Artificial snow and Acrylics
Around this time of year we see a lot of artificial snow. A favourite trick of the special effects experts is to exploit an unusual acrylic polymer. Sodium polyacrylate, a powder which swells with water to produce convincing looking ‘snow’.
Polyacrylates are cousins of the most important member of the acrylic polymer family, poly(methyl methacrylate) (PMMA). Better known by its trade names of ‘Perspex’, ‘Plexiglas’, ‘Oroglas’ and ‘Lucite’, PMMA has been around since 1933. It is still one of the best thermoplastics for optical properties and weathering resistance.
This is available in sheets or rods. It is easily machined and polished to produce components with a high quality finish. Examples include lenses and displays. Cast acrylic sheet, used as glass replacement in safety equipment and transport, is also suitable for thermoforming, from simple line bending for signs to large vacuum formings such as baths.
Unfortunately the melt viscosity of cast acrylic is too high for extrusion and injection moulding but moulding grades are available, with shorter chains and flow additives, giving a lower melt viscosity and suitable for complex optical mouldings such as back-lit displays in automotive fascia, using the wave guide principle, arising from the high refractive index of PMMA. However it must be remembered that the lower MW moulding grades have a lower impact resistance than cast acrylic, which some car drivers discovered when PMMA was first used in rear light clusters.