J. Larry Duda

Diffusion of toluene and n-heptane in polyethylenes of different crystallinity

Abstract Diffusivity and solubility data for toluene and n-heptane in semi-crystalline polyethylene were obtained by gravimetric sorption experiments conducted in two different laboratories. The effects of temperature, concentration and degree of crystallinity on the diffusion and solubility behaviour were investigated at 70°C. The diffusivity data were correlated using a modification of the Vrentas–Duda free-volume theory. All the parameters in the free-volume model were estimated from pure component data except the size of the jumping units, the tortuosity, and the free-volume characteristics of the polymers. These results indicate that both the diffusivity and penetrant solubility in the polymer amorphous phase decrease with increasing crystallinity. Further, the tortuosity or the length of the diffusion path around the crystals increases with the degree of crystallinity.

Modeling of multilayer drying of polymer films

A model was developed to predict the drying behavior of multilayer polymer films on inert substrates. The model considers simultaneous heat and mass transfer controlled by complex thermodynamic and transport properties of polymer solutions. Key components of the model are the incorporation of the free volume theory to predict diffusivities in each polymer layer, the use of heat and mass transfer coefficients to describe complex transport phenomena in the gas phase, the incorporation of exact equilibrium boundary conditions at polymer–polymer interface, and the use of the Flory–Huggins theory to describe both liquid–liquid and vapor–liquid equilibria. The model can be applied to guide processing, product formulation, scale-up, and oven design. As an example, the model is applied to simulate the drying of a two-layer coating of poly vinyl acetate (in toluene) over polystyrene (also in toluene) on a polyester substrate.

Mutual and self-diffusion of water in gelatin: experimental measurement and predictive test of free-volume theory

Abstract Self-diffusion of water in unhardened photographic gelatin is measured by pulsed-gradient n.m.r. spectroscopy. Mutual diffusion and activity of water in hardened and unhardened gelatin is measured by step-change gravimetric sorption methods. Predictions of mutual diffusion from the self-diffusion data and published thermodynamic data by using the Vrentas-Duda theory are in agreement with the measured mutual diffusivities. Hardening (i.e. crosslinking) of the gelatin reduces the diffusivity as predicted by an extension to the Vrentas-Duda theory. The water activity increases with crosslinking.

Transport of blowing agents in polyurethane

Desorption experiments are conducted for several blowing agents in polyurethane at room temperature and with various blowing agent pressures. The diffusivity and solubility data for blowing agents are compared with the corresponding values for chlorofluorocarbon 11 (CFC 11). In addition, the solubility and diffusivity for these blowing agents in polyurethane are explained in terms of the solubility parameter and van der Waals volume, respectively. The calculated permeabilities based on the measured diffusivities and solubilities indicate that among the nine blowing agents investigated in this study, eight blowing agents can be possible candidates for substitutes of CFC 11 in polyurethane foams.

Thermal stability of esters under simulated boundary lubrication conditions

Abstract Oxidation and thermal instability are two important causes of lubricant degradation at the high temperature and thin film conditions prevalent in boundary lubrication. In this study, the “Penn State” microreactor test system was used in an inert atmosphere (nitrogen) to evaluate the thermal stability of trimethylolpropane triheptanoate (TMPTH), a typical polyolester basestock component of aircraft gas turbine lubricants. The Penn State microreactor test can produce the high temperature and thin film conditions found in boundary lubrication. Thermal stability tests showed that several metals had catalytic effects on the thermal degradation of TMPTH. The thermal instability threshold temperature was much lower under these thin film conditions than for the bulk conditions of previous thermal stability tests. The increased rates of decomposition at lower temperatures in the thin film mode appear to be related to the fluid-volume-to-metal-surface-area ratios.

Temperature and concentration dependence of diffusion coefficients in ethylene–propylene-diene copolymers

Self-diffusion and partition coefficients were measured for two commercial ethylene–propylene-diene copolymers (EPDM) and five solvents at infinite dilution using inverse gas chromatography. Mutual diffusion coefficients for solvents in EPDM also were measured for finite concentration using gravimetric sorption for three of the solvents. From the inverse gas chromatography experimental values for self-diffusion coefficients were obtained. Free-volume parameters were obtained through regression of the self-diffusion coefficient as a function of temperature. Mutual diffusion coefficients as a function of concentration were predicted using free volume theory and compared with experimental data obtained using gravimetric sorption.