Fibrillated PTFE

Membrane Fabrication, Lamination and Reinforcement. The thermoplastic copolymer of TFE and PVEX monomer can be extruded or molded into a thin film by conventional methods. Extrusion is most appropriate for continuous production of large membranes because it facilitates control of film thickness. Lamination can be performed with a roll press to obtain multilayer membrane. To improve their mechanical properties, membranes are generally reinforced with an inert material such as fabric made of PTFE (67, 68), fibriled PTFE (69), or wire netting (70). 

Figure 5.26 An example of biaxially oriented fibrillated PTFE structure. (Courtesy of Mr. Clay Jones, DuPont Fluoroproducts.)...

Fibrillated PTFE and molybdenum disulfide particles are other bitumen and asphalt modifiers. The copolymer comprises two incompatible polymers forming a two-phase copolymer including a thermoplastic and block polymer and an elastomeric mid-block polymer. The asphalt modifier is made by mixing together, under high shear, particles of thermoplastic elastomeric copolymer, and molybdenum disulfide until the PTFE is fibrillated and combined with the thermoplastic elastomer. 

Highly porous fabric stmetures, eg, Gore-Tex, that can be used as membranes have been developed by exploiting the unique fibrillation capabiHty of dispersion-polymerized PTFE (113). 

As manufactured, PTFE is of two principal types dispersion polymer, made by suspension polymerization followed by coagulation, and granular PTFE, polymerized and generally comminuted to a desirable particle size. Some details are given by Sperati. We have observed cast films of an aqueous colloidal dispersion and see that it consists of peanut-shaped particles, approximately 0.25 pm in size, which are composed of even finer particles. Electron micrographs of as-polymerized granular particles show three structures bands arranged in parallel, striated humps, and fibrils, some of which have the shish-kebab structure."... 

The morphology and microstructure of as-polymerized polytetrafluoro-ethylenes is a study in itself. We observe that fibrils are common in some lots of granular PTFE while other specimens consist of beadlike particles, the surfaces of which bear markings suggesting lamellar crystals. Of special note is the (rare) occurrence of shish-kebab structures in as-polymerized PTFE (Figure 1.3). 

As-polymerized PTFE has a number of interesting microstructures including highly developed crystals, fibrils, and occasionally, shish-kebab structures. 

An increasingly important development of PTFE is a proprietary process for the controlled stretching of sheets to produce microscopic fibrillation. Since the resulting material, often referred to by its trade name Goretex , is resistant to liquid water but porous to water vapor... 

Elastomers based on VDF and TFE-VDF-HFP consist of fine particles 16 to 30 nm in diameter in contrast to PTFE which has a rodlike microstructure in which the elementary fibrils are approximately 6 nm wide and the molecular chains are all extended.12 For example, the properties of a VDF-HFP elastomers such as their resilience and flexibility can be related to spherical domains with diameter approximately 25 nm that are interconnected.10 The diameter of these particles was found to be proportional to the molecular weight of the elastomer.12... 

Highly porous membranes are prepared by a process based on the fibrillation of high-molecular-weight PTFE. Since they have a high permeability for water vapor and none for liquid water, it is combined with fabrics and used for breathable waterproof garments and camping gear. Other uses for these membranes are for special filters, analytical instruments, and in fuel cells.13... 

The ability to dr aw approximately 100 - A diameter fibrils from PTFE dispersion particles, either by fracture after cold compaction [34] or by uniaxial or biaxial expansion of sheets or tubes after paste extrusion (extrusion of mixtures of the dispersion particles and lubricants such as mineral spirits) and lubricant removal [35], was demonstrated a number of years ago. The former process results in the development of a myriad of fibrils spanning the gap between the fracture faces these were utilized for ED characterization of the PTFE conformation and crystal packing. 

Fig. 12.27. Expanded PTFE micrograph (Microtex Membrane at 500x) showing a porous structure containing nodes interconnected by fibrils. (Courtesy Menardi-MikroPul, LLC.)...

PFSA lonomer with PTFE Fibril Reinforcement Asahi Glass Flemion.789... 

FIGURE 27.42 Fabrication of PTFE fibril-reinforced Flemion. (Reproduced from Nakao, M. and Yoshitake, M., in W. Vielstich, H.A. Gasteiger, and A. Lamm (Eds.), Handbook of Fuel Cells Fundamentals, Technology and Applications, Vol. 3, J. Wiley Sons, Chichester, 2003. With permission.)... 

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