Acrylic (Perspex / PMMA)

Acrylic is the trade name for poly(methyl methacrylate), or PMMA, a clear thermoplastic developed in the 1930s by chemists at Rohm and Haas in Germany and ICI in the United Kingdom. ICI marketed it as Perspex, Rohm and Haas as Plexiglas, and DuPont as Lucite. All three are the same base polymer, just sold under different brand names. Today most of the acrylic sold in Australia is supplied as Perspex, Plexiglas or generic cast and extruded sheet from manufacturers in Asia and Europe.

Chemically, acrylic is a long chain polymer built from methyl methacrylate monomers. The way those chains are formed determines whether the finished sheet is cast or extruded. Cast acrylic is made by pouring liquid monomer between two sheets of glass and curing it slowly, producing a sheet with very high molecular weight, excellent optical clarity and ideal properties for laser cutting and engraving. Extruded acrylic is forced through a die and is cheaper, has tighter thickness tolerances and bonds better with solvent cement, but its edge quality after laser cutting is not quite as good. For most signage and display work, cast is the default. For thermoforming and large area glazing, extruded often wins on price.

The headline property is optical clarity. A 3 mm sheet of clear cast acrylic transmits up to 92 percent of visible light, which is higher than most types of glass. It also holds that clarity for decades outdoors. UV stabilised grades are standard and will not yellow noticeably in normal use, which is why acrylic dominates illuminated signage. The other property fabricators love is how it behaves under heat. Heated to around 160 C, acrylic becomes pliable and can be bent over a strip heater or formed into curves and domes. Let it cool and the shape is locked in. This makes it ideal for everything from museum vitrines to point of sale display covers.

Where acrylic falls short is impact resistance and temperature. It is roughly six times more impact resistant than glass, which is meaningful, but it is also relatively brittle compared to other engineering plastics. A panel that takes a hard knock from a corner can crack or chip. The continuous service temperature sits around 80 to 90 C, so acrylic should not be used anywhere it might sit against a heat source or in a hot enclosure. Solvents are another consideration. Acetone, methylated spirits, ammonia based cleaners and many automotive chemicals will craze the surface, leaving a network of fine cracks that ruin the finish. For cleaning, warm soapy water and a soft microfibre cloth is the right answer.

Acrylic is generally the most affordable of the optically clear engineering plastics, sitting well below polycarbonate on a price per square metre basis. Standard clear sheet in 3 mm is usually the cheapest, with prices rising as thickness increases or when speciality finishes such as mirror, opal diffuser, frost or fluorescent colours are specified. Coloured cast acrylic typically costs around 30 to 60 percent more than clear, and large format sheets above 2440 x 1220 mm carry a premium.

Environmentally, acrylic is a thermoplastic and is technically recyclable. In practice, recycling streams in Australia are limited, although offcuts from fabrication shops are increasingly diverted to specialist recyclers who depolymerise PMMA back to methyl methacrylate monomer. Acrylic is not biodegradable, so designing parts for reuse and longevity is the best environmental strategy. Where acrylic is doing a job for decades on a building facade or in a public display, it is generally a much better choice than a short life material that ends up in landfill faster.

When you would not use acrylic: anywhere with high impact risk such as machine guarding or sports glazing, where polycarbonate is a much better choice. Anywhere that gets seriously hot, where polycarbonate, PETG or even glass make more sense. And anywhere chemicals are part of daily life, such as in laboratories or workshops with solvent based cleaners, where PETG or polypropylene will outlast acrylic by a wide margin.