Polytetrafluoroethylene nano/microfibers by jet blowing

Polytetrafluoroethylene (PTFE) fluoropolymer exhibits extreme chemical and thermal stability, low friction coefficients and many other exceptional properties. Unfortunately, very high molecular weight PTFE has an extremely high melt viscosity (∼10¹⁰-10¹² poise) and negligible solubility in common solvents. Under tensile stress, molten PTFE elongates and breaks rather than forming fibers and processing it is generally laborious and expensive. We have developed a simple, environmentally friendly, single step, solvent-free technique to process very high molecular weight PTFE inside of a high pressure jet of gases such as nitrogen or argon into mats of micro and nanofibers that are up to several millimeter long. Plasticization of PTFE by the hot, high pressure gases within the jet and extensional stretching in the jet nozzle appear to facilitate fiber formation even at temperatures below the melting point. Polarized Raman spectra demonstrate that the PTFE polymer chains exhibit substantial alignment along the fiber axis. The fibers are produced at a rapid rate and adhere to many different materials, allowing for facile fabrication of surface modifying coatings and dense fibrous mats to control properties such as surface hydrophobicity, drag, and biocompatibility. Jet blowing is also suitable for more conventionally processible polymers and formation of polycaprolactone (PCL) fibers is demonstrated.     

Influence of PTFE as a solid lubricant on the mechanical,electrical, and tribological properties of CF-reinforced PC composites

The objective of this research was to study the effects of polytetrafluoroethylene (PTFE) as a solid lubricant on the mechanical, electrical, and tribological properties of carbon fiber (CF)-reinforced polycarbonate (PC) composites. Samples were prepared by means of single-screw extrusion and injection molding processes. The mechanical tests included tensile, flexural, and failing weight impact tests, while the electrical tests consisted of surface and volume resistivity tests. The tribological testing was conducted under dry sliding conditions using pin-on-disk configuration. The results showed that the addition of CF managed to significantly reduce the electrical resistivity as the CF loading approached 10–15 wt%. The addition of PTFE managed to reduce the resistivity of the composite, that is, from 4.51 to 0.53 × 10 (Ωcm). The incorporation of 15 wt%. CF resulted with an increase of 45% in tensile strength and 51.5% in flexural strength, while the addition of PTFE had a negative impact on both properties. It was shown that PTFE was able to reduce the friction coefficient, μ and wear rate, K up to 0.257 and 6.35 × 10⁶ (mm³/Nm), respectively, which can be attributed to the excellent abilities of PTFE to form transfer film. The composite consisting of 15 wt% CF and 10 wt%. PTFE showed highest improvement in term of electrical resistivity, and is deemed the most suitable composition for this study. Scanning electron microscopy was also carried out to further elucidate the fracture and wear mechanism of the PC/CF/PTFE composites.     

Emulsifier-free emulsion polymerization of tetrafluoroethylene by radiation. IV. Effects of additives on polymer molecular weight

Poly(tetrafluoroethylene) (PTFE) of high molecular weight, 4.5 × 10⁷, was incidentally obtained at earlier study of an emulsifier-free emulsion polymerization of tetrafluoroethylene by radiation. In order to clarify this phenomenon, the effects of additives, in particular radical scavengers, on the molecular weight of PTFE and its polymerization behavior were studied. It was found that the molecular weight of PTFE is increased by the addition of hydroquinone, benzoquinone, α-pinene, dl-limonene, and ethylenediamine but is decreased by oxygen and triethylamine. A PTFE latex with molecular weight higher than 2 × 10⁷ was obtained in the presence of hydroquinone. It is concluded that additives such as hydroquinone and benzoquinone, which rapidly scavenge the primary radicals (OH·, H·, and e_aq^?) in the aqueous phase but not the growing polymer radicals in PTFE particles, are most effective in increasing the molecular weight.     

Controlling of threadline dynamics via a novel method to develop ultra‐high performance polypropylene filaments

