THE DISTRIBUTION OF PLASTICIZERS BETWEEN AQUEOUS AND POLYMER PHASES IN AQUEOUS COLLOIDAL POLYMER DISPERSIONS

The distribution of water-soluble (triethyl citrate and triacetin) and water-insoluble (acetyltriethyl citrate, acetyltributyl citrate, dibu tyl phthalate, dibutyl sebacate, diethyl phthalate and tributyl citrat e) plasticizers between the aqueous and polymer phases in an aqueous c olloidal ethylcellulose dispersion, Aquacoat(R), was determined. A sep aration scheme was developed, which allowed the determination of the a mounts of plasticizers dissolved and, in the case of water-insoluble p lasticizers, also emulsified in the aqueous phase, and dissolved in th e colloidal polymer particles. The plasticized ethylcellulose dispersi on was separated by centrifugation and/or ultracentrifugation to obtai n the various plasticizer-containing fractions. The plasticizer concen tration in each phase was determined by a HPLC assay. The extent of th e plasticizer partitioning was investigated with respect to the type ( water-soluble or water-insoluble) and concentration of the plasticizer , and the solids content of the polymer dispersion. Water-insoluble pl asticizers mainly partitioned into the polymer particles due to the hi gher affinity towards the polymer phase, however, the amount of emulsi fied plasticizer droplets increased with increasing plasticizer concen tration after a plasticization time of 24 h. An 'association' coeffici ent, which was obtained from the ratio of the plasticizer concentratio n in the polymer to the concentration in the aqueous phase, was used t o characterize the plasticizer partitioning. The fraction of plasticiz er taken up by the colloidal polymer particles increased with increasi ng solids content of the polymer dispersion. It is therefore recommend ed to add the plasticizer to the undiluted dispersions followed by dil ution to the desired solids content just prior to coating, rather than first diluting the dispersion followed by addition of the plasticizer .