COMMON MATERIALS AND OF fiCE SUPPLY PRODUCTS:RUBBER CEMENT AND SPRAY PAINT.

RUBBER CEMENT

Rubber cement is commonly used as an adhesive that serves to bond two objects together with a degree of flexibility. In the early 1800s, a viscous mixture of natural rubber dispersed in benzene or gasoline was used to cement seams of garments to ensure that they would be watertight. This mixture was later used to completely waterproof wool and cotton garments. The ability of rubber cement to form a durable and flexible bond is the main reason it is chosen as an office adhesive product. Little has changed in the formulation of rubber cement from the 1800s. Because of the flammability and toxicity of benzene and gasoline, these solvents are no longer found in modern rubber cement formulations. Today, rubber cement is a mixture of natural or synthetic rubber dispersed in isopropyl alcohol and heptane. These solvents, although safer, should not be considered innocuous. Isopropanol may cause reproductive disorders, and heptane is extremely flammable. For these reasons, rubber cement should be used in a ventilated area and away from open flames. Inhalation may cause irritation to the nose, throat, and lungs. Ingestion is equally hazardous, causing burns to the esophagus and gastrointestinal tract.

SPRAY PAINT

The idea of delivering a controlled spray of liquid was developed in the early 1930s by Eric Rotheim. This delivery system is used for a number of applications in industry and in homes. The design of the spray can is very simple. The metal can contains a propellant, paint, and a nozzle for delivering the spray. You may have noticed that the bottom of a spray can has a concave shape. This is done to strengthen the can and allow pressure within the can to be distributed to the walls of the can. The propellant is a fluid or gas stored under pressure and expels the paint out of the can. The propellant is generally a substance that is a gas at room temper- ature and pressure. Under pressure, the propellant is liquefied and will remain liquid even though it is well above its boiling point. The other liquid, in this case liquid paint, is also stored in the sealed metal can. In the metal can container, a long plastic tube runs from the valve at the top of the can all the way to the bottom of the can. The curved shape of the bottom of the can ensures that no paint is wasted in the bottom of the can. The nozzle has a very fine opening that serves to break the liquid paint into small droplets, ensuring controlled coverage of the paint. When the valve on the nozzle is opened, the pressure within the can is reduced, allowing the liquefied propellant to form a gaseous layer at the top of the can. The pressure exerted by this gas layer forces the paint at the bottom of the can to travel up the plastic tube connected to the nozzle, where it is released as a fine spray. You may have noticed that spray cans instruct you to shake the can for several minutes before painting. A small plastic or metal ball inside the can mixes up the propellant and paint to ensure a uniform consistency of paint as it is expelled from the nozzle. Until the 1980s, most manufacturers used chlorofluorocarbons (CFCs) as propellants in spray cans. It has been concluded that the use of CFCs is harmful to the ozone layer, and CFC-based propellants were phased out. Today, the most popular alternative propellant is liquefied petroleum gas, which does not harm the ozone layer but must be used with care because of its extreme flammability.