How To Make Acrylic Sheets
Acrylic Plastic
Groundwork
Acrylic plastic refers to a family of constructed, or homo-made, plastic materials containing one or more than derivatives of acrylic acid. The almost common acrylic plastic is polymethyl methacrylate (PMMA), which is sold under the brand names of Plexiglas, Lucite, Perspex, and Crystallite. PMMA is a tough, highly transparent material with first-class resistance to ultraviolet radiation and weathering. It can be colored, molded, cut, drilled, and formed. These properties make it platonic for many applications including aeroplane windshields, skylights, motorcar taillights, and outdoor signs. One notable awarding is the ceiling of the Houston Astrodome which is composed of hundreds of double-insulating panels of PMMA acrylic plastic.
Like all plastics, acrylic plastics are polymers. The discussion polymer comes from the Greek words poly, meaning many, and meros, significant a part. A polymer, therefore, is a material fabricated up of many molecules, or parts, linked together like a chain. Polymers may accept hundreds, or even thousands, of molecules linked together. More than importantly, a polymer is a material that has backdrop entirely dissimilar than its component parts. The procedure of making a polymer, known as polymerization, has been likened to shoveling chip glass, copper, and other materials into a box, shaking the box, and coming back in an hour to discover a working color idiot box set. The drinking glass, copper, and other component parts are nonetheless in that location, but they have been reassembled into something that looks and functions entirely differently.
The first plastic polymer, celluloid, a combination of cellulose nitrate and camphor, was developed in 1869. It was based on the natural polymer cellulose, which is present in plants. Celluloid was used to make many items including photographic film, combs, and men's shirt collars.
In 1909, Leo Baekeland developed the outset commercially successful synthetic plastic polymer when he patented phenol formalde-hyde resin, which he named Bakelite. Bakelite was an immediate success. Information technology could be machined and molded. It was an excellent electrical insulator and was resistant to rut, acids, and weather. It could too be colored and dyed for apply in decorative objects. Bakelite plastic was used in radio, telephone, and electrical equipment, every bit well as counter tops, buttons, and knife handles.
Acrylic acid was first prepared in 1843. Methacrylic acrid, which is a derivative of acrylic acid, was formulated in 1865. When methacrylic acid is reacted with methyl booze, it results in an ester known equally methyl methacrylate. The polymerization process to plough methyl methacrylate into polymethyl methacrylate was discovered by the German chemists Fittig and Paul in 1877, but information technology wasn't until 1936 that the process was used to produce sheets of acrylic safety glass commercially. During World War II, acrylic drinking glass was used for periscope ports on submarines and for windshields, canopies, and gun turrets on airplanes.
Raw Materials
Methyl methacrylate is the basic molecule, or monomer, from which polymethyl methacrylate and many other acrylic plastic polymers are formed. The chemical notation for this material is CH 2 =C(CH iii )
Figure one shows the polymerization of methyl methocrylate into polymethyl methacrylate (PMMA). Figure 2 shows other acrylic plastic monomers that may exist copolymerized with methyl methacrylate.
COOCH 3 . Information technology is written in this format, rather than the more than mutual chemical notation C 5 H 8 O 2 , to prove the double bail (=) betwixt the two carbon atoms in the middle. During polymerization, one leg of this double bond breaks and links upwards with the eye carbon atom of another methyl methacrylate molecule to start a chain. This process repeats itself until the concluding polymer is formed. (See Figure 1)
Methyl methacrylate may be formed in several means. One common way is to react acetone [CH three COCH 3 ] with sodium cyanide [NaCN] to produce acetone cyanhydrin [(CH 3 ) two C(OH)CN]. This in turn is reacted with methyl booze [CH 3 OH] to produce methyl methacrylate.
Other like monomers such as methyl acrylate [CH 2 =CHCOOCH,] and acrylonitrile [CH 2 =CHCN] can be joined with methyl methacrylate to form different acrylic plastics. (See Figure 2) When two or more monomers are joined together, the result is known as a copolymer. Only as with methyl methacrylate, both of these monomers take a double bail on the middle carbon atoms that splits during polymerization to link with the carbon atoms of other molecules. Controlling the proportion of these other monomers produces changes in elasticity and other properties in the resulting plastic.
The Manufacturing
Process
Acrylic plastic polymers are formed past reacting a monomer, such every bit methyl methacrylate, with a catalyst. A typical catalyst would be an organic peroxide. The goad starts the reaction and enters into it to go on it going, but does not become office of the resulting polymer.
Acrylic plastics are bachelor in three forms: apartment sheets, elongated shapes (rods and tubes), and molding pulverization. Molding powders are sometimes fabricated past a process known as suspension polymerization in which the reaction takes place between tiny droplets of the monomer suspended in a solution of water and catalyst. This results in grains of polymer with tightly controlled molecular weight suitable for molding or extrusion.
Acrylic plastic sheets are formed by a procedure known as majority polymerization. In this procedure, the monomer and catalyst are poured into a mold where the reaction takes place. Two methods of bulk polymerization may exist used: batch cell or continuous. Batch cell is the most common because it is elementary and is easily adjusted for making acrylic sheets in thicknesses from 0.06 to 6.0 inches (0.16-xv cm) and widths from 3 feet (0.9 grand) up to several hundred feet. The batch cell method may also be used to course rods and tubes. The continuous method is quicker and involves less labor. It is used to make sheets of thinner thicknesses and smaller widths than those produced by the batch cell method.
