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Polymeric alloys of polyphosponates and acetyl cellulose. I. Sorption and diffusion of benzene and cyclohexane
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1974
Year
Membrane StructureEngineeringMembrane CharacterizationOrganic ChemistryChemistrySelf-diffusion CoefficientsPolymersChemical EngineeringPolymer TechnologyMolecular ThermodynamicsAcetyl CelluloseMembrane TechnologyNanocellulosePolymer ChemistryWood ComponentMaterials ScienceI. SorptionPolymer EngineeringPhysical ChemistryPolymer AnalysisMembrane PermeationPolymer MembraneMembrane FormationPolymer SciencePolymeric AlloysSelf-diffusion Experiments
The solubility of benzene in the polymeric alloys (P/A) consisting of polyphosphonates (PPN) and acetyl cellulose (AC) is nearly two orders of magnitude larger than that of cyclohexane. The preferential absorption of benzene by P/A membranes is also maintained upon its dilution with cyclohexane, though the solubility of the latter in the P/A membranes is affected by their swelling with benzene. Absolute values of solubilities increase exponentially with increase in the weight fraction of PPN in P/A membranes. They are also affected by the thermal and solvent “history” of a membrane. For the sorption of benzene by a P/A-50 membrane The diffusion coefficients of benzene in the solvent-swollen membranes are strongly concentration dependent and increase exponentially up to ∼10−6 cm2/sec with the increase in the volume fraction of benzene. Values of D0 are of the order of 10−11 to 10−10 cm2/sec. Sorption experiments indicate a pronounced time dependence of the diffusion coefficients. Self-diffusion experiments conducted with 14C-labeled benzene revealed that values of D* derived from the steady-state permeation measurements are in certain membranes much larger than those derived from the “time-lag.” It was observed that the discrepancies between the two sets of values depend strongly upon the thermal “history” of the membranes and vanish when the membranes are swollen to a high degree at elevated temperatures. The above phenomenon is discussed in terms of differences in the membrane structure; a model is proposed. The apparent energy of activation of diffusion of benzene at 10–40°C in the swollen P/A-50 membrane EBD 14.4 kcal/mole was derived from the temperature dependence of the self-diffusion coefficients. For the same temperature range at C(B) → 0, EB = 8.3 kcal/mole was derived from the final slopes of the desorption curves. The small difference between the energies of activation in a swollen and in an unswollen system is due to the fact that at room temperature it remains below Tg even upon extensive swelling with benzene.