Granular resins polytetrafluoroethylene

Polytetrafluoroethylene is manufactured and sold in three forms granular, fine powder, and aqueous dispersion each requires a different fabrication technique. Granular resins are manufactured in a wide variety of grades to obtain a different balance between powder flows and end use properties (Fig. 1). Fine powders that are made by coagulating aqueous dispersions are also available in various grades. Differences in fine powder grades correspond to their usefiilness in specific applications and to the ease of fabrication. Aqueous dispersions are sold in latex form and are available in different grades. A variety of formulation techniques are used to tailor these dispersions for specific applications. 

Compounds, known as granular powders, are made with granular polytetrafluoroethylene resin. The choice and concentration of the filler depends on the desired properties of the final part. Glass fiber, bronze, steel, carbon, carbon fiber, and graphite are among the common filler materials. Up to 40% by volume of filler can be added to the resin without complete loss of physical properties. The impact of additives below 5% by volume of filler on the properties of compounds is insignificant. Above 40%, most physical properties of the compounds drop sharply. 

Polytetrafluoroethylene selection. Polymer selection for compounding granular PTFE is relatively straightforward. Fine cut resins are used as a starting point to produce filled compounds. These powders have relatively small particle size and form the most uniform compounds. Typically, smaller particle size resins produce compounds with higher physical properties. 

Filled PTFE—production techniques. Granular polytetrafluoroethylene compounds containing fillers are converted into parts by the same molding techniques as those used for neat resin. The compounding techniques aim at producing uniform blends of PTFE with fillers that can be processed in the same molding equipment. The rest of this section describes methods by which compounds can be made. 

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