Depending on their properties plasticizers can be classified as :
1. Polyols
  • Glycerol
  • Propylene glycol
  • PEG 200-6000 grades
2. Organic esters
  • Triacetin
  • Diethyl phthalate (DEP)
  • Dibutyl phthalate (DEB)
  • Tributyl citrate (TBC)
3. Oils/Glycerides
  • Castor oil
  • Fractionated coconut oil
  • Acetylated monoglycerides
 4. Newer Plasticizers – DBS

5. Can be used for the very plasticizing effect in both aqueous and solvent based pharmaceutical coatings

6. Under this category both the hydrophilic as well as lipophilic esters are available.


CLASSIFICATION ON BASIS OF WATER SOLUBILITY


Plasticizers can be divided into water-soluble and -insoluble plasticizers.  Water-soluble plasticizers are dissolved, while insoluble plasticizers have to be emulsified in the aqueous phase of the  polymer dispersions. The effectiveness of plasticization is resulted from the partition of plasticizer from the solvent phase into the polymer phase and subsequently diffuses throughout the polymer to disrupt the intermolecular interactions. The rate and extent of this partitioning for an aqueous dispersion have been found to be dependent on the solubility of the plasticizer in water and its affinity for the polymer phase. The partitioning of water-soluble plasticizers in an aqueous dispersion occurs rapidly, whereas significantly  longer equilibration times are required for water-insoluble plasticizing agents. The amount of lipophilic plasticizer taken up by the polymer phase in aqueous dispersion as a function of contact time was elucidated.

1. Water Soluble
  • PEG
  • TEC
  • Triacetin

2. Water insoluble
  • DEP
  • DBS
  • DBP
  • ATEC (Acetyl Triethyl Citrate)

Water soluble plasticizers make solutions whereas the insoluble plasticizer are emulsified into dispersions.

With insoluble plasticizers, their dispersion is described as a 3 phase systems containing water phase, polymer phase and plasticizer emulsified droplets.

The rate and the extend of plasticizers uptake by the colloidal polymers was explained by conducting the effect of type and concentrations of plasticizers on Aquacoat and the plasticized films so formed were characterized by HPLC.

It showed that the water soluble plasticizers like triacetin was in higher concentrations in the aqueous phase due to higher concentrations in the aqueous phase due to higher solubility in aqueous phase.

Whereas the water insoluble plasticizers i.e. DBS partitioned about 90% or more into the polymer phase. And the rest form was present as emusilfied droplets.

Under such conditions when the plasticized droplet containing coating dispersions are sprayed onto the tablets they generate rough, brittle and uneven films which potentially alters mechanical properties and release profile of drug from the coated dosage forms.

The rate of uptake of plasticizers by the polymers is as function of plasticizing time. But in case of water soluble plasticizers like triacetin or TEC uptake is not affected by the agitation time or mixing time.

But for water insoluble plasticizers like DBS incomplete plasticizing is observed even after long plasticization time for ethylcellulose latex.

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