Italiano
Membranes coated with PTFE, commonly referred to as “PTFE coated” membranes, have been the subject of discussions and often inaccurate or vague claims regarding their characteristics and performance. In this report, we will clarify some key arguments used to promote products with this coating.
Membrane composition
It is important to note that “PTFE coated” membranes are not entirely made of PTFE. The membranes are made of EPDM, sulphur vulcanized by some competitors, a vulcanization technique that guarantees lower mechanical and durability properties compared to the peroxide vulcanization used in WTE membranes. A few-micron-thick layer of PTFE coating is applied on the side of the membrane that comes into contact with the treated liquid. It is crucial to emphasize that the coating layer is susceptible to abrasion from sand or solid particles present in the treated liquid, which limits the coating’s lifespan over time. We have observed that due to our competitors’ method of applying the coating layer to the membrane, there are areas where the membrane may be left uncovered, as highlighted in the pictures.
How the PTFE lining works
Contrary to what is often claimed, the PTFE coating does not penetrate the membrane’s pores, as visible in the microscope image. Especially with low submergence, there could be leakage of the treated liquid through the perforations during the operation standstill. Upon system restart, this liquid is eliminated through evaporation or the purge pit. It is important to consider that if the treated liquid contains substances that are chemically incompatible with EPDM, they could damage the membrane upon contact with unprotected EPDM areas.
Advantages of the PTFE coating of Teflon-coated membranes
One of the advantages of the PTFE coating is its ability to counteract the adhesion of sludge and salts on the membrane surface. This is made possible by the low coefficient of friction of PTFE.
To this end, comparative tests were conducted on three types of membranes:
- WTE EPDM membranes
- WTE PTFE coated membranes
- and competitor membranes with PTFE-based coating.
The results clearly indicate that the PTFE coating of WTE membranes exhibits significantly lower static and dynamic friction compared to the coating proposed by competitors. This data confirms the effectiveness of the WTE coating in reducing the adhesion of sludge and salts, thereby improving the overall system performance.
| WTE EPDM MEMBRANES | WTE PTFE COATED MEMBRANES | COMPETITOR PTFE COATED MEMBRANES | |
| Static friction coefficient | 4,28 | 0,93 | 3,12 |
| Dynamic friction coefficient | 3,61 | 0,77 | 2,06 |
The PTFE coating of WTE has a static friction that is 70% lower and dynamic friction that is 62% lower compared to the coating proposed by competitors. These tests were conducted by an independent laboratory in accordance with ATE N 553 59 25 00 – Continental standards based on DIN 53375-B and ASTM D 1894.
What is the composition of the PTFE coating?
It is important to delve into the composition of the coating proposed by competitors to understand the significant distinctions from the WTE membrane coating. After careful analysis, it has been noted that the substance most present in the competitors’ coating is a urethane resin, not PTFE as often implied. It is interesting to note that those who have made this type of product a selling point do not provide information regarding the amount of PTFE contained in the coating. It would, therefore, be more accurate to refer to these membranes as “urethane coated with PTFE membranes” rather than simply “PTFE coated”.
Why to use PTFE coating?
As mentioned earlier, one of the main reasons for using PTFE coating is its low coefficient of friction, which helps reduce the adhesion of sludge and salts to the membrane surface. However, another reason cited by competitors for using the coating is the “protection” provided by the coating against the migration of certain components of the EPDM compound into the treated liquid. This claim implicitly suggests lower quality of the EPDM used as the base of the coating. However, it is important to emphasize that WTE has implemented diffuser applications with EPDM membranes that have operated for over ten years without significant issues. If the EPDM is of good quality, with low plasticizer content and good cross-linking achieved through peroxide vulcanization, the problem of migration of membrane constituents does not exist. Therefore, WTE membranes, even without any coating, have been able to operate for long periods without substantial increases in pressure loss or membrane shrinckage incompatible with the required service.
Find out more about the WTE offer!