied. The experimental results show that all studied laminates have uniform thickness with designed values and no obvious defects form inside the laminates. Compared with the composite without CNTs, depositing CNTs with E20 increases by 24% in the average propagation G_Ic, by 11% in the propagation G_IIc and by 12% in the ILSS, while it preserves the in‐plane mechanical properties, However, depositing CNTs without E20 reduces interlaminar fracture toughness. These phenomena are attributed to the differences in the distribution of CNTs and the fiber/matrix interfacial bonding for different spraying processing. POLYM. COMPOS., 2013. © 2012 Society of Plastics Engineers     

Interfacial microstructure and properties of carbon fiber-reinforced unsaturated polyester composites modified with carbon nanotubes

To improve the interfacial properties in carbon fiber (CF)-reinforced unsaturated polyester (UP) composites, we directly introduced functionalized carbon nanotubes dispersed in the fiber sizing onto the fiber surface. For comparing the influence of polymer type on sizing effect, two different polymers (UP MR13006 and water-soluble epoxy (EP)) were used to prepare sizing agent. Morphology and surface energy of CFs were examined by scanning electron microscopy and dynamic contact angle analysis test. Tensile strength was investigated in accordance with ASTM standards. Mechanical properties of the composites were investigated by interlaminar shear strength (ILSS) and impact toughness. Test results indicate that TS, ILSS, and impact toughness were enhanced simultaneously. For UP matrix, the sizing agent containing UP has better reinforcing and toughening effect than the sizing agent containing water-soluble EP.     

Effects of novolac resin modification on mechanical properties of carbon fiber/epoxy composites

The epoxy resin matrix of carbon fiber (CF)‐reinforced epoxy composites was modified with novolac resin (NR) to improve the matrix‐dominated mechanical properties of composites. Flexural strength, interlaminar shear strength (ILSS), and impact strength were measured with unfilled, 7 wt% NR, 13 wt% NR, and 18 wt% NR filled to epoxy to identify the effect of adding NR on the mechanical properties of composites. The results showed that both interfacial and impact properties of composites were improved except for flexural property. The largest improvement in ILSS and impact strength were obtained with 13 wt% loading of NR. ILSS and impact strength were improved by 7.3% and 38.6%, respectively, compared with the composite without NR. The fracture and surface morphologies of the composite specimens were characterized by scanning electron microscopy. Intimate bonding of the fibers and the matrix was evident with the content of 7–13 wt% NR range. Decrease of crosslinking density and formation of NR transition layer were deduced with adding NR. POLYM. COMPOS., 2011. © 2010 Society of Plastics Engineers     

Interface improvement of carbon fiber/methylphenylsilicone resin composites by fiber surface coating of polyhedral oligomeric silsesquioxanes

To enhance interfacial properties of carbon fibers (CFs)-reinforced methylphenylsilicone resin (MPSR) composites, we introduced an appropriate interface reinforced by trisilanolphenyl-polyhedral oligomeric silsesquioxanes (trisilanolphenyl-POSS) between CFs and MPSR with a liquid phase deposition strategy. Chemical bonds among silanol groups of trisilanolphenyl-POSS, hydroxyl-functionalized CF (CF–OH), and silanol end groups of MPSR in the coating were expected to be formed through condensation reaction during the prepared process. CFs with and without sizing treatment-reinforced MPSR composites were prepared by a compression molding method. X-ray photoelectron spectroscopy revealed that trisilanolphenyl-POSS particles enhanced the contents of fiber surface oxygen-containing groups and silicon-containing functional groups. Scanning electron microscopy and atomic force microscopy images showed that trisilanolphenyl-POSS nanoparticles have been introduced onto the fiber surface obviously and the surface roughness increased sharply. Dynamic contact angle analysis indicated that trisilanolphenyl-POSS-modified sizing agent could improve the fiber wettability and surface energy significantly. Short-beam bending test and impact toughness test results showed that the interlaminar shear strength and impact resistance of the sized CFs composites were enhanced greatly with increasing amplitudes of more than 35 and 27% in comparison with those of untreated CF composites, respectively. Cryo-fractured surface topographies of composites confirmed that interfacial adhesion between CFs and MPSR has been improved after sizing treatment. Meanwhile, the sizing treatment does not decrease single fiber tensile strength.     

