John R. Schlup

Etherification versus amine addition during epoxy resin/amine cure : An in situ study using near-infrared spectroscopy

The reactions between a multifunctional epoxy resin, tetraglycidyl 4,4′-diaminodiphenylmethane (TGDDM) and a monofunctional amine, methylaniline (mAnil) are studied. Due to the existence of a tertiary amine catalytic center within the TGDDM molecule, the etherification reaction during cure of TGDDM is usually more significant than in other epoxide systems. The importance of this reaction relative to the amine addition reactions is investigated. In situ near-infrared spectroscopy is used to obtain kinetic data during the cure reactions. The reaction rate constants are calculated from linear regression analysis for both amine addition and etherification reactions based on the reaction mechanisms proposed. Arrhenius relationships are observed for all the reaction rate constants involved.

Monitoring the process of curing of epoxy/graphite fiber composites with a recurrent neural network as a soft sensor

Abstract Controlling the curing of fiber-reinforced composites involves an on-line evaluation of their properties such as viscosity, resin content, and degree of cure (DOC). Infrared spectroscopic and dielectric sensors have commonly been considered for monitoring these properties. Nevertheless, they are expensive, and yet do not yield a precise cure history during the entire process. Artificial neural networks have successfully been adopted for the dynamic modeling of nonlinear systems. Inasmuch as the actual DOC of a composite cannot readily be measured in situ during the cure, long-term prediction of the DOC is critical. In the present study, a unique integrated sensor has been constructed that comprises a dual heat-flux sensor serving as a hard sensor for determining the Damkohler number (Da) and a recurrent neural network (RNN) serving as a soft sensor for evaluating and predicting the DOC on the basis of the Da obtained. At the outset, the prototype soft sensor, i.e., RNN, was configured through a series of repeated and rapid simulations of an analogous model system with known performance equations for learning and testing. Subsequently, this prototype RNN was tuned and validated through a minimum number of laborious experiments, so that the resultant soft sensor is capable of effectively monitoring on-line the DOC of the prepreg of a commercial epoxy/graphite fiber composite in a bag-molding process.

Application of Near-Infrared Attenuated Total Reflectance Spectroscopy for Monitoring Epoxy Resin/Amine Cure Reactions

Product quality in composite processing will be improved by dependable methods for monitoring the process. In this paper, the feasibility of using near-infrared attenuated total reflection (NIR ATR) spectroscopy as a sensor for monitoring epoxy resin cure is demonstrated. An ATR crystal serves as a contact sensor, which has several potential advantages over embedded optic fiber techniques previously reported. NIR ATR spectra obtained from several epoxy/amine systems show that both primary amine and epoxy functional groups have well-isolated absorption peaks in the near-infrared region. The utility of NIR ATR spectroscopy for in situ cure monitoring is demonstrated by following the reaction between phenyl glycidyl ether and butylamine at ambient temperature.

Synthesis and characterization of leather impregnated with bismaleimide (BMI)-Jeffamine resins

Leather/polymer composites were prepared by impregnating chrome-tanned cattlehide with a solution containing 1,1′-(methylenedi-4,1-phenylene)bismaleimide and Jeffamine® D-230. The mechanical properties in tension, glass transition temperatures, dynamic storage moduli, and moisture absorption of the composites were measured. Impregnated samples showed significant changes in tensile properties, such as the Youngs modulus and strain at break, when compared with chrome-tanned cattlehide. In addition, impact energy increased significantly upon formation of the leather/polymer composite over that of the bismaleimide–Jeffamine® resin itself.

Mid- and near-infrared spectroscopic investigations of N-phenylmaleimide (NPM)/amine reactions

The reactions between N-phenylmaleimide (NPM) and several amines have been examined by both mid-infrared (mid-IR) and near-infrared (near-IR) spectroscopy. Significant overlap exists among several functional groups of NPM/amine systems in the mid-IR spectral region. Interference between these absorptions significantly reduces the utility of mid-IR spectroscopy for quantitative studies of NPM/amine reaction kinetics. In contrast, the absorption bands of these functional groups are well separated in near-IR spectra. The ability of near-IR spectroscopy for studying the kinetics of the reactions between the maleimide-containing compound with amines is clearly established. Near-IR absorptions suitable for quantitative studies of these reactions are identified.

