Nobuo Ikuta

Weight-change analysis of the interphase in hygrothermally aged FRP: Consideration of debonding

Abstract This study deals with the experimental and analytical evaluation of weight changes in the interphase in hygrothermally aged fiber-reinforced plastics (FRP). The influence of debonding on the weight change is mainly discussed. The weight change of the interphase was evaluated by comparing the weight change of FRP with that of the plain resin. This method showed that both weight gain and weight loss occurred in the interphase, and these changes were closely related to each other. The volume of debonding at the interphase was evaluated quantitatively by microscopic observation of the aged FRP. Weight gain in the interphase was calculated from the volume of debonding, and the calculated results showed good agreement with experimental data. This result clarified that the weight gain in the interphase was caused by water penetration into debonds at the interphase. The results obtained suggested that improvement in the water resistance of the binder at the interphase is important to enhance the water resistance of glass-fiber-mat reinforced plastics.

Fourier Transform Near-Infrared Attenuated Total Reflectance Spectroscopy of Silane Coupling Agents on Glass IRE

Attenuated total reflectance (ATR) has been shown to be highly sensitive for surface analysis. The major advantage of ATR is that the region of the specimen is restricted to a thin layer adjacent to the internal reflectance element (IRE). In an investigation of the surface reactions and interfacial effect of silane coupling agents on the surface of glass, a glass IRE was used in the near-infrared region (7000–4000 cm−1). This technique is useful for analyzing the near-surface of the glass IRE. By a comparison between each measured ATR spectrum and the transmission spectrum of the same glass IRE, it is possible to determine the mechanism of reaction of the silane coupling agent on the glass substrate. The process of dehydration was also investigated by calibration, with the use of the intensity of the band due to Si-OH groups. A condensation reaction occurs between molecules of the silane coupling agent in the bulk film. However, a small fraction of the agent reacts with the Si-OH groups of the glass at a lower rate. In this study, we show the transmission and ATR spectra of silane coupling agent reacted on a glass plate used for the IRE in the ATR method. With the use of the ATR method, the state of the dehydration condensation reaction, which involves hydrolyzing Si-OH at the surface, can be observed. Furthermore, the process of dehydration condensation reaction on the substrate of glass can also be compared with the bulk reactions measured by transmission.

Pyrolysis-GC/FT-IR Analysis for Silane Coupling Treatment of Glass Fibers

Pyrolysis gas chromatography coupled with FT-IR (Py-GC/FT-IR) has been applied to the study of silane treatment of E-glass fiber. The glass fiber treated with a silane coupling agent, γ-anilinopropyltrimethoxy-silane (AnPS), is pyrolyzed at 750°C. The pyrolysates are fractionated by GC and analyzed by FT-IR. The main fraction is assigned to the organofunctional group of the coupling agent. Thus, Py-GC/FT-IR enables us to identify the treated coupling agent qualitatively. A mixture of two different coupling agents, AnPS and γ-methacryloxypropyltrimethoxysilane on glass fiber, is separated and characterized from the spectra of fractions resulting from each coupling agent. Py-GC/FT-IR also provides quantitative information regarding the coupling agents on glass fiber. The total amount of the treated coupling agent is estimated according to the calibration curves, which are proportional to the amount of the coupling agent. Moreover, Py-GC/FT-IR enables us to evaluate the fixing ratio of the coupling agent to the total amount through washing the samples with methanol. The fixing ratio falls significantly above treatment concentration. This tendency is consistent with the results from nondestructive sampling preparation techniques in infrared spectroscopy. The above results indicate the usefulness of Py-GC/FT-IR for the evaluation of silane treatment.

An analytical investigation of silane coupling agents on glass fibres

Abstract Pyrolysis gas chromatography coupled with FTIR (Py-GC/FTIR) has been applied to the investigation of silane treatment of E-Glass fibres. The thermal decomposition products are fractionated organofunctional groups from the coupling agent. The fragments from the coupling agent can be identified by FTIR. Moreover, for a qualitative analysis, a mixture of structurally similar coupling agents can be analysed using Py-GC/FTIR. Thus this technique is useful for the qualitative identification of coupling agents or mixtures of coupling agents on treated fibres.

