Properties of polyacrylonitrile/single wall carbon nanotube composite films prepared in nitric acid

Nanocomposite films were prepared by casting the solution of polyacrylonitrile (PAN) and single wall nanotube (SWNT) in nitric acid subsequent to sonication. Even though SWNT shows good dispersion visually, the reinforcing effect was not satisfactory. The G-band Raman spectra of the drawn film clearly demonstrated that SWNTs in the film are well-oriented along the drawing axis of the film. The electrical resistivity of the film prepared using nitric acid was lower than that of the film using DMF. Thus, nitric acid is presumably more effective in dispersing nanotubes than DMF.     

Tensile behavior and structural evolution of poly(lactic acid) monofilaments in glass transition region

A series of amorphous poly(lactic acid) (PLA) monofilaments with various D-isomer contents of 1∼9 mol% have been prepared and then elongated uniaxially at 25∼65 °C in the glass transition region. Both initial modulus and maximum strength of PLA monofilaments are appreciably decreased with increasing the temperature, especially at ∼50 °C, and they were somewhat lower for the monofilament with higher D-isomer content. Structural evolution, chain orientation, and thermal properties of PLA monofilaments drawn uniaxially with various draw ratios at 65 °C were then investigated by using wide-angle X-ray diffraction, polarized Raman spectroscopy, and differential scanning calorimetry, respectively. X-ray diffraction patterns clearly exhibited the development of chain orientation and stain-induced crystallization of the monofilaments as a function of draw ratio (DR). The dichroic ratio, a measure of the chain orientation, was quantitatively evaluated from the polarized Raman spectra. It was revealed that the dichroic ratios increased up to DR=4 and decreased slightly at DR>4 owing to the strain-induced crystallization for PLA monofilaments with D-isomer contents of 1 and 4 mol%. The glass transition and cold-crystallization temperatures of PLA monofilaments increased and decreased, respectively, with the increment of DR. The strain-induced enthalpy relaxation endothermic peak appearing in glass transition region became intense with increasing the DR.     

Electrospinning and microwave absorption of polyaniline/polyacrylonitrile/multiwalled carbon nanotubes nanocomposite fibers

Electrical conductive nanocomposite fibers were prepared with polyaniline (PANI), polyacrylonitrile (PAN) and multi-walled carbon nanotubes (MWCNTs) via electrospinning. The morphology and electrical conductivity of the PANI/PAN/MWCNTs nanocomposite fibers were characterized by scanning electron microscope (SEM) and Van De Pauw method. Electrical conductivity of nanocomposite fibers increased from 1.79 S·m^?1 to 7.97 S·m^?1 with increasing the MWCNTs content from 3.0 wt% to 7.0 wt%. Compared with PANI/PAN membranes, the mechanical property of PANI/PAN/MWCNTs nanocomposites fiber membranes decreased. The microwave absorption performance of composite films was analyzed using waveguide tube, which indicated that with the thickness increasing the value of R_L reduced from ?4.6 to ?5.9 dB.     

The effect of multi-walled carbon nanotubes on the molecular orientation of poly(vinyl alcohol) in drawn composite films

Poly(vinyl alcohol) (PVA)/multi-walled carbon nanotube (MWNT) composite films were prepared by casting a DMSO solution of PVA and MWNTs, whereby the MWNTs were dispersed by sonication. A significant improvement in the mechanical properties of the PVA drawn films was achieved by the addition of a small amount of MWNTs. The initial modulus and the tensile strength of the PVA drawn film increased by 30% and 45% respectively, with the addition of 1 wt% MWNTs, which are close to those calculated from the rule of mixtures, and were strongly dependent upon the orientation of the PVA matrix. The mechanical properties, however, were not improved with a further increase in the MWNT content. The orientation of MWNTs in the composite was not well developed compared to that of the PVA matrix. This result suggests that the improvement of the molecular orientation of the PVA matrix plays a major role in the increase of the mechanical properties of the drawn PVA/MWNT composite films.     

Carbon nanofiber/poly(vinylidene fluoride-hexafluoro propylene) composite films: The crystal structure and thermal properties with various drawing temperatures

Carbon nanofiber (CNF)/polyvinylidene fluoride-hexafluoro propylene (PVDF-HFP) composite film was prepared by solution casting and melt pressing. The resultant 2 % CNF/PVDF-HFP composite films were uniaxially drawn at 50 °C, 75 °C, and 100 °C, respectively. In the SEM images, the morphology of drawn CNF/PVDF-HFP composite film confirmed the orientation of the CNF and the polymer matrix. The WAXD results showed the coexistence crystal phase of PVDF-HFP. The drawn CNF/PVDF-HFP composite film demonstrates improved electrical properties. The DSC thermogram results indicated no change in the melting temperature but slightly increased crystallinity with increasing drawing temperature. Dynamic mechanical analysis and tensile test showed an improvement in the storage modulus and stress at a drawing temperature of 75 °C.     

Preparation and properties of polarizing films for liquid crystal display prepared using iodine vapor

The properties of polarizing films prepared using iodine vapor and using I₂/KI solution are compared to investigate the possibility of using vapor phase iodine adsorption in preparing polarizing film. The structure of PVA films drawn to different draw ratios and the amount of iodine adsorbed in drawn PVA films using iodine vapor were investigated. Increases in the degree of crystallinity, crystalline orientation index and birefringence with increase in draw ratio of PVA film, were observed by WAXD and polarizing microscope analysis. The amounts of iodine adsorbed by PVA film were 2–4 wt% for 20 min. UV-visible analysis suggests that I₃ ^? and I₅ ^? structures of iodine exist in the polarizing film after drawing in boric acid solution. Single transmittance and degree of polarization of polarizing films prepared using iodine vapor were about 30–50 % and over 99 %, respectively, at total draw ratios of over 3. The possibility of employing vapor phase adsorption of iodine instead of solution adsorption to prepare commercial polarizing film is suggested.     

Uniaxially drawn polylactic acid film based physiological sensor for monitoring sleeping parameters

In this study, we investigated the effect of cutting angle, draw ratio (DR), and degree of orientation on the shearpiezoelectric behavior of uniaxially drawn PLA film. Piezoelectric results suggest that the PLA film with DR=4.5 and cutting angle of 45^o exhibit maximum shear-piezoelectricity as expected. Piezoelectric output signals of drawn PLA films well correlated with birefringence rather than draw ratio due to the fact that the degree of chain orientation is not directly proportional to draw ratio. A physiological sensing belt (PSB) was developed by implanting silicone rubber coated PLA film in between two elastic textile bands and mounted on the mattress to monitor physiological signals such as heartbeat and respiration rate. Physiological signals were acquired during sleeping of the human subject through the elongation of PLA film implanted in the PSB sensor. Heartbeat and respiration rates of the subject during sleep were easily estimated to be 70 min^-1 and 18.6 min^-1, respectively. Monitoring of cardio-respiratory signals during sleep using our PLA film based PSB sensor was found to be very useful for diagnosing sleep related disorders such as sleep-apnea, snoring, insomnia, etc.     

Influence of the draw ratio on the mechanical properties and electrical conductivity of nanofilled thermoplastic polyurethane fibers

Electrically conducting textile fibers were produced by wet-spinning under various volume fractions using thermoplastic polyurethane (TPU) as a polymer and carbon black (CB), Ag-powder, multi-walled carbon nanotubes (MWCNTs), which are widely used as electrically conducting nanofillers. After applying the fiber to the heat drawing process at different draw ratios, the filler volume fraction, linear density, breaking to strength, and electrical conductivity according to each draw ratio and volume fraction. In addition, scanning electron microscopy (SEM) images were taken. The breaking to strength of the TPU fiber containing the nanofillers increased with increasing draw ratio. At a draw ratio of 2.5, the breaking to strength of the TPU fiber increased by 105 % for neat-TPU, 88 % for CB, 86 % for Ag-powder, and 127 % for MWCNT compared to the undrawn fiber. The breaking to strength of the TPU fiber containing CB decreased gradually with increasing volume fraction, and in case of Ag-powder, it decreased sharply owing to its specific gravity. The electrical conductivity of the TPU fiber containing CB and Ag-powder decreased with increasing draw ratio, but the electrical conductivity of the TPU fiber containing MWCNT increased rapidly after the addition of 1.34 vol. % or over. The moment when the aggregation of MWCNT occurred and its breaking to strength started to decrease was determined to be the percolation threshold of the electrical conductivity. The heat drawing process of the fiber-form material containing the anisotropic electrical conductivity nanofillers make the percolation threshold of the electrical conductivity and the maximum breaking to strength appear at a lower volume fraction. This is effective in the development of a breaking to strength and electrical conductivity.     

Fine structure and physical properties of poly(buthylene terephthalate) sheets prepared by roller drawing method

Poly(butylene terephthalate) sheets were prepared by roller-drawing method with various draw ratio. The drawing temperature is 100 °C and draw ratios were varied 2, 2.5, 3, 3.5 and 4. The effect of draw ratio on the crystal structure, the molecular orientation, dynamic viscoelastic properties, sonic modulus and tensile properties of the roller-drawn PBT sheets were investigated. In WAXD results, with increasing of the draw ratio, (010) and (100) planes of preferred orientation have the strongest intensity on the equator. In the meridional scans, it was confirmed that α and β crystal co-existed in the roller drawn PBT sheets with various draw ratio. Uniaxially roller-drawn PBT sheets clearly increased orientation along the stretched direction at high draw ratio. And the four-methylene groups of PBT orient along the surface of the sheet. The mechanical properties of PBT sheets were improved by orientation-induced crystallization during roller drawing process at 100 °C.     

Crystal structure and thermal properties of poly(vinylidene fluoride)-carbon fiber composite films with various drawing temperatures and speeds

PVDF-CF composite films were prepared using a melt pressing method. The PVDF-CF composite films were cut into rectangular shapes with a gauge length and width of 10 and 5 mm, respectively. The films were drawn using a universal testing machine equipped with a hot chamber. The drawing temperatures and speeds were 50∼150 °C and 100∼000 %/min, respectively. The crystal structure and physical properties of the resulting PVDF-CF films were investigated by wide angle X-ray diffraction, Fourier transform infrared spectroscopy, differential scanning calorimetry, dynamic mechanical analysis and scanning electron microscopy. The crystal form of the initial films was the 〈alpha〉 phase (non polarity, lamellar structure) of PVDF. The maximum draw ratio was 4.2. The drawn PVDF-CF films prepared at 100 °C were mainly the 〈beta〉 phase (polarity, fibrillar structure) of PVDF. With increasing drawing speeds, the 〈alpha〉 phase became the dominant phase of PVDF in the PVDF-CF films. The thermal properties of the PVDF-CF films improved with increasing drawing temperature, and the dynamic mechanical properties improved with increasing drawing speed.     

Polyester-based thermoplastic elastomer/MWNT composites: Rheological, thermal, and electrical properties

Polyester-based thermoplastic elastomer (Hytrel®) was melt-compounded with multi-walled nanotubes (MWNTs) using an internal mixer and the changes in the thermal, electrical and rheological properties were investigated using a range of nanotube contents (from 0.1 to 7 wt%). Even at nanotube concentrations as low as 0.1 wt%, the crystallization temperature was remarkably elevated by 15 °C and it increased further up to 22 °C with a 5 wt% loading. On the contrary, the melting temperature increased by 2 °C with 0.1 wt% MWNTs and it was slightly decreased by further additions of MWNTs. Electrical conductivity measured by the four probe method was detected from the 1 wt% MWNTs, indicative of electrical percolation. In addition, MWNTs starting from 4 wt% and above had no significant effect on the electrical conductivity, while it rapidly increased with nanotube contents below 4 wt%. Dynamic rheological properties were measured using a strain controlled rotational rheometer. The complex viscosity increased with MWNT contents giving an abrupt increase between 0.5 and 1 wt% loadings. In addition, the storage and loss modulus increased in a different manner depending on the range of the nanotube concentration. In the Cole-Cole plot, the slope of the nanocomposites decreased from 1.63 to 0.74 with increasing nanotube contents. In the Casson plot, the addition of MWNTs up to 0.5 wt% did not show any yield behavior giving an extremely low value for the yield stress, but further additions of nanotubes increased it notably. The presence of nanotubes in the elastomer increased the relaxation time with nanotube contents and their effect became weak as the frequency increased.     

Preparation and characterization of modified collagen/PAN blending fibers

Graft modification of collagen with acrylonitrile in concentrated aqueous solution of sodium thiocyanate (NaSCN) is developed in this paper. This modification can largely change it’s solubility in water and can be applied in fiber production. Grafting modified collagen is characterized by infrared spectrum and wide angle X-ray diffraction. Wet spinning of PAN fibers containing several content of modified collagen is performed. The tests about these fibers show that breaking strength and sonic orientation decrease as the amount of collagen is raised. The addition of collagen can largely improve the moisture regain of PAN fiber. Micro-appearance of fibers observed under scanning electron microscope (SEM) presents circular cross section and longitudinal grooves on surface, the depth of grooves increases with the increasing draw ratio.     

Polypyrrole/polyacrylonitrile composite films: Dielectric, spectrophotometric and morphologic characterization

Spectrophotometric, morphologic and dielectric properties of polyacrylonitrile (PAN) composite films in the presence of pyrrole derivatives were reported in this paper. The composite films were fabricated by oxidative polymerization of pyrrole (Py), N-methyl pyrrole (NMPy) and N-phenyl pyrrole (NPhPy) by cerium(IV) on polyacrylonitrile matrix. The effect of temperature on the dielectric properties was studied in the frequency range from 0.05 Hz up to 10 MHz and in the temperature range from 0 °C up to 250 °C. Conductivity was increased with temperature due to increase of the mobility of charge carriers in the composite films. By increasing the temperature, the dipoles become free and respond to the applied electric field in composite structure; thus, the polarization and dielectric constant increases. PNPhPy-PAN composite films exhibited the highest dielectric constant, AC conductivity and tan delta.     

Structure,electrical and mechanical properties of polyamide 66/acid-treated MWCNT composite films prepared by solution mixing in the presence of nonionic surfactant

Two different sets of polyamide 66(PA66)-based composite films containing 2.0-10.0 wt% acid-treated multiwalled carbon nanotubes (MWCNT) were manufactured by solution mixing and casting method in the presence or absence of a nonionic surfactant. For the improved dispersion and interfacial interaction of MWCNTs in the PA66 matrix, carboxylic acid-functionalized MWCNTs were prepared by the acid-treatment of pristine MWCNTs. The uniform dispersion of the acidtreated MWCNTs in the PA66 matrix was confirmed from FE-SEM images of the fractured composite film surfaces. DSC thermograms supported that the acid-treated MWCNTs served as nucleating agents for the melt-crystallization of PA66 in both composite films prepared with/without the addition of the surfactant. The electrical and tensile mechanical properties of the composite films prepared with the surfactant were ~20 % higher than those of the composite films manufactured without the surfactant. For both composite films, sheet resistivity and tensile mechanical properties were found to be highly decreased and increased, respectively, with the increment of the acid-treated MWCNT content.     

Effect of conformation on the properties of uniaxially drawn polylacide films upon drawing temperature

Polylactide(PLA) films were drawn at various drawing temperature of 65, 90 and 120 °C. The effects of drawing temperature on structural conformation and properties of PLA films were investigated. It was confirmed that the PLA films at drawing temperature of 65 and 90 °C were composed of α′ phase crystal form. The strain-induced crystallization and molecular orientation increased with increasing the draw ratio, which result in improving the mechanical and thermal properties of α′ phase PLA films. However, at drawing temperature of 120 °C, the strain-induced crystallization and molecular orientation of PLA films were not distinctly detected. It was supposed that the rate of the chain relaxation was faster than chain orientation and strain-induced crystallization during uniaxial drawing process.     

Decay of electrical conductivity in p-toluene sulfonate doped polypyrrole films

Long term performance of conductivity of p-toluene sulfonic acid (pTSA) doped electrochemically synthesized polypyrrole (PPy) films was estimated from accelerated aging studies between 80 °C and 120 °C. Conductivity decay experiments indicated that overall aging behavior of PPy films deviated from first order kinetics at prolonged aging times at elevated temperatures. However, an approximate value for the activation energy of the conductivity decay of PPy was calculated as E=47.4 kJ/mol, enabling an estimate of a rate constant of k=8.35×10⁻⁶/min at 20 °C. The rate of decrease of conductivity was not only temperature dependent but also influenced by the dopant concentration. A concentration of 0.005 M pTSA in the electrolyte resulted in a conductive film and when this film was exposed to 120 °C for a period of 40 h, the conductivity decayed to about 1/20 of its original value. The concentration of pTSA was increased to 0.05 mol/l and when the resulting film was aged in the same way, it showed a decrease in the conductivity to about 1/3 of its original value. Both microwave transmission and dc conductivity data revealed that highly doped films were considerably more electrically stable than lightly doped films. The dopant had a preserving effect on the electrical properties of PPy.     

Microstructures and electrical properties of composite films based on carbon nanotube and para-aramid containing cyano side group

We report the microstructures and electrical properties of poly(2-cyano-1,4-phenylene terephthalamide) (cyPPTA)-based composite films including pristine multi-walled carbon nanotube (MWCNT) of 0.3-10.0 wt%, which were manufactured by ultrasonication-based solution mixing and casting techniques. FT-IR spectra of the composite films revealed the existence of specific interaction between cyPPTA and MWCNT. Accordingly, the pristine MWCNTs were found to be dispersed uniformly in the cyPPTA matrix, as confirmed by TEM images. The electrical resistivity of the composite films decreased considerably from ~10¹⁰ Ω cm to ~10⁰ Ω cm with the increase of the MWCNT content by forming a conductive percolation threshold at ~0.525 wt%. The composite films with 3.0-10.0 wt% MWCNT contents, which have sufficiently low electrical resistivity of ~10²-10⁰ Ω cm, exhibited excellent electric heating performance by attaining high maximum temperatures and electric power efficiency under given applied voltages of 10-100 V. Since the thermal decomposition of the composite films took place at 520-600 °C under air atmosphere, cyPPTA/MWCNT composite films could be used for high performance electric heating, antistatic, and EMI shielding materials.     

Effects of drawing speed and water on microstructure and mechanical properties of artificially spun spider dragline silk

The effects of drawing speed and water on the microstructures and mechanical properties of Araneus Ventricosus spider dragline silk were investigated with polarized Raman spectroscopy and mechanical property tester. The major ampullate silk (MAS), spider dragline silk was made by drawing from major ampullate glands of Araneus Ventricosus spider at the rates of 1, 10, 20, 40, and 110 mm/s, respectively. It was found that MAS silk drawn at 20 mm/s contained the most of β-sheet polypeptides with the high orientation and the least of α-helix. The results also revealed that dragline silk spun at aqueous condition (WDS) had lower content and orientation of β-sheets than those at ambient condition (DDS); the existence of water led to smaller tensile strength at break and initial modulus, but larger tensile strain at break of dragline silk.     

Synthesis and characterization of electrically conductive composite films of polypyrrole/poly(acrylonitrile-co-styrene)

Homogeneus Polypyrrole (PPy)/poly(acrylonitrile-co-styrene) (SAN) composite thin films were prepared by chemical polymerization of pyrrole on poly(acrylonitrile-co-styrene) matrix. Ce (IV) is used as an oxidant for in-situ polymerizion of pyrrole on SAN matrix, having an advantageous over the impregnation method. The formation and incorporation of PPy in the copolymer matrix were confirmed by FTIR-ATR and UV-Visible spectrophotometric measurements. Thermal analyses showed that after polymerization of Py in copolymer matrix, thermal behavior of SAN was changed and derivative of weight loss at this temperature was increased by increasing of PPy content. XPS and FTIR-ATR analysis of composite films indicated cerium salt with nitrate ion acted as a dopant. The increase in the AC electrical conductivity of the PPy/SAN composites over pure SAN was observed. At lower frequency up to 10⁵ Hz, conductivity was shown an independent behavior from frequency; but at high frequencies (10⁵–10⁷ Hz), dependence on frequency was explained by polaron and bipolaron formations of PPy. The dispersion of PPy particles in copolymer matrix was proven by SEM, AFM and digital camera. By the increase of PPy content in the composite films, increase in AC conductivities, and decrease in dielectric constants and loss were observed.     

Effect of multi walled carbon nanotube on the crystalline structure of polypropylene fibers

Polypropylene fibers containing varying amounts of multi walled carbon nanotube (MWCNT) have been spun using a conventional melt spinning and drawing apparatus. Changes in morphology and crystalline structure of composite fibers induced by addition of MWCNT were studied by small angle X-ray scattering (SAXS), wide angle X-ray scattering (WAXS), Fourier transform infrared spectroscopy (FTIR) and birefringence measurements. The results of SAXS experiments showed an increase in lamellar thickness, long period and crystallinity of the composite fibers in comparison to pure polypropylene fibers. Molecular orientation and helical content of the fibers were increased due to the addition of MWCNT to the polypropylene matrix. WAXS results, being in agreement with the SAXS results, also showed an increase in crystallinity of the composite fibers due to the increase in MWCNT content. This is probably because of nucleating effect of nanotubes in the fiber matrix, causing more crystallization and orientation of molecules to take place around them.