Fluoropolymers examination

Over the last decade, selected papers1114 have examined the deposition of fluoropolymers, using RF magnetron sputtering. All of these papers have examined the deposition of PTFE, with some of them2314 also studying the deposition of polyimide (PI) films. This chapter extends these studies and will report on the sputter deposition behavior of PTFE (polytetrafluoroethylene), PVDF (polyvinylidenefluoride), and FEP (fluorinated ethylene propylene copolymer) films. 

A good example of the difficulties involved in accessing toxicological data of organo-fluorine compounds can be seen by examining the work of Hodge, Smith and Chen,5 published in 1963. This included results many of which were mainly preliminary toxicity data, reported in the literature until 1961. Much data that was not comparable in depth of focus, meaningfulness, mode of application, animal material, doses, and quality of research was summarized in this article. Information contained within such an article is difficult for experimental chemists to assess. Further data on the toxicity of fluoroalkanes, fluoroalkenes and fluoropolymers has been published.6... 

It is obvious that the special characteristic of fluoropolymers for NMR is the incorporation of the F nucleus, which is in many ways particularly suitable for study and can act as a unique probe to examine the chemical microstructure, domain structure and mobility at the molecular level for these materials. However, some special techniques are frequently required for the best results from F NMR of solid polymers. These are fully described in Section 6.6. The net result of the difficulties encountered in obtaining high-resolution solid-state F spectra is that relatively few research papers to date have reported spectra with optimised resolution. Therefore, most reported F... 

According to the test, five specimens (each 50 mm long, 100 mm wide, and 1 mm thick) are conditioned at ambient temperature as specified in the test, and placed in a forced draft oven equipped with a biaxial rotator. Specimens should be attached to the rotator by metal slips lined with fluoropolymer film and should not directly contact with the metal clips or metal parts of the oven. The frequency of rotation about the horizontal and vertical axes of the rotator should be 1-3 min . The time to failure is determined by regular visual examination of the specimens as the number of days after which the specimen shows localized crazing, crumbling, or discoloration, or a combination thereof. According to the standard procedure, the oven temperature shall be 150°C (302°F). 

Currently, only a direct visual examination of the plastics including fluoropolymer offers any real... 

Fluoropolymers have been used as processing aids because small quantities can reduce signih-cantly the overall viscosity and thus facilitate extrusion. Feng et al. [1996] examined the mechanism of viscosity reduction in the capillary flow of HDPE/fluoroelastomer blends. X-ray photoelectron spectroscopy, used to characterize the composition of the extmdates surface, indicated only very small traces of the fluoroelastomer on the extrudate, pointing to the fact that the viscosity reduction is due to adhesive failure between the fluoropolymer layer and HOPE. 

We examined the evaporation of microdrops of water with different initial volumina on a silicon surface coated with a 30 nm thin fluoropolymer film (perfluoro-1,3-dimethylcyclohexane). The initial contact angle was = 90° and remained constant for more than half of the evaporation time. During the experiments, the temperature (T = 25 °C) and the relative humidity (RH 99%) were constant. We used a video microscope to track the dimensions of the evaporating drop from the side [23,30]. 

Li et al. [5] used a combination of 2D-NMR methods to study a similar perflu-oropolyether. They examined carboxyl-terminated low MW oligomers of PHFPO which served as a model for Dupont s Krytox fluoropolymers. They used spectra from selective one- and two-bond Fj C HSQC experiments, similar to the data shown in Figure 24.8, to identify the atomic connectivities within each polyether unit. Note that the correlations to F resonances A3 and Aj occur at slightly different chemical shifts in the one-bond experiment (top spectra) compared to those in the two-bond spectra (bottom spectra). This is due to a one-bond C isotope effect which shifts resonances of attached fluorines up-field by approximately 0.1 ppm compared to the resonances of fluorines attached to C. The two-bond isotope effect is 10-fold smaller and is too small to notice in these 2D-NMR spectra. Similar sets of correlations were observed for each monomer unit in the structure. 

Kawai s (7) pioneering work almost thirty years ago in the area of piezoelectric polymers has led to the development of strong piezoelectric activity in polyvinylidene fluoride (PVDF) and its copolymers with trifluoroethylene and tetrafluoroethylene. These semicrystalline fluoropolymers represent the state of the art in piezoelectric polymers. Research on the morphology (2-5), piezoelectric and pyroelectric properties (6-70), and applications of polyvinylidene fluoride 11-14) are widespread in the literature. More recently Scheinbeim et al. have demonstrated piezoelectric activity in a series of semicrystalline, odd numbered nylons (75-77). When examined relative to their glass transition tenq>erature, these nylons exhibit good piezoelectric properties (dai = 17 pCTN for Nylon 7) but have not been used commercially primarily due to the serious problem of moisture uptake. In order to render them piezoelectric, semicrystalline polymers must have a noncentrosynunetric crystalline phase. In the case of PVDF and nylon, these polar crystals cannot be grown from the melt. The polymer must be mechanically oriented to induce noncentrosynunetric crystals which are subsequently polarized by an electric field. In such systems the amorphous phase supports the crystalline orientation and polarization is stable up to the Curie temperature. 

Microscopic examination of a polyethylene (PE) containing PPA reveals discrete micron-sized, droplet-shaped particles of the fluoropolymer. Figure 1 shows an ideally dispersed PPA in a PE matrix. Typical PPA use levels vary from 200 to 1000 ppm, depending on the application. 

The objective of this work was the utilization of some recently developed techniques that may be of value in the characterization of the adhesive process between a titanium alloy and a variety of polylmide resin systems. The techniques utilized were electron spectroscopy for chemical analysis (ESCA), specular reflectance infrared spectroscopy, and scanning electron microscopy. Contact angles of various liquids on the titanium alloy were also measured. Specifically, the question arises to what extent are any of these techniques of value in the characterization of the interface and in the determination of interactions for the titanium 6-4/polyimide resin systems. Dwight and Riggs (5) successfully used ESCA, soft X-ray spectroscopy, contact angle hysteresis and electron microscopy to examine fluoropolymer surfaces. 

This chapter examines why fluoropolymers exhibit extreme properties. It focuses on the reasons that replacement of hydrogen with fluorine in hydrocarbon macromolecules improves their thermal stability, chemical resistance, electrical properties, and coefficient of friction. Understanding the role of fluorine in determining the properties of a polymer will contribute to a more in depth appreciation of some of the other information in this book. It will also allow the readers to make more informed judgments about fluoropolymers and their applications. 

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