GC Method for Determining Polyadipate Plasticizers in Foods: Transesterification to Dibutyl Adipate, Conversion to Migrating Polyadipate

The determination of the migration of polyadipates (plasticizers in PVC) into foods or food simulants for compliance testing involves three principal steps. (1) Adipate from the polyadipate material in the food or simulant is measured through transesterification to the butyl esters directly in the homogenated food, which presupposes tight control of the kinetics. Butyl esters are more easily extracted, and the butanol used for transesterification also serves as principal extraction solvent. (2) To check compliance with the specific migration limit, adipate is determined in the material of a molecular mass below 1,000 Da, which involves preparative preseparation by size exclusion chromatography followed by transesterification. (3) The migrated polyadipate material is calculated from the adipate measured by a conversion factor determined from the qualitative and quantitative analysis of the polyadipate components <1,000 Da.     

Mixtures of charged colloid and neutral polymer: influence of electrostatic interactions on demixing and interfacial tension

The equilibrium phase behavior of a binary mixture of charged colloids and neutral, nonadsorbing polymers is studied within free-volume theory. A model mixture of charged hard-sphere macroions and ideal, coarse-grained, effective-sphere polymers is mapped first onto a binary hard-sphere mixture with nonadditive diameters and then onto an effective Asakura-Oosawa model [S. Asakura and F. Oosawa, J. Chem. Phys. 22, 1255 (1954)]. The effective model is defined by a single dimensionless parameter-the ratio of the polymer diameter to the effective colloid diameter. For high salt-to-counterion concentration ratios, a free-volume approximation for the free energy is used to compute the fluid phase diagram, which describes demixing into colloid-rich (liquid) and colloid-poor (vapor) phases. Increasing the range of electrostatic interactions shifts the demixing binodal toward higher polymer concentration, stabilizing the mixture. The enhanced stability is attributed to a weakening of polymer depletion-induced attraction between electrostatically repelling macroions. Comparison with predictions of density-functional theory reveals a corresponding increase in the liquid-vapor interfacial tension. The predicted trends in phase stability are consistent with observed behavior of protein-polysaccharide mixtures in food colloids.