Polytetrafluoroethylene effects

Brown, R. G., Vibrational Spectra of Polytetrafluoroethylene Effects of Temperature and Pressure, J. Chem. Phys., 40 2900, 1964. 

Rye RR, Arnold GW. Depth dependence of alkali etching of polytetrafluoroethylene effect of X-ray radiation. Langmuir. 1989 5 1331-1334. 

Radiation Effects. Polytetrafluoroethylene is attacked by radiation. In the absence of oxygen, stable secondary radicals are produced. An increase in stiffness in material irradiated in vacuum indicates cross-linking (84). Degradation is due to random scission of the chain the relative stabiUty of the radicals in vacuum protects the materials from rapid deterioration. Reactions take place in air or oxygen and accelerated scission and rapid degradation occur. 

There are thus no solvents at room temperature for polyethylene, polypropylene, poly-4 methylpent-l-ene, polyacetals and polytetrafluoroethylene. However, as the temperature is raised and approaches F , the FAS term becomes greater than AH and appropriate solvents become effective. Swelling will, however, occur in the amorphous zones of the polymer in the presence of solvents of similar solubility parameter, even at temperatures well below T. ... 

Fig. 11. Effect of polyolefin primers on bond strength of ethyl cyanoacrylate to plastics. All assemblies tested in accordance with ASTM D 4501 (block shear method). ETFE = ethylene tetrafluoroethylene copolymer LDPE = low-density polyethylene PFA = polyper-fluoroalkoxycthylene PBT = polybutylene terephthalate, PMP = polymethylpentene PPS = polyphenylene sulfide PP = polypropylene PS = polystyrene PTFE = polytetrafluoroethylene PU = polyurethane. From ref. [73].

Fig. 6.9. Normalized fracture toughness, (Kc - AKQ)/K. of short glass fiber-thermoplastics injection molded composites as a function of reinforcing effectiveness parameter, ft (O) polyetheretherketone (PEEK) matrix (K = 6.5 MPa m) (A) polytetrafluoroethylene (PTFE) matrix (K = 1.9 MPaym).

Polymers such as polystyrene, poly(vinyl chloride), and poly(methyl methacrylate) show very poor crystallization tendencies. Loss of structural simplicity (compared to polyethylene) results in a marked decrease in the tendency toward crystallization. Fluorocarbon polymers such as poly(vinyl fluoride), poly(vinylidene fluoride), and polytetrafluoroethylene are exceptions. These polymers show considerable crystallinity since the small size of fluorine does not preclude packing into a crystal lattice. Crystallization is also aided by the high secondary attractive forces. High secondary attractive forces coupled with symmetry account for the presence of significant crystallinity in poly(vinylidene chloride). Symmetry alone without significant polarity, as in polyisobutylene, is insufficient for the development of crystallinity. (The effect of stereoregularity of polymer structure on crystallinity is postponed to Sec. 8-2a.)... 

The opacity of plastic foams, and polymers with scratched surfaces, is also governed by Fresnel s law. The n value of the gas which occupies the scratch indentation is much lower than that of the polymer. Light may be directed through rods of transparent polymers, such as PMMA. This effect may be enhanced when the rod or filament is coated with a polymer with a different refractive index, such as polytetrafluoroethylene (ptfe). Optical fibers utilize this principle. 

Polytetrafluoroethylene (PTFE) is an attractive model substance for understanding the relationships between structure and properties among crystalline polymers. The crystallinity of PTFE (based on X-ray data) can be controlled by solidification and heat treatments. The crystals are large and one is relieved of the complexity of a spherulitic superstructure because, with rare exceptions, spherulites are absent from PTFE. What is present are lamellar crystals (XL) and a noncrystalline phase (NXL) both of which have important effects on mechanical behavior. 

Conformational energy estimates are employed to determine the conformational characteristics of polyfvinyl fluoride) (PVF), polyfluoromethylene (PFM), and polytrifluoroethylene (PTF3). Effects of stereoconfiguration and, in the case of PVF and PTF3, the presence of head-to-head tail-to-tail (HH TT) defect structures are considered. The calculated results are compared to corresponding values found for polyfvinylidene fluoride), polytetrafluoroethylene, and polyethylene, and the equilibrium flexibilities of PVF, PFM, and PTF3 are discussed on this basis. 

Bio-Rex membranes (AG1, AG50), which are crosslinked anion- and cation-exchange resins enmeshed in polytetrafluoroethylene, are an alternative to ion-exchange resins. These membranes achieve the same effectiveness as open ion-exchange columns, but analysis times are shorter (51). 

In Gee s (1957) Tilden Lecture he quotes entropies of fusion calculated in the case of polytetrafluoroethylene from the effect of pressure on the melting point... 

Slichter, (1959) found that a narrowing of the proton resonance line width occurred 10—20° C above Tg in the case of polyisobutylene and natural rubber but closely at Tg in the case of atactic polypropylene. The two room temperature transitions in polytetrafluoroethylene, which are so clearly visible in the specific heat-temperature curve, Fig. 12, were found by Slichter (1958a) in a fluorine nucleus magnetic resonance study to cause a drop in the second moment with rise of temperature, but the whole effect occurred over the wide temperature range of 225 to 320° K. The slight bulge" in the specific heat-temperature curve of polymethyl methacrylate from 130 to 180° K, Fig. 13, might possibly be correlated with the drop in the NMR second moment between 150° and 200° K found by Powles (1956). 

---