N. Chikhi

Bio: N. Chikhi is an academic researcher from Sonatrach. The author has contributed to research in topics: Izod impact strength test & Ultimate tensile strength. The author has an hindex of 2, co-authored 2 publications receiving 442 citations.

Modification of epoxy resin with kaolin as a toughening agent

Abstract: Epoxy resins are widely used as high-performance thermosetting resins for many industrial applications, but unfortunately, some are characterized by a relatively low toughness. In this respect, many efforts have been made to improve the toughness of cured epoxy resins by the introduction of rigid particles, reactive rubbers, interpenetrating polymer networks, and thermoplastics within the matrix. In this work, kaolin as a modifier was added at different contents to improve the toughness of diglycidyl ether of bisphenol A epoxy resin with polyamino-imidazoline as a curing agent. The chemical reactions suspected of taking place during the modification of the epoxy resin were monitored and evaluated with Fourier transform infrared spectroscopy. The glass-transition temperature (Tg) was measured with differential scanning calorimetry. The mechanical behavior of the modified epoxy resin was evaluated in terms of the Izod impact strength (IS), the critical stress intensity factor (KIC), and tensile properties at different modifier contents. Scanning electron microscopy (SEM) was used to elucidate the mechanisms of deformation and toughening in addition to other morphological features. Finally, the adhesive properties of the modified epoxy resin were measured in terms of tensile shear strength (TSS). With the addition of kaolin, the reactivity test revealed that the gel time and temperature, exotherm peak, and cure time were reduced. Infrared spectra showed the existence of a chemical reaction between kaolin and the epoxy resin. The presence of kaolin caused a steady decrease in Tg by about 10°C until 15-phr kaolin was reached prior to leveling off. Most of the tensile properties attained a peak at an approximately 10-phr kaolin content where the toughening reached its maximum. The modulus increased linearly from 1.85 to 2.7 GPa with increasing kaolin content. For both notched and unnotched specimens, a twofold increase in Izod IS was obtained by the addition of just 10-phr kaolin compared to the unfilled resin. On the addition of kaolin, the Izod IS varied from 0.85 to 1.53 kJ/m2 for notched specimens and from 4.19 to 8.32 kJ/m2 for unnotched specimens, whereas KIC varied from 0.91 to 2.63 MPa m1/2 with increasing kaolin content. The adhesive properties, evaluated in terms of TSS, increased from 9.14 to 15.02 MPa. SEM analysis revealed that the prevailing toughening mechanism for the epoxy resin under consideration was localized plastic shear yielding induced by the presence of kaolin particles associated with crack pinning. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 82: 861–878, 2001

Pyroreflectometry as a technique for the accurate measurement of very high temperatures in molten materials.

Abstract: Experimental research into severe nuclear accidents often requires the accurate measurement of high temperatures of molten materials. Measurements of very high temperatures (1500-2500 °C) in liquid materials using standard pyrometry can entail uncertainties in the order of 5%-10%. Pyroreflectometry is a powerful technique with the potential to significantly reduce these uncertainties. A method is proposed to optimize pyroreflectometry temperature measurements in the 1500-2500 °C range and to allow more easily the detection of the solid-liquid phase transition. The originality of this research essentially relies on the use of pyroreflectometry based on two wavelengths (1.3 and 1.55 μm) and its application to liquid materials at high temperature, which implies to adapt technological elements and metrological procedures. The proposed procedure first requires temperature calibration, which is undertaken using three eutectic fixed-point cells, reducing temperature uncertainty. Second, precise settings are adopted to enable reflectivity measurements on specular surfaces, such as the surfaces of molten metals. Pyroreflectometry measurements on liquid surfaces have been validated on an iron sample. Subsequently, the application of pyroreflectometry at very high temperatures was validated on various materials: metal (iron and 18MND5 steel), oxide (alumina), and carbide (rhenium-carbon eutectic). For each of these samples, the uncertainties of temperature measurements in the 1500-2500 °C range were estimated in the range of 1%-2%, performing well against standard pyrometry measurements. The principal difficulties encountered during the pyroreflectometry characterization were the fine-tuning of parameters (optical head orientation and lens focusing) to enable measurements on highly specular surfaces and ensuring inert interactions between the samples and the crucible.

Rubber-Toughened Epoxies: A Critical Review

Abstract: Epoxy resins have been used as structural materials since the late 1940s. Despite their desirable properties such as high strength, excellent creep resistance, and good adhesion, they suffer from low fracture energy. Rubber modification as a major toughening approach to overcome the inherent brittleness of epoxy polymers was introduced during the early 1970s. Since then, a large number of investigations have been conducted to elucidate different aspects of rubber-toughened epoxies. The present work is a critical review of the field focusing on the important parameters affecting rubber-toughening. The studies reviewed are classified in five categories including roles of matrix ductility, rubber concentration, blend morphology, particle cavitation, and particle/matrix interface. It has been tried to provide an in-depth view of the state-of-the-art knowledge in the field and to direct future studies towards exploring new approaches for toughening of epoxy polymers.

Fabrication and characterization of carbon/epoxy composites mixed with multi-walled carbon nanotubes

Abstract: In this study, a high-intensity ultrasonic liquid processor was used to obtain a homogeneous mixture of epoxy resin and multi-walled carbon nanotubes (CNTs). The CNTs were infused into epon 862 epoxy resin through sonic cavitation and then mixed with W curing agent using a high-speed mechanical agitator. The trapped air and reaction volatiles were removed from the mixture using a high vacuum. Flexural tests and fracture toughness tests were performed on unfilled and CNT-filled epoxy to identify the effect of adding CNTs on the mechanical properties of epoxy. The highest improvement in strength and fracture toughness was obtained with 0.3 wt% CNT loading. The nanophased matrix filled with 0.3 wt% CNT was then used with weave carbon fabric in a vacuum-assisted resin transfer molding (VARTM) set up to fabricate composite panels. Flexural tests, thermogravimetric analysis (TGA), and dynamic mechanical analysis (DMA) were performed to evaluate the effectiveness of adding CNTs on the mechanical and thermal properties of the composite. The glass transition temperature, decomposition temperature, and flexural strengths were improved by infusing CNTs. Based on the experimental result, a linear damage model has been combined with the Weibull distribution function to establish a constitutive equation for neat and nanophased carbon/epoxy. Simulated result show that that infusing CNTs increases Weiubll scale parameter, but decrease Weibull shape parameter.