Sized Carbon Fibers Research Articles

Quantitative evaluation of iPP nucleation in the presence of carbon fibres: Induction time approach

Crystallization and nucleation behavior in model composites based on iPP and differently sized carbon fibres have been analyzed in this work. The investigations were performed in the isothermal regime (120?127 ?C) using PLM and DSC. The results were analyzed by applying the Avrami and Muchova-Lednicky methods. It was shown that the carbon fibre surface acts as a nucleating agent during the crystallization of the iPP matrix. The highest effect was obtained with the fibres of PP-compatible size (C-T) related to unsized carbon fibres (C-U). The induction time, ti, and half-time of crystallization decreased with increasing carbon fibre content. The energy effect on the thickness of the critical nucleus decreased in the presence of C-fibres, a fact confirmed by a decrease in the nucleation parameter Q and the difference energy parameter ?? (Q decreased from ? 4.96 for iPP to ?21.32 for C/iPP model composites, and ?? decreased from 6.14x10-7 J/cm2 for iPP to 1.63x10-7 J/cm2 for model composites). The results of the model composites and their comparison with published data confirmed that the Muchova-Lednicky method could be successfully applied for the quantitative evaluation of the nucleation parameters not only in the temperature range previously suggested (130?138?C), but also at lower crystallization temperatures (Tc=121?127?C).

Modificação da rugosidade de fibras de carbono por método químico para aplicação em compósitos poliméricos

O presente trabalho aborda o tratamento superficial de fibras de carbono por ácidos clorídrico e nítrico, visando o aumento controlado da rugosidade superficial da fibra e assim melhorar a ligação fibra/matriz no processamento de compósitos poliméricos reforçados com fibras longas. Foram utilizadas fibras de carbono com size, da empresa Toray. Essas foram tratadas com os ácidos clorídrico e nítrico, a 103°C, em concentrações de 35,5 % e 97 %, em massa, respectivamente, em tempos de exposição de 5, 10, 20, 30, 40 e 60 minutos. As fibras modificadas quimicamente foram caracterizadas por microscopia eletrônica de varredura e por ensaios mecânicos de tração e os dados foram tratados pelo método estatístico de Weibull. Os resultados mostram que os tratamentos empregados modificam a superfície da fibra e que períodos de tratamento superiores a 20 minutos as danificam, degradando de maneira significativa as suas propriedades mecânicas.

Effects of molecular relaxation behavior on sized carbon fiber–vinyl ester matrix composite properties

The mechanical and viscoelastic properties of unidirectional vinyl-ester carbon fiber composites were investigated. A cooperativity analysis of the composites was performed on storage (E′) and loss modulus (E″) master curves obtained from dynamic mechanical analysis. The temperature sensitivity of the horizontal logarithmic shift factors (logaT), cooperativity, obtained from E′ data, was found to vary with the sizing used to pretreat the carbon fibers. The observed variations in the experimental trends in cooperativity with fiber sizing for the composite materials were found to deviate significantly from theory. However, the trends in tensile and apparent shear strength of the composites matched the observed qualitative trends in viscoelastic cooperativity obtained from the storage modulus master curves. These results may suggest that the viscoelastic and ultimate mechanical properties of a composite material are related. However, several inconsistencies were observed when comparing the E″ and E′ data which should also be considered in the interpretation of the experimental results.

Simultaneous determination of phenol isomers in binary mixtures by differential pulse voltammetry using carbon fibre electrode and neural network with pruning as a multivariate calibration tool

Neural networks with pruning were applied to model overlapped peaks obtained in differential pulse voltammetry (DPV) with modified carbon fibre electrode with TiO 2 of binary mixtures of catechol and hydroquinone. The best condition for electrochemical response was obtained with 0.05 mol l −1 Tris–HCl buffer at pH 6.0 and T-800 sized carbon fibre electrode. Initially the voltammograms were processed using Fourier transform filter and principal component analysis (PCA) to noise reduction and data compression, respectively. The scores of these principal components were the input into the neural network and the optimal brain surgeon (OBS) was the procedure employed for pruning the neural network. The results obtained with pruning procedure were slightly better in relation to hydroquinone in comparison to the PLS1 and PLS2. However, the similar errors were obtained to catechol when using PLS or neural networks models. Using neural networks with pruning was possible to determine catechol and hydroquinone by DPV using carbon fibre electrode, in concentration range of 1.0×10 −4 up to 6.0×10 −4 mol l −1 with root mean square errors of predictions (%RMSEP) of 7.42 and 8.02, respectively. The good results show that the proposed methodology is a good alternative to simultaneous determination of catechol and hydroquinone in binary mixtures.

