Crystal structure and thermal properties of poly(vinylidene fluoridehexafluoropropylene) films prepared by various processing conditions

Poly(vinylidene fluoride-co-hexafluoropropylene)(PVDF-HFP) films were prepared using either a melt pressing or solution casting methods. The resulting PVDF-HFP films were drawn uniaxially at various drawing temperatures and speeds. The mp-PVDF-HFP films were more transparent and had more drawability than the sc-PVDF-HFP films. The crystal form of the initial films was the alpha-phase (non polarity) of PVDF. The maximum draw ratio was 7.6. The mp-PVDF-HFP films were prepared at a drawing speed of 2500 %/min at 100 °C. With increasing drawing speed, the beta-phase (polarity) became the dominant phase of PVDF in mp-PVDF-HFP films. The thermal properties of the resulting PVDF-HFP films improved with increasing drawing temperature.     

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.     

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.     

A study of hydrophobic electrospun membrane applied in seawater desalination by membrane distillation

In this study, two composite nanofibrous membranes of Polyvinylidenefluoride (PVDF) and [poly(vinylidenefluorideco-hexafluoropropylene)] (PVDF-co-HFP) prepared by the electrospinning process were employed in a direct contact membrane distillation (DCMD) system. We changed the pump flow rate and temperature difference to examine their effects on permeate flux and salt rejection. The SEM observations, porosity analyzer technique, and contact angle measurement indicated the nanobrous membrane with an average fiber diameter of 170 nm and maximum pore diameter distribution of 0.3 ??m is the best membrane for the DCMD system. However, the ability of the hydrophobic membrane affects the filtration efficiency of the DCMD system. The contact angle of the PVDF-HFP electrospun membrane (128°) shows better hydrophobic than the PVDF electrospun membrane (125 °). From the experiment of 12 hours, the salt rejection of PVDFHFP (99.9901 %) was better than that of PVDF composite membrane (99.9888 %) and was almost the same as that of the PTFE commercial membrane (99.9951 %). In addition, the permeate flux of the PVDF-HFP composite membrane is 4.28 kg/ m²hr higher than the PTFE commercial membrane.     

Study of microstructure of oriented PET fibres exposed to supercritical carbon dioxide

Samples of partially oriented yarn (POY) PET fibers were uniaxially drawn at temperatures below, near, and above the glass transition temperature at a constant draw ratio before exposure to supercritical carbon dioxide (scCO₂) in the presence of tension at a temperature of 80 °C and a pressure of 220 bar. The effects of drawing temperature and scCO₂ exposure on structural changes and on mesomorphic transitions, in particular, were investigated using differential scanning calorimetry (DSC), Fourier transform infrared spectroscopy (FTIR), and birefringence and density measurements. A good correlation was obtained among the results obtained from various techniques. Results indicated that the development of a transient mesophase structure depended strongly on process temperature. By drawing PET fibers in the samples at temperatures below the glass transition (cold-drawing), a mesophase structure developed in which the highly extended chains played a key role in structural changes incurred. Meanwhile, exposure to scCO₂ led to the plasticization of the samples accompanied by their reduced glass transition and cold crystallization temperatures. This process also gave rise to the appearance of a second melting peak at about 135 °C that is related to the melting of imperfect and thin crystals, thereby inducing structural changes in the treated fibers. In the case of samples subjected to cold drawing and to scCO₂ exposure, the transformation of the mesophase structure into the crystalline phase was found to be strongly affected by scCO₂ exposure, while this same effect was negligible in the case of hot drawn samples.     

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.     

Effect of temperature on germination and early growth of subterranean clover, capeweed and Wimmera ryegrass

Germination of annual pasture species was studied under controlled‐environment conditions in south‐western Australia at temperatures in the range from 4°C to 35°C. Subterranean clover (Trifolium subterraneum) and Wimmera ryegrass (Lolium rigidum) had a germination of 90% between 12°C and 29°C, whereas capeweed (Arctotheca calendula) had a high germination percentage in a much narrower temperature range with an optimum of 25°C. Growth of subterranean clover, capeweed and Wimmera ryegrass between 28 and 49 days after sowing (DAS) was also studied at two photon flux densities, 13 and 30 mol m^?2 d^?1, and at diel temperatures in the range from 15/10°C to 33/28°C. Pasture species grown at a density of 1000 plants m^?2 accumulated at least twice the amount of shoot dry matter when subjected to temperatures of 21/16°C and 27/22°C, compared with a lower temperature of 15/10°C and a higher temperature of 33/28°C. Except at the highest temperature and at high photon flux density, capeweed had lower green area indices (GAI) than the other two species at 28 DAS. Crop growth rates between 28 and 49 DAS were higher in Wimmera ryegrass than in the other two species, whereas subterranean clover had a lower relative growth rate than the other two species at all temperatures and both photon flux densities. Subterranean clover and capeweed intercepted a greater proportion of the incident radiation compared with Wimmera ryegrass. The values of radiation interception and GAI were used to estimate the number of DAS to reach 75% radiation interception [f_(0·75)]. The number of days to reach f_(0·75) decreased with increasing temperature from 15/10°C to reach a minimum at 27/22°C. The time taken to achieve f_(0·75) was always shorter by about 10 d when the photon flux density was 30 mol m^?2 d^?1 in the autumn compared with 13 mol m^?2 d^?1 in the winter. These results are discussed in relation to the early growth of annual pasture in the field.     

Synthesis and characterization of acrylic fibers-<Emphasis Type="Italic">g</Emphasis>-polyacrylamide

Graft copolymerization of acrylamide onto commercial acrylic fibers was carried out using benzoyl peroxide as a free-radical initiator in aqueous medium within the 75–95 °C temperature range. In this study, the effects of initiator and monomer concentration, the amount of fiber, polymerization time, and temperature on the graft yield were investigated. The optimum concentration for initiator was found to be 2.0×10⁻³ mol/l and the optimum temperature of 85 °C. The activation energy of the reaction was calculated to as 35.81 kJ/mol at the temperature interval of 75–95 °C. The structures and morphologies characterization of grafted fibers was investigated by Fourier transform infrared spectroscopy (FTIR), scanning electron microscopy (SEM), and thermogravimetric analysis (TGA). The thermogravimetric analysis data showed that the thermal stability of the acrylic fibers increased with graft yield. The scanning electron photographs showed that the homogeneous appearance of the fiber surface changed and a shell-like heterogeneous structure occurred at the surface with an increasing degree of grafting. The moisture content, water absorption, dyeability, and antimicrobial activity of grafted acrylic fibers were also reported. The results showed that grafting of polyAAm improved the moisture contain, water absorption, dyeability, and antimicrobial activity of fiber.     

On-line interferometric study on the mechanical fracture behaviour by crazing observed in stretched polypropylene fibres

Two-beam polarizing light interference microscope devised by Pluta is used for in situ investigation of fracture mechanism of as-spun isotactic polypropylene (iPP) fibres by crazing during cold drawing process. The study includes characterization of crazing of polypropylene fibres (involving craze initiation, craze propagation and craze breakdown) as a function of crazing strain, crazing temperature and stretching speed. The investigation of craze damage showed that it is increased rapidly with stretching speed and then increased slowly to level off. Also it was found that, stretching iPP fibre at relatively low speed (lower than 0.015 cm/sec) at constant temperature 19 °C would reduce the effect of fracture on the stretched filaments. The time to crazing, the time to failure and the areal craze density of iPP fibres during cold drawing process are estimated. Finally, observing the craze formation at different temperatures showed that there was a critical value of stretching temperature for the formation of crazes in iPP fibre, and it was found to be 40 °C. The obtained results are correlated to the corresponding variations in some optical and structural properties of iPP fibres due to stretching.     

Film preparation by melt- or compression-process using poly(vinyl chloride) powder swollen with dimethylformamide

A melt-process was used to prepare high molecular weight Poly(vinyl chloride) (PVC) films without the use of a conventional plasticizer and heat stabilizer. Rigid PVC powder was swollen with dimethylformamide containing 4∼10 vol% water to reduce its melting temperature. The swollen powder was pressed at a relatively low temperature of 75∼125 °C to form a film shape, and then washed and dried. The visible light transmittance, X-ray diffraction, density and the tensile properties of the resulting films were examined to estimate the success or failure of film formation. The films could be produced by not only the melt-process but also a compression-process using the rigid, highly swollen PVC powder. The resulting films had no voids, which are generally observed in PVC products formed by a solution process. The minimum temperature for these processes decreased with decreasing water content in the mixture: The minimum temperatures according to the water content in the mixture to produce faultless films through the melt-process were 4 %–105 °C, 6 %–115 °C, 8 and 10 %–125 °C, while those through the compression process were 4 %–95 °C, 6 and 8 %–105 °C, 10 %–115 °C.     

Reinforcement of wet milled jute nano/micro particles in polyvinyl alcohol films

Textile industry generate significant amount of waste fibres in form of short lengths during mechanical processing. However these short fibres possess excellent properties suitable for many other applications. The objective of this work was to use them for the preparation of nanoparticles/nanofibres as fillers in biodegradable composite applications such as food packaging, agriculture mulch films, automotive plastics, etc. The present paper concerns with jute fibres as a source of nanocellulose for reinforcement of PVA mulch films. Jute fibres were first refined to micro/nanoscale particles in form of nanofibrillar cellulose (NFC) by high energy planetary ball milling process in dry and wet condition. Wet milling was observed more efficient than dry milling in terms of unimodality of size distribution with reduction in size below 500 nm after milling for 3 hours. Later the obtained particles were used as fillers in Poly vinyl alcohol (PVA) films and their reinforcement evaluated based on thermal properties. It was observed that glass transition temperature (T_g) of PVA films improved from 84.36 °C to 95.22 °C after addition of 5 % jute particles without affecting % crystallinity and melting temperature (T _m) of PVA. Dynamic mechanical analysis of composite films with 5 % jute particles showed higher value of 14×10⁸ Pa for storage modulus in comparison to 9×10⁸ Pa of neat composite film. The percolation effect was observed more above glass transition temperature which consequently resulted in improved transfer of stiffness from jute particles to PVA matrix above 50 °C. The percolation phenomena also explained the improvement in thermal stability by 10 °C for every increased loading of jute particles due to formation of hydrogen bonds with PVA matrix.     

Synthesis,analysis and simulation of carbonized electrospun nanofibers infused carbon prepreg composites for improved mechanical and thermal properties

This paper reports the fabrication, characterization and simulation of electrospun polyacrylonitrile (PAN) nanofibers into pre-impregnated (prepreg) carbon fiber composites for different industrial applications. The electrospun PAN nanofibers were stabilized in air at 270 °C for one hour and then carbonized at 950 °C in an inert atmosphere (argon) for another hour before placing on the prepreg composites as top layers. The prepreg carbon fibers and carbonized PAN nanofibers were cured together following the prepreg composite curing cycles. Energy dispersive X-ray spectroscopy (EDX) was carried out to investigate the chemical compositions and elemental distribution of the carbonized PAN nanofibers. The EDX results revealed that the carbon weight % of approximately 66 (atomic % 72) was achieved in the PAN-derived carbon nanofibers along with nitrogen and lower amounts of nickel, oxygen and other impurities. Thermomechanical analysis (TMA) exhibited the glass transition regions in the prepreg nanocomposites and the significant dependence of coefficient of thermal expansion on the fiber directions. The highest value of coefficient of thermal expansion was observed in the temperature range of 118-139 °C (7.5×10^-8 1/°C) for 0 degree nanocomposite scheme. The highest value of coefficient of thermal expansion was observed in the temperature range of 50-80 °C (37.5×10^-6 1/°C) for 90 degree nanocomposite scheme. The test results were simulated using ANSYS software. The test results may be useful for the development of structural health monitoring of various composite materials for aircraft and wind turbine applications.     

Influence of Drawing and Annealing on the Crystallization,Viscoelasticity, and Mechanical Properties for Middle-molecular-weight Polyethylene Fishing Monofilaments

The influence of drawing and annealing on the crystallization, viscoelasticity and mechanical properties for middle-molecular-weight polyethylene (MMWPE) fishing monofilaments was investigated. It was found that the drawing procedure had a positive effect on the crystallization of the MMWPE fishing monofilaments. Meanwhile, the glass transition temperature of the MMWPE monofilaments shifted to higher temperature, and the α-relaxation associated with crystalline phases became higher and broader with the increase in the drawing ratio. Moreover, the breaking strength of MMWPE fishing monofilaments can be effectively improved by increasing the drawing ratio. Meanwhile, the knot strength increased first and then decreased. However, the increase in annealing temperature improved the knot strength. With increasing annealing temperature, the orientation factor decreased and induced the γ-relaxation peak at high magnitude. This indicated that the amorphous structure could become disordered during annealing treatment. In addition, the annealing temperature can clearly influence the working temperature dependence of the stress-strain behavior. When the working temperature rose from 20 °C to 30 °C, the MMWPE monofilaments after annealing at 120 °C exhibited low modulus loss due to their high α- transition temperature. Thus, an important method for improving the mechanical properties by controlling the drawing and annealing conditions was established.     

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.     

Preparation and characterization of melt-spun PVC filament yarns

Polyvinyl chloride (PVC) fibers were melt-spun to prepare mono and multifilament yarns. To find optimum spinning and drawing conditions, various parameters such as spinning temperature, spinneret diameter, drawing temperature, and drawing ratio were examined. From the observation of the spinnability under various conditions, we found that the optimum conditions were as following: the extrusion temperature and die temperature were 175–180°C and 185–190°C, and the drawing temperature and drawing ratio were 85–95°C and 3.4, respectively. Under these conditions, the spinneret diameter could be reduced to the minimum value, 0.5 mm. Spun PVC filament yarns were subjected to the different yarn texturing process of stuffing box and pin false-twist method. The PVC yarn fabric was prepared by the knitting of textured yarns. Finally, the anion-emission and antibiotic properties of the knitted PVC fabrics were precisely evaluated.     

Evaluation of Laundering Durability of Electro-conductive Textile Dip-coated on Para Aramid Knit with Graphene/Waterborne Polyurethane Composite

This study aims to fabricate an electro-conductive textile dip-coated with graphene/waterborne polyurethane (WPU) composite, and an evaluation of the laundering durability of this composite was conducted in order to confirm the application of the protective clothing. Samples were coated five times on the para-aramid knit with the graphene/WPU composite by the dip-coating method, and then hot-pressed processes were applied with various temperatures. The samples were washed 5, 10, 15, and 20 times, and then, morphology, surface resistance, and surface temperature were measured. After five laundering cycles, control and hot-pressed samples maintained surface resistivity from 10 kΩ/sq to 100 kΩ/sq. The surface resistivity of the control sample, however, was gradually increased up to 20 laundering cycles. The sample that was hot-pressed at 120 °C showed the lowest value of about 15 kΩ/sq with almost no variation from zero laundering cycles to 20, thus, it is the most stable sample up to 20 laundering cycles. When applied voltage at 50V, the surface temperature of the nonlaundering samples was presented as over 40.0 °C. In the case of the control sample, there was almost no electrical heating performance remaining after the fifth laundering test, but the hot-pressed samples maintained 40.0 °C or more at 50 V after the 10th laundering test. The sample that was hot-pressed at 120 °C in particular could maintain electrical heating performance at about an 80 % level up to the 10th laundering cycle. Therefore, the sample that was hot-pressed at 120 °C was the most stable in terms of electrical properties after 20 laundering cycles, and its electrical heating performance could be maintained even after 10 laundering cycles. It is expected that this process can be applied and used to make functional clothes for apparel and other applications.     

An effective and simple process for obtaining high strength silkworm (Bombyx mori) silk fiber

This article describes a new process for strengthening natural silk fibers. This process is simple yet effective for mass production of high strength silk fibers, enabled by drawing at a lower temperature and immediately heat setting at a higher temperature. The processing conditions were investigated and optimized to improve the strength. Silk fibers drawn to the maximum ratio at room temperature and then heat set at 200 °C show best tensile properties. Some salient features of the resulting fibers are tensile strength at break reaching 533±10.2 MPa and Young’s modulus attaining 12.9±0.57 GPa. These values are significantly higher than those of natural silk fibers (tensile strength increased by 44 % and Young’s modulus by 135 %). Wide-angle X-ray diffraction and FTIR confirm the transformation of silk I to silk II crystalline structure for the fiber obtained from this process. DSC and TGA data also provide support for the structural change of the silk fiber.     

Characteristics of Electrical Heating Elements Coated with Graphene Nanocomposite on Polyester Fabric: Effect of Different Graphene Contents and Annealing Temperatures

This paper reports the fabrication of electrical heating elements based on the graphene/waterborne polyurethane (WPU) composite coated on polyester fabric with toughness like that of artificial leather. Samples were prepared with 0, 4, 8, and 16 wt% of graphene by using the knife edge method, and then, the samples were annealed from 100 oC to 160 °C. The graphene content had a large effect on the electrical and electrical heating properties. The surface resistivity was decreased by approximately 6 orders of magnitude with an increase from 0 wt% to 16 wt% graphene/WPU composite fabric. The electric heating properties were also improved, as indicated by the percolation threshold. Samples with various graphene contents were annealed, and it was found that the electrical and electrical heating properties were improved, and the most enhanced properties were obtained when the samples were annealed at 120 °C. The initial modulus and tensile strength were increased in comparison with those of 0 wt% and 16 wt% graphene/WPU composite coated on fabrics, but the elongation at break value was slightly decreased with an increasing graphene content. When the samples were annealed, initial modulus and tensile strength of samples were improved at 120 °C and 140 °C, and they were slightly decreased at 160 °C. However, the elongation at break showed an opposite tendency to the tensile strength. With the increase in content of graphene and annealing at 120 °C and 140 °C, the samples were more stiff and tough, and at 160 °C, the samples were softer. Therefore, graphene/WPU composite coated on polyester fabric by use of the annealing process may have applications in electrical heating elements due to its excellent heating performance and toughness like that of artificial leather.     

Modeling and differential evolution optimization of PAN carbon fiber production process

In this research, results of an experimental and artificial neural network fuzzy interface system (ANFIS) modeling of operating parameters on tensile strength of the carbon fibers are investigated. To do these experiments, the commercial polyacrylonitrile (PAN) fiber of Polyacryl Iran Corporation (PIC) was used as the precursors. The results show that increasing all of parameters improves tensile strength performance. ANFIS was applied to predict tensile strength of carbon fibers as a function of stabilization temperature at first stage (STFIS), stabilization temperature at second stage (STSS), stabilization temperature at third stage (STTS), stabilization temperature at fourth stage (STFOS), and carbonization temperature (CT). The optimum levels of influential factors, determined for tensile strength are STFIS 200 °C, STSS 225 °C, STTS 240 °C, STFOS 260 °C, CT, and 1400 °C. The modeling results showed that there is an excellent agreement between the experimental data and the predicted values. Furthermore, the fiber process is optimized applying differential evolution (DE) algorithm as an effective and robust optimization method.     

Thermal and oxidation protection of carbon fiber by continuous liquid phase pre-ceramic coatings for high temperature application

Thermal and oxidation resistant coating is necessary for carbon fiber (CF) in CF reinforced concrete (CFRC) composite application in order to fulfil a high level of safety standard in case of fire. Pre-ceramic coatings such as Polysilazane, Polysiloxane, and Methyl silicone resin have been deposited on CF filament yarn by means of wet chemical continuous dip coating method. The surface analyses e.g. scanning electron microscopy (SEM), X-ray photoelectron spectroscopy (XPS) and infrared spectroscopy (IR) results showed the changes of surface morphology by the coatings. Thermo gravimetric analysis (TGA) revealed that the high temperature (up to 800 °C) oxidation stability of CF was significantly improved with coatings. Thermo-mechanical properties also significantly enhanced up to 600 °C. CF yarn retains its original strength and elasticity modulus/stiffness at 700 °C due to thermal and oxidation resistant coatings.