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TPX
TPX has a very wide range of applications due to its outstanding and unique transparency, heat resistance and chemical resistance. Typical applications include medical equipment, laboratory equipment, small appliances, ovenware, baking boxes, release paper, wire and cable coating, and some industrial uses. Currently, Mitsui Chemicals is the only manufacturer/seller of TPX in the world. TPX is a 4-methylpentene based polyolefin. 4-methylpentene can be obtained by dimerization of propylene, and TPX is a copolymer of 4-methylpentene, as shown below:
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main features
mechanical properties
The properties of TPX are somewhat similar to polyolefins. For example, some mechanical properties of TPX are quite similar to polypropylene. Of course, TPX also has its special features. The glass transition temperature (Tg) of TPX is approximately between 20°C and 30°C. Therefore, the mechanical properties of TPX at or below room temperature are different from those at high temperatures. The mechanical properties of TPX at or below room temperature are similar to polypropylene, but the elongation at break and impact strength are slightly lower. However, at high temperature, TPX exhibits better flexibility, so it has relatively high elongation at break and impact strength. As long as the molded products of transparent grade TPX can maintain a good shape and have no notch, its impact resistance strength can be compared with that of polypropylene homopolymer, and is better than that of polystyrene (general grade). In addition, the bending modulus of transparent grade TPX is also similar to that of polypropylene.
TPX has excellent creep resistance. The creep behavior of TPX at 20°C and a stress of 50 kg/cm2 is shown in Figure 1. It can be seen from Figure 1 that the creep resistance of TPX is superior to that of polypropylene copolymer and high-density polyethylene.
optical properties
Transparent grade TPX is colorless, and its light transmittance can reach 90%. Figure 2 compares the light transmittance of TPX and various materials at different wavelengths. In the range of visible light, the light transmittance of TPX is comparable to that of PMMA (polymethyl methacrylate), slightly better than that of PS (polystyrene). In the ultraviolet range, the light transmittance of transparent grade TPX is better than that of glass and other transparent resins.
thermal properties
The melting point of TPX is about 240°C, so it has excellent temperature resistance. The heat distortion temperature of TPX is comparable to that of polypropylene (homopolymer), but the high melting point of TPX makes its Vicat softening point higher than that of polypropylene. The effect of temperature on the tensile yield strength of TPX is shown in Figure 3. It can be seen from the figure that TPX can still maintain some strength at a temperature above 150°C, while polypropylene has softened. Generally speaking, the service temperature of TPX is higher than that of polypropylene. In addition, the heat deflection temperature of mineral-filled grade MBZ 230 will be improved due to the increase of flexural modulus.
If it is clamped with a 2×120×20 mm test piece, observe the amount of deformation after it is maintained at the test temperature for 5 hours. The thermal deformation test results of TPX and some resins are shown in Figure 4. It is obvious that the deformation of TPX at high temperature is much smaller than that of other resins. From this point of view, TPX has very good temperature resistance.
The high temperature aging resistance of TPX is extremely outstanding. If you put TPX in an oven for aging and observe whether it breaks, you can know its service life. The service life of TPX at high temperature is shown in Fig. 5. It can be seen from Figure 5 that the long-term temperature resistance of TPX is quite good. However, it must be noted that the service life of TPX will be affected by the stabilizer formulation and usage conditions. On aging, TPX will turn yellow and become brittle if a certain limit is reached.
electrical properties
There are no polar groups in TPX molecules, so TPX has excellent electrical insulation properties. The dielectric constant of TPX is very low (2.12), almost the lowest among all synthetic resins. So FR-TPX has excellent electrical properties. The dielectric loss of TPX is very low, as shown in Figure 6 and Figure 7. Overall, the electrical properties of TPX are comparable to polytetrafluoroethylene (PTFE) and wire and cable grade low-density polyethylene (LDPE), and sometimes better.
density
The density of TPX is only 0.83 g/cm3, which can be said to be the lowest among all commercial thermoplastics. Therefore, the specific volume of TPX is larger than other resins, as shown in Figure 8. Compared with other transparent resins such as polymethyl methacrylate (PMMA) (density 1.20), polycarbonate (PC) (density 1.20) and polystyrene (PS) (density 1.05), TPX per unit volume The weight is much less.
Chemical Resistance
TPX has excellent resistance to many chemicals. However, TPX will be affected by some aromatic solvents and halogenated hydrocarbon solvents, depending on the environmental conditions. The table below compares the chemical resistance of TPX with other polymers. TPX has excellent acid resistance and alkali resistance, and has excellent resistance to edible oils, but it has poor resistance to some solvents such as acetone and trichlorethylene. Compared with some transparent resins such as polymethyl methacrylate (PMMA), polycarbonate (PC) and polystyrene (PS), the chemical resistance of TPX is quite good.
Remark:
A: No change or little impact; (A): A little change in weight and slightly lower cargo performance;
B: Swelling, decreased physical properties or changed appearance;
C: Severely swollen, with obvious changes in appearance; (C): Dissolved;
(D): Crack occurred.
