Cross-linking of polytetrafluoroethylene during room-temperature irradiation

Exposure of polytetrafluoroethylene (PTFE) to α-radiation was investigated to determine the physical and chemical effects, as well as to compare and contrast the damage mechanisms with other radiation types (β, γ, or thermal neutron). A number of techniques were used to investigate the chemical and physical changes in PTFE after exposure to α-radiation. These techniques include: Fourier transform infrared spectroscopy (FTIR), differential scanning calorimetry (DSC), and fluorescence spectroscopy. Similar to other radiation types at low doses, the primary damage mechanism for the exposure of PTFE to α-radiation appears to be chain scission. Increased doses result in a change-over of the damage mechanism to cross-linking. This result is not observed for any radiation type other than α when irradiation is performed at room temperature. Finally, at high doses, PTFE undergoes mass-loss (via small-fluorocarbon species evolution) and defluorination. The amount and type of damage versus sample depth was also investigated. Other types of radiation yield damage at depths on the order of mm to cm into PTFE due to low linear energy transfer (LET) and the correspondingly large penetration depths. By contrast, the α-radiation employed in this study was shown to only induce damage to a depth of approximately 26 μm, except at very high doses.     

Synthesis of polytetrafluoroethylene/polyacrylate core-shell nanoparticles via emulsifier-free seeded emulsion polymerization

Polytetrafluoroethylene (PTFE)/polyacrylate core-shell nanoparticles were produced via the emulsifier-free seeded emulsion polymerization of acrylate monomers with PTFE latex as seed. The monomer conversions under different synthesis parameters were monitored by a gravimetric method. The polymerization conditions for preparing PTFE/polyacrylate core-shell nanoparticles were surveyed and optimized. The chemical component of the PTFE/polyacrylate particles was confirmed by comparing the Fourier-transform infrared spectra of PTFE and PTFE/polyacrylate particles. The core-shell structure of the resulting PTFE/polyacrylate nanocomposite particles was investigated by transmission electron microscopy. The water contact angles of the films prepared from PTFE/polyacrylate nanocomposite particles showed that the films were hydrophilic, which confirmed that polyacrylate covered the surface of the PTFE particles. This kind of PTFE/polyacrylate core-shell nanoparticles might advance the compatibility of PTFE with other materials due to the covering of the polyacrylate shell on the surface of PTFE, which would make them promising in various fields.     

Structure development in multistage stretching of PTFE films

The structure of expanded poly(tetrafluoroethylene) (ePTFE) films that were produced by uniaxial or biaxial stretching of a calendared sheet were studied by wide angle X‐ray diffraction (WAXD), small angle X‐ray scattering, differential scanning calorimetry (DSC), and scanning electron microscopy. The molecular orientation of the stretched films was analyzed by WAXD flat films and pole figures. Biaxial orientation factors were computed to interpret the level of orientation quantitatively. DSC scans showed that oriented samples exhibited two melting peaks, one at the commonly observed temperature in the range 340–345 °C and one around 380 °C. The possible causes of this high‐temperature melting peak and its relation to previously described processes is discussed. The microporous nature of the ePTFE films is also briefly discussed. © 2010 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys, 2010     

Preparation and properties of polytetrafluoroethylene-modified polyacrylate via emulsion polymerization

One method of preparation of polytetrafluoroethylene(PFTE)-modified polyacrylate emulsion has been studied. Through pre-emulsion technology, PTFE powder could be dispersed by high speed shearing with high-speed dispersor. PFTE-modified polyacrylate has been prepared by in situ copolymerization of n-butyl acrylate, n-methyl methacrylate, n-styrene, and α-methacrylic acid in the presence of seed particles of dispersed PTFE by semi-starved addition method. The properties of the emulsion under various polymerization conditions were investigated. The morphology of the latex particles with about 180 nm were observed by scanning electron microscopy (SEM). It was shown that the particles with linear PTFE/core–polyacrylate/shell could eventually be dispersed homogeneously. TG showed that the heat-stability was improved obviously.     

A novel crystalline structure - poly(tetrafluoroethylene) spherulitic crystal and its crystallization kinetics

Spherulitic crystals of Poly(tetrafluoroethylene) (PTFE), for the first time, are observed in a kind of PTFE composite, and are verified by polarized optic microscopy (POM). Differential scanning calorimetry (DSC) is used to study the isothermal crystallization kinetics of PTFE matrix at different temperatures. The result shows that Avrami parameter is near 3, which may be elucidated that PTFE crystallizes three-dimensionally from preexisting nuclei. The result is in accordance with scanning electric microscopy (SEM) and POM observation of the crystalline morphology of PTFE. Compared with the rate of one-dimension crystallization, the rate of three-dimension crystallization is lower. So the three-dimension crystallization is easier to control than the one-dimension crystallization of PTFE.     

