Preservatives plastics interactions

Preservative availability may be appreciably reduced by interaction with packaging materials. Examples include the permeation of phenolic preservatives into the rubber wads and teats of multi-dose injection or eye-drop containers and by their interaction with flexible nylon tubes for creams. Quaternary ammonium preservative levels in formulations have been significantly reduced by adsorption onto the surfaces of plastic and glass containers. Volatile preservatives such as chloroform are so readily lost by the routine opening and closing of containers that their usefulness is somewhat restricted to preservation of medicines in sealed, impervious containers during storage, with quite short use lives once opened. 

The a-mGI motif operates primarily through the induced dipole of the a helices directed toward DNA phosphates (Fig. 13a) and was termed the paired element motif (PEM) [17], although paired ends of helices is more descriptive. The guanido group is restrained from binding deeply into the mGI by a threonine from another histone. This steric hindrance preserves the avidity of the histone core for DNA, but prevents overly strong binding that would disrupt the plasticity of the histone-DNA interaction. 

The packaging material must not interact with the product either to adsorb substances from the product or to leach chemicals into the product. Plastics contain additives to enhance polymer performance. PVC may contain phthalate diester plasticizer, which can leach into infusion fluids from packaging. Antimicrobial preservatives such as phenylmercuric acetate are known to partition into rubbers and plastics during storage, thus reducing the formulation concentration below effective antimicrobial levels. 

McCarthy TJ. Interaction between aqueous preservative solutions and their plastic containers III. Pharm Weekbl 1972 107 1-7. 

Coagulational contacts are those developed between the interacting particles with the thermodynamically stable water interlayer preserved at the contact (Fig. la). In nature, coagulational contacts are met in water-saturated unconsolidated or weakly consolidated clay sediments, i.e., mud, weakly lithified clayey sediment, and swelled clay of plastic or fluid consistency. 

---