Fluoropolymers factor

The Du Pont HaskeU Laboratory for Toxicology and Industrial Medicine has conducted a study to determine the acute inhalation toxicity of fumes evolved from Tefzel fluoropolymers when heated at elevated temperatures. Rats were exposed to decomposition products of Tefzel for 4 h at various temperatures. The approximate lethal temperature (ALT) for Tefzel resins was deterrnined to be 335—350°C. AH rats survived exposure to pyrolysis products from Tefzel heated to 300°C for this time period. At the ALT level, death was from pulmonary edema carbon monoxide poisoning was probably a contributing factor. Hydrolyzable fluoride was present in the pyrolysis products, with concentration dependent on temperature. 

Electrical Applications. Plastics are used for electrical insulation, conduit and enclosures, lighting fixtures, and mechanical devices. The most widely used plastic for wire and cable insulation is flexible, plasticized PVC, which constitutes well over half the market in insulating wires for buildings, automobiles, appHances, and power and control lines. Polyethylene is also a factor. Higher performance plastics such as nylon and fluoropolymers also play a smaller role in this area. 

However, one should not forget that apart from the complexity of the synthesis fluoropolymers are very expensive. For example, the price of fluoro-rubber is more than 30-fold that of an ordinary rubber such as butadiene-styrene (SBR) or ethylene-propylene (EPDM). Cost was one of the factors that gave impetus to research polymer surface fluorination, with the object of imparting the properties of fluoropolymers to the surfaces of less expensive polymers without changing their bulk properties. 

In general, fluoropolymers possess the unique combination of high thermal stability, chemical inertness, unusual surface properties, low dielectric constants and dissipation factors, low water absorptivities, excellent weatherability and low flammabilities. Therefore there appears to be an ever-increasing market for fluoropolymers in spite of their relatively high cost [211,212],... 

Coefficient of friction is inversely proportional to pressure and proportional to velocity. Wear rate of fluoropolymers is proportional to load (/ ) and velocity (V). Combinations of pressure and velocity are defined where the material can be used, thus a FV limit is defined. Above this PV limit, the wear increases exponentially because of the heat that is generated as a result of motion. Generally, a polymer or its compounds can be characterized by PV limit, deformation under load, and wear factor. Wear factor or specific wear rate is defined as the volume of material worn away per unit of sliding distance and per unit of load. 

A number of factors should be considered in the design of a screw for plastication of fluoropol5miers in addition to those considered for conventional injection molding of other thermoplastics. The most significant additional factors are the high processing temperature, corrosive nature, high melt viscosity, and low critical shear of fluoropolymers. 

Failure of parts, irrespective of plastic t5 e, is an inevitable fact of the operation of chemical plants. Fluoropolymers are no exception in spite of their excellent chemical, thermal, and mechanical properties. These plastics form the processing surfaces of equipment where they are exposed to the most aggressive and corrosive chemicals. The repeated exposure of fluoroplastics to these chemicals, in addition to other factors, can affect the integrity and surface quality of the parts. The chapters dealing with properties and part fabrication techniques of fluoropolymers should be consulted extensively. An understanding of the limitations of fluoropolymers and flaws created by fabrication methods is required for successful failure analysis of parts. 

---