Acrylic glass – acrylic glass description
AdvantagesThe advantages of polymethyl methacrylate are as follows:
- high hardness, stiffness and strength
- homopolymers are brittle, copolymers are tough
- high surface quality:high gloss, scratch resistance, polishability
- excellent optical properties, especially high transparency - copolymers are slightly yellowish
- high heat resistance
- good electrical and dielectric properties
- resistance to weak acids and alkalis, non-polar solvents, fats, oils and water
- high resistance weathering
- can be well processed and subsequently mechanically processed
- propensity to crack on impact
CopolymersPolymethyl methacrylate is a brittle material. By mixing or graft polymerization with polybutadiene or other elastomers, this property can be suppressed and tough materials can be produced.Unfortunately, this loses good optical properties and such PMMA becomes milky cloudy.
Adding acrylonitrile to PMMA by copolymerization will increase solvent resistance. In particular, if the acrylonitrile content exceeds 50%, toughness is improved. Clear Plexiglas products have a yellowish colour due to the formation of cyclic structures.
ManufacturePlexiglas is produced by block polymerization of methyl methacrylate (cast plexiglass) or by extrusion of methyl methacrylate (extruded plexiglass). Both methods lead to clear materials. Block polymerization is mainly used for the production of blocks and plates, or semi-finished products of other shapes. If we use rotational moulds, we can also produce tubes. High polymerisation rates are achieved by block polymerisation. This improves the mechanical properties of the plates and especially the surface quality. Extruded Plexiglas plates have a better thickness tolerance than cast Plexiglas plates and are less costly.
PerformancePolymethyl methacrylate is supplied as a granulate for further thermoplastic processing. In its natural state it is clear, copolymers and modified types are cloudy. It can be coloured to beautiful transparent shades or opaque colours. Semi-finished products are mainly supplied as slabs or blocks, but tubes, bars or various profiles are also available.
Modulus of elasticityPMMA material stands out above all for its high stiffness. Its tensile modulus is between 2300 and 3300 MPa. PMMA loses its stiffness with increasing temperature, similar to other thermoplastics. This means that the modulus of elasticity decreases with increasing temperature. It appears that the decrease in stiffness with increasing temperature is slower the higher the molar mass.
Other mechanical propertiesAs temperature increases, the strength of PMMA decreases similarly to other thermoplastics. The impact and notch toughness is not great compared to other thermoplastics. Similar to polystyrene, it is virtually independent of temperature, meaning that PMMA retains its brittle character even at higher temperatures. The behaviour of PMMA under dynamic fatigue can be seen from the Wöhler curve of flexural strength versus number of cycles.
Fusion propertiesThe glass transition temperature of PMMA is 106 °C, up to 115 °C for cast blanks. The softening temperature according to Vicat B varies from 84 to 111 °C depending on the value of the mean molar mass. It follows that PMMA is one of the thermoplastics with good temperature resistance.products can be used for long periods of time at temperatures up to 70 °C.
Optical propertiesPMMA excels in its optical properties. It is colorless, clear and hardly absorbs visible light. Its light transmittance is 92% and its refractive index is 1.491. It has the highest light transmission of all plastics. Permeability can be maintained even when PMMA is colored with transparent dyes. The surface gloss is also excellent. PMMA sheets absorb ultraviolet light. A plate with a thickness of 2 mm is enough to absorb all the UV radiation. Due to their optical properties similar to those of glass, acrylics are also called organic or acrylic glasses. This is also where the oldest trade name for hard and transparent plates and blocks produced from methyl esters of methacrylic acid by Röhm and Haas in Darmstadt, which has spread throughout the world, comes from 1933.
Electrical propertiesPMMA is a good electrical insulator at low frequencies. At high frequencies, its insulating capabilities are below those of polyethylene and polystyrene. Both the loss factor and the surface resistance do not change during normal use. Therefore, PMMA is advantageously used for the production of parts in the electrical industry. On the other hand, a surface charge is created on the surfaces of parts made of PMMA, so it is often necessary to use antistatic additives.
Chemical resistancePMMA resists weak acids and alkalis, salt solutions, aliphatic hydrocarbons, non-polar solvents, fats, oils, water, detergents. It is attacked by strong acids and alkalis, benzene, polar solvents, ketones, esters, ethers, aromatic and chlorinated hydrocarbons. It is susceptible to stress corrosion cracking. This reduces its usability at elevated temperatures or long-term contact with solvents.
Weather resistanceResists weather and ultraviolet radiation . The effect of external influences does not leave traces of yellowing or loss of surface gloss under any climatic conditions. However, for long-term external use, UV stabilization is recommended. It absorbs very little water.
FlammabilityPMMA is easily flammable. It burns with a luminous flame even after the flame source is moved away. The gases released during burning have a typical sweet smell. According to UL 94, it is classified as class HB. The auto-ignition temperature is between 400-465 °C.
Food safetyPMMA is physiologically safe. It can be used for products that come into contact with food or drinking water.
ThermoformingPMMA sheets can be easily thermoformed. The usual procedure is to bend the plexiglass. Depending on the molar mass, the forming temperatures are between 150 and 180 °C, exceptionally they can reach up to 200 °C for high molar types.
MachiningChip machining is easy to do with PMMA. These include cutting, milling, grinding, drilling and polishing. The machining speed must be selected so that the material does not melt. A laser beam, for example, can be advantageously used for cutting.
Surface treatmentVarnishing and printing can also be done without prior surface treatment. The durability of the print is so great that thermoforming can also be carried out afterwards. Products can also be plated, both by painting and by vacuum evaporation.
Gluing plexiglassSemi-finished products and products made of PMMA can be glued with advantage, because it is a polar, easily soluble plastic. Solvent, reactive, hot-melt and instant adhesives are used for gluing. It is most suitable to use solvent adhesives with a small amount of dissolved PMMA, about 10-15%. Solvent adhesives modified in this way are called adhesive varnishes. Their advantage is that they do not leave traces of gluing. The plexiglass adhesive layer has high transparency and the glued area is practically not visible after gluing. Glues based on acetone and chloroform are very good. However, it should be borne in mind that these are highly flammable liquids, so it is necessary to strictly observe safety measures.
Gluing plexiglass with other plasticsPMMA can be glued and other plastics. Without major problems, PMMA can be bonded with crystalline and tough polystyrene, polycarbonates, cellulose derivatives, ABS terpolymers or SAN copolymers. Suitable solvents and adhesive varnishes are used for this. Other plastics are bonded to PMMA using reactive or hot melt adhesives. There are plenty of suitable adhesives on the market today. An important prerequisite for the creation of solid joints is that the glued surfaces are perfectly clean, free of dust and other impurities. Either water with the addition of detergents or alcohols can be used as cleaning agents. When gluing PMMA, the monomer itself, methyl methacrylate, is also used, which creates a strong glued joint by subsequent polymerization activated by chemical initiators or irradiation with ultraviolet light.
UsagePMMA is used wherever its advantages are used, especially optical, i.e. high transparency. Various transparent covers, lamp covers, displays are made from it. It found a considerable expansion of application in the automotive industry in the production of light covers, shields, tachometers, etc.. In optics, it was used as a raw material for the production of lenses for devices and glasses. In the consumer industry, these are vases, bowls, costume jewelry, advertising items, advertising stands. It occupies an important place in illuminated advertising , both for outdoor and for indoor use, and exhibition business. Another application of PMMA is found as acrylic sanitary ware. Modern bathtubs, sinks, shower enclosures, etc. are produced by thermoforming boards.
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