What is Acrylic (PMMA), and What is it Used For?
Acrylic is a transparent thermoplastic homopolymer known more commonly by the trade name “plexiglass.” The material is similar to polycarbonate in that it is suitable for use as an impact-resistant alternative to glass (particularly when the high impact strength of PC is not required). It was first produced in 1928 and was brought to market five years later by Rohm and Haas Company. It is generally considered one of the clearest plastics on the market. Some of the first applications were in WWII when it was used for submarine periscopes as well as airplane windows, turrets, and canopies. Airmen whose eyes were injured due to shards of broken acrylic fared much better than those affected by shards of shattered glass.
Acrylic in the modern era and in general is used for a variety of applications that typically take advantage of its natural transparency and the impact resistance of certain variants. Common uses include lenses, acrylic nails, paint, security barriers, medical devices, LCD screens, and furniture. Because of its clarity, it is also often used for windows, tanks, and enclosures around exhibits.
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From Left to Right (Top to Bottom): Acrylic paint by Reeves, Acrylic Lens by Creative Mechanisms, Acrylic Nails, Acrylic Chairs by HStudio
We recently created a magnifying glass by machining a solid piece of square acrylic stock into a lens and 3D printing the handle. You can read about the project more here.
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Light Being Redirected by an Acrylic Lens
Although they are made commercially available in a variety of colors (perhaps translucent and perhaps not), the raw material allows for the internal transmission of light nearly in the same capacity as glass which makes it a wonderful substitute. This is very much the same as Polycarbonate. A few of the key differences include the fact that Acrylic doesn’t contain the potentially harmful substance bisphenol-A (BPA) and Polycarbonate tends to have higher impact strength (see chart below). For a full comparison of Polycarbonate and Acrylic (PMMA) read here.
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Image From ptsllc.com
Acrylic is readily available and inexpensive. It is a good alternative to Polycarbonate when material strength is not a decision factor. Acrylic is sometimes laminated on top of Polycarbonate (PC) in order get the scratch resistance of Acrylic and the impact strength of PC. Some bullet resistant “glass” is made this way. The PC stops the bullet, the Acrylic on the outside is there for scratch resistance during everyday use.
What are the Characteristics of Acrylic (PMMA)?
Now that we know what it is used for, let’s examine some of the key properties of Acrylic. PMMA is classified as a “thermoplastic” (as opposed to “thermoset”), and the name has to do with the way the plastic responds to heat. Thermoplastic materials become liquid at their melting point (160 degrees Celsius in the case of Acrylic). A major useful attribute about thermoplastics is that they can be heated to their melting point, cooled, and reheated again without significant degradation. Instead of burning, thermoplastics like Acrylic liquefy, which allows them to be easily injection molded and then subsequently recycled.
By contrast, thermoset plastics can only be heated once (typically during the injection molding process). The first heating causes thermoset materials to set (similar to a 2-part epoxy) resulting in a chemical change that cannot be reversed. If you tried to heat a thermoset plastic to a high temperature a second time it would simply burn. This characteristic makes thermoset materials poor candidates for recycling.