We will describe both the batch prison cell and continuous bulk polymerization processes typically used to produce transparent polymethyl methacrylic (PMMA) sheets.
Batch cell majority polymerization is the almost common way to make acrylic plasfic sheets because information technology is unproblematic and hands adapted for making sheets in thicknesses from 0.06 to half dozen inches.
Batch cell bulk polymerization
- The mold for producing sheets is assembled from ii plates of polished glass separated by a flexible "window-frame" spacer. The spacer sits forth the outer perimeter of the surface of the glass plates and forms a sealed crenel between the plates. The fact that the spacer is flexible allows the mold cavity to shrink during the polymerization procedure to recoup for the volume contraction of the material equally the reaction goes from individual molecules to linked polymers. In some production applications, polished metal plates are used instead of glass. Several plates may be stacked on height of each other with the upper surface of one plate becoming the lesser surface of the adjacent higher mold crenel. The plates and spacers are clamped together with spring clamps.
- An open up comer of each mold cavity is filled with a pre-measured liquid syrup of methyl methacrylate monomer and catalyst. In some cases, a methyl methacrylate prepolymer is also added. A prepolymer is a material with partially formed polymer chains used to further help the polymerization process. The liquid syrup flows throughout the mold cavity to fill information technology.
- The mold is and then sealed and heat may exist practical to help the catalyst start the reaction.
- Every bit the reaction proceeds, it may generate significant heat past itself. This estrus is fanned off in air ovens or by placing the molds in a h2o bathroom. A programmed temperature cycle is followed to ensure proper cure time without boosted vaporization of the monomer solution. This too prevents bubbles from forming. Thinner sheets may cure in 10 to 12 hours, but thicker sheets may require several days.
- When the plastic is cured, the molds are cooled and opened. The drinking glass or metal plates are cleaned and reassembled for the side by side batch.
- The plastic sheets are either used as is or are annealed by heating them to 284-302°F (140-150°C) for several hours to reduce any residual stresses in the material that might cause warping or other dimensional instabilities.
- Any excess material, or flash, is trimmed off the edges, and masking paper or plastic moving-picture show is practical to the surface of the finished sheets for protection during handling and shipping. The newspaper or motion picture is often marked with the fabric'south brand name, size, and treatment instructions. Conformance with applicative condom or building code standards is also noted.
Continuous bulk polymerization
- The continuous process is similar to the batch cell procedure, simply because the sheets are thinner and smaller, the process times are much shorter. The syrup of monomer and catalyst is introduced at 1 cease of a prepare of horizontal stainless steel belts running parallel, one above the other. The distance between the belts determines the thickness of the sail to exist formed.
- The belts agree the reacting monomer and catalyst syrup between them and motion information technology through a series of heating and cooling zones according to a programmed temperature cycle to cure the material.
- Electric heaters or hot air may and so amalgamate the textile every bit it comes out of the end of the belts.
- The sheets are cutting to size and masking newspaper or plastic film is applied.
Quality Control
The storage, handling, and processing of the chemicals that brand acrylic plastics are done nether controlled ecology weather to prevent contamination of the material or dangerous chemical reactions. The control of temperature is specially disquisitional to the polymerization process. Even the initial temperatures of the monomer and goad are controlled before they are introduced into the mold. During the entire process, the temperature of the reacting material is monitored and controlled to ensure the heating and cooling cycles are the proper temperature and duration.
Samples of finished acrylic materials are too given periodic laboratory assay to confirm physical, optical, and chemical properties.
Toxic Materials, Safety
Considerations, and
Recycling
Acrylic plastics manufacturing involves highly toxic substances which require careful storage, handling, and disposal. The polymerization process tin can result in an explosion if non monitored properly. It also produces toxic fumes. Recent legislation requires that the polymerization process be carried out in a closed surroundings and that the fumes exist cleaned, captured, or otherwise neutralized earlier discharge to the atmosphere.
Acrylic plastic is not easily recycled. It is considered a grouping vii plastic among recycled plastics and is not collected for recycling in most communities. Big pieces can be reformed into other useful objects if they have not suffered besides much stress, crazing, or cracking, simply this accounts for merely a very small portion of the acrylic plastic waste. In a landfill, acrylic plastics, like many other plastics, are non readily biodegradable. Some acrylic plastics are highly flammable and must exist protected from sources of combustion.
The Future
The average almanac increase in the rate of consumption of acrylic plastics has been most 10%. A future annual growth charge per unit of about 5% is predicted. Despite the fact that acrylic plastics are one of the oldest plastic materials in utilize today, they still hold the same advantages of optical clarity and resistance to the outdoor environs that brand them the textile of choice for many applications.
Where To Learn More
Books
Baird, Ronald J. and David T. Baird. Industrial Plastics. The Goodheart-Willcox Company, 1986.
Cowie, J.K.1000. Polymers: Chemistry and Physics of Mod Materials. Chapman and Hall, 1991.
Encyclopedia of Polymer Science and Applied science, Volume ane. John Wiley & Sons, 1985.
Rosato, Dominick Five. Plastic Encyclopedia and Dictionary. Hanser Publications, 1993.
Seymour, Raymond B. Engineering Polymer Sourcebook. McGraw-Colina, 1990.
Smith, Edward H., ed. Mechanical Engineer's Reference Book. Social club of Automotive Engineers, 1994.
— Evelyn S. Dorman /
Chris Cavette
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