A Brief Analysis Of Why Waterproof And Breathable Membranes Can Be Used Normally Under High Temperatures

Waterproof and breathable membrane PTFE is a highly crystalline polymer, and its raw material crystallinity is as high as 92% to 98%. However, after processing or sintering-cooling, the crystallinity is reduced to no more than 70% of the raw material crystallinity. When PTFE is at 19°C, it has a spatial helical conformation in which every 13 links rotate 180°C. Above 19°C, the number of chain link units required for the same rotation of 180°C increases to 15. This is because of the spacing between each link. The rise is 0.195nm. This change means that there is a significant difference in the hardness of powder particles below and above 19°C. Above 19°C, the bond has a certain degree of angular displacement, which increases as the temperature rises; above 30°C, this energy displacement trend continues to increase until 327°C. This means that above 19°C the particles are softer and easier to deform. This has very important guiding significance for the selection of post-treatment process of PTFE resin, the movement method of materials on the assembly line and the planning of equipment, the determination of packaging method and storage temperature. It is also very important for the use of dispersed PTFE resin after paste extrusion. The temperature used to make films using the stretching method also plays a key role.

When the temperature is below 19°C, the crystal state of PTFE is a triclinic lattice. At 19°C, the crystal form changes, the rotation of the chain segments becomes slightly smaller, and the unit lattice changes to a hexagonal crystal system. At 30°C, the PTFE crystal shows crystallization relaxation, and the orderly rotation of the bonds changes to random winding. These two temperature points are generally called phase change points.

The high crystallinity and high molecular weight of waterproof and breathable membrane PTFE resin result in PTFE having extremely high melt viscosity. The kinematic viscosity measured at 380°C is 1010~1011Pa.s. It also has no fluidity at the melting point temperature. Therefore, general PTFE resin cannot be processed with the processing methods generally suitable for melt-processable plastics. Suspended PTFE resin can only be processed with methods similar to powder metallurgy. The suspended PTFE resin powder is placed in the mold and compressed and preformed to disperse the PTFE resin. A booster (lubricant) needs to be added to form a paste before the preform can be pushed, and they must be sintered to become finished products.