Effect of acid–base properties of unsized and sized carbon fibers on fiber/epoxy matrix adhesion

The surface energies and acid–base character of unsized and sized Zoltek fiber were investigated using dynamic contact angle analysis. The surface’ acid–base property were characterized by calculating the work of acid–base interaction according to Fowkes’ and Good’s theory. To evaluate the effect of sizing on carbon fiber surface properties, Ultem® polyimide and polyurethane (PU) sized fibers were studied in comparison with unsized fibers. It was found that the sizing on the carbon fiber tended to reduce the surface energy and cover acid–base sites. The surface of unsized and sized carbon fibers were analyzed by XPS to investigate changes in surface chemistry. XPS analysis indicated that hydroxyl groups on the fiber surface decreased with sizing (Ultem® and polyurethane). These changes in chemistry are reflected in a decrease in the polar γ s p and basic γ s − contribution of the surface energy of the fibers. Single fiber fragmentation testing of unsized and Ultem® and polyurethane sized fibers in epoxy matrix showed that there is a direct effect of the surface chemical changes on the fiber/matrix adhesion.

Surface analysis of unsized and sized carbon fibers

Atomic force microscopy (AFM), X-ray photoelectron spectroscopy (XPS), and contact angle analyses were performed on unsized and sized carbon fibers to better understand the mechanism of adhesion in carbon fiber/polymer matrix composites. AFM images and surface roughness analyses showed that the sizing changes the surface topography on a microscopic scale. The total surface energy decreased from 70 mJ/m 2 for unsized fiber to 54 mJ/m 2 for Ultem® sized and to 36 mJ/m 2 for PTPO sized fibers. The percentage of functional groups on the sized fibers decreased slightly compared to the unsized fibers. The surface functional groups and surface energies of fibers are critical properties in predicting fiber/matrix adhesion. Angle dependent XPS, voltage contrast XPS, and perimeter measurements revealed that the thickness of the poly(thioarylene phosphine oxide) (PTPO) sizing on the carbon fiber surface was greater than for the poly(etherimide) (Ultem®) sizing.

Fatigue performance of carbon fibre/vinyl ester composites: the effect of two dissimilar polymeric sizing agents

Carbon fibre/vinyl ester composites were made from sized carbon fibres. The carbon fibres were sized with an in-house sizing process and then formed into a unidirectional fabric. This fabric was processed into composite panels by a resin film infusion (RFI) technique. The effects of two dissimilar sizing agents—a brittle thermoplastic K-17 poly(vinyl pyrrolidone) (PVP) and a ductile thermoplastic polyhydroxyether (phenoxy resin)—on notched fatigue, short-beam shear, transverse flexure properties and compression properties were studied.The fatigue properties of carbon fibre/vinyl ester composites were influenced drastically by the type of sizing agent used. A 20-fold increase in lifetime was demonstrated at a loading level of 207 MPa for the ductile phenoxy-sized composite compared with the unsized composite. The brittle PVP-sized composite panel showed a sixfold increase in lifetime compared with the unisized case. The phenoxy-sized composite panel showed a 40% increase in flexural modulus and the PVP-sized panel showed a 20% increase compared with the unsized composite panels. Negligible differences in the shear strength, flexural strength and static compressive strength were observed for the different interphase agents. The implications of these results for tailoring polymeric interphases in vinyl-ester-matrix composites are discussed.

Effect of sizing materials of carbon fiber on solid-state cure of poly(p-phenylene sulfide)

The effect of sized carbon fibers on the solid-state cure of poly(p-phenylene sulfide) (PPS) was studied using differential scanning calorimetry. PPS resin reinforced with sized carbon fiber exhibited the largest cure peak for all cure temperatures and showed a second peak at low cure temperature which was absent in both PPS reinforced with desized carbon fiber and neat PPS resin. In a separate experiment in which epoxy prepolymer/PPS mixture was cured, the exothermic reaction was related to the presence of the epoxy sizing used on the carbon fiber. © 1998 John Wiley & Sons, Ltd.