Water absorption and boiling water resistance
As a polyolefin, TPX has particularly good chemical resistance, especially solvent cracking resistance. To evaluate the resistance to solvent cracking, dip the test piece in a solvent and observe whether there is cracking after applying stress for a period of time. The stress at which cracking begins is called the threshold stress of solvent cracking. Generally speaking, the higher the initial stress, the better the solvent cracking resistance. However, changing the stress in a solvent is quite cumbersome. The stress can be calculated by using the amount of bending deformation and the flexural modulus, and the test piece can be deformed to different degrees by using the special fixture whose curvature changes continuously. The size of the test piece used is 120X12.5X3.1 mm, and the fixture with an elliptical circumference as shown in Figure 9 has a major axis of 240 mm and a minor axis of 80 mm, which can provide different curvatures. After soaking the deformed test piece in the solvent for 1 hour, observe its cracking phenomenon. The initial stress δ of solvent cracking can be obtained from the curvature (radius) r of the cracking point according to the following formula:
Here, E is the flexural modulus of the test piece, the unit is kg/cm2, t is the thickness of the test piece, the unit is cm, and the unit of curvature r of the cracking point is cm, so the unit of the initial stress δ is kg/cm2. The initial stress of solvent cracking of TPX and some transparent resins is shown in the table below. From the comparison in the table below, it can be seen that PMMA and PC are prone to solvent cracking, while TPX has excellent solvent cracking resistance.
Water absorption and boiling water resistance
The water absorption rate of TPX is extremely low, only 0.01%, so it has high resistance to water and water vapor. Resin may deform due to water absorption, so water resistance can be evaluated by observing deformation after water absorption. A test piece with a size of 120x130x2 mm is brought into contact with the surface of water, and its deformation a is observed at regular intervals, as shown in Figure 11. The deformation ratio is defined as (at)/t, where t is the thickness of the test piece. The deformation ratio of TPX and some resins versus the time of exposure to water is shown in Figure 11. It is obvious that TPX has excellent water resistance. TPX and some transparent resins were immersed in boiling water, and their optical properties were measured after a certain period of time. The results are shown in Figure 12. After PC and polyarylate are soaked in boiling water for dozens of days, the light transmittance is greatly reduced, and the haze is also greatly increased, indicating that their resistance to boiling water is not good. However, TPX has a small decrease in light transmittance in boiling water and a small increase in haze, so it has excellent boiling water resistance.
weather resistance
The weather resistance of TPX is comparable to that of polypropylene. TPX deteriorates under the influence of ultraviolet rays. As shown in Figure 13, when irradiated with ultraviolet rays in a weathering tester, the tensile yield strength of TPX gradually decreases due to deterioration. However, this problem can be solved by using UV stabilizers. For example, the use of UV stabilizers can improve the resistance of TPX to ultraviolet rays. As shown in Figure 13, after adding 5% of UV stabilizers, TPX has excellent ultraviolet resistance.
health and safety
Basically, TPX is an inert, non-toxic material that is not dangerous to human health.
Some food-grade TPX that can be in contact with food conforms to the regulations of the US FDA (Code of Federal Regulations Title 21, Section 177.1520), and also complies with the Drug Master File 3621 (Drug Master File 3621) and the German BGA recommendation (BGA recommendation) (A-XLIII ) requirements.
Food grade TPX complies with Japanese Government Standards (Notification No. 20, Ministry of Health and Welfare, 1982) on plastic household products, containers and packaging applications that come into contact with food.
Food grade TPX also complies with the Japan Hygienic Olefin and Styrene Plastics Association (the Japan Hygienic Olefin and Styrene Plastics Association) standard specifications for plastic household products, containers and packaging materials that come into contact with food.
Flammability
The flammability of TPX is roughly equal to that of polypropylene, and the flammability of UL 94 belongs to the HB class. TPX RT18 has a UL 746B temperature index of 115°C.
application
TPX offers an excellent combination of properties suitable for a wide range of applications. The table below describes the recommended grades and properties utilized for various applications of TPX.
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Physical property table
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processing method
PX (transparent grade) does not require pre-drying before processing. Therefore, TPX colloidal particles do not have the problem of moisture absorption in essence.
Injection Molding
TPX can be easily molded using injection molding machines that generally have appropriate heat capacity and good temperature control. Typical processing temperatures range from 270 to 330°C, while the mold temperature should be controlled between 20 and 60°C. The mold shrinkage of TPX is about 1.2 – 1.5%.
blow molding
TPX can be molded using traditional blow molding machines. In order to avoid the formation of weld lines, it is recommended to use a barrier torpedo (barriered torpedo) to increase the die pressure. Due to the low melt viscosity of TPX, the blow molding machine used should be equipped with a parison controller and an accumulator.
push out
TPX can be extruded using conventional single or twin screw extruders. If a single-screw extruder is used, screws designed for polypropylene and high-density polyethylene are suitable for TPX processing, but long L/D (length to diameter ratio) double flighted screws give the best results . Alternatively, choose a longer die for best results. The flow characteristics of TPX are shown in Figure 14 and Figure 15.
