PTFE Micropowders

PTFE micropowders (also referred to as fluoroadditives) are homopolymers of tet-rafluoroethylene with molecular weight significantly lower than normal PTFE (see Table 7.6). They are prepared mainly by irradiation of PTFE (often of PTFE scrap) by high-energy electron beam [104]. The effect of radiation dose is illustrated by 

Property ASTM Test Method Modified PTFE Conventional PTFE 

Comparison of PTFE Micropowders with Standard PTFE Resin 

Effect of Radiation Dose on Micropowder Particle Size 

Feedstock (PTFE) Irradiation Dose, kCy Particle Size, jm 

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The PTFE micropowders are commonly used in plastics, inks, lubricants, and finishes such as lacquer. Lubricants containing micropowders are used for bearings, valve components, and other moving parts where sliding friction must be minimized or eliminated. Nonstick finishes that require good release properties, for example, in the food and packaging industry, commonly use PTFE micropowders. 

PTFE films, 18 334 PTFE micropowders, 18 306 PTG black and white developers, 19 346-347... 

NBR containing irradiated PTFE micropowder for high performance tribological applications [23]. 

ETFE, FEP, PFA, FEVE, PVDE, fluorocarbon elastomers (TFE/P), PTEE, amorphous PTFE, PTFE micropowders Fluorocarbon TPE... 

EFEP, ETFE, FEP, PCTFE, PEA, PTEE, PTFE micropowders, fluorocarbon elastomers (FKM, fluorinated TPE), FKM latex Fluorosilicones... 

ETFE, FEP, HTE fluoroplastic, THV fluoroplastic, PTFE, modified PTFE, PTFE micropowders, PFA, PVDF, fluorocarbon elastomers (FKM, FFKM) PCTFE... 

PTFE micropowders or fluoroadditives (e.g., Zonyl TE-3887, DuPont) are available in aqueous dispersions with 50% to 60% solids. They have very small particle size, typically in the range of 2 to 20 pm, and contain typically 6% of nonionic wetting agent and stabilizer. Usual pH of these dispersions is 10. PTFE micropowders are used as additives to paints and coatings, for demolding, and for lubrication (for details see Publication L-13812, 01/07, DuPont). 

Table 7.7. Another method of producing PTFE micropowders is by controlled polymerization of TFE to a lower molecular weight [105]. Fluoroadditives are used as additives for plastics, elastomers, coatings, printing inks, paints, lacquers and lubricants, where they provide nonstick and/or sliding properties [106]. Benehts provided by PTFE micropowders are summarized in Table 7.8 [107].

Thermal degradation of PTFE is one of the methods to produce PTFE micropowders (for details, see Chapter 7)... 

Examples of Selected PTFE Micropowders (Nominal Values)... 

The use of modified PTFE micropowder in combination with the mechanism of the controlled degradation of polyamide and the utilisation of melt-mixing devices like a lab melt mixer or twin-screw extruders are the basis of the reactive compa-tibilisation of the completely immiscible polymers. On the basis of the discussed mechanism PTFE polyamide block copolymers are formed by reactive extrusion ... 

In order to form PTFE polyamide block copolymers high shear rates are necessary under melt processing conditions, to receive a good distribution and a further break down of PTFE micropowder particles. The particle size of the added PTFE micropowder is in the order of 2-8 pm. The crucial point for a successful coupling reaction is the contact between the carboxylic acid groups on the surface of the PTFE microcrystals and the amide groups of the molten polyamide matrix. As a result, a very homogeneous distribution of PTFE in the PA matrix is observed after reactive extrusion [21-23]. 

Upon dissolution of physical mixtiues (blends) of PTFE micropowders (without carboxylic acid groups) and PA-6 in formic acid, pure PTFE separates very fast from the solution. If the new melt-modified PTFE polyamide materials (PTFE irradiated 2,000 kGy) are dissolved in formic acid, the separation is very difficult. After separation of the insoluble content by centrifugation and ehmination of the soluble pure polyamide, the presence of an amide bond R1-CF2-CO-NH-CH2-PA between the PTFE and e.g. PA-6 was proved by IR spectroscopic investigations. The 1,708-cm band in the IR difference spectrum (Fig. 8 blue line) deriving from the direct PTFE polyamide linkage was in agreement with the IR spectra of low molecular model substances. 

It was found that the degree of the fractionated crystallisation grows with the increase of the melt viscosity, shear rate and radiation dose. Electron microscopy and AFM investigations indicate that the added PTFE micropowders are reduced in size to very small particles. 

The melt flow index of PTFE-PA-6 materials decreases with increasing amount of added PTFE micropowder but the MFI also demonstrates the processability of such compounds. 

As seen in Fig. 10 the steel surface of the wheel is modified by PTFE-PA material. The surface morphology is the same as the disc surface (used the PTFE-PA-6 test specimen). The examined PTFE PA-6 material consisting of 15-wt% PTFE micropowder (= 8.1 vol%) has only a small volume content but the AFM picture shows nearly 50% of the area of low adhesion. This means a surface modification takes place during tribological application. PTFE particles are degraded, removed and distributed on the surface by wear and tear and fixated on PA... 

Figure 16 shows the values for the tensile strength of the sandwich test specimen (skin component PTFE PA-6 with different contents of PTFE micropowder, core component reinforced PA-6 with 30% glass fibre). The tensile strength is mainly determined by the reinforced material, the PTFE polyamide material contributes only to a lesser degree. In a first approximation it is possible to calculate the skin content and the skin thickness. 

MP Injection molding Delrin 500P with 20% Teflon PTFE micropowder, with low-wear and low-friction properties Specialty friction and wear applications... 

Figure 3.3 Stress vs. strain for DuPont Engineering Polymers Delrin 500MP NC010—general purpose, medium viscosity, containing Teflon PTFE micropowder acetal resin.

Polylite Profile, Mold-making resin, Reichhold Polylube, PTFE micropowder. Custom Compounding, A Div. of Dyneon LLC Polyman, ABS alloys, Schulman, A., Inc. Polymeric Series Foams, Synthetic rubber substitute, Gaska-Tape Inc. 

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