The influence of pre-carbonization on the properties of PAN-based carbon fibers developed by two-stage continuous carbonization and air oxidation

The Properties of three kinds of carbon fibers, which were pre-carbonized at 500, 550, and 600°C during two-stage continuous carbonization, were measured after being air oxidized for periods of 1 to 6 min at 550°C. The effects of precarbonization temperatures on mechanical properties, density, morphology, elemental compositions, and microstructure of the carbon fibers are discussed. The pre-carbonization process affected strongly the surface properties and mechanical properties of the final carbon fibers, as measured after air oxidation. Carbon fibers measured one to six min after air oxidation showed a different oxidation behavior in the surface morphology for each pre-carbonization temperature. Optimum conditions not only improved the tensile strength and modulus by over 50%, but also increased the density and oxygen content.     

Continuous carbonization of polyacrylonitrile-based oxidized fibers: Aspects on mechanical properties and morphological structure

By following the progression of continuous carbonization (300–1250°C) of polyacrylonitrile (PAN)-based oxidized fibers, variations in tensile mechanical properties and morphological structure are reported in detail along the carbonization line. The tensile strength and Young's modulus of the fibers generally increase throughout the carbonization stage. Meanwhile, the fiber diameter displays a significant decrease. The preferred orientation of carbon layer planes is observed to increase remarkably for temperatures over 400°C. In a similar manner, the stacking size increases significantly but reaches saturation around 600°C, a changing point corresponding to that observed for the variation of the Young's modulus. However, beyond about 1200°C, the stacking size again displays a marked increase. Results thus obtained are interpreted in relation to each other. Possible implications are also discussed. © 1994 John Wiley & Sons, Inc.     

The influence of cobaltous chloride modification on physical properties and microstructure of modified PAN fiber during carbonization

Modification of polyacrylonitrile (PAN) fibers with cobaltous chloride has increased crystal size, crystallinity, and density, and also improved tensile strength and modulus of the resulting carbon fibers. In this study, the effect of cobaltous chloride modification on the physical properties, microstructure, and elemental composition of PAN fibers during the carbonization process was examined. The resultant carbon fibers developed from modified PAN fibers had a lower formation temperature of carbon basal planes than those fibers that developed from the original one. The modification process not only improved the tensile strength but also increased the tensile modulus by about 15% of the resulting carbon fibers at carbonization temperature of 1300°C. A higher stacking size (L_c), or a greater carbon basal plane in crystalline, is one of the reasons to improve the modulus and conductivity of the final carbon fibers. The modification process also increased the electrical conductivity by about 15% at 1300°C and by about 150% at 2500°C. © 1998 John Wiley & Sons, Inc. J Appl Polym Sci 70: 2409–2415, 1998     

Microstructure evolution and mechanical behavior of a mullite fiber heat-treated from 1100 to 1300°C

In this paper, the effect of phase transformation on microstructure evolution and mechanical behaviors of mullite fibers was well investigated from 1100 to 1300°C. In such a narrow temperature range, the microstructure and mechanical properties showed great changes, which were significant to be studied. The temperature of the alumina phase transformation started at below 1100°C. The main phases in fibers were γ-Al₂O₃ and δ-Al₂O₃ with amorphous SiO₂ at 1150°C. The stable α-Al₂O₃ formed at 1200°C. Then the mullite phase reaction occurred. As the alumina phase reaction took place, the tensile strength increased with the increasing temperature. In particular, the filaments achieved the highest strength at 1150°C with 1.98 ± 0.17 GPa, and the Young's modulus was 163.08 ± 4.69 GPa, showing excellent mechanical performance. After 1200°C, the mullite phase reaction went on with the crystallization of orthorhombic mullite. The density of surface defects increased rapidly due to thermal grooving, which led to mechanical properties degrade sharply. The strength at 1200°C was 1.01 ± 0.15 GPa with a strength retention of 63.13%, and the Young's modulus was 184.14 ± 10.36 GPa. While at 1300°C, the tensile strength was 0.64 ± 0.14 GPa with a strength retention of only 40.00%.     

Axial compressive strength of carbon fiber with tensile strength distribution

Measuring the fiber lengths of the broken pieces and estimating the mean tensile strength from the length just before the final fragment length in tension, efforts were made to estimate the axial compressive strengths of carbon fibers when the tensile strength varies with the length. The estimated compressive strength of carbon fibers decreases with increasing temperature. This decrease in compressive strength may be accounted for by a decrease in the radial compressive force owing to a decrease in the residual thermal stress and a decrease in Young's modulus of the resin matrix. There is a linear relationship between the estimated compressive strength and radial compressing force in the temperature range from room temperature to 80°C. The real compressive strength of the fibers, determined by extrapolating this straight line until the radial compressing force is zero, is about 20% higher than the compressive strength estimated by assuming that the tensile strength is uniform. It is approximately 10–50% of tensile strength. A linear relationship between the fiber axial compressive strength and compressive strength of the unidirectional composites is found. The experimental values agree with the values calculated by the rule of mixtures.     

