Polytetrafluoroethylene Fiber Research Articles

The preparation and the application of grafted polytetrafluoroethylene fiber as a cation exchanger for adsorption of heavy metals

A novel type of weakly acidic cation exchange fiber have been prepared by 60Co irradiation grafting with acrylic acid onto the polytetrafluoroethylene (PTFE) fiber. The exchange capacity of the grafted fiber is 3.06 mmol/g. The pH titration curve of the grafted fiber showed there is a sudden jump when pH is round 6–10, and the acidity of the grafted fiber is stronger than that of commercial weakly acidic exchange D-152 resin. The grafted fiber showed the excellent selectivity of static and dynamic adsorption for Cu 2+, La 3+ and Pb 2+ when Mg 2+, Ca 2+, Cr 3+, Co 2+, Ni 3+, Cu 2+, Ag +, La 3+, Pb 2+ were coexisted. The grafted fiber could be regenerated completely with almost equimolar diluted hydrochloric acid.

Acrylic acid grafted polytetrafluoroethylene fiber as new packing for flow injection on-line microcolumn preconcentration coupled with flame atomic absorption spectrometry for determination of lead and cadmium in environmental and biological samples

In this work, acrylic acid grafted PTFE fibers were prepared as a new packing material for flow injection (FI) on-line microcolumn preconcentration coupled with flame atomic absorption spectrometry (FAAS) for determination of trace lead and cadmium in environmental and biological samples. Effective preconcentration of trace cadmium and lead was achieved in a pH range of 3.5–6.5 on a microcolumn packed with the developed new packing material. The retained lead and cadmium were efficiently eluted, respectively, with 1.0 mol/l HNO3 and 0.5 mol/l HCl for on-line FAAS determination. The developed sorbent exhibited fairly fast kinetics for the adsorption of Pb(II) and Cd(II), permitting the use of high sample flow rates up to at least 10.8 ml/min for the FI on-line microcolumn preconcentration system without loss of the retention efficiency. With a preconcentration time of 45 s at a sample loading flow rate of 10 ml/min, the enhancement factor was found to be 49 for Pb and 73 for Cd at a sample throughput of 55 h−1. The detection limits (3σ) was 0.26 and 0.10 μg/l for Pb and Cd, respectively. The precision (RSD) for 11 replicate measurements was 1.9% at the 25 μg/l Pb level, and 0.9% at the 10 μg/l Cd level. The developed method was successfully applied to the determination of trace Pb and Cd in a variety of environmental and biological samples.

Acrylic acid grafted polytetrafluoroethylene fiber as new packing for flow injection on-line microcolumn preconcentration coupled with flame atomic absorption spectrometry for determination of lead and cadmium in environmental and biological samples

In this work, acrylic acid grafted PTFE fibers were prepared as a new packing material for flow injection (FI) on-line microcolumn preconcentration coupled with flame atomic absorption spectrometry (FAAS) for determination of trace lead and cadmium in environmental and biological samples. Effective preconcentration of trace cadmium and lead was achieved in a pH range of 3.5–6.5 on a microcolumn packed with the developed new packing material. The retained lead and cadmium were efficiently eluted, respectively, with 1.0 mol/l HNO 3 and 0.5 mol/l HCl for on-line FAAS determination. The developed sorbent exhibited fairly fast kinetics for the adsorption of Pb(II) and Cd(II), permitting the use of high sample flow rates up to at least 10.8 ml/min for the FI on-line microcolumn preconcentration system without loss of the retention efficiency. With a preconcentration time of 45 s at a sample loading flow rate of 10 ml/min, the enhancement factor was found to be 49 for Pb and 73 for Cd at a sample throughput of 55 h −1. The detection limits (3 σ) was 0.26 and 0.10 μg/l for Pb and Cd, respectively. The precision (RSD) for 11 replicate measurements was 1.9% at the 25 μg/l Pb level, and 0.9% at the 10 μg/l Cd level. The developed method was successfully applied to the determination of trace Pb and Cd in a variety of environmental and biological samples.