Surface characterization of PVP-sized and oxygen plasma-treated carbon fibers

The objectives of this work were to characterize the surface of commercial carbon fibers, focusing on the effect of polymer sizing and the effect of oxygen radiofrequency plasma treatment. The fiber surface composition was determined by x-ray photoelectron spectroscopy (XPS) and the surface topography was examined by scanning transmission electron microscopy (STEM) and atomic force microscopy (AFM). Voltage-contrast XPS distinguished between unsized and sized carbon fibers, by which the former behaved as a conductive material whereas the latter behaved as a mixture of both conductive and non-conductive materials due to a contribution from a polymeric sizing material. The AFM measurements revealed that oxygen plasma treatment for 30 s roughened the unsized fiber surfaces; however, further treatment smoothed the overall topography. Oxygen plasma treatment for 30 s also increased the surface oxygen content. © 1998 John Wiley & Sons, Ltd.

The Effect of Surface Activation in Polymer Matrix-Carbon Fiber Interactions

Various carbon fibers (CF) were surface modified by chemical and electrochemical treatments for the purpose of establishing organic functional groups on the fiber surface. A series of fibers, surface oxidized for various periods of time, was prepared. The amounts of surface functionalities formed were assessed by means of contact angle measurements on single fibers. A suitable set of probe liquids was used to determine the LW (Lifshitz-van der Waals) and acid-base components of carbon fiber surfaces. Similar tests were made on commercial, sized carbon fibers, polystyrene (PS) and polymethyl methacrylate (PMMA), and their surface energies determined in terms of LW, surface acidity and surface basicity components. Work of adhesion values were calculated of all combinations of CF and polymer matrix couples by using these surface energies of both constituents. The calculated work of adhesion values were correlated to the ILSS values obtained from single fiber pull out tests with PS and PMMA as matrices.

An XPS study of the fibre-matrix interface using sized carbon fibres as a model

This work is part of a larger project whose main objective is a better understanding of the mechanism of adhesion between the surface of carbon fibres and resins in composites. The effect over the surface of commercial PAN-based carbon fibres (Courtaulds IM CG43-750) induced by several degrees of a commercial wet oxidative surface treatment (STL) as well as the nature of the fibre-size interface have been studied by X-ray photoelectron spectroscopy. As far as functional groups are concerned, a good qualitative and quantitative characterization of the fibre surface has been achieved, using a criterium based on the requirement of internal consistency between results obtained with photoelectrons from C 1s, O 1s and N 1s peaks. Oxidative treatment induces an enrichment in oxygen and nitrogen at the surface; the presence of the former on the surface is due to the treatment but strong evidence for a residual origin of nitrogen is obtained. Coating of the commercial fibres by a prepolymer similar to the resin used as the matrix, has been used to test the type of bonding between fibre and resin before curing. Evidence is given supporting the idea that the coating (size) does not entirely cover the surface of the fibre and that only a part of it is covalently bound, alcohol groups seeming to play an important role in the adhesion mechanism.

The significance of the fibre coating in the production of carbon fibre-reinforced carbons from HT carbon fibres I. Poly(dimethylsiloxane) and poly(methylphenylsiloxane) coatings

This paper is concerned with the role of carbon fibre coatings in the production of carbon fibre-reinforced carbons from high tenacity (HT) carbon fibres and phenolic resin as a matrix precursor. In order to reduce the adhesion of the matrix to the carbon fibre surface, various HT carbon fibres were coated with polyldimethylsiloxane) and poly(methylphenylsiloxane) using solutions of these materials with very different concentrations. The surface activity of the commercially surface-treated and coated carbon fibres was studied by contact-angle measurements. One of the fibres studied contains sodium, which effected partial conversion of the polysiloxanes to silicon dioxide already during curing at 360 C in humid air. In studies with unidirectional (UD) composites (fibre volume fraction 60 vol%) such a coating was found to be very effective up to 1000 C. but the composites did not withstand the graphitization treatment. In all other cases, two-dimensional coatings, which just block active sites and surface functional groups of the carbon fibres. are shown to be extremely effective, as follows from the flexural strength data after curing, carbonization and graphitization treatment (values obtained with commercially surface-treated carbon fibres and commercially surface-treated and sized carbon fibres are given in parenthesesl: after curing, 2300 M Pa (1300 1600 M Pa); after carbonization, 410 MPa (180/220 M Pal: after graphitization treatment. 800 MPa (480400 MPa). Polyldimethylsiloxane) and poly(methylphenylsiloxane) are equally effective.

