Half-sorption time method

The results were compared with the oxygen diffusion, solubility, and permeability coefficients obtained for PET films under the same conditions. The water sorption isotherm for polylactide films was also determined. Diffusion coefficients were determined with the half-sorption time method. Also, a consistency test for continuous-flow permeability experimental data was run to obtain the diffusion coefficient with the lowest experimental error and to confirm that oxygen underwent Eickian diffusion in the polylactide films. The permeability coefficients were obtained from steady-state permeability experiments. The results indicated that the polylactide films absorbed very low amounts of water, and no significant variation of the absorbed water with the... 

The basic information in the study of sorption processes is the quantity of substances on the interfaces. In order to measure the sorbed quantity accurately, very sensitive analytical methods have to be applied because the typical amount of particles (atoms, ions, and molecules) on the interfaces is about I0-5 mol/m2. In the case of monolayer sorption, the sorbed quantity is within this range. As the sorbed quantity is defined as the difference between quantities of a given substance in the solution and/or in the solid before and after sorption processes (surface excess concentration, Chapter 1, Section 1.3.1), all methods suitable for the analysis of solid and liquid phases can be applied here, too. These methods have been discussed in Sections 4.1 and 4.2. In addition, radioisotopic tracer method can also be applied for the accurate measurement of the sorbed quantities. On the basis of the radiation properties of the available isotopes, gamma and beta spectroscopy can be used as an analytical method. Alpha spectroscopy may also be used, if needed however, it necessitates more complicated techniques and sample preparation due to the significant absorption of alpha radiation. The sensitivity of radioisotopic labeling depends on the half-life of the isotopes. With isotopes having medium half-time (days-years), 10 14-10-10 mol can be measured easily. 

The actual rate of volatilization of plasticizers from water apparently has not been experimentally measured. The rates of volatilization, however, estimated using the Sonth-worth Method to estimate gas-phase and liqnid-phase mass transfer coefficients, were reported in HSDB, and summarized in Table 18.10. VolatiUzation was estimated nnder two scenarios (Figure 18.1) a shallow (1-m deep) river moving at a rate of 1 m/sec below an air mass moving at 3 m/sec. The second scenario was a shallow (1-m deep) lake moving at 0.05 m/sec below a breeze of 0.5 m/sec. The estimated volatilization half-lives of the plasticizers followed the trend established by their Heniy Law constants. Consequently, the predicted half-lives of ditridecyl phthalate, di-(2-ethylhexyl) adipate, di-(2-ethylhexyl) azelate, diundecyl, diisooctyl, dihexyl, dinonyl phthalate were less than 6 days. The same plasticizers would likely be more persistent in the lake scenario. The volatilization rates of the other plasticizers appeared to be much slower, and volatilization from water may not be a significant environmental pathway. Furthermore, the Southworth estimation technique does not take into acconnt sorption of dissolved chemicals by suspended particles. Sorption would increase the residence time of dissolved plasticizers. The predicted volatilization rates, however, were based on Hemy s Law constants which are themselves only estimates. 

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