Collaborative test programme results for 0°BD tensile properties on carbon–epoxy AS4/8552 and carbon– cyanate M55J/954-3 composite materials and some considerations on EN 2561 test standard

Abstract

A collaborative test programme has been undertaken on modified epoxy matrix 8552 reinforced with AS4 carbon fibres, and cyanate 954-3 reinforced with M55J high modulus carbon fibre, both in the form of unidirectional prepreg. To date more than 300 specimens have been tested according to the EN 2561 standard (tensile test parallel to the fibre direction). Different testing conditions such as tabbed and untabbed specimens, dry and wet conditioning, 23 and 70°C test temperature, 7° bevelled or squared off 90° tabs, and the influence of different gripping systems (mechanical and hydraulic) were studied. Average strength values and Young's modulus values are presented with their standard deviations for these materials at every tested condition. In tensile strength measurements, the importance of using tabs for the gripping system and tested material is demonstrated.     

Young's Modulus of Elasticity of Carbon‐Bonded Alumina Materials up to 1450°C

Investigating Young's modulus at elevated temperatures supports the understanding of microstructural changes as a function of application temperature. A sintered alumina and three carbon‐bonded alumina materials with carbon contents of 20 and 30 wt% and alumina grain size of 0.6–3 mm were investigated. Young's modulus was measured in a temperature range from 25°C to 1450°C by the impulse excitation technique. The Young's modulus of carbon‐bonded materials increases up to 140% at 1450°C. After one cycle, a decrease of the Young's modulus up to 50% is registered at room temperature. There is a strong hysteresis behavior during one cycle. Thermal expansion measurements show highest expansion for the highest graphite content material. The expansion of alumina grains and graphite flakes, resulting in microcrack generation during cooling and microcrack healing during heating, is reflected in the registered values of the Young's modulus as a function of the temperature. It is assumed, that higher graphite amounts as well as coarse grains lead to lower sintering effects of the microstructure at elevated temperatures and as a result lower values of the Young's modulus have been registered.     

Investigation of 3D printing strategy on the mechanical performance of coextruded continuous carbon fiber reinforced PETG

Fused filament fabrication (FFF) has been used to create prototypes and functional parts for various applications using plastic filaments. It has also been extended to the use of continuous fibers for reinforcing thermoplastic polymers. This study aims to optimize the deposition design of a coextruded continuous carbon fiber (CCF) composite filament with a polyethylene terephthalate glycol-modified (PETG) filament. The characterizations on the raw materials revealed that the matrix polymer in CCF composite filament had similar physicochemical properties as PETG, and carbon fibers were homogeneously distributed in CCF filament. The effect of raster orientation and shells number on the mechanical properties of non-reinforced and coextruded CCF-reinforced PETG was investigated. The highest mechanical properties were obtained at a raster orientation of 0° for both reinforced and non-reinforced materials. With the increase of raster orientation, Young's modulus and ultimate tensile strength decreased. The presence of shells improved the tensile strength of non-reinforced PETG. For composite samples printed with unreinforced shells, Young's modulus decreased due to decrease in fibers content, and elongation at break and ultimate tensile strength increased. Tomographic observations showed that the mechanical behavior of printed specimens depended on the anisotropy of porosity in printed specimens.     

Properties of isocyanate‐reactive waterborne polyurethane adhesives: Effect of cure reaction with various polyol and chain extender content

Three series of isocyanate‐reactive waterborne polyurethane adhesives were prepared with various contents of chain extender (4.25/8.25/12.50 mol %) and polyol (20.75/16.75/12.50 mol %). Each series had a fixed amount of excess (residual) NCO group (0.50–2.00 mol %). FTIR and ¹H‐NMR spectroscopy identified the formation of urea crosslink structure mainly above 80°C of various cure temperatures (20–120°C) with excess diisocyanate. The molecular weight, tensile strength, Young's modulus, and adhesive strength depend on excess NCO content and cure temperature and also varied with polyol and chain extender content. The optimum cure temperature was 100°C for all the samples. The tensile strength, Young's modulus, and adhesive strength increased with increasing cure temperature above 60°C up to the optimum temperature) (100°C) and then almost leveled off. Among all the samples, the maximum values of tensile strength, Young's modulus, and adhesive strength were found with 63.22 wt % polyol, 0.93 wt % chain extender, and 1.50 mol % excess (residual) NCO content at 100°C optimum cure temperature. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