The role of sizing resins in carbon fibre-reinforced polyethersulfone (PES)

The role of sizing resin in carbon fibre-reinforced polyethersulfone has been studied using surface-treated Type A carbon fibre sized with different polymeric coatings. To investigate their influence on the adhesion of the carbon fibre to the matrix, the single embedded filament fragmentation test was used. Sized carbon fibres showed a higher interfacial shear strength than the unsized ones. Analysis by time-of-flight secondary ion mass spectrometry suggests that this arises from a strong interaction between sizing resin, the fibre and the matrix.

Crystallization and fiber/matrix interaction during the molding of PEEK/carbon composites

AbstractThe objective of this work was to investigate the effects of molding conditions (molding temperature, residence time at melt temperature, and cooling rate) on the crystallization behavior and the fiber/matrix interaction in PEEK/carbon composites made from both prepreg and commingled forms. In order to investigate the crystallization behavior of the PEEK matrix, the molding process was simulated by differential scanning calorimetric analysis, DSC. The results show that the prepreg and commingled systems do not have the same matrix morphology; prepreg tape was found to be at its maximum of crystallinity, whereas the commingled system was found to be only partially crystalline. The results show that processing must be carried out at a temperature sufficiently high to destroy the previous thermal history of the PEEK matrix; this is an essential requirement to produce efficient fiber/matrix adhesion in the commingled fabric system. Optical microscopic observations also suggest that matrix morphology near the fibers is dependent on the melting conditions; a well‐defined transcrystalline structure at the interface is observed only when the melt temperature is sufficiently high. However, the high temperature of molding can easily result in degradation of the PEEK matrix such as chain scission and crosslinking reactions. Thermal degradation of the matrix during processing is found to affect the crystallization behavior of the composites, the fiber/matrix adhesion, and the matrix properties. This effect is more important in the case of a commingled system containing sized carbon fibers because the sizing agent decomposes in the molding temperature range of PEEK/carbon composites. This produces a decrease of the matrix crystallinity and an elimination of the nucleating ability of the carbon fibers. A transition between cohesive and adhesive fracture is observed when the cooling rate increases from 30°C/min to 71°C/min for the composite made from the commingled fabric. This critical cooling rate is found to closely correspond to a change in the mechanism of crystallization of the PEEK matrix.

Modification of petroleum-derived mesophase pitch by blending naphthalene-derived partially isotropic pitches

Two kinds of naphthalene-derived, partially isotropic pitches were blended into the mesophase pitch from decant oil to modify the molecular association of the mesophase pitch and performances of its derived carbon fibers. A pitch (C-65: anisotropic content 60%) could be blended up to 50% into the 100% mesophase pitch, maintaining its complete anisotropy. Another pitch of P-77, which contained more soluble portions of smaller molecular weight, could be accommodated up to only 20%, although its anisotropic content was much the same as that of C-65. Blending partially isotropic pitch with the petroleum-derived 100% mesophase pitch intensified both aromatic and aliphatic resonances at around 130 and 30 ppm, respectively, in high-temperature 13C-NMR. Blending isotropic pitches with the petroleumderived 100% mesophase pitch lowered the melting viscosity to allow at spinning better alignment of the mesophase constituent molecules along the fiber axis than those of parent mesophase pitch, leading to higher orientation of the graphite layers, crystalline size and Young's modulus of resultant carbon fibers. The blending of 20%–50% naphthalene-derived, partially isotropic pitch with the 100% petroleumderived mesophase pitch certainly enhanced the oxidation reactivity of whole mesophase pitch to shorten the time for complete stabilization at the same level as naphthalene-derived 100% mesophase pitch. Blending of only 20% naphthalene, partially isotropic pitch with the parent mesophase pitch certainly improved the Young's modulus, orientation of the crystallines along the fiber axis and crystalline size of the resultant carbon fibers. It should be noted that there was a dominant partner or synergistic influence of the blended naphthalene, partially isotropic pitch in their improvement. The chemical and physical functions of blended isotropic components are discussed.

