384 JOURNAL OF THE SOCIETY OF COSMETIC CHEMISTS POLYVINYL CHLORIDE AS A PACKAGING MATERIAL K. G. JOHNSON, B.Sc., Ph.D., A.R.I.C.* Following a briet review of the various sheet plastic materials used for packaging, the author describes the composition and physical properties ot polyvinyl chloride sheets in detail. Particular attention is given to the effect oi the product on the sheet and oi interaction between them. THE PRACTICE of packing cosmetic preparations in containers fabricated from plastic sheet is becoming increasingly popular. The container generally consists of either two sheets of plastic welded together all round or a piece of plastic tubing welded at each end. The plastic .sachet so formed may be a variety of shapes---square, triangular or imitation bottle shape are all commonly used. The quantity of the preparation packed is sufficient for one application, so that after use the packing material is discarded. There are several types of cosmetic preparations which are suitable for packing in this form, including powders, liquids and creams. The choice of polymers is also quite wide, but many of the plastics available in sheet form have only a limited usage in the cosmetic field. Regenerated cellulose sheets are affected considerably by moisture or humidity changes and tend to become dimensionally unstable. They are normally only used in laminated sheets. Cellulose acetate sheets are dimensionally more stable than regenerated cellulose, but the moisture resistance is poor and sealing presents problems. Rubber hydrochloride is quite resistant to moisture and gives welds of great strength, but it ages rapidly, especially in sunlight, becoming brittle and losing hydrochloric acid. Polystyrene sheets are too brittle for general use. Polyvinylidene chloride possesses extremely high resistance to water and gases and is very resistant to attack by most chemicals and solvents. The sheets are quite resistant to humidity changes. They are, however, somewhat rigid and present difficulties in welding and printing operations. Straight polyvinylidene chloride is not produced commercially on a large scale, usually being in the form of a co-polymer with polyvinyl chloride. 'This co-polymer is more flexible than the straight polyvinylidene chloride and has a water resistance between those of polyvinylidene chloride and polyvinyl chloride. The main disadvantages are poor printing properties-- usually a soft co-polymer coating is necessary to facilitate the adhesion of printing inks--and high cost due to the high specific gravity (1.85) and the * County Laboratories, Ltd., Stanmore, Middlesex.