Acrylic Encyclopedia

Comprehensive Properties of Acrylic | YUEFENG

August 26, 2021

Acrylic, also known as PMMA or plexiglass, is derived from the English acrylic (acrylic plastic), and its chemical name is polymethyl methacrylate.

Acrylic Characteristic

1. It has crystal-like transparency, the light transmittance is above 92%, the light is soft, and the vision is clear. The acrylic colored with dyes has a good color development effect.

2. Acrylic sheet has excellent weather resistance, high surface hardness and surface gloss, and good high temperature performance.

3. Acrylic sheet has good processing performance, which can be processed by thermoforming or mechanical processing.

4. The transparent acrylic sheet has a light transmittance comparable to that of glass, but the density is only half that of glass. In addition, it is not as fragile as glass, and even if it is broken, it will not form sharp fragments like glass.

5. The abrasion resistance of acrylic sheet is close to that of aluminum, it has good stability and is resistant to corrosion by various chemicals.

6. Acrylic sheet has good printability and sprayability, and the use of appropriate printing and spraying processes can give acrylic products an ideal surface decoration effect.

7. Flammability: It is not spontaneously combustible but is flammable and does not have self-extinguishing property.

Acrylic Features

1. Hardness

Hardness is one of the parameters that best reflects the production process and technology of cast acrylic sheet, and it is an important part of quality control. The hardness can reflect the purity of the raw material PMMA, the weather resistance of the sheet and the high temperature resistance. The hardness directly affects whether the sheet will shrink and bend, and whether the surface will crack during processing. Hardness is one of the rigid indicators for judging the quality of acrylic sheets.

2. Thickness (Acrylic Tolerance)

Acrylic sheet thickness has acrylic tolerance, so the control of acrylic tolerance is an important manifestation of quality management and production technology. Acrylic production has an international standard ISO7823

Tolerance requirements for cast plates: Tolerance = ± (0.4 + 0.1 x thickness)

Tolerance requirements for extruded plates: Tolerance=< 3 mm Thickness: ± 10 %> 3 mm Thickness: ± 5%

3. Transparency/Whiteness

Strict raw material selection, advanced formula follow-up and modern production technology production ensure excellent transparency and pure whiteness of the board. Crystal clear after flame polishing.

Acrylic Attributes

1. Mechanical properties

Polymethyl methacrylate has good comprehensive mechanical properties and ranks in the forefront of general-purpose plastics. The tensile, bending, and compression strengths are all higher than polyolefins, and higher than polystyrene, polyvinyl chloride, etc., and its impact toughness is poor. But it is also slightly better than polystyrene. The cast bulk polymerized polymethyl methacrylate sheet (such as aerospace plexiglass sheet) has higher tensile, bending, and compression mechanical properties, and can reach the level of engineering plastics such as polyamide and polycarbonate.

Generally speaking, the tensile strength of polymethyl methacrylate can reach the level of 50-77MPa, and the bending strength can reach the level of 90-130MPa. The upper limit of these performance data has reached or even exceeded some engineering plastics. Its elongation at break is only 2%-3%, so the mechanical properties are basically hard and brittle plastics, and have notch sensitivity, and are easy to crack under stress, but the fracture is not like polystyrene and ordinary inorganic glass. That's sharp and jagged. 40°C is a secondary transition temperature, which is equivalent to the temperature at which the pendant methyl group starts to move. If it exceeds 40°C, the toughness and ductility of the material will be improved. Polymethyl methacrylate has low surface hardness and is easy to scratch.

The strength of polymethyl methacrylate is related to the stress time, and the strength decreases as the time increases. After stretching and orientation, the mechanical properties of polymethyl methacrylate (oriented plexiglass) have been significantly improved, and the notch sensitivity has also been improved.

The heat resistance of polymethyl methacrylate is not high. Although its glass transition temperature reaches 104°C, the maximum continuous use temperature varies between 65°C and 95°C depending on the working conditions, and the heat distortion temperature is about 96 ℃ (1.18MPa), Vicat softening point is about 113℃. The heat resistance can be improved by copolymerization of monomers with propylene methacrylate or ethylene glycol diester acrylate. The cold resistance of polymethyl methacrylate is also poor, and the embrittlement temperature is about 9.2°C. The thermal stability of polymethyl methacrylate is moderate, better than polyvinyl chloride and polyformaldehyde, but not as good as polyolefin and polystyrene. The thermal decomposition temperature is slightly higher than 270℃, and its flow temperature is about 160℃. There is a wide range of melt processing temperature.

The thermal conductivity and specific heat capacity of polymethyl methacrylate are in the middle level of plastics, which are 0.19W/M.K and 1464J/Kg.K, respectively.

2. Electrical performance

Since polymethyl methacrylate contains polar methyl ester groups in the side of the main chain, its electrical properties are not as good as those of non-polar plastics such as polyolefin and polystyrene. The polarity of the methyl ester group is not too great, and polymethyl methacrylate still has good dielectric and electrical insulation properties. It is worth pointing out that polymethyl methacrylate and even the entire acrylic plastics have excellent arc resistance. Under the action of an arc, the surface will not produce carbonized conductive paths and arc tracks. 20°C is a secondary transition temperature, which corresponds to the temperature at which the pendant methyl ester groups start to move. Below 20°C, the pendant methyl ester groups are in a frozen state, and the electrical properties of the material will be improved compared to those above 20°C.

3. Solvent resistance

Polymethyl methacrylate can withstand relatively dilute inorganic acids, but concentrated inorganic acids can make it corroded, and it can be resistant to alkalis, but warm sodium hydroxide and potassium hydroxide can make it corrode and can be salt-resistant And grease, resistant to aliphatic hydrocarbons, insoluble in water, methanol, glycerin, etc., but can absorb alcohol and swell and cause stress cracking. It is not resistant to ketones, chlorinated hydrocarbons and aromatic hydrocarbons. Its solubility parameter is about 18.8 (J/CM3) 1/2, and it can be dissolved in many chlorinated hydrocarbons and aromatic hydrocarbons, such as dichloroethane, trichloroethylene, chloroform, toluene, etc., vinyl acetate and acetone can also make it Dissolve.

Polymethyl methacrylate has good resistance to gases such as ozone and sulfur dioxide.

4. Weather resistance

Polymethyl methacrylate has excellent atmospheric aging resistance. After 4 years of natural aging test, the sample has a slight decrease in tensile strength and light transmittance, a slight yellowing in color, and a decrease in crazing resistance. Obviously, the impact strength has been slightly improved, and other physical properties have hardly changed.

5. Flammability

Polymethyl methacrylate is easy to burn, and its limiting oxygen index is only 17.3.

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