A comparison of optical properties between solid PTFE (Teflon) and (low density) sintered PTFE

Abstract

Materials with similar chemical compositions often exhibit different optical properties due to their structural composition. PTFE is widely used in many applications for both its mechanical and optical properties. Low density sintered PTFE has optical properties that make it desirable for use as a white diffuser in applications such as remote sensing. The contrast between the commonly available high density material and the low density material may be useful for those interested in optical modeling of scattered light. Additionally, some applications may find high density PTFE suitable for some optical applications. This paper describes measurements of BRDF, 8º/hemispherical reflectance, and directional hemispherical transmittance for both high density (HD) and low density (LD) sintered PTFE. *Benjamin.tsai@nist.gov; phone 1 301 975-2347; fax 1 301 869-5700; nist.gov 1. BACKGROUND Description of high density PTFE and low density PTFEPolytetrafluoroethylene (PTFE) is a synthetic fluoropolymer, which is made either by the emulsion polymerization of tetrafluoroethylene or by the direct substitution of hydrogen atoms on polyethylene with fluorine. It is most well known by its trademark, Teflon. PTFE has many desirable properties, because it is hydrophobic, non-reactive, chemically inert, is a good lubricant, and has a high melting point, low coefficient of friction, and excellent dielectric properties.Sintering is a method for making PTFE from powder by heating it below its melting point until its particles adhere to each other. The result is a porous plastic fused together as a cohesive mass of resin particles. Particle size and shape of resin powders can be manipulated to optimize pore size, void volume, surface texture, and strength. Some advantages of sintering include: the possibility of very high purity, great uniformity, the preservation of purity from the strict fabrication process, and the stabilization of the details of repetitive operations by control of grain size in the input stages. ApplicationsSince water-containing substances do not wet PTFE, PTFE is often used as a non-stick coating for pans and cooking utensils. Also, because it is very non-reactive, it is used in containers and pipework for reactive and corrosive chemicals. Due to its excellent dielectric properties, PTFE is used as an insulator in cables and printed circuit boards. Its extremely high bulk resistivity makes it an ideal material for fabricating long life electrets, useful devices that are the electrostatic analogues of magnets. Due to its low friction, PTFE is used to make computer mice feet and in applications involving bearings, bushings, and gears. PTFE has also been used in body piercings, machinery lubricant, armor-piercing bullets, thread seal tape, grafts to bypass stenotic arteries in peripheral vascular disease, and painted surfaces to prevent insects from climbing. PTFE's high corrosion resistance makes it ideal for laboratory environments as containers, magnetic stirrers and tubing for highly corrosive chemicals such as hy...

Measurement of the absolute reflectance of polytetrafluoroethylene (PTFE) immersed in liquid xenon

“…The reflectance decreases for ultraviolet light, being 93.4% at 200 nm. It is also known that, at least between 250 and 3400 nm, the optical properties differ for low-and high-density PTFE [10]: in this wavelength range, low-density PTFE (1.55 g/ml) shows a lower transmittance and a higher reflectance compared to the high-density material (2.17 g/ml).…”

Performance properties and applications of polytetrafluoroethylene (PTFE)—a review

“…To cover the entire wavelength of the spectrum, the aforesaid measurements were carefully done with the help of Fourier transform infrared Raman spectroscopy (FTIR) and LAMBDA 950 spectrophotometer. The results shown were in favor of LD PTFE because of the order of magnitude for DHR is less than HD PTFE [42].…”

Predicting liquid loss of frozen and thawed cod from hyperspectral imaging

“…The successive frames F(λ, x) are stored as a hyperspectral image R i (λ, x, y). In order to correct for changes in camera sensitivity and illumination with time, a calibration sample of Teflon, which has stable optical properties (Tsai, Allen, Hanssen, Wilthan, Zeng, 2008), is measured before each set. The calibration sample used is a square 300 mm on each side with a thickness of 25 mm.…”