A detailed study was conducted to investigate the effects of horizontal isothermal bath (hIB) on the production of ultra‐high performance polypropylene filaments. Two different commercial PP polymers were used with the melt flow rate of 4.1 and 36 g/10 min. The optimum process conditions depended on polymer molecular weight. Fibers showed distinct precursor morphology for each at each optimum process condition. However, two sets of filaments demonstrated similar fiber tenacity and modulus of about 7 and 75 g d^?1, respectively, for as‐spun and more than 12 g d^?1 for tenacity and more than 190 g d^?1 for modulus values of drawn fibers after just 1.49 draw ratio. The mean value for the modulus after the drawing process for the high melt flow rate was 196 g d^?1. The theoretical modulus of PP is 35–42 GPa¹⁹, (275–330 g d^?1), shows the hIB fiber's modulus performance is approaching its theoretical maximum value. Fibers had greatly improved thermal properties, degree of crystallinity, crystalline and amorphous orientation factors. The hIB spinning system produced highly oriented and predominantly amorphous structure for as‐spun fibers and a well‐defined, highly oriented crystalline fibrillar and amorphous structure after drawing process with the draw ratios lower than 1.5. POLYM. ENG. SCI., 55:327–339, 2015. © 2014 Society of Plastics Engineers     

Tribological properties of porous PPS/PTFE composite filled with mesopore titanium oxide whisker

Nano‐micro hierarchical porous polyphenylene sulfide/polytetrafluoroethylene (PPS/PTFE) composites were prepared by mold‐leaching and vacuum melting process under high temperature condition. The tribological behaviors of porous PPS/PTFE composites and the synergism as a result of incorporation of both micro‐porogen (NaCl) and mesoporous TiO₂ whiskers were investigated. The effects of mesoporous TiO₂ whiskers and nonperforated TiO₂ whiskers on the friction and wear properties of PPS/PTFE composites were comparatively studied, respectively. Results indicated that the wear rate of porous PPS/PTFE composites with 30 wt % NaCl and 7 wt % mesoporous TiO₂ whiskers obtained the lowest values under the load of 100 N. Compared with pure PPS, the wear resistance of nano‐micro porous PPS/PTFE composite was enhanced by 6.45 × 10³ times, showing outstanding wear resistance. During sliding condition, grease could be squeezed through the nano‐micro pores under the coupling effect of load and friction heat, and formed a lubricanting layer on friction surface, providing self‐lubricating effect and high wear resistance. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013     

Sliding Wear Behavior of TaC‐Containing Ti(CN)‐WC‐Ni/Co Cermets

Four compositions of TiCN‐WC‐Ni/Co cermets with or without TaC were prepared by pressureless sintering of respective powders, and unlubricated sliding wear behavior against bearing grade steel ball was studied at 5, 10, or 20 N load. Maximum hardness and fracture toughness were obtained for Ti(CN)‐5WC‐10Ni‐10Co‐5TaC (in wt%) cermet. With change in the cermet composition and sliding load, coefficient of friction varied from 0.3 to 1.0 and wear rate varied from 3 × 10^?7 to 7 × 10^?7 mm³/Nm. The increased material transfer and formation of iron oxide‐rich tribochemical layer were responsible for the reduction in friction and wear for Ti(CN)‐5WC‐10Ni‐10Co‐5TaC cermet.     

Mechanical properties,crystallization characteristics,and foaming behavior of polytetrafluoroethylene‐reinforced poly(lactic acid) composites

In this study, poly(lactic acid) (PLA)/polytetrafluoroethylene (PTFE) composites containing different amounts of PTFE were prepared by melt blending. The mechanical, crystallization, and foaming properties of the prepared composites were investigated. Tensile test results indicated that the mechanical properties of the composite with PTFE showed significant reinforcement and toughening effects. The average elongation‐at‐break of the composite increased by 72% compared with pure PLA. Scanning electron microscopy (SEM) showed that the PTFE elongated into fibrils during blending and formed a physical network of entanglements in the melt. Differential scanning calorimetry (DSC) also showed that PTFE had a significant nucleation effect on polymer crystals and greatly increased the crystallinity of the PLA matrix. Moreover, PTFE dramatically enhanced the melt viscosity of PLA, which was investigated by rheological tests. The injection molding foaming experiments revealed that adding 1 wt% PTFE had the most notable heterogeneous nucleation effect on foamed cells, with the cell size decreasing from 81.5 μm for neat PLA to 25.2 μm, and the cell density increasing from 1.34 × 10⁸ cells/cm³ to 2.53 × 10⁹ cells/cm³. POLYM. ENG. SCI., 57:570–580, 2017. © 2016 Society of Plastics Engineers     

Influence of organic montmorillonite nanoparticles on the microstructures and thermal and tribological properties of polyethersulfone and polytetrafluoroethylene composites

