Plexiglass is an acrylic plastic that has many applications. It is strong, durable and resistant to breakage, weather and electricity. It is useful whenever you need a clear substance but the conditions are more than regular glass can handle. Plexiglass does have a few weaknesses, including chemicals, combustion and heat.
Dr. Leo Baekeland patented the first plastic in 1909. It was a phenol-formaldehyde plastic, which was able to be heated and then formed into shape while under pressure. Acrylic resins were first produced in 1931 for industrial uses and were introduced as sheet plastic, or early plexiglass, in 1936. It was first used as windows in war planes in World War II and is now commonly used in households.
There are several different types of plexiglass, including polycarbonate, Lexan, acrylic, copolyester and clear polyvinyl chloride, or PVC. Polycarbonate is the most basic type of plexiglass and is fairly rigid but the most susceptible to scratching and cracking. It is available with UV resistance. Lexan is a brand name plexiglass and is more flexible, is UV resistant and is less susceptible to scratching and cracking. Acrylic is similar to polycarbonate but is more flexible and is not available with UV resistance. Copolyester is more flexible and has a higher impact strength than acrylic, but is also not available with UV resistance. Clear PVC is rigid, but is more resistant to scratches and cracks than polycarbonate.
One weakness of plexiglass is the ability for certain chemicals to damage it. These chemicals include gasoline, certain solvents, organic acids and lacquer thinners. Plexiglass is not affected by gasoline quickly, but after seven days of exposure the plexiglass shows some effect. Solvents such as methylene chloride, benzene and turpentine cause immediate damage. Organic acids such as acetic acid at 50 percent concentration also cause immediate effects. Lacquer thinners also have immediate effects on the plexiglass.
Since plexiglass is a plastic and is composed of natural oil, it is combustible. Spontaneous combustion can occur between 850 and 869 degrees F and plexiglass will ignite with a flame between 550 and 570 degrees. While ignition will not happen at low temperatures, plexiglass burns vigorously and rapidly. Burning plexiglass does not produce toxic gases.
Plexiglass can withstand a wide range of temperature differences, but it does respond to prolonged exposure to heat. Sustained temperatures over 180 to 200 degrees F will cause the plexiglass to soften and lose its shape.