Effect of carbon nanotubes grown temperature on the fracture behavior of carbon fiber reinforced magnesium matrix composites: Interlaminar shear strength and tensile strength

The design of an interfacial structure is particularly important for load transfer in composites. In this paper, different amounts of carbon nanotubes (CNTs) were grafted onto the carbon fiber (CF) surface by adjusting grown temperature using injection chemical vapor deposition (ICVD). The prepared CF preform grafted with CNTs (CNTs-CF) were used to reinforce magnesium alloy by squeeze casting process. The microstructures were analyzed by means of optical microscope (OM) and scanning electron microscope (SEM), and the interlaminar shear strength (ILSS) and tensile strength of the composites were determined by double-notch shear test and tensile test. The results indicated that moderate ILSS was more conducive to improving the tensile properties of carbon fiber reinforced magnesium matrix (C_f/Mg) composites. Compared with C_f/Mg, the tensile strength of composite with CNTs increased by about 80%. For C_f/Mg composites grafted with CNTs, CNTs had the effects of delaying crack propagation and increasing energy consumption by the pull-out and bridging mechanism, which were the main reasons for improving the strength. The analysis of shear fracture surface showed that the crack propagation path can be optimized by adjusting the amounts of grafted CNTs. The presence of CNTs affects the stress distribution and consequently the crack initiation as well as the crack propagation.     

Enhanced interfacial strength and mechanical properties of carbon fiber composites by introducing functionalized silica nanoparticles into the interface

Introducing nanoparticles onto the surface of carbon fibers (CFs) is a useful method for enhancing the quality of fiber-matrix interface. In this work, a liquid sizing agent containing functionalized silica nanoparticles (SiO₂) was well prepared to improve interfacial strength and mechanical properties of composites. In order to enhance the dispersion of SiO₂ nanoparticles in sizing agent, SiO₂ nanoparticles were chemically grafted with 3-aminopropyltriethoxysilane (APS), and then silanized silica (SiO₂-APS) was introduced into the interphase by a conventional sizing process as well. Fourier transform infrared spectroscopy (FTIR), X-ray photoelectron spectroscopy (XPS), and thermogravimetric analysis (TGA) confirmed the successful preparation of SiO₂-APS. Scanning electron microscopy (SEM) showed that a uniform distribution of SiO₂-APS on the fiber surface and the increased surface roughness. The sized fibers (CF/SiO₂-APS) exhibited a high surface free energy and good wettability based on a dynamic contact angle testing. Interfacial microstructure and mechanical properties of untreated and sized CFs composites were investigated. Simultaneous enhancements of interlaminar shear strength (ILSS) and impact toughness of CF/SiO₂-APS composites were achieved, increasing 44.79% in ILSS and 31.53% in impact toughness compared to those of untreated composites. Moreover, flexural strength and modulus of composites increased by 32.22 and 50.0% according to flexural test. In addition, the hydrothermal aging resistance of CF/SiO₂-APS composites has been improved significantly owing to the introduced Si-O-Si bonds at the interface.     

Interfacial improvement of carbon fiber/epoxy composites using a simple process for depositing commercially functionalized carbon nanotubes on the fibers

An aqueous suspension deposition method was used to coat the sized carbon fibers T700SC and T300B with commercially carboxylic acid-functionalized and hydroxyl-functionalized carbon nanotubes (CNTs). The CNTs on the fiber surfaces were expected to improve the interfacial strength between the fibers and the epoxy. The factors affecting the deposition, especially the fiber sizing, were studied. According to single fiber-composite fragmentation tests, the deposition process results in improved fiber/matrix interfacial adhesion. Using carboxylic acid-functionalized CNTs, the interfacial shear strength was increased 43% for the T700SC composite and 12% for the T300B composite. The relationship between surface functional groups of the CNTs and the interfacial improvement was discussed. The interfacial reinforcing mechanism was explored by analyzing the surface morphology of the carbon fibers, the wettability between the carbon fibers and the epoxy resin, the chemical bonding between the fiber sizing and the CNTs, and fractographic observation of cross-sections of the composites. Results indicate that interfacial friction, chemical bonding and resin toughening are responsible for the interfacial improvement of nanostructured carbon fiber/epoxy composites. The mechanical properties of the CNT-deposited composite laminate were further measured to confirm the effectiveness of this strategy.     

