Acrylic, Perspex, Plexiglas, they’re all the same, well sort of. Acrylic is the simple name for Polymethylmethacrylate (PMMA). Perspex and Plexiglas on the other hand are brand names.
Discovered in 1865, but not sold commercially until 1933, the process for making acrylic has changed little. Lighter than glass, but with a higher optical quality it was a favoured for use in aircraft and submarines in WW2. This incredible material has since been used for point of sale displays, visors, fibre optic cables, bulletproof panels, and even corneal replacement!
Acrylic is fascinating. It’s an amorphous polymer (long strands mixed together); you can usually tell amorphous material by optical clarity, other examples include PET and Polycarbonate (PC). There are two main processes to make acrylic sheet (Cast and Extrusion), but how it’s made changes the mechanical properties of the material. Here’s why:
Imagine you have two bowls of spaghetti. One is all mixed up nice in a bowl with the Bolognese sauce, it's imperfect. You aren’t going to trace one piece end-to-end without getting in there with your fork. That’s cast acrylic.
Now imagine another bowl, it arrives on your table served on a six-foot plate, stretched across and the strands have been pulled in one direction. You can see where one piece starts and ends. This is extruded acrylic.
To make things easier we’ve created a table to help inform design decisions.
Take a look at our range of cast acrylic material.
Now available in 1000x500mm and 1000x600mm sheet sizes, perfect for maximising your bed space on your laser cutter.
OK so you know the history, and what material works best for your project. The big question, how do they make it?
It starts with petroleum (to produce 1kg of acrylic, you need 2kg of petrolium). The by-product of the refinement process creates what we need to produce acrylic.
Acetone (used in nail polish remover) is reacted with sodium cyanide (used to extract gold from ore). This produces acetone cyanhydrin, which is reacted with methyl alcohol (the same stuff the ancient Egyptians used while embalming!). This creates methyl methacrylate, a monomer. When more than one monomer chain is connected together (using a catalyst) this creates a polymer. And so we have Polymethylmethacrylate or Acrylic.
It’s pretty simple really; a mould is created with two sheets of glass separated by a window spacer. This forms a cavity. During the polymerisation process shrinkage occurs, so the glass plates must be free to move.
A pre-measured volume of methyl methacrylate and the catalyst is added.
The moulds are moved to an oven or autoclave for polymerisation, this runs on a pre-programmed temperature cycle to prevent bubbles forming. Once out of the mould, sheets are annealed to remove residual stress (like warping), they do this by running an additional heat cycle at around 140°C.
Browse our cast acrylic sheet range...
Extrusion is an industrial process where material is forced through a die (which has a pre-defined shape), and at the other end comes out as sheet.
Here’s how it works:
Material is loaded into a hopper, and below it a feeder allows a quantity of material to drop onto a barrel and screw below. The screw uses sheer force (like the force exerted when cutting paper with scissors) to mix the methyl methacrylate and the catalyst. The screw pushes the material to the die form.
As the material is shaped it is pulled through a three-roll stack which handles the acrylic as it cools, it also measures thickness to ensure tolerances are met. The sheet is covered with a protective layer and then cut to size. The conditions are set to prevent residual stress, and so exhibit low shrinkage.
