Although fluoropolymers have many unique excellent properties and play important roles in various industries, there are still some external environmental impacts that you need to understand before you choose the right material. Here, Alfa Chemistry Fluoropolymers provides you with the influence of some common factors on fluoropolymer materials for your reference. If there is any other information you want to know that is not mentioned here, you are welcome to contact us. Our professional team is very willing to provide detailed answers about fluoropolymers for your project.
Factors affecting fluoropolymers
Generally, fluoropolymers are organic materials with the highest resistance to thermal degradation. However, there are significant differences between them.
PTFE is extremely inert and stable at temperatures up to 250°C (482°F). When heated above this temperature, it begins to decompose very slowly, producing a small amount of gaseous product. The initial weight loss rate of granular PTFE is 0.0001%/h at 260°C (500°F) and 0.004%/h at 371°C (700°F). The thermal degradation of PTFE at different temperatures is shown in Table 1.
The thermal stability of FEP is much lower than that of PTFE, and it starts to degrade at temperatures above 200°C (392°F). The degradation of FEP basically has two stages. The first involves preferential elimination of hexafluoropropylene (HFP) from the main chain; in the second, the remaining main chain decomposes at the same rate as PTFE.
Due to the presence of stable ether groups in the side chain, PFA is more stable than FEP. However, due to the presence of reactive end groups (such as -COF or -CH2OH), it will degrade during processing or use at high temperatures. The result is that when the end groups decompose to form free radicals, a cross-linking reaction occurs and the molecular weight increases, and then the free radicals recombine. PFA resin can be processed at temperatures up to 445°C (883°F). Aging at temperatures below but close to 285°C (545°F) will increase the strength of PFA.
| Thermal Degradation of Polytetrafluoroethylene |
|---|
| | Rate of Decomposition, %/h |
| Temperature, °C | Fine Powder | Initial | Steady State |
| 232 | 0.0001-0.0002 | 0.00001-0.00005 | 1×10-11 |
| 260 | 0.0006 | 0.0001-0.0002 | 100×10-11 |
| 316 | 0.005 | 0.0005 | 0.000002 |
| 371 | 0.03 | 0.004 | 0.0009 |
Reference: Gangal, S. V., in Kirk-Othmer Encyclopedia of Chemical Technology, Vol. 11, 3d ed., John Wiley & Sons, New York, p. 11, 1980
- Effect of Ionizing Radiation
Like many other polymer materials, ionizing radiation electron beams or EB and gamma radiation have multiple effects on fluoropolymers. It may crosslink them, cause chain scission or affect their surface. In many cases, these effects may occur at the same time. The final result depends on the nature of the material, dose, dose rate and radiation energy.
PTFE will be attacked and degraded by γ-rays, high-energy electron beams or X-rays. The degradation of polymers in air or oxygen occurs due to chain scission and is quite rapid. This cleavage leads to a decrease in molecular weight. When irradiated by an electron beam, the molecular weight is reduced by as much as six orders of magnitude to produce fine powder.
FEP is degraded by radiation in a similar way to PTFE, that is, through chain scission and the resulting reduction in molecular weight. If FEP is lightly irradiated at elevated temperature in the absence of oxygen, cross-linking will counteract molecular decomposition. Under aerobic or anaerobic conditions, the radiation tolerance of FEP is 10:1 higher than that of PTFE. However, if the polymer is irradiated above its glass transition temperature (80°C), cross-linking dominates, leading to an increase in viscosity.
PFA/MFA, like other perfluoropolymers, is not resistant to radiation. Compared with FEP or PTFE, the radiation resistance in vacuum is improved, and the strength and elongation increase more after low doses (up to 3 Mrad, or 30 kGy). At 3 to 10 Mrad (30–100 kGy), it is close to the performance of PTFE, and it becomes brittle above 10 Mrad (100 kGy). After exposure to a dose of 50 Mrad (500 kGy), PTFE, FEP and PFA are all degraded.
The fluoropolymer as a whole is inherently highly resistant to degradation by ultraviolet radiation. The strength of fluorocarbon bonds makes them resistant to pure photolysis. In addition, they do not contain any light-absorbing chromophore in their structure or as an impurity.The outdoor durability of a fluorinated coating is directly related to its fluorine content and is evaluated through gloss retention. In general, the degradation of fluoropolymers occurring outdoors is very slow. Unlike FEP and other perfluoropolymers, ultraviolet light will greatly accelerate the degradation of PCTFE. The copolymer of TFE and HFP breaks and crosslinks when exposed to ultraviolet radiation.
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