Carmina Menchaca-Campos

Nylon/Graphene Oxide Electrospun Composite Coating

Graphite oxide is obtained by treating graphite with strong oxidizers. The bulk material disperses in basic solutions yielding graphene oxide. Starting from exfoliated graphite, different treatments were tested to obtain the best graphite oxide conditions, including calcination for two hours at 700°C and ultrasonic agitation in acidic, basic, or peroxide solutions. Bulk particles floating in the solution were filtered, rinsed, and dried. The graphene oxide obtained was characterized under SEM and FTIR techniques. On the other hand, nylon 6-6 has excellent mechanical resistance due to the mutual attraction of its long chains. To take advantage of the properties of both materials, they were combined as a hybrid material. Electrochemical cells were prepared using porous silica as supporting electrode of the electrospun nylon/graphene oxide films for electrochemical testing. Polarization curves were performed to determine the oxidation/reduction potentials under different acidic, alkaline, and peroxide solutions. The oxidation condition was obtained in KOH and the reduction in H2SO4 solutions. Potentiostatic oxidation and reduction curves were applied to further oxidize carbon species and then reduced them, forming the nylon 6-6/functionalized graphene oxide composite coating. Electrochemical impedance measurements were performed to evaluate the coating electrochemical resistance and compared to the silica or nylon samples.

Long-term irradiation effects on gamma-irradiated Nylon 6,12 fibers

Long-term effects on Nylon 6,12 crystalline fibers irradiated six years ago have been determined, including chemical structure and morphology, and their relationship with storage time. Results from x-ray diffraction, small-angle x-ray scattering, scanning electron microscopy, and atomic force microscopy are reported for those fibers and for freshly irradiated ones. Some results for non-irradiated samples are included for comparison. Changes in the shape and size of the crystals (crystallinity degree) are found; the crystallite size increases with storage time. Both surface and bulk changes are seen in the morphology. Surface damage increases with storage time. Changes observed can be attributed to irradiation causing chain scission, which, in turn, causes crystal reorganization. The present results reinforce interpretation of earlier results obtained for concretes reinforced with irradiated Nylon fibers.

On Tuning the Fluorescence Emission of Porphyrin Free Bases Bonded to the Pore Walls of Organo-Modified Silica

A sol-gel methodology has been duly developed in order to perform a controlled covalent coupling of tetrapyrrole macrocycles (e.g., porphyrins, phthalocyanines, naphthalocyanines, chlorophyll, etc.) to the pores of metal oxide networks. The resulting absorption and emission spectra intensities in the UV-VIS-NIR range have been found to depend on the polarity existing inside the pores of the network; in turn, this polarization can be tuned through the attachment of organic substituents to the tetrapyrrrole macrocycles before bonding them to the pore network. The paper shows clear evidence of the real possibility of maximizing fluorescence emissions from metal-free bases of substituted tetraphenylporphyrins, especially when these molecules are bonded to the walls of functionalized silica surfaces via the attachment of alkyl or aryl groups arising from the addition of organo-modified alkoxides.

Electrospinning Smart Polymeric Inhibitor Nanocontainer System for Copper Corrosion.

This work presents the electrochemical evaluation of a proposed copper corrosion protection coating acting as a smart system. This consists in nylon fibers acting as a diffusion barrier and inhibitor nanocontainer, under different conditions. These include nylon fibers/benzotriazole as inhibitor mixture using the electrospinning technique and/or painted with alkyd varnish. Also the varnish was applied over as a drop. Submicron diameter electrospun nylon 6,6 fiber nanocontainers were prepared from a polymeric solution containing benzotriazole (BTA) inhibitor at different concentrations. Cu samples were coated with the electrospun nylon fibers and a varnish drop as coating. Optical and SEM microscopy were used to characterize the nanocontainers. Cu samples immersed in a chloride ammonium sulfate solution were evaluated using electrochemical impedance and noise, for six weeks. Comparison was made with bare Cu and varnish coated samples. For long periods of immersion good corrosion protection performance was observed, for the Cu samples electrospun coated system.

Post-irradiation effects on gamma-irradiated nylon 6,12 fibers

Abstract Post-irradiation effects on nylon 6,12 crystalline fibers gamma-irradiated 6 years previously (6YI) were studied, including thermal stability and morphology; their relationship with storage time was also studied. The results of these studies were compared with those obtained for non-irradiated (NI) and namely freshly irradiated (FI) crystalline fibers. The results include analyses like thermogravimetric analysis (TGA), differential thermal analysis (DTA), scanning electron microscopy (SEM) and optical images for (6YI and FI) both kinds of nylon 6,12 fibers. The results showed that the most prominent effect is related to the reaction progress. The chain scission and/or crosslinking mechanisms, as well as the free radicals, allow proceeding with the reaction, and consequently, changes on the properties of the FI samples. The melting point, degree of crystallinity, degradation temperature and morphology prove that additional chemical reactions and surface modifications keep occurring in the fibers long after the irradiation process has ended. With storage time, the surface becomes rougher, the color turns yellowish, the melting point diminishes and the degree of crystallinity increases.