Because of high wear rate and low thermal deformation temperature, the generalization and application of polytetrafluoroethylene (PTFE) in the field of tribology is restrained to a certain extent. In order to improve the wear resistance and thermal stability of this self‐lubricating polymer, organic montmorillonite (OMMT) nanoparticle reinforced polyethersulfone (PES) and PTFE ternary composites were prepared by the cold molding and vacuum sintering technology. The effects of sodium montmorillonite (Na‐MMT) and OMMT on the microstructures, thermal stabilities and tribological properties of PTFE composites were comparatively studied. The results show that the thermal stability of the PES/PTFE composites is clearly improved by the incorporation of OMMT nanoparticles. Not only the friction coefficients but also the wear rates of OMMT/PES/PTFE composites are less than those of Na‐MMT/PES/PTFE composites under identical tribological tests. Of all these PTFE composites, the PES/PTFE composite containing 10.0 wt% OMMT nanoparticles exhibits the best friction and wear properties (μ = 0.14, k = 5.78 × 10^?15 m³ N^–1 m^?1). This can be attributed to the existence of a polymer multicomponent layer consisting of PTFE, PES and OMMT on the composite surface as well as the formation of uniform PTFE transfer film on the worn surfaces of metal counterparts.     

The Estimation of the Molecular Weight of Polytetrafluoroethylene Based on the Heat of Crystallisation. A Comment on Suwa's Equation

Summary: The influence of number‐average molecular weight ranging from 1.4 · 10⁴ to 1.2 · 10⁶ g/mol on the thermal behaviour of polytetrafluoroethylene (PTFE) has been studied. Samples have been prepared by radiation‐induced degradation of commercial PTFE. The molecular weight has been calculated using end‐group concentration determined by infrared (IR) spectroscopy and ¹⁹F solid‐state nuclear magnetic resonance (NMR) spectroscopy. Melting and crystallisation heats were investigated by differential scanning calorimetry (DSC). The results have been discussed with respect to quantitative relationships between number‐average molecular weight and heat of crystallisation of PTFE described in the literature. The molecular weight calculated from Suwa's equation, which is often used in the literature, has been found to be too low.

Concentration of end‐groups and the molecular weight of PTFE versus the irradiation dose.     

Post‐extrusion solid‐state polymerization of fully drawn polyester yarns

Post‐extrusion solid‐state polymerization (SSP) of a commercial fully drawn filament yarn (FDY) of poly(ethylene terephthalate) was carried out at 220°C, 230°C, and 240°C for a duration of 30 min to 2 h under inert atmosphere. Molecular weight of the solid‐state polymerized polyester filaments was increased from 1.67 × 10⁴ gm/mol to a maximum of 2.61 × 10⁴ gm/mole for the sample subjected to 240°C for 2 h. The kinetics of the SSP in the highly oriented crystalline FDY polyester filaments was investigated using an empirical relation between initial molecular weight and time of SSP and was found to be greatly enhanced, compared to amorphous unoriented polyester chips. Though the free annealing (i.e., under no tension) of samples at high temperature during solid‐state polymerization had a detrimental effect on the orientation of the FDY yarn, the simultaneous increase in the molecular weight compensated the loss in mechanical properties to a great extent. Application of tension during SSP was found to improve the mechanical properties of the SSP yarn by a small value. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 102: 5113–5122, 2006     

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     

Tribological behavior of carbon nanotube and polytetrafluoroethylene filled polyimide composites under different lubricated conditions

The friction and wear behavior of polyimide (PI) composites reinforced with carbon nanotube (CNT) and polytetrafluoroethylene (PTFE) were comparatively evaluated under dry sliding, water‐, oil‐ or alkali‐lubricated condition. The wear mechanisms of the composites were also discussed. Results indicate that, when comparison with the dry friction situation, PI‐based composites results lower friction coefficients and wear rates under oil‐ or alkali‐lubricated condition. The lowest wear rate of the CNT/PTFE/PI composite is recorded as 1.2 × 10⁻⁶ mm³/Nm during the composite sliding in alkali, which is only about 40% of the value sliding under dry friction condition. The worn surface of neat PI under dry sliding is characterized by severe adhesive wear, whereas abrasive wear is the main character for CNT/PTFE/PI composites. The worn surfaces of CNT/PTFE/PI composites sliding in oil or alkali lubricated condition are smoother than those under dry or water condition. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

Graft copolymerization of acrylonitrile onto allylated caesarweed fibres by ceric ion in the presence of 2‐mercaptoethanol

