Tensile and impact properties of carbon filled nylon‐6,6 based resins

Electrically and thermally conductive resins can be produced by adding conductive fillers to insulating polymers. Mechanical properties such as tensile modulus, ultimate tensile stress, strain at ultimate tensile stress, and notched Izod impact strength are also important and cannot be ignored. This study focused on performing compounding runs, followed by injection molding and evaluation of tensile and impact properties of carbon filled nylon‐6,6 based resins. The three carbon fillers investigated include an electrically conductive carbon black, synthetic graphite particles, and a surface treated polyacrylonitrile (PAN) based carbon fiber. Resins containing varying amounts of these single carbon fillers were produced and tested. In addition, combinations of fillers were investigated by conducting a full 2³ factorial design and a complete replicate. The addition of carbon fiber increased the composite tensile modulus, ultimate tensile stress, and impact strength. Also, in many cases, combining two or three different fillers caused a statistically significant effect at a 95% confidence level. When comparing the results of this study with prior work, it appears that increased heteroatoms present on the carbon fiber surface likely improve composite ultimate tensile stress and impact strength. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 91: 2881–2893, 2004     

Reactive compatibilization and performance evaluation of miscanthus biofiber reinforced poly(hydroxybutyrate‐co‐hydroxyvalerate) biocomposites

Dicumyl peroxide (DCP) initiated reactive compatibilization of poly(hydroxybutyrate‐co‐hydroxyvalerate) (PHBV)/miscanthus fibers (70/30 wt %) based biocomposite was prepared in a twin screw extruder followed by injection molding. In the presence of DCP, both the flexural and the tensile strength of the PHBV/miscanthus composites were appreciably higher compared with PHBV/miscanthus composite without DCP as well as neat PHBV. The maximum tensile strength (29 MPa) and flexural strength (51 MPa) were observed in the PHBV/miscanthus composite with 0.7 phr DCP. The enhanced flexural and tensile strength of the PHBV/miscanthus/DCP composites are attributed to the improved interfacial adhesion by free radical initiator. Unlike flexural and tensile strength, the modulus of the PHBV/miscanthus/DCP composites was found to slightly lower than the PHBV/miscanthus composite. The modulus difference in the PHBV/miscanthus composite with and without DCP has good agreement with the observed crystallinity. However, the flexural and tensile modulus of all the prepared biocomposites was at least two fold higher than the neat PHBV. The storage modulus value of the PHBV/miscanthus and PHBV/miscanthus/DCP biocomposites follows similar trend like tensile and flexural modulus. The melting temperature and crystallization temperature of PHBV/DCP and PHBV/miscanthus/DCP samples were considerably lower compared with the neat PHBV and PHBV/miscanthus composites. The surface morphology revealed that the PHBV/miscanthus/DCP composites have good interface with less fiber pull‐outs compared with the corresponding counterpart without DCP. This suggests that the compatibility between the matrix and the fibers is enhanced after the addition of peroxide initiator. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017 , 134, 44860.     

Synergistic effects of carbon fillers on tensile and flexural properties in liquid‐crystal polymer based resins

One emerging market for thermally and electrically conductive resins is bipolar plates for use in fuel cells. Adding carbon fillers to thermoplastic resins increases the composite thermal and electrical conductivity. These fillers have an effect on the composite tensile and flexural properties, which are also important for bipolar plates. In this study, various amounts of three different types of carbon (carbon black, synthetic graphite particles, and carbon fibers) were added to Vectra A950RX liquid‐crystal polymer. In addition, composites containing combinations of fillers were also investigated via a factorial design. The tensile and flexural properties of the resulting composites were then measured. The objective of this study was to determine the effects and interactions of each filler with respect to the tensile and flexural properties. The addition of carbon black caused the tensile and flexural properties to decrease. Adding synthetic graphite particles caused the tensile and flexural modulus to increase. The addition of carbon fiber caused the tensile and flexural modulus and ultimate flexural strength to increase. In many cases, combining two different fillers caused a statistically significant effect on composite tensile and flexural properties at the 95% confidence level. For example, when 40 wt % synthetic graphite particles and 4 wt % carbon black were combined, the composite ultimate tensile and flexural strength increased more than what would be expected from the individual additive effect of each single filler. It is possible that linkages were formed between the carbon black and synthetic graphite particles that resulted in improved ultimate tensile and flexural strength. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