Flow injection on-line sorption preconcentration coupled with hydride generation atomic fluorescence spectrometry using a polytetrafluoroethylene fiber-packed microcolumn for determination of Se(IV) in natural water

Polytetrafluoroethylene (PTFE) fiber was demonstrated as a new sorbent for flow injection on-line sorption preconcentration of trace elements. The on-line PTFE fiber packed microcolumn preconcentration system was coupled with hydride generation atomic fluorescence spectrometry (HG-AFS) for the determination of (ultra)trace selenite (Se(IV)) in natural water. Selective determination of Se(IV) in aqueous solution was achieved by on-line formation of Se(IV)–pyrrolidinedithiocarbamate (PDC) complex over a wide sample acidity range of 0.01–50% v/v HCl, its sorption onto the surface of the PTFE fiber in the microcolumn, elution with 3% m/v KBH4 in 0.5% m/v KOH, hydride generation with 15% v/v HCl solution and determination with atomic fluorescence spectrometry. The alkaline KBH4 solution was employed not only as an efficient eluent but also as the reductant to produce selenide anion for subsequent hydride generation. With a consumption of 12.4 ml of sample solution, a detection limit (3σ) of 4 ng l−1 was achieved at a sample throughput of 26 samples h−1. The retention efficiency was 67%, being five times that obtained with a PTFE knotted reactor (KR). The linear ranges of the diagrams of signal intensity against sample loading flow rate, and sample loading time, were much wider than those achieved with a KR, offering more potential for obtaining high sensitivity by increasing sample loading rates and/or sample loading time. The precision for 11 replicate measurements of 0.5 µg l−1 Se(IV) was 1.5% (RSD). The recoveries of Se(IV) from natural water samples varied from 96 to 108%. The concentration of Se(IV) in a certified reference material (NASS-5, sea-water) determined by the present method with a simple aqueous standard curve calibration was in good agreement with the certified value. The developed method was also successfully applied to the detection of Se(IV) in local river water, lake water and sea-water samples.

The effect of interface modification between POM and PTFE on the properties of POM/PTFE composites

A plasma technique was applied to modify the surface of polytetrafluoroethylene (PTFE) fiber to improve the compatibility between PTFE and polyacetal (POM). This technique used argon (Ar) plasma to treat PTFE fiber first and then grafting the fiber with acrylic acid (AAc) by peroxidation. The Ar plasma-treated PTFE (PPTFE) fiber and AAc-grafted PPTFE (AAc-g-PPTFE) fiber were added into POM to increase the wear resistance and to decrease the friction coefficient of POM. The variables of the experiments were plasma treatment time, monomer concentration of AAc, and grafting time. The graft copolymer was characterized by Fourier transform infrared (FTIR) spectroscopy. The stress–strain behavior, impact strength, Taber wear factor, friction coefficient, and morphology of composites were also investigated. The properties of POM/PTFE composites could be successful modified by surface modification of PTFE in this investigation. The impact strength of POM/AAc-g-PPTFE composites was more than twice of that of POM/PTFE composites. The Taber wear factor and friction coefficient of POM/AAc-g-PPTFE composites decreased markedly. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 78: 800–807, 2000

Transcrystallization of PTFE fiber/PP composites. II. Effect of transcrystallinity on the interfacial strength

It has been found that transcrystallinity of polypropylene (PP) develops easily on the polytetrafluoroethylene (PTFE) fiber surface in spite of the low surface energy of the fiber. Effect of the transcrystallinity on the interfacial strength has been extensively investigated using a single-fiber pull-out test. By controlling the crystallization temperature, range 25-130°C, the thickness of the transcrystalline layer varied from 0 to 175 μm for thick specimens, ca. 1 mm thick. Measurements of the adhesive fracture energy, the interfacial shear strength and the frictional stress were carried out for specimens with different embedded fiber lengths. Results show that interfacial strength and fracture energy are independent of the transcrystalline thickness. The calculated value of interfacial shear strength is 3.6 MPa, and the fracture energy for debonding is 2.1 J/m 2 . The presence of transcrystallinity does not promote the level of adhesion in PTFE/PP composites. However, the frictional stresses at the debonded fiber/matrix interface increase with transcrystalline thickness. It is attributed to the residual stresses which arise from shrinkage when specimens are cooled from crystallization temperature to room temperature.