Polyacrylonitrile was grafted onto caesarweed fibers and on the allyldervative in aqueous media by ceric ion‐2‐mercaptoethanol redox pair. The allylfibre was obtained by treatment of caesarweed fibers with sodium hydroxide followed by allylchloride in diisoproylether to yield an average degree of substitution of 3.24 allyl moieties per anhydroglucose unit (AGU). The graft yield dependence on 2‐mercaptoethanol concentration, in the range, 10.7–64.0 × 10^?4M was characterized by a minimum followed by an enhanced yield. This suggested the existence of two initiating species, a thioglycol radical and mercaptoethoxyl radical. A fivefold increase in the concentration of 2‐mercaptoethanol was accompanied by reduction in the frequency of graft, F_g from 75.6–0.79 Ng/10⁴ AGU and a concomitant increase, by two orders of magnitude, in the average molecular weight of grafted polymer M_v, with values of up to 11.78 × 10⁵. Infrared spectroscopy of allylfibre‐g‐polyacrylonitrile copolymer showed evidence of radical coupling reaction involving thioglycol radical species and allylic macroradicals of the allylfibre. The unmodified fiber was more reactive than the allylfibre by as much as a factor of 2, and was ascribed to resonance stabilization of allylic macro radicals derived from the latter. For the allyl fiber, a 150% increase in monomer concentration resulted in nominal increase in graft yield, not higher than 7%. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

Tribological behavior of three‐dimensional braided carbon fiber reinforced polyetheretherketone composites

Three‐dimensional (3D) braided carbon fiber reinforced polyetheretherketone (denoted as CF_3D/PEEK) composites with various fiber volume fractions were prepared via hybrid woven plus vacuum heat‐pressing technology and their tribological behaviors against steel counterpart with different normal loads at dry sliding were investigated. Contrast tribological tests with different lubricants (deionized water and sea water) and counterparts made from different materials (epoxy resin, PEEK) were also conducted. The results showed that the incorporation of 3D braided carbon fiber can greatly improve the tribological properties of PEEK over a certain range of carbon fiber volume fraction (V_f) and an optimum fiber loading of ∼54% exists. The friction coefficient of the CF_3D/PEEK composites decreased from 0.195 to 0.173, while the specific wear rate increased from 1.48 × 10⁻⁷ to 1.78 × 10⁻⁷ mm³ Nm⁻¹ with the normal load increasing from 50 to 150 N. Abrasive mechanism was dominated when the composites sliding with GCr15 steel counterpart under dry and aqueous lubrication conditions. Deionized water and sea water lubricants both significantly reduced the wear of the CF_3D/PEEK composites. When sliding with neat PEEK counterpart, the CF_3D/PEEK composites possess lower friction coefficient than those against epoxy resin and GCr15 steel counterparts. In general, CF_3D/PEEK composites possess excellent tribological properties and comprehensive mechanical performance, which makes it become a potential candidate for special heat‐resisting tribological components. POLYM. COMPOS., 36:2174–2183, 2015. © 2014 Society of Plastics Engineers     

Molecular weight and the Mark‐Houwink relation for ultra‐high molecular weight charged polyacrylamide determined using automatic batch mode multi‐angle light scattering

This study presents an automatic batch mode (i.e., off‐line) multi‐angle light scattering (MALS) method for the molecular weight (MW) determination of ultra‐high MW (UHMW) polyacrylamide (PAM) homopolymer and acrylamide copolymers. This method combines a MALS detector with a sample dilution and injection device that automatically delivers a concentration gradient from a stock solution. The automation makes it practical to use the batch MALS method for routine MW analysis of UHMW polymers. The automatic batch MALS analyses of a series of poly(sodium acrylate‐co‐acrylamide) (30:70 mol %) in 1.0M NaCl show a non‐linear Mark‐Houwink relation in the MW range of 1.2 × 10⁶ to 12.6 × 10⁶ g mol^?1. The entire molecular weight range can be fit with a quadratic relation or two linear equations, one for molecular weight up to 5.3 × 10⁶ g mol^?1 and the other from 5.3 × 10⁶ to 12.6 × 10⁶ g mol^?1. The non‐linear Mark‐Houwink relation suggests that the extrapolation of the Mark‐Houwink equation beyond the measured MW range into the UHMW regions can significantly overestimate the MW of the UHMW polymers. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016 , 133, 43748.     

