Nylon 66 nanofibers prepared by CO2 laser supersonic drawing

Nylon 66 nanofibers were prepared by irradiating as‐spun nylon 66 fibers with radiation from a carbon dioxide (CO₂) laser while drawing them at supersonic velocities. A supersonic jet was generated by blowing air into a vacuum chamber through the fiber injection orifice. The fiber diameter depended on the drawing conditions used, such as laser power, chamber pressure, laser irradiation point, and fiber supply speed. A nanofiber obtained at a laser power of 20 W and a chamber pressure of 20 kPa had an average diameter of 0.337 μm and a draw ratio of 291,664, and the drawing speed in the CO₂ laser supersonic drawing was 486 m s^?1. The nanofibers showed two melting peaks at about 257 and 272°C. The lower melting peak is observed at the same temperature as that of the as‐spun fiber, whereas the higher melting peak is about 15°C higher than the lower one. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2014 , 131, 40015.     

Poly(ethylene terephthalate) nanofibers prepared by CO2 laser supersonic drawing

Poly(ethylene terephthalate) (PET) nanofibers were prepared by irradiating a PET fiber with radiation from a carbon dioxide (CO₂) laser while drawing it at supersonic velocities. A supersonic jet was generated by blowing air into a vacuum chamber through the fiber injection orifice. The flow velocity from the orifice was estimated by computer simulation; the fastest flow velocity was calculated to be 401 m s⁻¹ at a chamber pressure of 6 kPa. A nanofiber obtained using a laser power of 8 W and a chamber pressure of 6 kPa had an average diameter of 193 nm and a draw ratio of about 900,000. This technique is a novel method for producing nanofibers.     

Poly(ethylene‐2,6‐naphthalate) nanofiber prepared by carbon dioxide laser supersonic drawing

Poly(ethylene‐2,6‐naphthalate) (PEN) nanofiber was prepared by a carbon dioxide (CO₂) laser supersonic drawing. The CO₂ laser supersonic drawing was carried out by irradiating the laser to the as‐spun PEN fiber in a low‐temperature supersonic jet. The supersonic jet was generated by blowing off air into a vacuum chamber from a fiber supplying orifice. The flow velocity from the orifice can be estimated by applying Graham's theorem from the pressure difference between the atmospheric pressure and the pressure of the vacuum chamber. The fastest flow velocity estimated was 396 m s^?1 (Mach 1.15) at a chamber pressure of 6 KPa. The nanofiber obtained at Mach 1.15 was the oriented nanofibers with an average diameter of 0.259 μm, and its draw ratio estimated from the diameters before and after the drawing reached 430,822 times. The CO₂ laser supersonic drawing is a new method to make nanofiber without using any solvent or removing the second component. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

Poly(p‐phenylene sulfide) nanofibers prepared by CO2 laser supersonic drawing

Poly(p‐phenylene sulfide) (PPS) nanofibers are prepared by irradiating a PPS fiber with a carbon dioxide (CO₂) laser while drawing it at supersonic speeds. A supersonic jet is generated by blowing air into a vacuum chamber through the fiber injection orifice. Nanofibers obtained at a laser power of 30 W and chamber pressure of 10 kPa exhibit an average diameter of 600 nm and a draw ratio of 110,000. Scanning electron microscopy, differential scanning calorimetry, and wide‐angle X‐ray diffraction analyses are employed to investigate the relationships among the chamber pressure, fiber morphology, and crystallization behavior. The nanofibers exhibit two melting temperatures (T_m): approximately 280°C and 320°C. The endothermic peak at T_m = 280°C is ascribable to lamellar crystals and that at T_m = 320°C to the highly complete crystals, since the polymer molecular chain is highly oriented. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014 , 131, 40922.     

Mechanical properties of poly(ethylene terephthalate) nanofiber three‐dimensional structure prepared by CO2 laser supersonic drawing

CO₂‐laser supersonic drawing method can produce bulky fluffy poly(ethylene terephthalate) (PET) nanofibers (NFs) by only irradiating CO₂‐laser to as‐spun PET fibers in the supersonic air jet. Cylindrical PET NF three‐dimensional structure (NF‐3DS) was fabricated by compression‐molding the obtained fluffy PET NFs using the cylindrical metal mold. NF‐3DS mold was completely disordered 3DS without a laminated structure because NFs were disorderly packed in the metal mold. The porosity of NF‐3DS can be changed by varying the filling weight of NF into the metal mold, and the highest porosity was 95.4%. The shape recovery ratio after 50% uniaxial compression in the height of NF‐3DS increases as the porosity increases, and NF‐3DS with a porosity of 95.4% had a shape recovery ratio of 98.1%. NF‐3DS with a desired shape will be produced if the metal mold can be prepared. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2018 , 135, 45763.     

Poly(ethylene terephthalate) nanosheets prepared by CO2-laser supersonic multi-drawing

Poly(ethylene terephthalate) (PET) nanosheets were fabricated by winding nanofibers onto a spool. The nanofibers were prepared by irradiating PET fibers with radiation from a carbon dioxide laser while drawing them at supersonic velocities. A supersonic jet was generated by blowing air into a vacuum chamber through the fiber injection orifice. A new vacuum chamber was developed to produce nanosheets; it has seven fiber injection orifices and a spool to collect the nanofibers. A rectangular nanosheet that was 17 cm wide, 18 cm long, and 30 μm thick was obtained by collecting nanofibers for 10 min. The nanosheet is composed of nanofibers with an average fiber diameter of 350 nm. This technique is a novel method for producing nanosheets.     

The effect of CO2 dissolved in a diesel fuel on the jet flame characteristics

This paper is concerned with an experimental study of the jet diffusion flame characteristics of fuel containing CO₂. Using diesel fuel containing dissolved CO₂ gas, experiments were performed under atmospheric conditions with a diesel hole-type nozzle of 0.19 mm orifice diameter at constant injection pressure. In this study, four different CO₂ mass fraction in diesel fuel such as 3.13%, 7.18%, 12.33% and 17.82% were used to study the effect of CO₂ concentration on the jet flame characteristics. Jet flame characteristics were measured by direct photography, meanwhile the image colorimetry is used to assess the qualitative features of jet flame temperature. Experimental results show that the CO₂ gas dilution effect and the atomization effect have a great influence on the flame structure and average temperature. When the injection pressure of diesel fuel increased from 4 MPa to 6 MPa, the low temperature flame length increased from 18.4 cm to 21.7 cm and the full temperature flame length decreased from 147.6 cm to 134.7 cm. With the increase of CO₂ gas dissolved in the diesel fuel, the jet flame full length decreased for the jet atomization being improved greatly meanwhile the low temperature flame length increased for the CO₂ gas dilution effect; with the increase of CO₂ gas dissolved in the diesel fuel, the average temperature of flame increases firstly and then falls. Experimental results validate that higher injection pressure will improve jet atomization and then increased the flame average temperature.     

Higher‐order structural analysis of nylon‐66 nanofibers prepared by carbon dioxide laser supersonic drawing and exhibiting near‐equilibrium melting temperature

Extended chains and/or extended chain crystals (ECC) are important structures for improving the mechanical properties of polymer fibers. ECC have so far been produced using specially prepared materials or manufacturing methods. In our study on the production of nanofibers by carbon dioxide (CO₂) laser supersonic drawing, we succeeded in producing nylon‐66 nanofibers having a high melting point near the equilibrium melting point (T_m⁰). Two melting points (T_m) of 260 and 276°C were observed for the nanofibers, with the latter temperature being close to the T_m⁰ (280°C) of nylon‐66. A nanofiber that was heat treated at 279°C for 10 min displayed a large stacked lamellar structure with an average crystal thickness of 140 nm. That value was close to the average molecular chain length of 212 nm, which was calculated from the average molecular weight of the nanofibers. It was inferred from these results that ECC corresponding to the average molecular chain length were present in the nanofibers. The CO₂ laser supersonic drawing process is applicable to general purpose thermoplastic polymers and uses a simple drawing system. It is expected that this drawing method will help to improve the fundamental performance of general purpose polymers. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014 , 131, 40361.     

Anti-solvent effect in the production of lysozyme nanoparticles by supercritical fluid-assisted atomization processes

Particles of lysozyme in the range of 0.1–5 μm were generated by high pressure CO₂ or N₂ (at pressures between 8 MPa and 25 MPa) from aqueous ethanol solutions using an atomization process similar to the supercritical assisted atomization technology. Perfect nanosized spheres of lysozyme were produced using both supercritical fluids. However, while N₂ assisted atomization-produced spheres at all experimental conditions reported here, supercritical CO₂ assisted atomization produced particles of two distinct morphologies depending on the pre-mixing conditions. This work shows that CO₂ assisted atomization produces particles by two different mechanisms depending on the mixture pre-expansion phase equilibria conditions: anti-solvent crystallization and spray drying crystallization. Depending on the governing precipitation mechanism (anti-solvent or spray drying), fibers or spherical particles were obtained with CO₂. Lysozyme activity was severely affected by pure anti-solvent processing, while N₂ processed lysozyme conserved mostly its activity.     

Melt‐electrospinning of poly(ethylene terephthalate) and polyalirate

Rodlike polymer samples were made from three kinds of poly(ethylene terephthalate) (PET) pellets with different intrinsic viscosities (IV), and from polyalirate (Vectra) pellets. PET and Vectra fibers were produced using a melt‐electrospinning system equipped with a CO₂‐laser melting device from these rodlike samples. The effects of IV value and laser output power on the fiber diameter of PET were investigated. Furthermore, the effect of the laser output power on the fiber diameter of Vectra was investigated. The crystal orientation of these produced fibers was also investigated by X‐ray photographs. The following conclusions were reached: (i) the diameter of PET fiber decreases with increasing laser output power; (ii) the minimum average diameter of PET fibers is scarcely influenced by the value of IV; (iii) the electrospun PET fibers show isotropic crystal orientation; (iv) fibers having an average fiber diameter smaller than 1 μm cannot be obtained from PET and Vectra using the system developed; and (v) preferred liquid crystal orientation can be seen in electrospun Vectra fibers. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 2007     

Effect of supercritical carbon dioxide dyeing conditions on the chemical and morphological changes of poly(ethylene terephthalate) fibers

Commercially available regular denier poly(ethylene terephthalate) (PET) fabrics were used in this investigation. PET fabric samples were wound on a bobbin and then exposed to supercritical CO₂ under conditions representing a typical supercritical CO₂ dyeing cycle. Infrared spectroscopy, X‐ray diffraction, differential scanning calorimetry, and scanning electron microscopy were used to characterize the chemical and morphological changes of the PET fibers. The results showed that exposure to supercritical CO₂ did not cause chemical changes in the fibers; the crystal size and the T_mp of the PET fabric after treatment in supercritical CO₂ did not significantly change; the crystallinity decreased; and the treatment in supercritical CO₂ at higher temperature caused surface morphology changes (increased oligomer migration). However, there was no pitting, cracking, or crazing on the surface of the treated fibers. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 92: 2008–2012, 2004     

Initiation of homogeneous combustion in a high-velocity jet of a fuel–air mixture by an optical discharge

The effect of a focused pulsed-periodic beam of a CO₂ laser on initiation and evolution of combustion in subsonic and supersonic flows of homogeneous fuel–air mixtures (H₂ + air and CH₄ + air) is experimentally studied. The beam generated by the CO₂ laser propagates across the flow and is focused by a lens at the jet axis. The flow structure is determined by a schlieren system with a slot and a plane knife aligned in the streamwise direction. The image is recorded by a high-speed camera with an exposure time of 1.5 μs and a frame frequency of 1000 s^?1. The structure of the combustion region is studied by an example of inherent luminescence of the flame at the wavelengths of OH and CH radicals. The distribution of the emission intensity of the mixture components in the optical discharge region is investigated in the present experiments by methods of emission spectroscopy.     

PET microfiber prepared by carbon dioxide laser heating

In preliminary experiments to optimize the condition of a laser heating, zone drawing for poly(ethylene terephthalate) (PET) fiber, a microfiber was prepared by a continuous‐wave carbon dioxide (CW CO₂) laser heating. CW CO₂ laser heating was carried out at an extremely low applied tension (σ_a) at a higher laser power density (PD) as compared to the optimum condition for the laser heating, zone drawing of PET fiber reported previously. The microfibers were obtained by CO₂ laser heating carried out at a PD of 15.8 W cm^?2 and under a σ_a of 0.66 MPa or lower. The diameter of the fiber decreased with a decreasing σ_a and increasing PD. The smaller the diameter, the higher was its birefringence. The smallest diameter fiber obtained at σ_a = 0.17 MPa at PD = 21 W cm^?2 had a diameter of 4.5 μm and a birefringence of 0.112, and its draw ratio estimated from the diameter reached 3086 fold. Such a high draw ratio was not previously attained by any drawing method. In a wide‐angle X‐ray diffraction photograph of the smallest diameter fiber, indistinct reflections due to oriented crystallites were observed. An SEM micrograph of the smallest diameter fiber showed a smooth surface without any crack and was uniform in diameter. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 88: 3297–3283, 2003     

Superstructure and mechanical properties of nylon 66 microfiber prepared by carbon dioxide laser‐thinning method

Nylon 66 microfibers were obtained by a carbon dioxide (CO₂) laser‐thinning method. A laser‐thinning apparatus used to continuously prepare microfibers consisted of spools supplying and winding the fibers, a continuous‐wave CO₂‐laser emitter, a system supplying the fibers, and a traverse. The diameter of the microfibers decreased as the winding speed increased, and the birefringence increased as the winding speed increased. When microfibers, obtained through the laser irradiation (at a power density of 8.0 W cm^?2) of the original fiber supplied at 0.23 m min^?1, were wound at 2000 m min^?1, they had a diameter of 2.8 μm and a birefringence of 46 × 10^?3. The draw ratio calculated from the supplying and winding speeds was 8696×. Scanning electron microscopy showed that the microfibers obtained with the laser‐thinning apparatus had smooth surfaces not roughened by laser ablation that were uniform in diameter. To study the conformational transition with winding speed, the changes in trans band at 936 cm^?1 and gauche band at 1136 cm^?1 were measured with a Fourier transform infrared microscope. The trans band increased as the winding speed increased, and the gauche band decreased. Young's modulus and tensile strength increased with increasing winding speed. The microfiber, which was obtained at a winding speed of 2000 m min^?1, had a Young's modulus of 2.5 GPa and tensile strength of 0.6 GPa. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 99: 802–807, 2006     

Coaxial nozzle for control of particle morphology in precipitation with a compressed fluid antisolvent

A coaxial nozzle was developed to achieve further control over the morphology of microparticles precipitated from solution by carbon dioxide as a compressed fluid antisolvent. The polymer solution was sprayed through the core of the nozzle and CO₂ through the annulus. For the coaxial nozzle versus a standard nozzle, polystyrene and poly(L-lactic acid) particles can be larger by a factor of 3–8 with less flocculation. A reduction in the Weber number reduces atomization and larger droplets are formed in the jet, delaying precipitation. However, because of the much higher Reynolds number for the high velocity CO₂, the mass transfer in the suspension outside of the jet is faster leading to less flocculation and agglomeration. For polyacrylonitrile, the delayed precipitation produces a transition from highly oriented microfibrils to microparticles. © 1997 John Wiley & Sons, Inc. J Appl Polym Sci 64: 2105–2118, 1997     

Dynamic CO2 adsorption performance of internally cooled silica‐supported poly(ethylenimine) hollow fiber sorbents

The dynamic adsorption behavior of CO₂ under both nonisothermal and nearly isothermal conditions in silica supported poly(ethylenimine) (PEI) hollow fiber sorbents (Torlon®‐S‐PEI) is investigated in a rapid temperature swing adsorption (RTSA) process. A maximum CO₂ breakthrough capacity of 1.33 mmol/g‐fiber (2.66 mmol/g‐silica) is observed when the fibers are actively cooled by flowing cooling water in the fiber bores. Under dry CO₂ adsorption conditions, heat released from the CO₂‐amine interaction increases the CO₂ breakthrough capacity by reducing the severity of the diffusion resistance in the supported PEI. This internal resistance can also be alleviated by prehydrating the fiber sorbent with a humid N₂ feed. The CO₂ breakthrough capacity of prehydrated fibers is adversely affected by the release of the adsorption enthalpy (unlike the dry fibers); however, active cooling of the fiber results in a constant CO₂ breakthrough capacity even at high CO₂ delivery rates (i.e., high adsorption enthalpy delivery rates). In full RTSA cycles, a purity of 50% CO₂ is achieved and the adsorption enthalpy recovery rate can reach ～72%. Studies on the cyclic stability of uncooled fiber sorbents in the presence of SO₂ and NO contaminants indicate that exposure to NO at 200 ppm over 120 cycles does not lead to a significant degradation of the sorbents, but SO₂ exposure at a similar high concentration of 200 ppm causes 60% loss in CO₂ breakthrough capacity after 120 cycles. A simple amine reinfusion technique is successfully demonstrated to recover the adsorption capacity in poisoned fiber sorbents after deactivation by exposure to impurities such SO₂. © 2014 American Institute of Chemical Engineers AIChE J, 60: 3878–3887, 2014     

Preparation and properties of PET/SiO2 composite micro/nanofibers by a laser melt-electrospinning system

Poly(ethylene terephthalate) (PET)/SiO₂ composite micro/nanofibers were successfully prepared by a laser melt-electrospinning system. The fibers with diameter ranging from 500 nm to 7 μm were obtained. The effect of laser current and applied voltage on the fibers morphologies was investigated by scanning electron microscopy (SEM), and the results showed that the relationship of process parameters and fibers diameter was complicated. The EDS analysis confirmed the presence of SiO₂ in the PET fibers matrix. The crystallization behavior of the electrospun PET/SiO₂ micro/nanofibers was investigated using X-ray diffraction (XRD) analysis and differential scanning calorimetry (DSC), and it was found that the as-electrospun fibers exhibited an amorphous phase. After heat-treatment at 120 and 160°C for 1 h, respectively, the fibers showed a high crystallinity. The thermal properties of fibers were studied using thermogravimetry-differential thermal analysis (TG–DTA), and showed the electrospun PET/SiO₂ composite fibers was not effective difference of thermostability compared with PET fibers when used for fibers materials. © 2012 Wiley Periodicals, Inc. J Appl Polym Sci, 2012     

Controlling sandwich‐structure of PET microcellular foams using coupling of CO2 diffusion and induced crystallization

Controlling sandwich‐structure of poly(ethylene terephthalate) (PET) microcellular foams using coupling of CO₂ diffusion and CO₂‐induced crystallization is presented in this article. The intrinsic kinetics of CO₂‐induced crystallization of amorphous PET at 25°C and different CO₂ pressures were detected using in situ high‐pressure Fourier transform infrared spectroscopy and correlated by Avrami equation. Sorption of CO₂ in PET was measured using magnetic suspension balance and the diffusivity determined by Fick's second law. A model coupling CO₂ diffusion in and CO₂‐induced crystallization of PET was proposed to calculate the CO₂ concentration as well as crystallinity distributions in PET sheet at different saturation times. It was revealed that a sandwich crystallization structure could be built in PET sheet, based on which a solid‐state foaming process was used to manipulate the sandwich‐structure of PET microcellular foams with two microcellular or even ultra‐microcellular foamed crystalline layers outside and a microcellular foamed amorphous layer inside. © 2011 American Institute of Chemical Engineers AIChE J, 58: 2512–2523, 2012     

Particle formation of an edible fat (rapeseed 70) using the supercritical melt micronization (ScMM) process

The supercritical melt micronization (ScMM) process, also known as particles from gas saturated solutions (PGSS) was applied, in a continuous operated pilot plant, for the particle formation of the edible fat, rapeseed 70 (RP70). The effect of variables like the CO₂ concentration, the melt temperature and the atomization pressure were studied in order to investigate particle morphology, density and the particle size distribution. The experiments were performed at CO₂ concentrations between 0 and 50 wt%, atomization pressure between 70 and 180 bar and melt temperature between 60 and 100 °C. Particles obtained as a function of the CO₂ concentration, showed completely solid, spherical–hollow and aggregated particles with a decrease in particle mean size as the concentration of CO₂ was increased. The results obtained as a function of atomization pressure showed no significant influence on particle morphology and size distribution. Experiments carried out as a function of the melt temperature showed distorted, spherical–hollow and aggregated particles. Furthermore, a theory was developed to explain the mechanism for particle formation as a function of the CO₂ concentration and the melt temperature. The crystallinity of the final product of RP70, showed an alpha polymorph with a crystallinity of 84%.     

Drawing in high pressure CO2—a new route to high performance fibers in memory of late Roger Porter

In this paper, we introduce a new draw technique for polymer orientation and apply it to different polymer fibers: poly(ethylene terephthalate) or PET, nylon 6,6, and ultra‐high molecular polyethylene (UHMWPE). In this technique, a polymer is drawn uniaxially in supercritical CO₂ using a custom high‐pressure apparatus. This technique can be used in replacement of a traditional drawing process or as a post‐treatment process. With PET, the technique is not effective at temperatures at or below 130°. In contrast, the process is highly effective for nylon 6,6 where CO₂ drawn fibers show significantly higher crystallinity and orientation along with improved mechanical properties. While the fibers are plasticized, the drawability of the fibers is only slightly dependent on temperature. High pressure CO₂ drawing of ultrahigh molecular weight polyethylene (UHMWPE) fibers is equally effective. Commercial high performance fibers can be drawn up to a ratio of 1.9 in asecond stage, resulting in large increases in tensile modulus and small improvements in tensile strength.