Question

Ansell Inc. produces chemical-resistant gloves. Their chemicalpermeation test cell is shown in the illustration to the right. Theglove material is used as a thin membrane separating a liquidcompartment from a

gas compartment. Nitrogen gas iscontinuously pumped through the gas side of the chamber to keepthe concentration of liquid vapor that has diffused across themembrane close to zero. Their test liquid is epichlorohydrin, a chemical we have used inour lab to crosslink polymers. According to Ansell, gloves made ofa neoprene-natural rubber blend (0.67 mm thick, density of 1.18g/cm3) are rated as "Good" in terms of permeation rate, whichmeans that the steady state permeation rate is no more than 90ug/cm2-min (or 1.6 x 10-8 mol/cm2-s).(E a) A typical value of a diffusion coefficient of a small organic molecule in a polymer is 5 x 10-7 cm2/s. Calculate thepartition coefficient HA of epichlorohydrin in neoprene-natural rubber using this value of DAB. b) Diffusion coefficients of molecules in most polymers are much higher than in other solids. Hence manipulation of HAlsa promising way to reduce permeation rates in polymeric gloves. Does the value of Ha found in part a) suggest that Ansell has successfully developed a material that will do a “good" jobof protecting your hands from epichlorohydrin? Explain your reasoning briefly. c) Sketch the steady-state molar concentration profile of epichlorohydrin in the neoprene rubber from the liquid phase,through the rubber and into the gas phase. That is, sketch the mass transfer equivalent of WRF Fig 16.2 for steady-state heat conduction as shown below. Only a qualitatively reasonable sketch is expected (no calculations are necessary), but draw it in terms of molarconcentration for each phase (liquid/solid/gas). Note that the density of the liquid and rubber phases are equal.

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