Thermoplastic Applications

Thermoplastics are often used to replace lubricated metal parts providing corrosion protection, reduced weight, and lower maintenance cost. For dynamic load-bearing applications such as gears, cams, bearings and slides, Zonyl® fluoroadditives can help the host provide better wear resistance, increased pressure X velocity limits, and reduced friction and stick-slip response. The mechanism for these improvements is the formation of a dry film of PTFE between the plastic part and the mating surface. This film is formed during the break-in period for the plastic, as randomly dispersed particles of Zonyl® fluoroadditive are sheared to form a film on the bearing surface.

Fluoropolymers are also used in thermoplastics to improve anti-drip properties.

Zonyl® fluoroadditives can enhance some properties of thermoplastic host resins even when added in small amounts. This is because the Zonyl® fluoroadditive powder can resist the effects of hostile processing conditions and because it resides in the host resin with its properties virtually unchanged.

Simple mixtures with thermoplastics are not always simple to produce because they involve dissimilar generic materials mixed in a high temperature melt. Finely divided powder is a desirable product form for an additive which must be mixed uniformly in a larger quantity of molten thermoplastic resin. The Zonyl® fluoroadditive product line provides powders with the characteristics needed for proper mixing in a variety of processes and host resins.

Comparative wear and friction data for thermoplastics can be obtained by use of ASTM test method D3702. A sample of material is rotated under load against a stationary steel washer. The amount of thickness lost per unit time (wear rate) is measured. Weight loss also can be measured, and volume loss can be calculated. These data can be used to calculate a more complex basis for comparing materials called Wear Factor (K). The formula for K requires definition of pressure, velocity and time. Changes in either volume or thickness can be used to calculate K. Smaller values are best.

Table 3 (below) shows the effect on wear factor, wear rate, and coefficient of friction, of adding 15 percent by weight of Zonyl® fluoroadditives to each of four thermoplastics widely used for mechanical applications. The test samples were machined from injection molded plaques. The tests were run at a PV of 2000 using 50 ft/min and 40 lb/in². These comparative data are presented only to illustrate, in general, the effect of the fluoroadditives on wear and friction properties. Results are not necessarily optimum and may be changed in either direction with differences in experimental technique, test conditions, or materials.

Processing

In general, 5 to 20 percent weight of fluoroadditive is used to achieve optimum wear properties. For evaluation, 15 percent is a good starting point. Feed stock is first prepared with the desired loading of fluoroadditive powder. Natural host resin beads can be dry-blended with the powder and extruded into strands, which are cut into new beads containing the additive. The beads containing the additive then become feed for another molding machine or extruder which is used to make the end product from molten plastic. The blending process should be chosen to provide uniform dispersion of the additive.

Recommended Grades

Zonyl® MP 1000 and MP 1300 are recommended for most thermoplastics, including polycetal, polyester, nylon, polycarbonate, polyphenylene oxide, polyphenylene sulfide, ABS, polyethersulfone, PEEK, polypropylene, polyethylene, and polystyrene. MP 1300 is the best choice for ease of dispersion within the host plastic, best surface appearance, and minimal plateout. MP 1000 has a higher specific surface area and is more friable, (can be reduced to a smaller particle size during compounding). Both products may be used in EEC countries for food contact applications.

MP 1400 should be used when the end product must be in compliance with FDA regulations as a component of articles for repeated use in contact with food.

Table 3: Thrust Bearing Wear Test Results