Characterization of a novel oil-in-water emulsion adjuvant for swine influenza virus and Mycoplasma hyopneumoniae vaccines

Vaccines consisting of subunit or inactivated bacteria/virus and potent adjuvants are widely used to control and prevent infectious diseases. Because inactivated and subunit antigens are often less antigenic than live microbes, a growing need exists for the development of new and improved vaccine adjuvants that can elicit rapid and long-lasting immunity. Here we describe the development and characterization of a novel oil-in-water emulsion, OW-14. OW-14 contains low-cost plant-based emulsifiers and was added to antigen at a ratio of 1:3 with simple hand mixing. OW-14 was stable for prolonged periods of time at temperatures ranging from 4 to 40°C and could be sterilized by autoclaving. Our results showed that OW-14 adjuvanted inactivated swine influenza viruses (SIV; H3N2 and H1N1) and Mycoplasma hyopneumoniae (M. hyo) vaccines could be safely administered to piglets in two doses, three weeks apart. Injection sites were monitored and no adverse reactions were observed. Vaccinated pigs developed high and prolonged antibody titers to both SIV and M. hyo. Interestingly, antibody titers were either comparable or greater than those produced by commercially available FluSure (SIV) or RespiSure (M. hyo) vaccines. We also found that OW-14 can induce high antibody responses in pigs that were vaccinated with a decreased antigen dose. This study provides direct evidence that we have developed an easy-to-use and low-cost emulsion that can act as a powerful adjuvant in two common types of swine vaccines.

Synthesis and mechanical properties of leather-epoxy interpenetrating polymer networks

Leather–epoxy interpenetrating polymer networks (IPNs) were synthesized; these IPNs have an approximate epoxy concentration of 25 wt %. The flexural and tensile moduli of the IPNs prepared are equivalent to those of the epoxy resin. The Izod impact energy and fracture toughness measured for the IPNs, however, exceed those attained by the epoxy resin alone by at least a factor of 4. The glass transition of leather–epoxy IPNs occurs over a wide temperature range, thus indicating that the IPN is an intimate admixture of the epoxy resin throughout the collagen matrix of the hide.

Impact of oil composition on formation and stability of emulsions produced by spontaneous emulsification

ABSTRACT In this study, triglycerides of different chain lengths were mixed with paraffin oil, and their effectiveness in forming emulsions produced by spontaneous emulsification upon the addition of water was investigated. The emulsion droplet size exhibited a similar trend as a function of the triglyceride/paraffin oil composition for medium-chain (MCTs) (C8–C10) and long-chain (C18) triglycerides (LCTs). However, emulsions formulated with MCTs and LCTs have a much smaller droplet size (about 50 nm) than emulsions based upon short-chain (C4) triglycerides (SCTs). The addition of SCTs resulted in droplet sizes around 800 nm and the emulsions formed were very unstable. The droplet size, polydispersity index, zeta potential, and emulsion stability of these systems will be described as a function of the oil phase composition. GRAPHICAL ABSTRACT

Infrared Spectroscopic Characterization of CIT-6 and a Family of *BEA Zeolites

Infrared spectroscopy is known to be a useful tool for identifying local structure changes in zeolites. Infrared spectroscopy is often employed to complement X-ray diffraction data. Local structure changes in zeolite CIT-6 and its zeolite beta (*BEA) analogs caused by calcination, altering framework composition, and ion exchange have been identified with mid- and far-infrared spectroscopy. Differences in the local structures of the samples were observed in mid- and far-infrared spectra, including changes in the intratetrahedral asymmetric stretch, the double-ring mode, and the intratetrahedral bending mode regions. The infrared spectra indicate that calcination or acetic acid extraction changed the structure of CIT-6 to that of zeolite beta (*BEA). Zinc ion exchange or the substitution of aluminum into the framework structure of acetic acid extracted samples retained the CIT-6 structure.

Critical thermodynamic analysis of differential scanning calorimetry for studying chemical kinetics

A critical thermodynamic analysis of differential thermal calorimetry is reported herein to gain further insight into the phenomena leading to the reported differences between kinetic parameters extracted from isothermal DSC methods and those from dynamic DSC methods. The sources have been identified for the variations observed in the total heat of reaction as a function of the heating rate in dynamic DSC experiments. The analysis clearly indicates that these variations are, in fact, to be anticipated. The relationships necessary for extracting kinetic data from both isothermal and dynamic experiments are derived rigorously by resorting to classical thermodynamics.