Bookbinding and the Conservation of Books
A Dictionary of Descriptive Terminology

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polyvinyl chloride

An ethenoid polymer produced as a fine white powder by both emulsion polymerization and suspension polymerization of the gas, vinyl chloride, when liquified under nitrogen pressure. The terms "PVC " and "vinyl" are commonly used with reference not only to the polymer, but to all materials of which polyvinyl chloride is a constituent. PVC compositions are prepared by hot mixing the polymer with plasticizers and small proportions of stabilizers, stearate lubricants, and coloring materials to give materials of a wide range of hardness, from rigid (with little or no plasticizer) to very soft (equal proportions of plasticizers and polymer), and in a wide range of colors, as well as crystal clear. Unplasticized flexible PVC foils are normally produced from vinyl chloride-acetate copolymers by calendering and stretching. The product is usually flexible, relatively nonflammable, hard wearing, and resistant to water and corrosion.

PVC film can be heat sealed, either by high frequency vibration (see: PLASTIC WELDING ), or by means of a press equipped with a special barrier to prevent the film from adhering to the heated jaws. Another method of sealing is to sew the sheets together, which is possible because of the remarkably high tear strength of the material when properly plasticized.

PVC film has an attractive matte surface; however, in the more hardwearing grades it is slightly opaque. The grades used for the protection of archival materials are readily available in a wide range of thicknesses and widths.

As with other highly chlorinated materials, the use of PVC should be very carefully considered in view of the possibility of the formation of hydrochloric acid. (81 , 198 , 235 )




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