Mechanical properties of natural fiber hybrid composites based on renewable thermoset resins derived from soybean oil,for use in technical applications

Natural fiber composites are known to have lower mechanical properties than glass or carbon fiber reinforced composites. The hybrid natural fiber composites prepared in this study have relatively good mechanical properties. Different combinations of woven and non‐woven flax fibers were used. The stacking sequence of the fibers was in different orientations, such as 0°, +45°, and 90°. The composites manufactured had good mechanical properties. A tensile strength of about 119 MPa and Young's modulus of about 14 GPa was achieved, with flexural strength and modulus of about 201 MPa and 24 GPa, respectively. For the purposes of comparison, composites were made with a combination of woven fabrics and glass fibers. One ply of a glass fiber mat was sandwiched in the mid‐plane and this increased the tensile strength considerably to 168 MPa. Dynamic mechanical analysis was performed in order to determine the storage and loss modulus and the glass transition temperature of the composites. Microstructural analysis was done with scanning electron microscopy. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

Processing and mechanical performance of 3D Cf/SiCN composites prepared by polymer impregnation and pyrolysis

The processing of 3D carbon fiber reinforced SiCN ceramic matrix composites prepared by polymer impregnation and pyrolysis (PIP) route was improved, and factors that determined the mechanical performance of the resulting composites were discussed. 3D C_f/SiCN composites with a relative density of ∼81% and uniform microstructure were obtained after 6 PIP cycles. The optimum bending strength, Young's modulus and fracture toughness of the composites were 75.2 MPa, 66.3 GPa and 1.65 MPa m^1/2, respectively. The residual strength retention rate of the as-pyrolyzed composites was 93.3% after thermal shock test at ΔT = 780 °C. It further degraded to 14.6% when the thermal shock temperature difference reached to 1180 °C. The bending strength of the composites was 35.6 MPa after annealing at 1000 °C in static air. The deterioration of the bending strength should be attributed to the strength degradation of carbon fibers and decomposition of interfacial structure.     

High-Performance Carbon Fibers Prepared by Continuous Stabilization and Carbonization of Electron Beam-Irradiated Textile Grade Polyacrylonitrile Fibers

The manufacturing of high-performance carbon fibers (CFs) from low-cost textile grade poly(acrylonitrile) (PAN) homo- and copolymers using continuous electron beam (EB) irradiation, stabilization, and carbonization on a kilogram scale is reported. The resulting CFs have tensile strengths of up to 3.1 ± 0.6 GPa and Young's moduli of up to 212 ± 9 GPa, exceeding standard grade CFs such as Toray T300. Additionally, the Weibull strength and modulus, the microstructure, and the morphology of these CFs are determined.     

High-strength polyethylene

Polyethylene (PE) continuous filaments having high tensile strength as well as high Young's modulus have been obtained from several linear polyethylene materials by stretching a partially oriented spun yarn to a draw ratio of ?30. The high draw ratio was readily attained for linear PE fiber extruded at a temperature of at least 250°C and quenched in air while under some intermediate tension. The number average molecular weight of the polymer was found to have the predominant effect on the ultimate tensile strength of the drawn fiber. Yarn with a tensile strength of 19 gpd (167 kg/mm²) and a Young's modulus of 854 gpd (7380 kg/mm²) was produced. Yarn with a Young's modulus of 1145 gpd (9890 kg/mm²) was made by sacrificing some tensile strength.     

Roller drawing of polyoxymethylene

The roller drawing of polyoxymethylene (POM) sheets was carried out in the temperature range of 140–157°C. The mechanical properties, the molecular orientation, and the microstructure of the roller-drawn POM sheets were investigated by means of tensile test, dynamic viscoelasticity, wide-angle X-ray diffraction, small-angle X-ray scattering, visible dichroic spectrum, electron microscopy, and so on. The Young's modulus and the tensile strength increased with increasing draw ratio up to draw ratio, λ of 14–15. The improvement of the mechanical properties is concerned with structural changes, such as the increase in orientation function in the crystalline and amorphous regions and the formation of taut tie molecules and crystalline bridges in the intercrystallite and interfibrillar regions. In the higher draw ratio range (λ > 15), the increase in Young's modulus and tensile strength was restricted by the formation of interfibrillar microvoids.     

