Polymethyl methacrylate has good comprehensive mechanical properties. It is in the forefront of general-purpose plastics. Its tensile, bending, and compression strengths are higher than polyolefins, and also higher than polystyrene and polyvinyl chloride. But it is also slightly better than polystyrene. The cast bulk polymer polymethyl methacrylate sheet (such as aviation plexiglass sheet) has higher mechanical properties such as tensile, bending and compression, 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 90-130MPa. The upper limit of these performance data has reached or even exceeded some engineering plastics. The elongation at break is only 2% -3%, so the mechanical properties are basically hard and brittle plastics, and have notch sensitivity, 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 second-order transition temperature, which is equivalent to the temperature at which the methyl side begins to move. Above 40 ° C, the toughness and ductility of the material have improved. Polymethyl methacrylate has low surface hardness and is easily scratched.
The strength of polymethyl methacrylate is related to the stress action time. As the action time increases, the strength decreases. After stretching and orientation, the mechanical properties of polymethyl methacrylate (oriented organic glass) 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 ℃, the maximum continuous use temperature varies between 65 ℃-95 ℃ with different 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 copolymerizing monomers with acrylic acid methacrylate or diester glycol acrylate. Polymethyl methacrylate also has poor cold resistance, with an embrittlement temperature of about 9.2 ° C. The thermal stability of polymethyl methacrylate is medium, better than polyvinyl chloride and polyoxymethylene, but not as good as polyolefin and polystyrene. Its 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 in plastics, respectively 0.19W / M.K and 1464J / Kg.K.