Spectra polytetrafluoroethylene

The use of chemical mapping is demonstrated in the following example involving the delamination of a silicone primer and polytetrafluoroethylene (PTFE) material. The positive mass spectrum acquired from the delaminated interface contains peaks known to be uniquely characteristic of PTFE (CF3 at mass 69) and the silicone primer (Si(CH3)3 at mass 73). Figures 6 and 7 are secondary ion im es of the CF3 and (Si(CH3)3 fragments taken from a 1-mm area of the delaminated interface. These maps clearly indicate that the PTFE and the silicone primer exist in well-defined and complementary areas. 

Powdered Teflon for use in pyrots is covered by US Mil Spec MIL-P-48296IPA) (1 May 1974), Polytetrafluoroethylene (TFE) . Three classes of material are specified (1,2 3). The requirements are purity, 99.4% min infrared spectrum, peaks consistent with figure shown color, TFE shall be opaque and the color shall range from white to gray moisture, 0.05% max ash, 0.1% max mp, 337° 10°C packing density, Class 1 — 1.18 0.13g/cc, Class 2 - 1.25 0.02g/cc, Class 3- 1.14 0.09g/cc particle size by sieve analysis, Class 1 — 95 15 microns, Class 2 — 237 27 microns, Class 3 — 200 30 microns particle size distribution by sieve analysis, as specified in Table 1... 

The EPR spectrum of irradiated polytetrafluoroethylene can be interpreted as arising from radicals of the type shown below ... 

Polytetrafluoroethylene (PTFE) has a chemical structure which can be designated by (CF2)k. From its resemblance to the chemical structure of polyethylene it might be thought that the spectra of these two polymers should be quite similar. They do in fact resemble each other, but there are also important differences. This is a consequence of the fact that the PTFE chain configuration is quite different from that of polyethylene, and also the intramolecular forces are undoubtedly significantly different in the two cases. As we shall see, the spectrum is moderately well understood, but not in quite as great detail as that of polyethylene. This is primarily a result of the lack of Raman data on the polymer and certain key polarization data in the infrared. 

Fig. 7. Infrared spectrum of oriented polytetrafluoroethylene. - perpendicular to stretching direction — E parallel to stretching direction [Liang and Krimm (777)]...

A routine method for determining relative crystallinity based on the amorphous bands in the spectrum has proved more rapid and precise than the x-ray method. In practice, the ratio of the 778 cm-1 (12.85 ft) and 2367 cm-1 (4.22 ft) band intensities is measured. Use of a ratio eliminates the thickness measurement and increases precision to about 1% at 50% crystallinity and considerably better at higher levels. A density measurement and an infrared crystallinity determination when combined give an estimate of the fraction of microvoids which can occur in molded specimens of polytetrafluoroethylene. The density of a sample is predicted on the basis of its crystallinity as measured by the infrared method and the difference between this density and the actual density measured by displacement in water is a measure of the microvoid content. This determination is precise to about 0,2% voids by volume. By the use of confirmatory infrared measurements, it is possible to check the possibility that the presence of a substantial percentage of voids may have led to erroneous indications of the molecular weight in the standard specific gravity test discussed earlier. 

Figure 9 Radio frequency glow discharge mass spectrometry (rf GD-MS) spectrum of a 1.5-mm-thick polytetrafluoroethylene (PTFE) sample (rf power = 20 W, Ar pressure = 0.075 mbar, logarithmic units of ion signal current). (From Ref. 70.)...

There are several disadvantages inherent in the alkali halide disk technique. The alkali halides which are generally used are hygroscopic and it is very difficult to exclude all traces of water. This often results in a hydroxyl band in the spectrum. A number of compounds containing hydroxyl groups either form hydrogen bonds with the alkali halide or are adsorbed on its surface, so the method is unsuitable if the hydroxyl band is to be examined. In such cases, polytetrafluoroethylene (PTFE) powder can sometimes be used in place of the alkali... 

The most intense absorptions in the spectrum are those due to the fluorocarbon main chain. The spectrum of Nafion therefore strongly resembles that of polytetrafluoroethylene (PTFE ... 

Chantry GW, Nicol EA, Jones RG, Willis HA, Cudby MEA ( 1977)On the vibrationalassignment problem for polytetrafluoroethylene 1. The infrared spectrum. Polymer 18 37... 

The observation of the broad line continuous wave (CW) spectrum of polyethylene (PE), and spectrum of polytetrafluoroethylene (PTFE) by... 