Study of the carbon fiber–poly(ether–ether–ketone) (PEEK) interfaces, 1: surface characterization of fibers and matrices, and interfacial adhesion energy

AbstractThe aim of this general study is to determine the physicochemical characteristics and mechanical properties of carbon fiber–PEEK interfaces. In the first part, the dispersive component of the surface energy and the electron acceptor–donor (acid–base) characteristics of PEEK polymer and different types of untreated and surface‐treated carbon fibers are determined by means of inverse gas–solid chromatography at infinite dilution. It appears, in particular, that the acid–base surface properties of PEEK and, consequently, the orientation of macromolecules near the surface, depend on the processing of this polymer. Moreover, according to previous work, an estimation of the adhesion energy, corresponding to physical interactions (London and acid–base interactions) at carbon fiber–PEEK interfaces is proposed. Whatever the surface characteristics of PEEK, the highest level of carbon fiber–PEEK adhesion is achieved in systems involving oxidized or sized carbon fibers.

Properties of carbon fibre-polymer interfaces

Two types of sized carbon fibre were used in this study, Besfight HTA-7-12000 and Besfight ST-III-7-6000, both from Toho Rayon Co. Some of the fibres were thoroughly washed in chloroform at room temperature to remove the epoxy sizing. The unsized carbon fibres, Hysol XA-S, were from Hysol Inc. The curing agents for di-glycidylether of bisphenol-A (Epon 828, Shell Chemical Co.) were methylene dianiline (MDA, Aldrich Chemical Co.) and 1, 3-phenylene diamine (Merck). Polysulphone (Vdel, Amoco) and polycarbonate (Lexan, G. E.) were chosen as the matrix systems for the interface studies of carbon fibre-thermoplastic composites. The high temperature cured Bismaleimide resin system consisted of 4,4'-bismaleimido-diphenyl-methane (IM-AD 94-306, BTL Company), diallyl bisphenol A (Matrimid 5292B, Ciba-Geigy Company) and polyetherimide (Item 1000, G. E.) The microbond method [7] was used to measure the interracial shear strengths. The procedure involved the deposition of a small amount of resin on to the surface of a fibre as shown in Fig. 1. After the curing process, the fibre specimens were pulled out of the microdroplet at a rate of 2 mm min -1, using a Shimazu tensile tester. The experimental arrangement is shown in Fig. 2. The interracial shear strength was calculated from 7; = f p/~ D L

The effect of sizing on composite properties for materials used in the shuttle filament wound case

AbstractAn epoxy resin and a sized carbon fiber have been used to produce a light‐weight filament wound case for the Space Shuttle. The sizing facilitates fiber handling during winding but may affect the amount of resin absorbed by the fiber during impregnation and the final mechanical properties of the composite. Naval Ordnance Lab rings were wound to study the effect of the sizing content on the resin absorption by the fiber bundles, the final tensile properties of the composite, and the type of failure observed at burst. The resin content of the rings studied was between 20 to 40 percent, and the sizing content, 0 to 1.6 percent by weight. Results showed that the sizing content was a critical parameter which determined the amount of resin absorbed by the fibers. The final tensile strength was dependent on the amount of sizing present. The tensile strength decreased by as much, as 60 percent when a low resin and high sizing content were present. The type of failure at burst was a function of resin content rather than size content.

Sized carbon fibers suitable for use in composites of improved impact resistance: Ying, L. and Carter Jr, T.P. (Celanese Corporation, New York, NY, USA) US Pat 4 446 255 (1 May 1985)

Sized carbon fibers suitable for use in composites of improved impact resistance: Ying, L. and Carter Jr, T.P. (Celanese Corporation, New York, NY, USA) US Pat 4 446 255 (1 May 1985)

4364993 Sized carbon fibers, and thermoplastic polyester based composite structures employing the same

The present invention is directed to carbon fibers which are coated on the surface with a sizing agent of either a polyisocyanate, such as polymethylene polyphenyl polyisocyanate, or a sorbitol polyglycidyl ether having a specifically defined total chlorine content and epoxide equivalent weight. The coated carbon fibers are employed to prepare carbon fiber composites wherein the matrix resin is a thermoplastic polyester such as poly(1,4-butylene terephthalate). The matrix resin of the composite exhibits improved bonding with the coated carbon fibers thereby imparting improved interlaminar shear strength to the composite.