Surface characterization and London dispersive surface free energy of functionalized single-walled carbon nanotubes with a blend of polytetrafluoroethylene by inverse gas chromatography

The SWCNTs and SWCNT-polytetrafluoroethylene (PTFE) blend were prepared by using simple reaction mixture in the presence of chromosorb (SiO₂). Surface morphology of SWCNTs and (SWCNT-PTFE) blend was characterized by Fourier transform infrared spectroscopy (FT-IR), X-ray diffraction (XRD), thermal gravimetric analysis (TGA), transmission electron microscopy (TEM), scanning electron microscopy (SEM), and surface BET analysis. In addition, the surface thermodynamic properties of n-alkanes and polar probe net retention volumes are measured by inverse gas chromatography (IGC). The London dispersive surface free energy values were found to be decreased linearly with increase of temperature. The specific component of the surface free energy of adsorption for the polar probes was obtained using the Donnet-Park method. The surface character “S” value (K_b/K_a) at SWCNTs was found to be 0.74, and SWCNT-PTFE blend surface character value was found to be 0.86. This result demonstrates that the (SWCNT-PTFE) blend surface contains relatively more acidic sites then that of SWCNT surface. Therefore, the IGC results provide useful complementary information on the (SWCNT-PTFE) blend surface.     

电热蒸发进样—等离子体原子发射光谱中钒和钛的蒸发机理研究

自1974年Nixon报道钽丝电热蒸发作为ICP-AES进样技术以来,这一技术已引起了人们的极大兴趣,受到越来越广泛的重视。电热蒸发(ETV)-ICP-AES是一种将蒸发和激发分步进行的联用技术。石墨是目前普遍使用的蒸发器材料。然而,在高温下某些元素和石墨材料可以发生碳化反应,形成热稳定的碳化物,使分析物蒸发不完全或根本不蒸发,从而影响分析结果的灵敏度和准确性。为了解决这一问题,我们曾提出了以聚四氟乙烯(PTFE)悬浮体为氟化剂,氟化辅助ETV-ICP-AES直接测定粉煤标样中钒和钛的新方法,其检出限     

Surface modification of polytetrafluoroethylene films via graft copolymerization for auto-adhesion

The surfaces of Ar plasma-pretreated polytetrafluoroethylene (PTFE) films are further functionalized via UV-induced graft copolymerization with amphoteric N,N′-dimethyl(methacryloylethyl)ammonium propansulfonate (DMAPS) either in Ar atmosphere, or under atmospheric conditions and in the absence of a polymerization initiator. The so-modified PTFE films from either process are capable of exhibiting adhesive-free adhesion or auto-adhesion with one another when brought into intimate contact in the presence of a small quantity of water. The lap shear adhesion strength increases with increasing graft concentration and can readily exceed the yield strength of the PTFE substrate. Two plasma-pretreated PTFE films also readily undergo thermal graft copolymerization with concurrent lamination when lapped together in the presence of a small quantity of the DMAPS monomer solution at elevated temperature in the atmosphere. The surface compositions of the graft-copolymerized PTFE films and the delaminated surfaces were characterized by X-ray photoelectron spectroscopy (XPS). In most cases, adhesional failure occurred near the graft-substrate interphase. © 1998 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 36: 3107–3114, 1998     

Long-term prediction of compressive creep development in expanded polystyrene

The results obtained in investigating the creep of expanded polystyrene (EPS) boards under compressive stress are presented. Power and exponential equations were used for describing creep compliance. It was found that the curves of creep compliance approximated by both equations adequately represent the research results, taking into account the scatter of the experimental data. Based on the calculation and empirical estimate of long-term creep of EPS under compressive stress σ_c=(0.25–0.45)σ_10%, its creep compliance was determined for a period of 10 years in the future. The dependence of on the density of polystyrene boards and the value of long-term compressive stress σ_c was established. The expected values of creep strain development in expanded polystyrene boards EPS 80–EPS 250 under constant compressive stress σ_c=(0.25–0.45)σ_10% are presented for the prediction period of 10 years. To obtain the expected creep values for any other period of time in the interval of 5T50 years, the values of should be multiplied by the empirical coefficient .     

PTFE Electrospun Stent Graft——Preparation,Properties and Its Industrialization Prospect

Stent graft(SG), isolating the diseased vessels from the normal blood circulation and preventing the rupture of the aneurysm wall in minimally invasive surgery, is normally composed of a metallic stent and a cover with a textile structure. In this study, the electrospinning method was used to prepare a new type of cover, and the preparing conditions and the performance of the SG were investigated. The polytetrafluoroethylene(PTFE) and polyethylene oxide(PEO) were blended at the ratios of 99:1, 98:2, 97:3 and electrospun to form precursor membranes. Then they were dried in a vacuum and sintered at different temperatures under different time periods to obtain PTFE membrane, which was compounded with a stent. Their morphology, mechanical properties, water permeability and biological properties were studied. The results showed that when the membrane was sintered at 380℃ for 10 min, it had the best tensile properties. The integral water permeability of the PTFE electrospun SG was close to 0. The hemolysis rate of the SG was 2.84%, and human umbillical vein endothelial cells(HUVECs) can adhere and proliferate well on the surface of the PTFE membranes. The PTFE electrospun SG had great potential for clinical application and industrialization.     

Hydrogel networks of poly(ethylene oxide) star-molecules supported by expanded polytetrafluoroethylene membranes: characterization, biocompatibility evaluation and glucose diffusion characteristics

The present work discusses the grafting by electron beam irradiation of poly(ethylene oxide) (PEO) star-shaped polymers onto porous expanded polytetrafluoroethylene (EXPTFE) surfaces. The resulting materials are intended to combine the good biocompatible properties of PEO with the outstanding mechanical properties of PTFE. The star-shaped PEOs were synthesized via anionic polymerization. 3 Mev electron beam irradiation was applied to graft these PEO stars onto porous EXPTFE surfaces. The hydrophobic EXPTFE surface had to be pre-modified with N-vinylpyrrolidone. ESCA was used to quantify the amount of grafted star-shaped PEO. Unmodified EXPTFE surfaces are well known, when implanted in a body, to be rapidly covered by a layer of cells and fibrin. The EXPTFE coated with PEO were implanted in the peritoneal cavity of rats (or under the back skin). This implantation did not induce any inflammation reactions and SEM analysis had attested the absence of adsorbed cells and fibrin. The glucose diffusion properties of these membranes were studied by a lag time analysis method and compared to those of pure PEO hydrogels. As expected, glucose diffuses through the hydrogel coated membrane and diffusion is not affected by the presence of the EXPTFE membrane.     

膜分离紫外连续测定水样中的二氧化氯

利用 Cl O2 能透过微孔性聚四氟乙烯膜 ( PTFE)的特性制成了 Cl O2 连续流动分离装置 ,实现了 Cl O2 与水相的分离。本法的检出限为 5.2× 1 0 - 2 mg/L,测定的线性范围 0 .2 4 mg/L～ 1 1 .81 mg/L,加标回收率为 96.8%～ 1 0 2 .8%。     

Exoemission near phase transitions of epitaxial films of manganites with colossal magnetic resistance

Intense exoemission near phase transitions of epitaxial films of the La_0.16Sr_0.84MnO₃ and La_0.35Pr_0.35Sr_0.3MnO₃, manganites, which exhibit the colossal magnetic resistance (CMR), is detected in a wide temperature range from 278 to 623 K including the Curie temperature. The role of the absorbed and lattice oxygen in the exoemission and CMR phenomena is discussed. The aftereffect of the magnetic field directed along the film plane on the intensity of photostimulated exoemission is discussed.     

聚四氟乙烯纤维的改性及其对胆红素的吸附

以聚四氟乙烯(PTFE)纤维为基质, 以甲基丙烯酸缩水甘油酯(GMA)为单体, 通过辐照接枝聚合制备了PTFE-g-GMA纤维, 用聚乙烯亚胺(PEI)与PTFE-g-GMA纤维进行开环反应制得新型吸附剂PTFE-g-GMA-PEI. 考察了PTFE-g-GMA-PEI吸附剂对溶液中胆红素的吸附动力学、吸附量及pH、离子强度及温度等因素对胆红素吸附的影响. 实验结果表明, 该吸附剂对胆红素有较高的吸附容量及良好的选择吸附性能, 其吸附行为遵循Langmuir吸附模式.     

磁控溅射法制备CeO_2/PTFE/Nafion复合膜及性能研究

采用磁控溅射法在聚四氟乙烯(PTFE)微孔膜表面溅射CeO_2,制备了CeO_2/PTFE复合膜.利用接触角、X射线光电子能谱(XPS)、扫描电子显微镜(SEM)和拉伸强度等对复合膜的亲水性、元素组成、形貌和机械强度进行测试,研究了溅射时间和溅射功率对膜性能的影响.结果表明,在溅射功率为40 W,溅射时间为120 s时,CeO_2/PTFE复合膜亲水性和拉伸强度都相对较好.在CeO_2/PTFE复合膜上浇铸Nafion树脂,制备的CeO_2/PTFE/Nafion复合膜含水率达到30%,离子电导率达到0.071 S/cm.     

Study on polytetrafluoroethylene aqueous dispersion irradiated by gamma ray

Gamma-radiation induced degradation of polytetrafluoroethylene (PTFE) in 60 wt.% dispersion was studied in the dose range of 20-200 kGy and the change in property of PTFE was characterized by differential scanning calorimetry (DSC), photon cross correlation spectroscopy (PCCS), X-ray diffraction (XRD), scanning electron microscopy (SEM), FT-IR spectroscopy and X-ray photoelectron spectroscope (XPS). It was found that the mean particle size of PTFE reduces from 250 nm of the control to 170 nm at 100 kGy, as confirmed by dynamic laser scattering and SEM. The crystallinity degree of PTFE increased at 20 kGy but remained unvaried at higher dose level. G-value of scission, G(s), was determined to be 0.46 μmol/J.     

Conversion of poly(ethylene‐alt‐tetrafluoroethylene) copolymers into polytetrafluoroethylene by direct fluorination: A convenient approach to access new properties at the ETFE surface

Direct fluorination of poly(ethylene‐alt‐tetrafluoroethylene) copolymer (ETFE) was carried out on commercially available ETFE films with pure fluorine gas at ambient atmosphere. Reaction temperature was either 95 °C or 150 °C and exposure time was 20 hours. Analysis of the fluorinated samples was performed by attenuated total reflection Fourier transform Infrared, confocal micro‐Raman and ¹H and ¹⁹F magic angle spinning nuclear magnetic resonance spectroscopies, scanning electron microscopy, electron diffraction and X‐Ray photoelectron spectroscopies, contact angle determination, atomic force microscopy and nanoindentation measurements, and compared to those of the virgin ETFE copolymer. Integrity of the bulk materials was verified by investigating the thermal behavior of the polymers by thermogravimetric analysis and differential scanning calorimetry. Evidence for the formation of a homogeneous layer of polytetrafluoroethylene with a thickness of several microns at the surface of the copolymers with no degradation of the materials was observed. © 2011 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2011     

Predictive modeling of creep in polymer/layered silicate nanocomposites

A predictive creep model is developed which uses the properties of matrix and reinforcement to predict the creep of polymer/layered silicate nanocomposites. Up to this point, primarily empirical creep models such as Findley and Burgers models have been used for creep of polymer/clay nanocomposites. The proposed creep model is based on the elastic-viscoelastic correspondence principle and a stiffness model of these nanocomposites. Also, the added stiffness of polymeric matrix due to the constraining effect of layered silicates on polymer chains in the nanocomposite is considered by a parameter termed constraint factor. The results of the proposed model show good agreement with experimental creep data for different clay contents, stresses and temperatures. Comparing the model predictions with experimental data, a logical relationship between the method of processing and the constraint factor is discovered which shows that in-situ polymerization can be more efficient for improving creep resistance of polymer/layered silicate nanocomposites relative to melt processing.     

Rheological properties for polypropylene modified by polytetrafluoroethylene

Linear and nonlinear viscoelastic properties for binary blends composed of isotactic polypropylene and polytetrafluoroethylene (PTFE) are studied. It is found that blending a small amount of PTFE greatly enhances the storage modulus in the low frequency region. Further, drawdown force and normal stress difference increase with the PTFE content. Electron microscope observation reveals that PTFE deforms into fine fibers whose diameter is smaller than 0.5 μm. The network structure composed of the fibers is responsible for the marked elastic properties. © 2009 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 47: 2008–2014, 2009     

Formation of nanoporous poly(aryl amide ether) (PAAE) films by selective removal of poly(ethylene glycol) (PEG) from PEG/PAAE composite films

Poly(aryl amide ether) (PAAE) thin films with nanometer-sized pores have been prepared in two steps: (1) solution casting of partially miscible poly(ethylene glycol) (PEG)/PAAE blends from one of their common solvents, dimethyl sulfoxide (DMSO), results in formation of PEG/PAAE nanocomposite films; (2) selective removal of PEG component by water washing yields nanosized, porous PAAE films. The pores have been found to have a small size variation and cover the whole surface homogeneously. With an increase in PEG contents, the sizes of the pores increase but the size distributions do not have much changes. This has been ascribed to formation of small PEG domains in PEG/PAAE composite films, which is facilitated by the strong interactions, mostly hydrogen bonds, between PEG and PAAE macromolecular chains.