Analysis by IGC

Most of the available data on diffusion and diffusion coefficients of volatile liquids or gases in polymers have been obtained by static sorption experiments (10, 11), which are time consuming and require extensive data analysis. In recent years, inverse gas chromatography, IGC, was found to have wide utility in measuring sorption tendency and diffusion coefficients of gases and volatile liquids in molten polymers (12-17). 

Data Analysis. A tacit assumption that the support material contributes little or no retention to the observed retention by the polymeric coating is usually made in the IGC literature. In a published work (17), and from a large body of recently gathered data, it has been confirmed that retention by the so-called inert support may actually account for up to 10% of the observed retention of the column. Furthermore, the support retention was found to be a function of the amount of probe injected, especially for strongly polar probes. It became clear that this factor alone could undermine the blend analysis if it were not handled properly. 

Measurement Procedure. IGC measurements were started after the thermal and flow equilibrium in the column were stable (2 to 3 h). To facilitate rapid vaporization of the probe (0.01 yL), the injector temperature was kept 30°C above the boiling point of the probe. Measurements were made at five carrier gas flow rates. The retention volumes of six injections for each probe and twenty injections of the marker (H2) at a given flow rate were averaged. The values obtained were extrapolated to zero flow rate to eliminate the flow rate dependence of the retention data. The net retention time (tR) is defined as the time difference between the first statistical moment of the solvent peak and that of the marker gas. Thus, tR was calculated by an on-line computer statistical peak analysis rather than the retention time at the peak maximum (tp,maY). This eliminated inaccuracies arising from slight peak asymmetry, which occurs even for inert and well-coated supports. The specific retention volumes (Vg°) derived from tR and tR max differed by as much as 5% for small retention times and slightly skewed peaks (11,12). 

An IGC method for the analysis of divided solids and fibers has been initiated by Gray et al. (2 ) It is illustrated here by the results obtained from the precipitated silica sample (PI). Injecting a series of n -alkanes at infinite dilution (at the limit of detection by the flame ionization detector) usually results in a linear variation of the logarithm of the net retention volumes (V ) with the number of carbon atoms in the n-alkanes. This is illustrated in Figure 1 for measurements performed between 71 and 130°C. Thermodynamic considerations show that and the standard free energy of adsorption of the alkanes are related by... 

The data reduction for finite concentration IGC by elution on a plateau is more complicated than for infinite dilution IGC via Equations [4.4.24 to 26] and will not be explained here. A detailed analysis of the elution on plateau mode was made by Conder and Purnell. 09 Pqj. Ujg determination of thermodynamic properties of polymer solutions by finite-concentration IGC the reader is referred to the paper by Price and Guillet" who provide a comprehensive derivation of all necessary equations. 

Evidenced has been obtained previously that the reinforcing effect of different grades of fumed silicas on silicone elastomers is influenced by the surface fractality [1] and that the surface roughness increases with the specific surface energy. The aim of the present work is to demonstrate variations by calling on NMR and infrared spectroscopic methods, which are applied to fumed silica samples that have been carefully characterized through adsorption methods including IGC analysis. 

The aim of the present study is to determine by XPS the chemical surface characteristics of different types of cotton fibers and to compare these characteristics with thermodynamic surface properties (surface energy) of the fibers, previously determined by means of inverse gas chromatography (IGC) at infinite dilution[3,4] Three types of cotton fibers of different varieties and exhibiting different maturities and wax contents are analyzed as received (raw fibers) or after having been extracted (extracted fibers) in hot ethanol for 6h. These results are compared with those previously obtained by inverse gas chromatography analysis. 

Abstract A CaCOs filler was coated with various mono- and dicarboxylic acids in a dry-blending process. The coated fillers were characterized by various techniques, including dissolution experiments, thermal analysis (differential scanning calorimetry) and inverse gas chromatography (IGC) to determine the amount of surfactant needed to achieve mono-layer coverage IGC proved to be the most convenient, reliable and universal method for this purpose. The dispersion component of the surface tension and the specific interaction potential of the coated filler can be derived from the results, but indirect conclusions can be also drawn from them about the orientation of the molecules on the filler surface and the structure of the layer formed. The coverage of the filler with an organic compound leads to a... 

Values of the Flory-Huggins X2i parameter expressing the magnitude of interactions between the polymer matrix and filler depend heavily on the type of test solute being used in IGC experiments. This causes problems when analyzing the influence of the type and amount of filler on the magnitude of these interactions however, such an analysis is clearly possible by using PCA. 

Zhang et al. [71] employed a packed-column IGC technique to determine the activity coefficients and diffiisivities of small molecules in phenol resins. For this, they applied the Romdhane-Danner approach for data analysis, and the Braun-Guillet approach to determine the thickness of the polymer layer on the support Subsequently, the authors reported that the IGC-derived difiusivity data were consistent with the theoretical data obtained from the Romdhane-Danner approach, and might be further used to predict the temperature- and concentration-dependence of diffusivity by the free volume theory. 

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