COSMETICS AND BATHROOM PRODUCTS:HAIRSPRAY.

HAIRSPRAY

The concept of a preparation to control the appearance of hair is quite an historical notion. Originally, the preparation was probably animal fat (or an emulsified version that led to the creation of hair cream), followed by the use of various gums and shellac lacquer by female populations. While the concept of an aerosol originated in eighteenth century France, scientists during World War II developed a small aerosol can pressurized by a liquefied gas (e.g., fluorocarbon). It was this design that made products such as hair spray possible, along with the work of an inventor in the 1950s that involved the creation of a crimp-on valve for dispensing gases under pressure, with the additional creation of the first clog-free valves for spray cans.

The ideal fixative allows the hair to flow naturally while remaining in style, resists high humidity while not being brittle, and is easy to comb. The fixative should also confer a good high gloss (e.g., in the “glassy” regime), not flake onto shoulders like dandruff when dry combed after application, and be readily removed upon washing.

Modern hairspray consists of a solution of long, chainlike molecules (called polymers) in a highly volatile solvent. Some brands may also con- tain oils such as resins and lanolin. In general, a volatile substance is one whose state is unstable at room temperature and may readily change from liquid to gas form. Thus, hairspray is in liquid form within the can, as air pressure has been removed. The can is frequently composed of compounds (e.g., aluminum monobloc or tri-layered steel) that allow for a decreased likeliness of puncturing. Spraying the product results in the deposit of a polymer layer around each hair after evaporation of the volatile solvent. The web of polymer molecules on the hairs yields a stiff texture and allows the hairs to resist changing shape.

A solvent once popularly used was a compound of carbon, fluorine, and chlorine (a chlorofluorocarbon [CFC]). In general, CFCs are considered nearly optimal aerosol propellants, having both nontoxic and nonflam- mable chemical characteristics. However, when it was discovered by scientists in the late twentieth century that their ubiquitous use and release into the atmosphere led to the destruction of the stratospheric ozone layer, they were eventually replaced with other solvents (e.g., alcohols and hy- drocarbons). Unfortunately, hydrocarbon propellants in combination with alcohol are extremely flammable, and consumers are warned to avoid heat, fire, and smoking during use until sprayed hair is fully dry. Thus, aerosol preparations are currently manufactured to decrease volatile organic com- pound content while also decreasing flammability performance.

In general, the characteristics of polymers change with temperature and chemical environment. PVP was one of the first hairspray polymer resins used, and it is also used to glue the layers of wood in plywood to- gether. Because PVP is water soluble, absorbing atmospheric moisture and becoming sticky, water-insoluble polymers (e.g., vinyl acetate or poly- dimethylsiloxane) may be added, which allows the spray to dry to a brittle film for a longer-lasting hold. Other types of polymers used in plastic- based hairsprays are copolymers with vinyl acetate and/or maleic anhydride. In addition, some “natural” hairsprays use water-soluble hair-stiffening herbal polymers such as gum arabic (found in the sap of Acacia senegal trees of Sudan), gum tragacanth (Astragalus gummifer), a gum also used to stiffen calico and crepe, or karaya gum (Sterculia urens).

Hair-holding and -stiffening resins are also available as mousses (foam or froth). As in hairsprays, the active ingredient is a resin such as PVP. In addition, silicone polymers may be added to provide a sheen or shiny texture to the hair.