Acrylic is a polymer of methyl methacrylate, hence the abbreviation PMMA. Acrylic is thermoplastic, meaning it is a type of plastic that becomes malleable when heated and solidifies into a rigid material when cooled. Acrylic can be processed in various ways, as it can be injection molded, thermoformed, and cast, based on the MMA monomer.
Acrylic as an Alternative to Glass
Acrylic (PMMA plastic) is often used as a substitute for glass because it is a plastic type that is as clear as glass but much lighter and has significantly higher impact strength. This is advantageous in many cases. However, acrylic is much less resistant to scratches. In some cases, it may not be advantageous to use acrylic instead of glass, such as for car windshields, as acrylic is more prone to scratching from windshield wipers, ice scrapers, and similar items.
Cast Acrylic and Extruded Acrylic
Acrylic is generally produced in two standard forms – cast acrylic and extruded acrylic.
Cast acrylic is formed by placing acrylic components in molds, where a chemical process takes place. This process creates a homogeneous material with consistent properties in all directions. An example of a material based on cast acrylic could be acrylic sheets formed between two glass plates.
Extruded acrylic is formed through a chemical process where the components (acrylic mass) are continuously pressed through a mold. The continuous pressing creates a heterogeneous material, with properties varying depending on the direction.
Both types of acrylic have their advantages and disadvantages. For instance, when bending acrylic sheets, there is a difference in how an extruded acrylic sheet bends depending on the direction, whereas this does not affect a cast acrylic sheet. However, cast acrylic sheets exhibit more thickness variations than extruded acrylic sheets. Cast acrylic thickness variations are around 15% for a 3 mm sheet, while variations for an extruded sheet are around 5%.
Challenges in the Use of Acrylic
It is important to note that acrylic is not resistant to strong acids and bases, as well as polar solvents, and should not come into contact with these.
It is also crucial to be aware of acrylic’s sensitivity to changing temperatures. For example, acrylic expands five times as much as metal when heated. Due to this high sensitivity to heat, caution must be exercised in placing acrylic in contact with other materials, as there is a risk of acrylic cracking if the surrounding materials do not expand to the same extent as acrylic. Despite this, acrylic is often used in measuring instruments because its dimensions do not change significantly unless exposed to the mentioned conditions.