Transcrystallization of PTFE fiber/PP composites (I) crystallization kinetics and morphology

Transcrystallization of polypropylene (PP) on the polytetrafluoroethylene (PTFE) fiber was investigated. Both nucleation rate and crystal growth rate were determined by a polarized optical microscope. Based on the theory of heterogeneous nucleation, it has been found that the induction time can correlate well with the nucleation rate in determining the interfacial free energy difference function Δσ. The ratio of Δσ in the bulk matrix to that at the interface is 1.63 which implies the transcrystalline growth is favorable from a thermodynamic point of view. No difference in crystal growth rate of PP has been found in either spherulites or transcrystalline layers. On the basis of regime theory, a transition between regimes II and III was observed at ΔT = 48K. From the morphology studies, it has been found that the thickness of the transcrystalline layer increases with crystallization temperature, from 30 to 120 μm in the temperature range of 110–140°C. The growth of transcrystalline layer is hindered by the spherulites nucleated in the bulk. Moreover, the radius of spherulites adjacent to the transcrystalline layer is much smaller than that distant to the fiber. No significant increase in nucleation density at fiber ends is observed. Effect of internal stresses of fibers on the fiber's nucleating ability is not pronounced. © 1996 John Wiley & Sons, Inc.

Effects of acidic fibroblast growth factor on normal and ischemic myocardium.

We sought to determine the effects of acidic fibroblast growth factor (FGF) on ischemic and normal myocardium and to determine whether direct application of acidic FGF to the heart could promote angiogenesis. Eighteen dogs underwent placement of an ameroid constrictor on the left anterior descending coronary artery (LAD). Three weeks later, a left internal mammary artery (IMA) pedicle was positioned over the LAD territory, with a sponge saturated with acidic FGF (n = 12) or saline (n = 4) interposed between the pedicle and the heart. Polytetrafluoroethylene fiber or collagen I sponges were used to deliver the acidic FGF. Weekly angiography of the IMA was performed in all dogs, but significant IMA to coronary collaterals were not demonstrable in any dog. Eight dogs had histological evidence of subendocardial infarction in the LAD territory (five acidic FGF, three control, p = NS). Striking smooth muscle cell hyperplasia was present in arterioles and small arteries exclusively in areas of subendocardial infarction in all of the acidic FGF-treated dogs but in none of the control dogs (p less than 0.05). Noninfarcted myocardium appeared normal in all dogs. In two additional dogs, ameroid constrictors were not placed on the LAD, such that acidic FGF-treated sponges were placed on normally perfused myocardium of the LAD territory. Histological evaluation of those hearts revealed normal myocardium, without evidence of myocardial infarction or smooth muscle cell hyperplasia. Thus, when acidic FGF is delivered to the myocardium via an epicardial sponge in dogs whose coronary flow is compromised, acidic FGF does not cause an angiogenic response in viable myocardium but causes vascular smooth muscle cell hyperplasia in areas subjected to ischemic injury.

Crystal Structure of High Pressure Phase of Polytetrafluoroethylene

The crystal structure of high pressure phase of polytetrafluoroethylene (PTFE) has been determined by X-ray methods. A high pressure X-ray diffraction apparatus which enables to get the fiber pattern of crystalline sample under purely hydrostatic high pressure at high temperature has been constructed. A small specimen of PTFE fiber was held in the bore of a beryllium window for X-ray. The fiber pattern of high pressure phase of this polymer has been recorded on a cylindrical film at 5500km/cm2, 78°C. It is found that in this phase the molecules have a planar zigzag arrangement different from that of a helix at atmospheric pressure. The unit cell is orthorhombic, with a=8.73 A, b=5.69 A, c=2.62 A. The result of the X-ray diffraction studies agrees with that of the other physical properties of PTFE in high pressure phase.