Nylon 6,12 fibers under low-dose gamma irradiation

Abstract One of the most important applications of gamma irradiation is in the area of polymer modification. Nylon fibers that were gamma-irradiated with a dose higher than 25 kGy show fusion temperature and fusion enthalpy higher than the nonirradiated nylon. Nevertheless, under certain applications, the influence of nylon-irradiated fibers is noticeable below 50 kGy; therefore, physicochemical characterization is indispensable. In the present work, nylon 6,12 crystalline fibers were irradiated at low dose (from 1 to 25 kGy) at environmental conditions to confirm the thermal behavior. The melting point and fusion enthalpy were measured with differential scanning calorimetry; structural changes were studied using infrared spectroscopy; and fiber surface morphology was studied using atomic force microscopy. The results show an increase in both fusion temperature and fusion enthalpy, which are effects of the newly ordered high-molecular-weight oligomers. Recrystallization and oligomer formation can be observed in infrared spectra. Such behaviors are directly related to the partial damage over the surface and the mechanical performance of manufactured composites.

Post-irradiation effects on Nylon-fibers reinforced concretes

Abstract Fiber-reinforced concretes (FRCs) have a wider application range than ordinary concretes. Properties of FRCs necessarily depend on the characteristics of the aggregates used. We have studied first effects of gamma radiation on mechanical properties of hydraulic concretes containing Portland cement, silica sand, marble, water and Nylon fibers. Compressive strength and dynamic elasticity modulus are of particular importance. In the second stage we have analyzed the changes in these mechanical properties after storage of our concretes for three years. The long storage results in a 97 % of increment in the compressive strength and simultaneous lowering by 35 % of the dynamic elastic modulus. We find a larger influence of the Nylon fibers than those of silica sand and marble on mechanical properties of the concretes.

Natural, Synthetic, and Recycled Polymers in Composite Materials

1 Laboratorio de Investigacion y Desarrollo de Materiales Avanzados (LIDMA), Facultad de Quimica, Universidad Autonoma del Estado de Mexico, Km 12 de la Carretera Toluca-Atlacomulco, 50200 San Cayetano, MEX, Mexico 2 Civil Engineering Department, Faculty of Engineering, Bartin University, 74100 Bartin, Turkey 3 Centro de Investigacion en Ingenieŕia y Ciencias Aplicadas (CIICAp), Universidad Autonoma del Estado de Morelos, 62210 Cuernavaca, MOR, Mexico

Transport of Protons and Capacitive Properties of the Nylon/Porphyrin/Graphene Oxide Coating

Electrochemical impedance (EI) measurements were performed to evaluate the nylon 66/-tetra(para-aminophenyl) porphyrin (H2T(p-NH2)PP)/graphene oxide (GO) film coating on stainless steel and compared to the nylon/H2T(p-NH2)PP and nylon/GO film samples using 1M H2SO4 as electrolyte. The nylon/H2T(p-NH2)PP and nylon/GO composite films showed high electrochemical impedance in the order of 109 ohm-cm2 and a system controlled by mass transfer, product of a diffusion process at low frequencies with a resistance up to 5 orders of magnitude, indicating the diffusion of protons through the coating and a decrease in the metal dissolution. Otherwise, the nylon/H2T(p-NH2)PP/GO film compound evaluated show good ionic conductivity and electrochemical stability in the acid environment, acting porphyrin as a catalyst to the passage of protons through the film, reducing its electrochemical impedance up to 7 orders of magnitude with respect to the compounds nylon/H2T(p-NH2)PP and nylon/GO. Likewise, good capacitance values are also shown by modifying the concentrations of porphyrin and GO reinforcing materials. These properties are important for technological applications, such as anticorrosion coating for bipolar plates or membrane in a fuel cell type PEM, super-capacitors, etc.

Waste and Recycled Materials and their Impact on the Mechanical Properties of Construction Composite Materials

In a world increasingly fixated on the demands of sustainable development, too much attention has been focused on the widely used building materials, mainly on those tools and strategies for their reuse and those characteristics for considering them as environmental-friendly materials. Among the strategies are the following: (a) increased reliability on waste and recycled materials—such action will have to incorporate the substitution of recycled for virgin materials; (b) improved durability through reduction of materials needed for their replacement; and (c) improved mechanical properties, which reduces the use of raw materials. Extensive research and development activities in recycling composite materials have been conducted, and various technologies have been developed: (a) mechanical recycling, (b) thermal recycling, and (c) chemical recycling. However, gamma radiation is an innovative and clean technology, alternative to conventional recycling procedures. Gamma irradiation has proved to be an adequate tool for modifications of the physicochemical properties of polymers, through different effects: (a) scission, branching as well as cross-linking of polymer chains and (b) oxidative degradation. Moreover, the reuse and recycling of waste materials and the use of gamma radiation are useful tools for improving the mechanical properties of concrete. In this chapter, we show results of the effects of gamma irradiation on the physicochemical properties of waste and recycled materials and their reuse to enhance the properties of construction composite materials.