The influence of addition of carbon nanotube and graphene platelets on characteristics of carbon/basalt fiber reinforced intra-ply hybrid composites

In this study, effects of addition of carbon nanotubes (CNTs) and graphene platelets (GPLs) on characteristics of carbon/basalt fiber reinforced intra-ply hybrid composites were investigated. The composites were fabricated using vacuum assisted resin infusion molding (VARIM) method in two types including bare and 0.1, 0.5 wt.% of GPL and CNT nanoparticles filled hybrid composites. Fabricated normal and multiscale composites were cut by water jet and mechanical properties of specimens were examined by tensile, flexural, SBS experiments. Therefore, the modulus of elasticity, flexural modulus, tensile and flexural strength and ILSS of bare and multiscale composites were compared. Thermomechanical properties of fabricated composites were evaluated by dynamic mechanic analyze (DMA), thermogravimetric analyze ( TGA) and thermal conductivity (TC) tests and storage modulus, loss modulus, damping ratio, glass transition temperature, weight loss and derivative weight loss were compared in fabricated normal and multiscale composites. Similarly, modal properties of fabricated composites such as natural frequency and damping factor were obtained by vibrational tests and compared in fabricated composites. According to the results, the addition of carbon-based nanoparticles improved the characteristics of carbon/basalt fiber intra-ply hybrid composites. The response of composites was directly proportional to the addition ratio of the carbon-based nanoparticles.     

Improvements in interfacial and heat-resistant properties of carbon fiber/methylphenylsilicone resins composites by incorporating silica-coated multi-walled carbon nanotubes

The multi-scale reinforcement and interfacial strengthening on carbon fiber (CF)-reinforced methylphenylsilicone resin (MPSR) composites by adding silica-coated multi-walled carbon nanotubes (SiO₂-CNTs) were investigated. SiO₂-CNT has been successfully prepared via the hydrolysis of tetraethoxysilane in the presence of acid-oxidized multi-walled carbon nanotubes. Transmission electron microscopy, X-ray diffraction, and Fourier Transform infrared spectroscopy were carried out to examine the functional groups and structures of CNTs. Then, SiO₂-CNT was incorporated into MPSR matrix to prepare CF/MPSR-based composites by the compression molding method. The effects of the introduced SiO₂-CNT on the interfacial, impact, and heat-resistant properties of CF/MPSR composites were evaluated by short-beam bend method, impact test, and thermal oxygen aging experiments, respectively. Experimental results revealed that the CF/MPSR composites reinforced with 0.5 wt% SiO₂-CNT showed a significant increase 34.53% in the interlaminar shear strength (ILSS) and 20.10% in impact properties. Moreover, the heat-resistant properties of composites were enhanced significantly by adding SiO₂-CNT hybrid nanoparticles. These enhancements are mainly attributed to the improved matrix performance resulted from the molecular-level dispersion of SiO₂-CNT in MPSR matrix and the strong interfacial adhesion between SiO₂-CNT and matrix resin, which are beneficial to improve the mechanical stress transfer from MPSR matrix to CFs reinforcement and alleviate stress concentrations.     

Effects of silanization of C/C composites and grafting of h-BN fillers on the microstructure and interfacial properties of CVI-based C/C-BN composites

A low-density carbon/carbon (C/C) composite/silane coupling agent/hexagonal boron nitride (h-BN) hybrid reinforcement was prepared by grafting polyethyleneimine (PEI)-encapsulated modified h-BN fillers onto a carbon fiber surface using 3-aminopropyltriethoxysilane (APS) as the connection to improve the distribution uniformity of h-BN fillers in quasi-three-dimensional reinforcements and the interfacial properties between the fibers/pyrocarbon (PyC) in the C/C-BN composites obtained after densification by chemical vapor infiltration (CVI). The microstructure and chemical components of the hybrid reinforcement were investigated. The transmission electron microscopy (TEM) sample was prepared using a focused-ion beam (FIB) for the h-BN/PyC interfacial zone. The interlaminar shear strength (ILSS) and impact toughness were analyzed to inspect the composites’ interfacial properties. The results show that APS and h-BN are uniformly grafted on the fiber surface in the chopped fiber web inside the C/C composite without a density gradient, and agglomeration occurred and significantly increasing the fiber surface roughness. The highly ordered h-BN basal plane may affect the order degree of PyC near the h-BN/PyC interface. The addition of h-BN reduces the PyC texture near it, causing the annular cracks to disappear gradually. The lower PyC texture and the rougher fiber surface strengthen the interfacial bond of the fiber/matrix. Consequently, the ILSS strength of the C/C-BN composites first increases and then decreases as the h-BN filler content increases and is always higher than that of the C/C composite, while the addition of h-BN fillers weakens its impact toughness. When the h-BN content in the C/C-BN composite is 10 vol%, the ILSS of the C/C-BN composites was 15.6% higher than that of the C/C composites. However, when the h-BN content is excessive (15 vol%), the densely grafted h-BN will bridge each other, reducing the subsequent CVI densification efficiency to form a loose interface, causing a decrease in the shear strength.     