Solid state extrusion of polytetrafluoroethylene fibers

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

Effects of heat treatment on tensile properties of high‐strength poly(vinyl alcohol) fibers

The tensile properties of high‐strength poly(vinyl alcohol) (PVA) fibers after heat treatment in air, water, and engine oil were studied. The results show that heat treatment in air, water, and engine oil have a different influence on the tensile properties of high‐strength PVA fibers. After heat treatment in air, the fibers possess excellent heat stability of the tensile properties. But in water, especially in hot water, the tenacity, Young's modulus, and specific work of rupture of the fibers decrease, while the elongation at break of the fibers increases. Similarly, engine oil has a significant influence on the tensile properties of the fibers. When the temperature of engine oil is above 120°C, the tensile properties of the fibers decrease drastically. We also discuss the influence of heat, water, and engine oil on the tensile properties of high‐strength PVA fibers in relation to the structure of the fibers. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 78: 237–242, 2000     

High‐strength regenerated cellulose fibers spun from 1‐butyl‐3‐methylimidazolium chloride solutions

High‐performance regenerated cellulose fibers were prepared from cellulose/1‐butyl‐3‐methylimidazolium chloride (BMIMCl) solutions via dry‐jet wet spinning. The spinnability of the solution was initially evaluated using the maximum winding speed of the solution spinning line under various ambient temperatures and relative humidities in the air gap. The subsequent spinning trials were conducted under various air gap conditions in a water coagulation bath. It was found that low temperature and low relative humidity in the air gap were important to obtain fibers with high tensile strength at a high draw ratio. From a 10 wt % cellulose/BMIMCl solution, regenerated fibers with tensile strength up to 886 MPa were prepared below 22 °C and relative humidity of 50%. High strengthening was also strongly linked with the fixation effect on fibers during washing and drying processes. Furthermore, an effective attempt to prepare higher performance fibers was conducted from a higher polymer concentration solution using a high molecular weight dissolving pulp. Eventually, fibers with a tensile strength of ～1 GPa and Young's modulus over 35 GPa were prepared. These tensile properties were ranked at the highest level for regenerated cellulose fibers prepared by an ionic liquid–based process. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017 , 134, 45551.     

Syndiotacticity-rich poly(vinyl alcohol) fibers spun from N-methylmorpholine-N-oxide/water mixture

Aqueous NMMO solutions containing NMMO above 50% are good solvents for syndiotacticity-rich poly(vinyl alcohol) (s-PVA). Although water is not a good solvent and dissolves s-PVA at temperatures above 100°C, the mixtures dissolve it at temperatures below 100°C. s-PVA fibers were prepared through gel-spinning of s-PVA/NMMO/water (NMMO: water = 70 : 30) mixtures in cold water and wet-spinning of the solution in methanol. The mechanical properties and fine structure of the drawn fibers were examined based on the results of measurements of tensile properties, thermal properties, birefringence, and optical and electron microscopic observations. The strength and Young's modulus of the drawn fibers were approximately to 2.0 and 45 GPa, respectively. The reason why the fibers with theoretical mechanical properties could not be prepared was surmised to be related to the structure of the amorphous regions. © 1993 John Wiley & Sons, Inc.     

Development of a gel spinning process for high‐strength poly(ethylene oxide) fibers

This article describes a new gel‐spinning process for making high‐strength poly(ethylene oxide) (PEO) fibers. The PEO gel‐spinning process was enabled through an oligomer/polymer blend in place of conventional organic solvents, and the gelation and solvent‐like properties were investigated. A 92/8 wt% poly(ethylene glycol)/PEO gel exhibited a melting temperature around 45°C and was highly stretchable at room temperature. Some salient features of a gel‐spun PEO fiber with a draw ratio of 60 are tensile strength at break = 0.66 ± 0.04 GPa, Young's modulus = 4.3 ± 0.1 GPa, and a toughness corresponding to 117 MJ/m³. These numbers are significantly higher than those previously reported. Wide‐angle x‐ray diffraction of the high‐strength fibers showed good molecular orientation along the fiber direction. The results also demonstrate the potential of further improvement of mechanical properties. POLYM. ENG. SCI., 54:2839–2847, 2014. © 2014 Society of Plastics Engineers     

High modulus semi-crystalline polymers by solid state rolling

Solid state rolling of semi-crystalline polymers is shown to be an effective method of producing high strength, high modulus tape at acceptable production rates. High density polyethylene tape was produced having a tensile strength exceeding 300 MPa and a tensile modulus of 8.7 GPa at production rates exceeding 8 m/min. A significant factor in producing highly oriented tape by the rolling process is roll temperature. Increasing the roll temperature from 25°C to 125°C not only increases the maximum extent of orientation achievable, but increases the mechanical properties at a given degree of thickness reduction. Internal frictional heat development limited the maximum thickness reduction ratio of polypropylene to 6.6:1. This reduction was reached by rolling at 150°C. The resultant tape had a tensile modulus of 5.1 GPa and a tensile strength of 300 MPa.