The Acrylic plastic substance, Polymethyl methacrylate or PMMA is a transparent thermoplastic, which has been instrumental in the new age of plastic use since the early 20th century. It is often used as a lightweight and/or shatter resistant alternative to glass. Historically this substance has sometimes need referred to as acrylic glass, even though there is no technical relation to glass. It is chemically the synthetic polymer of methyl methacrylate. In 1928, PMMA was developed in several laboratories by numerous chemists such as William Chalmers, Otto Rohm and Walter Bauer. Rohm and Hass Company first bought it to the market in 1933, under the trademark Plexiglas. The material has also been sold under many other commonly used names, such as Acrylite, Lucite and Perspex. Polymethyl methacrylate is an economical alternative, when extreme strength is not needed with the use of Polycarbonate otherwise known as PC. PMMA additionally does not contain the potentially harmful bisphenol-A subunits found in polycarbonate. It is often preferred for its sufficient properties, easy handling, processing and low cost. Polymethyl methacrylate that has not been modified behaves in a brittle manner when scratched or overloaded, mainly under an impact force, but modified PMMA can achieve a high resistance under scratches and impacts.
The material polymethyl methacrylate, is strong and lightweight as it has a density of 1.17 ‘ 1.20 g/cm3 which is less than half that of glass. The impact strength of this material is also high than that of both glass and polystyrene, but is also significantly lower than that of polycarbonate and even some other engineering polymers. The ignition temperature of PMMA is 460??C, once burning it excretes carbon dioxide, water, carbon monoxide and low molecular-weight compounds, such as formaldehyde. PMMA filters ultraviolet light similar to ordinary window glass, at wavelengths below about 300nm. Manufacturers sometimes add additives and/or coatings to improve absorption in the range of 300-400nm. Coloured varieties of PMMA allow specific IR wavelengths to pass through whilst blocking visible light. PMMA swells and dissolves in many organic solvents, it also has a poor resistants to many other chemicals because of its easily hydrolysed ester groups. Nevertheless, it is often chosen for outdoor applications because of its superior environmental stability compared to most other plastics such as polystyrene and polyethylene.
It is rare that pure polymethyl methacrylate homopolymer is sold as an end product, as it is not optimized for most applications. Modified formulations are created using varying amounts of other additives, fillers and comonomers for uses where specific properties are required. For example PMMA grades used for heat processing, have small amounts of acrylate comonomers since this stabilizes the polymer to depolymerization during processing. To improve impact strength butyl acrylate can often be added. 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 filter or protect against UV light. Fillers may be added to improve cost-effectiveness.
The first acrylic acid was developed in 1843. From acrylic acid derived methacrylic acid, which was formulated in 1865. The reaction between methacrylic acid and methanol results in the ester methyl methacrylate. The German chemist Wilhelm Rudolph Fittig discovered in 1877, the polymerisation process that turns methyl methacrylate into polymethyl methacrylate. The brand ‘Plexiglas’ came about in 1933, and was patented and registered by another German chemist, Otto Rohm. In 1936 ICI Acrylics, which is now known as Lucite International, began the first commercially viable production of acrylic safety glass. During World War II both Allied and Axis forces used acrylic glass for submarine periscopes, windshields, canopies, and airplane gun turrets. Incidentally, airplane pilots whose eyes were damaged by flying shards of PMMA fared much better than those injured by standard glass, this demonstrated compatibility between human tissue and PMMA as compared to glass. PMMA has been sold under a variety of generic and brand names. It is most usually called acrylic glass, even though it is not chemically related to glass. Sometimes it is simply called acrylic, but acrylic can also refer to polymers or copolymers containing polyacrylonitrile. Other known trade names are Acrylite, Lucite, Plexiglas, Optix, Plaskolite, Perspex, Oroglas or Altuglas.
Polymethyl methacrylate is most commonly known and used as a substitute for transparent glass in both residential and commercial products. With automobiles it is used in the lenses of exterior lights, motorbike windscreens and train windows. Historically, the design of aircraft windows was significantly improved by the introduction of PMMA. This made possible the transparent nose compartment in the Boeing B-17 Flying Fortress. It was also integrated for security and police use, such as impact proof windows, sometimes also used in police vehicles for riot control. PMMA is also used for the redirection of daylight. Laser cut panels of acrylic used in tubular skylights, otherwise known as light pipes used to spread natural light into indoor spaces, developed by Veronica Garcia Hansen, Ken Yeang and Ian Edmonds. Because of PMMA’s compatibility with human tissue it is only natural that it is largely used in medical technologies and implants. In ophthalmologic use, it has replaced many lenses in vision correction and protection spectacles, as well as the manufacture of rigid intraocular lenses, which are implants in the eye when the original lens has been removed through the treatment of cataracts disease. The historical use of hard contact lenses, were most commonly made of this material, where as soft contact lenses are usually created of a related polymer, where acrylate monomers containing one or more hydroxyl groups make them hydrophilic. PMMA bone cement is used in orthopedic surgery, to attach implants and remodel lost bone. This cement acts more as a grout rather than a glue as in arthroplasty’s. Dentures are often made of PMMA, and because of its ability to manipulate its colour, it can be color-matched to the patient’s teeth and gum tissue. PMMA is also used in cosmetic surgeries, such as the permanent reduction of wrinkles and scars through the infection of a biological fluid that contains microspheres of PMMA.
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