Conductive polymers/polyacrylonitrile composite fibers: Fabrication and properties

Polypyrrole/polyacrylonitrile, polyaniline/polyacrylonitrile, and poly(3,4‐ethylenedioxythiophene)/polyacrylonitrile composite fibres were fabricated successfully by in situ polymerization. The morphologic observations confirmed the uniformly‐covered polyacrylonitrile fiber surface by conductive conjugated polymers. These composite fibers exhibited conductivity in the range of 1.4 × 10⁻² to 5.2 × 10⁻¹ S cm⁻¹. Improved thermal stability of the composite fibers was observed from thermogravimetric analysis results. Structural analysis indicated that the interactions of both hydrogen‐bonding and the electrostatic attraction existed between polyacrylonitrile chains and conjugated polymers. These novel composite fibers still possessed original fibrillar morphology and strength properties and showed a good stability to atmosphere and washing. POLYM. COMPOS., 2010. © 2009 Society of Plastics Engineers     

Enhanced tribological performance of hybrid polytetrafluoroethylene/Kevlar fabric composite filled with milled pitch‐based carbon fibers

As self‐lubricating bearing liner materials, tribological properties of milled pitch‐based carbon fibers (CFs) modified polytetrafluoroethylene (PTFE)/Kevlar fabric composites were investigated, and the microscopic morphology of worn surface was studied. The results show that the appropriate incorporation of CFs can obviously reduce the wear rate of the fabric composite with almost unchanging friction coefficient. The wear rates of 5 wt % CF‐filled PTFE/Kevlar fabric composites are decreased by 30% and 48% for two kinds of composites made with fibers from different producers compared with unfilled fabric composites. Scanning electron microscopy observations show that the appropriate incorporation of CFs obviously improves the interfacial bonding and reduces pull‐out and fracture of Kevlar fiber. Meanwhile, the introduction of CFs at proper fraction is helpful to form smooth and continuous transfer film on the surface of metal counterpart. The improving mechanism of the CF is attributed to increasing mechanical strength, thermal conductivity and self‐lubricating effects. © 2018 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2018 , 135, 46269.     

Effect of neutron irradiation on the structural,mechanical, and thermal properties of jute fiber

This article describes the effect of neutron irradiation on jute fiber (Corchorus olitorius). The jute fibers (4.0 tex) were irradiated by fast neutrons with an energy of 4.44 MeV at different fluences ranging from 2 × 10⁹ to 2 × 10¹³ n/cm². An important aspect of neutron irradiation is that the fast neutrons can produce dense ionization at deep levels in the materials. Structural analysis of the raw and irradiated fibers were studied by small‐angle X‐ray scattering (SAXS), X‐ray diffraction (XRD), scanning electron microscopy (SEM), and Fourier transform infrared spectroscopy. Thermal analysis carried out on the raw and irradiated fibers showed that the thermal stability of the fibers decreased after irradiation. The mechanical properties of the jute fibers were found to decrease after irradiation. The SAXS study showed that the average periodicity transverse to the layer decreased after irradiation, which may have been due to the shrinkage of cellulosic particles constituting the fiber. The residual compressive stress developed in the fiber after irradiation resulted in a decrease in crystallite size as supported by our XRD analysis. Observation with SEM did not indicate any change produced in the surface morphology of the fiber due to irradiation. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

Polyacrylonitrile solution homogeneity study by dynamic shear rheology and the effect on the carbon fiber tensile strength

Poly(acrylonitrile‐co‐methacrylic acid) (PAN‐co‐MAA)/N,N‐dimethylformamide (DMF) solutions were prepared and dynamic shear rheology of these solutions were investigated. With increasing stirring time up to 72 h at 70°C, the polymer solution became less elastic (more liquid‐like) with a ～60% reduction in the zero‐shear viscosity. Relaxation spectra of the PAN‐co‐MAA/DMF solutions yield a decrease in relaxation time (disentanglement time, τ_d), corresponding to an about 8% decrease in viscosity average molecular weight. The log‐log plot of G′ (storage modulus) versus G″ (loss modulus) exhibited an increase in slope as a function of stirring time, suggesting that the molecular level solution homogeneity increased. In order to study the effect of solution homogeneity on the resulting carbon fiber tensile strength, multiple PAN‐co‐MAA/DMF solutions were prepared, and the precursor fibers were processed using gel‐spinning, followed by continuous stabilization and carbonization. The rheological properties of each solution were also measured and correlated with the tensile strength values of the carbon fibers. It was observed that with increasing the slope of the G′ versus G″ log‐log plot from 1.471 to 1.552, and reducing interfilament fiber friction during precursor fiber drawing through the addition of a fiber washing step prior to fiber drawing, the carbon fiber strength was improved (from 3.7 to 5.8 GPa). This suggests that along with precursor fiber manufacturing and carbonization, the solution homogeneity is also very important to obtain high strength carbon fiber. POLYM. ENG. SCI., 56:361–370, 2016. © 2016 Society of Plastics Engineers     

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