As plastic, PET can be used as film, polyester bottle, and engineering plastic once reinforced by glass fiber and other materials.
The refractive index of PET film is 1.655, and 90% of light with a wavelength of 4.00×10-7m or more can pass through, but it cannot pass through light with a wavelength of 3.15×10-7m or less; the air permeability is larger than that of polyvinylidene chloride, but it still belongs to the good air resistance variety. It has low hygroscopicity, soaked in water at 25°C for 168 hours, the water absorption rate is only 0.6%, and it can maintain good dimensional stability.
The tensile strength of PET film is comparable to that of aluminum film, 9 times that of polyethylene film, and 3 times that of polycarbonate film and nylon film.
| Physical and mechanical properties of PET film | |||
| Project | Thickness 25.4μm, Unstretched | Thickness 25.4μm,Stretched | |
| Density, g/cm3 | 1.385 | 1.377 | |
| Refractive Index（n25D） | 1.655 | – | |
| Friction Factor | 0.45 | 0.38 | |
| Tensile Strength，MPa | 176 | 281 | |
| Elongation，% | 120 | 6.63 | |
| Tensile Modulus of Elasticity，GPa | 3.87 | >880 | |
| Fold Persistence, Second | 3×105 | – | |
| Extended Tear Strength，N | 0.15 | 0.12 | |
| Initial Tear Strength，N | 5.88 | 4.41 | |
Effect of Stretching Method on Mechanical Properties of PET Film | ||||
Project | Unstretched | Unidirectional Longitudinal Stretch | Two-way Transverse Stretch | Two-way Stretch and Post-stretch |
Tensile Modulus of Elasticity，GPa | ||||
Portrait | 2.47 | 8.95 | 4.58 | 7.04 |
Horizontal | 2.47 | 1.78 | 4.58 | 3.52 |
Tensile Strength，MPa | ||||
Portrait | 52.8 | 290 | 176 | 267 |
Horizontal | 52.8 | 49.3 | 176 | 119 |
Elongation，% | ||||
Portrait | >500 | 48 | 120 | 52 |
Horizontal | >500 | 445 | 120 | 250 |
Tensile Strength at 5% Elongation, MPa | ||||
Portrait | 232 | 102 | 186 | |
Horizontal | 52.8 | 102 | 77.5 | |
The long-term use temperature of PET film can reach 120℃, and it still has a certain degree of flexibility at ultra-low temperatures of -200℃. After heating in air at 125℃ for 1000 hours, the strength and modulus of the film will only decrease by 10% to 15%.
Although PET is a polar polymer, it has excellent electrical insulation properties, and it still has good electrical insulation properties even at high frequencies. This is because its glass transition temperature is higher than room temperature, and the molecular dipole orientation is greatly restricted.
| Electrical properties of PET film (film thickness 25.4 μm) | |||
| project | Value | Project | Value |
| Dielectric Constant | 23℃，103Hz | 0.005 0 | |
| 23℃，60Hz | 3.30 | 23℃，106Hz | 0.016 0 |
| 23℃，103Hz | 3.25 | 150℃，60Hz | 0.004 0 |
| 23℃，106Hz | 3.00 | Volume Resistivity,Ω·cm | |
| Dielectric Loss Tangent | 23℃ | 1018 | |
| 23℃，60Hz | 0.0025 | 150℃ | 1014 |
In the frequency range of 103-106Hz, the dielectric loss of PET film is the smallest at 75℃, and the maximum is at 125℃ and below 25℃. When used as a high-voltage material, PET film has poor corona