Investigation on resin interphase produced near silane-treated glass fiber in vinyl ester resin

In order to investigate the reaction of silane-treated glass fiber with thermosetting resin, a set of spectra were measured near the interface between the glass fiber and vinyl ester resin using microscopic FT-IR spectroscopy. A thin-sliced sample was made from glass fiber/vinyl ester resin composite to be subjected to the spectroscopy. The spectra were obtained through a 20 × 40 μm of a mask window at each 20 μm step from the glass strand area to the matrix resin. The intensity at 1450 cm-1 of the spectra decreased from the glass strand area to the matrix resin. It was noticed, however, that the intensity kept the same value even in the matrix at a distance of 80 μm from the glass strand area. This meant that the resin in such an area was denatured by the reaction of silane to resin at the surface. This mechanism was supported by the significant size of the denatured area, which increased with amounts of silane at the surface of glass fiber.

Evaluation of the interfacial properties in the embedded-single-fibre coupon test

Abstract The embedded-single-fibre tension test is a very useful technique for the evaluation of interfacial properties in composite materials. There are, however, some problems with this method. A comparison is made between the normal embedded-single-fibre method characterized by critical fibre length and the interfacial transmissibility method proposed by the authors. The effects of resin properties, in particular, are discussed. As the results show, there is some difficulty in evaluating the interfacial properties by the normal embedded-single-fibre method in the case of brittle-matrix systems, whereas interfacial transmissibility provides the possibility of evaluating interfacial properties over a wide range of resin properties.

Fixation of silane coupling agents to glass fiber in silane treatment process

Fixation of silane coupling agents to glass fiber was quantitatively determined using pyrolysis-GC/FT-IR to explore the formation of chemical-bonded and physisorbed silanes. The silane coupling agent used was N-phenyl-1-aminopropyltrimethoxysilane (AnPS). In silane treatment, E-glass fiber was dipped into acetic acid solution containing AnPS and was cured under different temperature and time. The fixation of silane was obtained by determining the amount of AnPS at the glass surface after and before washing the treated fiber with methanol. The silane fixation increased with decrease in the silane concentration, but it fell significantly below a lower silane concentration. The change of fixation in curing temperature gave an optimum temperature for the fixing. The dependence of curing time on the fixing ratio showed that the fixation was depressed below the curing temperature of 100°C. These results suggested that more than a specific amount of AnPS deposit on glass fiber was necessary to form silane networ...

Photoacoustic FT-IR Study on Keratin Chemically Bound on the Surface of Silica Gel Particles

The conformation of keratin chemically bound to the surface of silica gel particles has been investigated by means of photoacoustic Fourier transform infrared (PA/FT-IR) spectroscopy. On the basis of the peak positions of the amide I and amide II bands, it is concluded that the keratin thin layer assumes the native α-helix form. It is also noted that the PA/FT-IR method is the only feasible method for observing the IR spectra of the very thin layer of keratin coating on the silica gel particles. The diffuse reflectance technique failed to provide any information on keratin, because of the strong spectral artifact due to the specular reflection at the surface of the silica gel.

Improvement of resin impregnation into glass cloth by silane treatment in resin transfer molding

An evaluation method was proposed for resin impregnation using resin transfer molding of unsaturated polyester matrix composites with silane-treated glass cloth. The determination of whitening of the composite was carried out as a parameter of incompleteness of resin impregnation. The change of whitening with silane concentration was compared with the bending modulus as a parameter of chemical reinforcement. The materials used were unsaturated polyester resin as a matrix and methacryloxypropyltrimethoxysilane as a silane coupling agent for glass cloth. Resin transfer molding was used to produce four plies of glass cloth laminates by impregnating the resin. The silane-treated glass cloth repressed whitening above 0.026 w/w% of silane in aqueous solution, while the chemical reinforcement due to silane gave no appearance below 0.2 w/w% based on the bending test of the laminates. The large difference between the concentrations suggested that silane has a couple of functions, that is, chemical reinforcement and physico-chemical resin wettability.

Interfacial reinforcement in composites with PPT aramid fiber modified by network-intercalation method

—A novel surface treatment for poly(p-phenylene telephthalamide) (PPTA) fiber is performed with silanes and urethane binder that are usually used as sizes for glass fiber treatment. The PPTA used for the surface treatment is modified by a spinning process to make the gaps between PPTA crystallites open. In this treatment, supercritical carbon dioxide fluid method is used to impregnate the sizing molecules into open gaps in PPTA fiber. After the impregnation, the fiber is heated at 100–170°C to make the gaps close and turn open-gapped fiber to the normal type of PPTA modified with sizes. The interfacial shear strength of fiber to epoxy resin is measured by microdroplet method. The modified PPTA improves the interfacial shear strength by ca. 67% to the interfacial shear strength given by normal PPTA without treatment. Those improvements are 33% without heating, 18% with only silanes, and 12% with only urethane instead of the mixture of silane and urethane. In addition, the fiber strength shows no remarkable decrease after the treatment.