Microporous Polyethylene Films. Disposable IR cards are available to which samples can be directly applied for infrared analysis (Fig. 8.8). These convenient IR cards have two 19-mm circular apertures containing a thin microporous film of chemically resistant polyethylene. Cards having microporous polytetrafluoroethylene are also available for special applications. The cards with polyethylene films may be used for infrared analysis from 4000-400 cm except for the region of aliphatic C-H stretching that occurs between 3000-2800 cm In this region of an FT-IR spectrum, there are several sharp... 

Polytetrafluoroethylene, — (CF2—CF2) —, is also known commercially as Teflon—see Reference Spectrum 23 for the IR and Raman spectra. The CF2 stretching vibration occurs as the most intense IR absorption band, near 1200 cm This band is a multiplet, and consists of three peaks at 1240, 1215, and 1150 cm Other major bands are located at 641, 554, and 515 cm and are assigned to the CF bending modes. The IR absorption band at 2366 cm is the overtone of the CF2 stretching vibration. 

If the dirt or contaminant spots can be dissolved in a low boiling-point solvent, solvent extraction (removal) may be an effective method for collecting the sample. If the base plate is a plastic material, the solvent must be carefully selected to ensure that none of the polymer support is dissolved. The solution obtained may then be slowly dripped from a syringe onto a thin film, for example, of polyethylene or polytetrafluoroethylene, and after the solvent has evaporated completely, the remaining powder can then be made into a KBr disk. If the solution is dropped directly onto an infrared-transparent window or a metal plate, the spot often tends to spread to form a circle of the sample after evaporation of the solvent, making the sample then not suitable for either the transmission or transmission-reflection measurement method. If the solution is dropped into a small hole (for example, with a diameter of 1 mm and a depth of 3 mm drilled into a metal support) filled with KBr powder, a diffuse-reflection spectrum may be measured from this after complete evaporation of the solvent. 

Figure 1. XPS surv ey spectrum of polytetrafluoroethylene obtained using Mg K x-radiation.

An early analysis of the heat capacity of polytetrafluoroethylene was made by Starkweather (1960). He fitted the Stockmayer and Hecht frequency spectrum (see Fig. IIL15B) in the region of 15 to 75° K using a maximum frequency of 8.3 10 cps.The number of vibrators was 2.83 in contrast to polyethylene with closer to two skeletal vibrations. A more detailed analysis was performed by Gotlib and Sochava (1962). They compared polytetrafluoroethylene with polyethylene assuming a planar... 

Because of the unique orientation of the oxygen mole-cule-with-unpaired spin (—O2"—with respect to the PE molecular axis, the peroxy radical produces (theoretically) asymmetric tines in the ESR spectrum with two g-values, gii and gj. Ranby and Rabek presented a discussion on the dependence of the ESR spectrum on the orientation of the peroxy end in polytetrafluoroethylene (Pl EE) radical [21]. Rabek provides an ESR spectrum of the peroxy radical in polypropylene and also in polyethylene (Chapter 3 [2]). The polypropylene-peroxy radical presented is a clear ESR spectrum, which can be considered as the fingerprint for the peroxy radical the ESR spectrum of the polyeth-ylene-peroxy (low density polyethylene) is not as well defined. Tor a better understanding, readers are referred to a survey of the mechanisms for production, propagation, and termination of the peroxy radicals in polyolefins, including PE, compiled by J. F. Rabek (Chapter 3 [2]) and by Dole (Chapter 13 [1]). 

Because of the strong electron negativity of fluorine atoms, the binding energy of the core level electron of carbon is shifted enough so that the amount of shift can be measured by the ESCA Clg spectrum. Consequently, ESCA can distinguish carbons that have one, two, or three fluorine atoms attached. Conventional polytetrafluoroethylene (Teflon) shows a singlet Clg peak, which corresponds to -CF2 at 291.5 e.v. This peak is shifted from the Clg peak of normal carbons (bound to H or C) at 284.5 e.v. 

A typical spectrum of ESCA shows peaks as a function of binding energy, as shown in Fig. 4.9 for polytetrafluoroethylene. Cls and FIs peaks on a clean surface indicate that the PTFE surface is comprised of only carbon and fluorine. The energy shift can be curve-fitted by trial and error to determine the functional groups on the surface. The most simplified report that ESCA generates is a survey of the atomic composition of the surface elements, with the exception of hydrogen. A helpful tool to... 

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