Tack experiments performed with petrolatum, a highly viscous semisolid did not show the region of "delayed elastic effects." This resulted in a rather short duration for filament elongation; hence theft was relatively small.
The above observations suggest that the response of the concentrated polymer solutions (semisolids) to applied pull stress is a combination of viscous and elastic forces. The "delayed elastic effects" observed are the result of configurational elasticity, which is a process associated with orientation, alignment, and elongation by the uncurling of large chain molecules. Therefore, theft required for the elongation of the filament will not only depend )n the viscosity of the liquid, but also on the internal structure of the ystem.
Earlier investigators (10-12) suggested that tackiness is related to the gemetry of the system and the rheological characteristics of the liquid. herefore, according to this definition, lecithin, petrolatum, and even water a d d with high concentration of finely divided solids will be considered tacky, nce these liquids or dispersions do offer resistance to flow. In actual practice. e above materials, unlike povidone solution, are not known to be tacky even ough impulse for liquid film separation is required in both cases. Based on ese observations, it can be concluded that a tacky material is one that disays "delayed elastic effects," and because of these effects it requires a long Wriod of time for filament elongation. This provides a rather large impulse fw a given force of separation.
Tack Effects in Tablet Coating-Coating solutions, when applied to the tablets during the coating process, are dilute solutions of polymers of lowviscosity grade. Separation of tablets stuck together by a freshly applied coating solution will occur by viscous flow. Therefore, the) required will be equal for solutions of similar viscosity. As the solvent evaporates during the diying phase of the coating process, the solution will reach a semisolid statc. At this point, resistance to filament elongation will depend on the molecular structure of the polymer.
Tablet coating solutions usually contain opacifier, plasticizers, and colorants to modify the physical characteristics and improve the film-forming properties of the polymers. The effect of these additives on the tack behavior of coating solutions is under investigation. REFERENCES ( I ) S. C. Porter, Pharm. Tech., 4(3), 67 (1980).
(2) H. A. Lieberman and L. Lachman, "Pharmaceutical Dosage Forms: