Reactive polytetrafluoroethylene/polyamide 6 compounds. II. Study of the reactivity with respect to the functionality of the polytetrafluoroethylene component and analysis of the notched impact strength of the polytetrafluoroethylene/polyamide 6 compounds

The formation of block copolymers as a result of an in situ chemical reaction during the reactive extrusion of electron‐beam‐irradiated polytetrafluoroethylene (PTFE) and polyamide 6 (PA) was detected indirectly with differential scanning calorimetry and Fourier transform infrared. As expected, the content of the block copolymers in the compound increased as the irradiation dose was increased. The notched impact strength showed an increase in the PTFE/PA compounds produced with highly irradiated PTFE. This behavior is discussed in the context of the degree of dispersion of the PTFE phase (as reported in part I of this series) and the adhesion changed by the in situ reaction. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 98: 1317–1324, 2005     

Viscosity characterization and flow simulation and visualization of polytetrafluoroethylene paste extrusion using a green and biofriendly lubricant

Polytetrafluoroethylene (PTFE) and expanded PTFE (ePTFE) are ideal for various applications. Because PTFE does not flow, even when heated above its melting point, PTFE components are fabricated using a process called paste extrusion. This process entails blending PTFE powder particles with a lubricant to form PTFE paste, which is subsequently preformed, extruded, expanded (in the case of ePTFE), and sintered. In this study, ethanol was proposed as an alternative green lubricant for PTFE processing. Not only is ethanol benign and biofriendly, it provides excellent wettability and processing benefits. Using ethanol as a lubricant, the shear viscosity of PTFE paste and its flow behavior during paste extrusion were investigated. Frequency sweeps using a parallel-plate rheometer were performed on PTFE paste samples and various grits of sandpaper were used to reduce wall slip of PTFE paste. A viscosity model was generated and a multiphysics software was used to simulate PTFE paste extrusion. The simulated extrusion pressure was compared to experimental data of actual paste extrusion. Flow visualization experiments using colored PTFE layers were conducted to reveal the flow profile of the PTFE paste. The morphology of the expanded ePTFE tubes was examined using scanning electron microscopy and the effect of expansion ratio on ePTFE morphology was quantified.     

Processibility and mechanical properties of micronized polytetrafluoroethylene reinforced silicone rubber composites

Various micronized polytetrafluoroethylene (PTFE) powders were compounded with silicone rubber (MQ) and mechanical properties of the MQ/PTFE composites were evaluated. The fracture surface morphologies of prepared composites were also investigated using scanning electron microscopy (SEM). At a level of only 5 wt %, the fractured surface of MQ/PTFE composites show layered structure morphology. This structure effectively improves the tear strength of MQ but it also led to lower the tensile properties of the composites. The addition of fluorosilicone rubber (FMQ) as compatibilizer, tensile and tear strength of the composites improved considerably. However, tensile properties of the MQ/solution of sodium in liquid ammonia treated PTFE composite decreased compared with those of the untreated one. To investigate the production potential of extrusion process, an electric wire was extruded with MQ/PTFE/FMQ composites. During the curing process, volatile molecules lead to bubble and void formation of extruded layer depending on the filler shapes. The spherical PTFE powder was suitable for extrusion process. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

Oriented crystallization and mechanical properties of polypropylene nucleated on fibrillated polytetrafluoroethylene scaffolds

It is known that friction deposited polytetrafluoroethylene (PTFE) layers are able to nucleate crystallization of thin films of isotactic polypropylene (iPP). In order to investigate the influence of PTFE on the crystallization behavior and morphology of iPP in bulk, PTFE‐particles of two different sizes in various concentrations were melt‐blended with iPP and subsequently processed by injection molding. For one size of particles, high resolution scanning electron microscopy (HR‐SEM) showed the presence of a PTFE scaffold consisting of highly fibrillated PTFE particles. With X‐ray diffraction (WAXD) pole‐figures, it was evidenced that, after melting and recrystallization of the iPP matrix, a strongly oriented crystallization of iPP on this PTFE scaffold takes place (quiescent crystallization conditions). With WAXD it was also shown that under processing conditions, PTFE acts as a nucleating agent for iPP and that PTFE strongly enhances the formation of processing induced morphologies. Impact and tensile performance of the mixtures were measured. Both the strain energy release rate (G_I) and the E‐modulus were found to increase upon introducing PTFE in iPP. POLYM. ENG. SCI., 45:458–468, 2005. © 2005 Society of Plastics Engineers.     

Rheological investigation of polyamide 6 TiO2‐ and BaSO4‐nanocomposites

Commercially available TiO₂ and BaSO₄ nanoparticles were incorporated in polyamide 6 (PA 6) via twin screw extrusion. The primary particle size of nanoparticles was 15 nm and 20 nm. The compounds were manufactured via multiple extrusion and dilution processing steps. The dispersion of the nanoparticles in the matrix was investigated by scanning electron microscopy and image analysis, micro‐tomography, and transmission electron microscopy. The rheological properties were determined via plate–plate‐rheometer. It was found that for TiO₂ fillers a threefold extrusion process is sufficient to realize a dispersion index of 94.4%. BaSO₄ fillers were hardly dispersible, ending up with a maximum dispersion index of 71%. Deagglomeration does not lead to a change in rheological properties but the number of extrusion steps decreases the rheological properties. A good particle‐matrix interaction leads to higher moduli and viscosity. The remaining agglomerates seem to act as defects decreasing the energy absorption of the respective compounds. © 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013     

Solid state extrusion of polytetrafluoroethylene fibers

Polytetrafluoroethylene (PTFE) was solid state extruded to fiber form at temperatures between 250 and 300°C and at pressures between 7000 and 15,000 psi. The PTFE fibers had a diameter of 0.0502 inches and the reduction ratio for extrusion was 55.8. The fibers were tested for mechanical strength, and examined with a scanning electron microscope, which revealed a fibrous structure at high magnifications. The melting point of the fibers was 342°C by differential scanning calorimetry. The tensile properties were enhanced with an increase in processing temperature and pressure, the highest properties resulting from an extrusion temperature of 300°C and pressures greater than 10,000 psi. A tensile strength of 5500 psi and a secant modulus of 250,000 psi were obtained.     

A comparative study of characteristics of polytetrafluoroethylene fibers manufactured by various processes

A series of polytetrafluoroethylene (PTFE) fibers were manufactured by three processing methods including extrusion process, split‐sheet process and split‐film process. The influence of processing methods on fiber properties were systematically studied using four PTFE powders with various molecular weights (3.86 × 10⁷, 4.71 × 10⁷, 4.92 × 10⁷ and 5.11 × 10⁷, respectively). Morphology, crystallinity, tensile behavior and friction properties of PTFE fibers were compared by scanning electron micrograph, X‐ray diffraction pattern, strength‐elongation curves and friction coefficients, respectively. The results showed that the in terms of flat filaments, mechanical properties became weak with the increase of molecular weight of PTFE powders at first, but were improved dramatically with further enhancement of molecular weight. In the case of both round filaments and split‐film fibers, fiber properties were improved with growth of molecular weight. Based on characteristics and friction coefficients, potential applications of three types of PTFE samples were analyzed. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016 , 133, 43553.     

Friction and wear properties of PTFE composites filled with PA6

Blending Polytetrafluoroethylene (PTFE) to PA6 at different compositions was produced in a corotating twin‐screw extruder, where PTFE acts as the polymer matrix and PA6 as the dispersed phase. The effects of PA6 content on the tribological properties of the composites were investigated. The worn surface morphologies of neat PTFE and its composites were examined by scanning electron microscopy (SEM), and the wear mechanisms were discussed. The presence of PA6 particles dispersed in the PTFE continuous phase exhibited superior tribological characteristics to unfilled PTFE. The optimum wear reduction was obtained when the content of PA6 is 30 vol%. POLYM. COMPOS., 2010. © 2009 Society of Plastics Engineers     

Melt processability of polytetrafluoroethylene: Effect of melt treatment on tensile deformation mechanism

It is widely accepted that the melt processibility of polytetrafluoroethylene (PTFE) is poor. In this article, a high‐molecular‐weight PTFE was extruded smoothly with a modified die; and critical shear rate could be raised to 4 s^?1, using a die with L/D (length to diameter) ratio of 200. Meanwhile, we compared the current PTFE fiber spinning method with melt spinning to investigate the effects of high‐temperature treatment on the drawability of PTFE and found that the processing sequence could play a key role. The deformation imposed before or after the high‐temperature treatment could determine whether the fibrillation can be achieved continuously and effectively. Based on the experiment phenomenon, together with the results of differential scanning calorimetry, X‐ray diffraction, and scanning electron microscopy characterization, we proposed a model to describe the submicron structural change of PTFE during extension. From this model, the fundamental mechanism for the poor melt processibility of PTFE was elucidated. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2012     

Influence of fibrillated poly(tetrafluoroethylene) on microcellular foaming of polyamide 6 in the presence of supercritical CO2

In this article, PA6/poly(tetrafluoroethylene) (PTFE) composites were prepared by internal mixer with high rotor speed. The existence of PTFE nano-fibrillation network structure was observed by scanning electron microscopy (SEM) analysis. The effect of PTFE on crystallization and rheological behavior of PA6 was evaluated. The result showed that the PTFE fibrils improved the crystallization properties of PA6 and do not change the crystal structure. The PTFE effectively enhanced the melt strength of PA6 by fibrillation. The PA6/PTFE composites were then foamed assisted by supercritical CO₂. The PTFE was used as cell nucleating agent, crystal nucleating agent and melt strength enhancement agent in the foaming process. Finally, the microcellular PA6 foams were successfully obtained with the cell density higher than 10⁹ cells/cm³, the cell size of ca. 14 μm and the volume expansion ratio of 16.     

Recycling and application of wasted polytetrafluoroethylene via high‐energy ball milling technology for nitrile rubber composites preparation

Wasted polytetrafluoroethylene fibers were recycled using high‐energy ball milling technique, and the recylced polytetrafluoroethylene (r‐PTFE) was employed to prepare nitrile rubber (NBR)/r‐PTFE composites. The structure of r‐PTFE and properties of NBR/r‐PTFE composites were investigated by polarized optical microscope, laser particle size analyzer, differential scanning calorimetry, and scanning electron microscopy, respectively. The results show that increasing the milling time from 4 to 7 h leads to decreasing the average particle size, the degree of crystallinity and the number‐average molecular weight of r‐PTFE, whereas no obvious change is found by further prolonging the milling time. It is also clear that the NBR/r‐PTFE composite with the r‐PTFE obtained from a longer milling time possesses a higher mechanical and solvent resistance property. Compared with pure NBR, NBR/r‐PTFE composites with r‐PTFE for 7 h milling show a 21.9% increase in modulus at 300% and 27.8% decrease in swelling index. POLYM. ENG. SCI., 56:643–649, 2016. © 2016 Society of Plastics Engineers     

Miscibility and Crystallization Behaviors of Polyamide 6/Polytetrafluoroethylene Blends

Summary: The miscibility and crystallization behaviors of polyamide 6 (PA 6)/polytetrafluoroethylene (PTFE) blends, prepared via reactive extrusion, are systematically investigated by means of wide‐angle X‐ray diffraction (WAXD), differential scanning calorimetry (DSC), and dynamic mechanical thermal analysis (DMTA). WAXD measurements show that no co‐crystallization occurred between two components, while DSC and DMTA measurements suggest that a certain degree of miscibility between them might exist due to the formation of some copolymers during the reactive extrusion.

DMTA curves for the pure PA 6 sample and PA 6/PTFE blends with various compositions.     

助剂挤出法制备高强度聚四氟乙烯单丝

将聚四氟乙烯(PTFE)与润滑助剂航空煤油混合后均匀挤出,挤出样条脱除助剂,在低于PTFE熔点的温度下高倍拉伸,后经高温紧张热定型,制备高取向PTFE单纤维;通过拉曼光谱、X射线衍射、差示扫描量热分析等方法研究挤出PTFE拉伸过程中材料微细结构的变化,并对PTFE纤维的性能进行表征.结果表明:PTFE在挤出过程中并不会...     

Compatibilization of PVDF/PA6 Blend by the Addition of a Third Polymer PTFE

The compatibilization of poly(vinylidene fluoride) (PVDF) with polyamide 6(PA6, higher acrylonitrile content) blend was improved by adding poly(methyl methacrylate) (PTFE). It was confirmed by characterizing the mechanical and tribological properties of the blends. More homogeneous morphology was formed when PTFE was added into PVDF/PA6 blend, which was shown in scanning electron microscopy (SEM). The surface tension of blends was increased due to the higher polar surface tension of PTFE. As the content of PTFE was increased further, the tensile strength of the blend was slightly decreased.     

Effect of clay on the morphology of blends of poly(propylene) and polyamide 6/clay nanocomposites

PP/NPA6 blends composed of poly(propylene) (PP) and polyamide 6/clay nanocomposites (NPA6) were prepared by twin‐screw extrusion and melt‐drawn into ribbons by a ribbon extrusion process. The influence of clay on the morphology of PP/NPA6 ribbons was investigated by means of field‐emission scanning electron microscopy and optical microscopy. The results show that at low clay content (3, 5 wt%), NPA6 exhibited continuous lamellar structure in PP as pristine PA6 did in a PP/PA6 blend, but at a higher clay content (10 wt%) only ellipsoids or elongated ellipsoids were observed. In order to explain the morphological difference, two factors, ie the compatibilization effect and melt rheology, have been taken into consideration. It has been found that both factors, and probably mainly the variation in melt rheology, were responsible for the morphological difference in the PP/NPA6 blends with different clay contents under the extensional flow field. Copyright © 2004 Society of Chemical Industry     

Superhydrophobic polytetrafluoroethylene nanofiber membranes prepared by vacuum sintering and their application in vacuum membrane distillation

Electrospinning-sintering is a general strategy to fabricate polytetrafluoroethylene (PTFE) nanofibrous membranes. In this study, vacuum atmosphere was created in the sintering process to obtain pure PTFE fibers. The effect of vacuum pressure on fiber morphology and material component of the sintered membrane was investigated by scanning electron microscopy (SEM) and X-ray photoelectron spectroscopy (XPS) characterization. A proper vacuum condition was believed to be beneficial to decrease poly(vinyl alcohol) residual and creating nanosize structures on the fiber surface, as porous, which contributes to a secondary roughness, while insignificantly influence membrane strength. As a result, the prepared membrane was superhydrophobicity with enhanced liquid entry pressure value. The anti-wetting property of the vacuum sintered membranes was further evaluated by vacuum membrane distillation process, and ensured the superior wetting resistance of the vacuum sintered PTFE membranes.     

Enhanced thermal conductivity and wear resistance of polytetrafluoroethylene composites through boron nitride and zinc oxide hybrid fillers

In this study, the thermal conductivity and wear resistance of the polytetrafluoroethylene (PTFE)/boron nitride (BN), PTFE/zinc oxide (ZnO), PTFE/tetra‐needle‐shaped zinc oxide whiskers (T‐ZnO), and PTFE/hybrid filler composites were investigated. Moreover, hot‐press molding was used to prepare the composites, and scanning electron microscopy was used to observe the morphology of the fillers and the friction interface of the composites. The results show that continuous thermally conductive paths could be formed in the PTFE/hybrid fillers (T‐ZnO and BN) composites so that the thermal conductivity of the PTFE was improved through addition of the hybrid fillers. Meanwhile, the synergistic effects of the hybrid fillers were useful for reducing the wear rate of the composites. In addition, for the pure PTFE, abrasive and adhesive wear was found. Compared to the worn surface of the pure PTFE, the worn surface of the PTFE composites filled with ZnO, T‐ZnO, BN, and hybrid fillers presented much smoother surfaces, and slighter ploughing occurred. Therefore, the hybrid fillers improved not only the thermal conductivity but also the wear resistance of the PTFE composites. The data obtained in this study contributed to the construction of a technical foundation for the preparation of composites with a high thermal conductivity and wear resistance. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 42302.     

Effect of polytetrafluoroethylene on the foaming behaviors of linear polypropylene in continuous extrusion

Linear polypropylene (PP) foams, blown in the continuous extrusion process using supercritical CO₂ as the blowing agent, exhibited poor cell morphology and narrow foaming window, because of their low melt strength. In this study, polytetrafluoroethylene (PTFE) was blended with PP resin with the aim of improving the foaming behavior of PP. It was found that the PTFE particles were deformed into fine fibers under shear or extensional flows during the extrusion process, which significantly increased the melt strength of PP from 0.005 N to 0.03 N (PP/PTFE with PTFE content of 4.0 wt %) at 230°C. The experimental results indicated that the presence of PTFE improved the cell morphology of PP foams and broadened the foaming window of PP. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013     

Tribological behaviors of polytetrafluoroethylene composites under dry sliding and seawater lubrication

The composites of polytetrafluoroethylene (PTFE) filled with expanded graphite (EG), poly(p‐oxybenzoyl) (POB), and basalt fiber (BF) were prepared by heating compression and sintering molding. The tribological behavior of PTFE composites was investigated with a pin‐on‐disk tester under dry conditions and seawater lubrication. The worn surface of PTFE composites and the transfer film on the counterface were observed with a scanning electron microscope. The results indicated that the incorporation of EG and POB improved the hardness of PTFE composites, and addition of BF led to greater load‐carrying capacity. Compared to pure PTFE, the coefficients of friction of PTFE composites slightly increased, but the wear rates were significantly reduced (the wear rate of composite with 3% EG being only 10.38% of pure PTFE). In addition, all the composites exhibited a lower coefficient of friction (decreases of about 0.03–0.07) but more serious wear under seawater lubrication than under dry sliding. The wear mechanism changed from serious abrasive wear of pure PTFE to slight adhesion wear of PTFE composites under both conditions. A transfer film was obviously found on the counterface in seawater, but it was not observed under dry conditions. Among all the materials tested, the PTFE‐based composite containing 20% POB (mass fraction), 2% EG, and 3% BF exhibited the best comprehensive performance. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 130: 2523–2531, 2013     

Rheology and processing of polytetrafluoroethylene (PTFE) paste

This is a review article on the paste extrusion of polytetrafluoroethylene (PTFE). The article begins with an overall presentation of the process. Important aspects related to this process are the physical properties of PTFE, its rheology, the morphological changes occurring during flow (fibrillation) that play a critical role on the dimensional stability of the final products, the geometrical characteristics, and types of dies used and temperature. PTFE is a compressible, zero Poisson's ratio material, and the mechanical properties of extrudates after extrusion are also discussed in view of fibrillation and Poisson's ratio.