Polypropylene–glass fiber/basalt fiber hybrid composites fabricated by direct fiber feeding injection molding process

Hybrid composites of polypropylene reinforced with glass fibers and basalt fibers were fabricated by vented injection molding machine which is named the direct fiber feeding injection molding (DFFIM) process. Polyamide 6 and maleic anhydride‐grafted polypropylene has been used as a coupling agent to improve the interfacial bonding between the fibers and matrix. Two types of vented injection molding machines with a different check ring and mold were used for making specimens. The fiber lengths were analyzed to identify the most suitable check ring and mold for the DFFIM process. The mechanical properties of the hybrid composites were investigated by tensile, flexural and Izod impact tests. The interfacial morphology of the fractured tensile specimens was studied by using scanning electron microscopy and showed that there is a fiber agglomeration phenomenon that occurs in the hybrid composites, and it has a significant effect on the mechanical properties of hybrid composites. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017 , 134, 45472.     

Hybrid carbon-glass fiber vinyl ester resin composites

Hybrid carbon-glass fiber composites of novolak epoxy-based vinyl ester resins have been investigated. The chemical resistance, the thermo-oxidative stability and the mechanical properties such as tensile strength and tensile modulus, as well as flexural strength and flexural modulus, interlaminar shear strength (ILSS) and impact strength have also been estimated. The combination of glass and carbon fibers in the hybrid turns out to be an excellent mix. These composites have good tensile and flexural properties as well as the good chemical resistance of the carbon fibers and the high impact strength of the glass fibers and also the thermo-oxidative stability of highly aromatic vinyl ester resins based on novolak epoxy.     

Improving delamination resistance of carbon fiber reinforced polymeric composite by interface engineering using carbonaceous nanofillers through electrophoretic deposition: An assessment at different in-service temperatures

In this article, modification of carbon fiber surface by carbon based nanofillers (multi-walled carbon nanotubes [CNT], carbon nanofibers, and multi-layered graphene) has been achieved by electrophoretic deposition technique to improve its interfacial bonding with epoxy matrix, with a target to improve the mechanical performance of carbon fiber reinforced polymer composites. Flexural and short beam shear properties of the composites were studied at extreme temperature conditions; in-situ cryo, room and elevated temperature (−196, 30, and 120°C respectively). Laminate reinforced with CNT grafted carbon fibers exhibited highest delamination resistance with maximum improvement in flexural strength as well as in inter-laminar shear strength (ILSS) among all the carbon fiber reinforced epoxy (CE) composites at all in-situ temperatures. CNT modified CE composite showed increment of 9% in flexural strength and 17.43% in ILSS when compared to that of unmodified CE composite at room temperature (30°C). Thermomechanical properties were investigated using dynamic mechanical analysis. Fractography was also carried out to study different modes of failure of the composites.     

Interfacial studies on the surface modified aramid fiber reinforced epoxy composites

In this work, solutions of rare earth modifier (RES) and epoxy chloropropane (ECP) grafting modification method were used for the surface treatment of aramid fiber. The effect of chemical treatment on aramid fiber has been studied in a composite system. The surface characteristics of aramid fibers were characterized by Fourier transform infrared spectroscopy (FTIR). The interfacial properties of aramid/epoxy composites were investigated by means of the single fiber pull‐out tests. The mechanical properties of the aramid/epoxy composites were studied by interlaminar shear strength (ILSS). As a result, it was found that RES surface treatment is superior to ECP grafting treatment in promoting the interfacial adhesion between aramid fiber and epoxy matrix, resulting in the improved mechanical properties of the composites. Meanwhile, the tensile strengths of single fibers were almost not affected by RES treatment. This was probably due to the presence of reactive functional groups on the aramid fiber surface, leading to an increment of interfacial binding force between fibers and matrix in a composite system. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 102:4165–4170, 2006