Extruded acrylic (extruded PMMA): properties and description

Acrylic is a synthetic material made from acrylic resins with a small proportion of various additives that give it specific properties. In international literature it is referred to as PMMA (polymethyl methacrylate).

Acrylic has a density of 1.19 g/cm3, making it almost 2.5 times lighter than ordinary glass and 17% lighter than rigid PVC. Its impact strength is 5 times that of ordinary glass. The service temperature range of acrylic is from -40°C to +80°C.

Acrylic has good resistance to ageing. It transmits up to 92% of visible light, more than any other polymer. Its mechanical properties and light transmission remain virtually unchanged over time under UV radiation and weathering (so acrylic needs no additional UV protection). Coloured acrylic may change colour during prolonged outdoor use (this depends on the specific colour and manufacturer).

Acrylic is used in a wide range of fields:

• lighting (lamp shades, partitions, front panels, diffusers),

• outdoor advertising (face panels for light boxes and illuminated letters, thermoformed 3D products),

• retail equipment (stands, displays, price tags),

• sanitary ware (bathroom fittings),

• construction and architecture (glazing of openings, partitions, domes, dance floors, thermoformed 3D products),

• transport (aircraft and boat glazing, fairings),

• instrument making (dials, inspection windows, housings, dielectric parts, containers).
  

Acrylic sheet is produced in two ways: by extrusion and by casting. The production method itself imposes certain limitations and determines some of the properties of the plastic.

Extruded acrylic (extruded PMMA) differs from cast acrylic (cast PMMA) primarily in its molecular bonds, which are stronger in cast acrylic. This shows above all in its thermal and chemical properties, impact resistance and the way the material behaves during processing.

It should be noted that extrusion is a continuous process that requires large quantities of raw material and is only cost-effective for large batches. As a result, extruded acrylic is available in far fewer colours than cast acrylic. Compared with cast acrylic, extruded acrylic also has the following characteristics:

• a narrower range of sheet thicknesses (approx. 1–24 mm instead of a virtually

• unlimited range), determined by the capabilities of the extruder,

• longer sheets are possible,

• less thickness variation within a batch (thickness tolerance of 5% instead of 30%),

• poorer surface finish,

• lower impact resistance,

• lower chemical resistance,

• greater sensitivity to stress concentration,

• better bondability,

• a narrower and lower thermoforming temperature range (approx. 150–170°C instead of 150–190°C),

• less forming force required,

• greater shrinkage on heating (6% instead of 2%).
  
  

Acrylic is highly flammable, but when burning it is less hazardous than other combustible plastics, as it does not give off toxic gases. Its ignition temperature is 260°C.

Acrylic is an environmentally friendly material: it releases no toxic substances and is completely safe. It can be used outdoors and indoors, including in children's and medical facilities. Acrylic is fully recyclable.
Acrylic has good water resistance and good resistance to alkalis and aqueous solutions of inorganic salts. It is attacked by dilute hydrofluoric and hydrocyanic acids, as well as by concentrated sulphuric, nitric and chromic acids.

Solvents for acrylic include chlorinated hydrocarbons (dichloroethane, chloroform), aldehydes, ketones and esters. Acrylic is also attacked by alcohols: methyl, butyl, ethyl and propyl. Brief exposure to 10% ethyl alcohol has no effect on acrylic.