Acrylic Glass - Properties
- PMMA has a density of 1,150–1,190 kg/m3. This is less than half the density of glass, and similar to that of other plastics.
- PMMA has a good impact strength higher than that of glass or polystyrene, but significantly lower than that of polycarbonate or engineering polymers. In the majority of applications, it will not shatter but instead breaks into large dull pieces.
- PMMA is softer and more easily scratched than glass. Scratch-resistant coatings (which may also have other functions) are often added to PMMA sheets.
- PMMA transmits up to 98% of visible light (per metre), and gives a ~4% reflection from each of its surfaces on account of its refractive index of 1.4893 to 1.4899.
- PMMA filters ultraviolet (UV) light at wavelengths below ~300 nm. Some manufacturers add coatings or additives to PMMA to improve absorption in the 300–400 nm range.
- PMMA allows infrared light of up to 2800 nm wavelength to pass. IR of longer wavelengths, up to 25,000 nm, are essentially blocked. Special formulations of colored PMMA exist to allow specific IR wavelengths to pass while blocking visible light (for remote control or heat sensor applications, for example).
- PMMA has excellent environmental stability compared to other plastics such as polycarbonate, and is therefore often the material of choice for outdoors applications.
- PMMA has poor resistance to solvents, as it swells and dissolves easily. It also has poor resistance to many other chemicals on account of its easily hydrolyzed ester groups.
Modification of properties
Pure poly(methyl methacrylate) homopolymer is rarely sold as an end product, since it is not optimized for most applications. Rather, modified formulations with varying amounts of other comonomers, additives, and fillers are created for uses where specific properties are required. For example,
- A small amount of acrylate comonomers are routinely used in PMMA grades destined for heat-processing, since this stabilizes the polymer to depolymerization ("unzipping") during processing.
- Comonomers such as butyl acrylate are often added to improve impact strength.
- Comonomers such as methacrylic acid can be added to increase the glass transition temperature of the polymer for higher temperature use such as in lighting applications.
- Plasticizers may be added to improve processing properties, lower the glass transition temperature, or improve impact properties.
- Dyes may be added to give color for decorative applications, or to protect against (or filter) UV light.
- Fillers may be added to improve cost-effectivness.