Thermal and mechanical properties of hybrid carbon/oxidized polyacrylonitrile fibers‐epoxy composites

Nowadays, hybrid composites are one of the important materials in industry due to their special properties. In this research, hybrid oxidized polyacrylonitrile (PAN) and carbon fibers reinforcement were used in epoxy matrix. The hybrid composites were fabricated using the hand lay‐up technique by placing the reinforcements in different layering sequences. Thermal and mechanical properties of these hybrid composites were investigated by thermal analysis, horizontal burning, tensile and bending tests. The tensile test results indicated that increasing oxidized polyacrylonitrile fibers (OPFs) to carbon fibers ratio decreased tensile strength and elastic modulus but increased failure strain. Hybrid oxidized PAN and carbon fibers reinforcement in composites led to decreasing flexural stress and modulus, and increasing flame retardancy. Thermal analysis results also showed that the maximum rate of mass loss in all composites was 370.6°C. It was also found that the maximum and minimum amounts of char residue at 900°C were related to the composites with four layers of carbon and OPFs, respectively. POLYM. COMPOS., 38:1412–1417, 2017. © 2015 Society of Plastics Engineers     

Effect of quasi‐carbonization processing parameters on the mechanical properties of quasi‐carbon/phenolic composites

In this work, quasi‐carbon fabrics were produced by quasi‐carbonization processes conducted at and below 1200°C. Stabilized polyacrylonitrile (PAN) fabrics and quasi‐carbon fabrics were used as reinforcements of phenolic composites with a 50 wt %/50 wt % ratio of the fabric to the phenolic resin. The effect of the quasi‐carbonization process on the flexural properties, interfacial strength, and dynamic mechanical properties of quasi‐carbon/phenolic composites was investigated in terms of the flexural strength and modulus, interlaminar shear strength, and storage modulus. The results were also compared with those of a stabilized PAN fabric/phenolic composite. The flexural, interlaminar, and dynamic mechanical results were quite consistent with one another. On the basis of all the results, the quasi‐static and dynamic mechanical properties of quasi‐carbon/phenolic composites increased with the applied external tension and heat‐treatment temperature increasing and with the heating rate decreasing for the quasi‐carbonization process. This study shows that control of the processing parameters strongly influences not only the mechanical properties of quasi‐carbon/phenolic composites but also the interlaminar shear strength between the fibers and the matrix resin. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

Hybrid effect on mechanical properties of M40‐T300 carbon fiber reinforced Bisphenol A Dicyanate ester composites

Interply and intraply hybrid composites based on Bisphenol A Dicyanate ester (BADCy), high strength carbon fibers T300, and high modulus carbon fibers M40 were prepared by monofilament dip‐winding and press molding technique. The tensile, flexural, interlaminar shear properties and SEM analysis of the hybrid composites with different fiber content and fiber arrangement were investigated. The results indicated that the mechanical properties of intraply hybrid composites were mainly determined by fiber volume contents. When the ratio of fiber volume content was close to 1:1, the intraply hybrid composites possessed lowest tensile and flexural strength. The mechanical properties of interply hybrid composite mainly depended on the fiber arrangement, instead of the fiber volume contents. The hybrid composites using T300 fiber layout as outside layer possessed high flexural strength and low flexural modulus, which was close to that of T300/BADCy composites. The hybrid composites ([(M40)_x/(T300)_y]_S) using M40 fiber layout as outside layer and T300 fibers in the mid‐plane had high flexural modulus and interlaminar shear strength. POLYM. COMPOS., 2010. © 2010 Society of Plastics Engineers     

Carbon fibers derived from wet‐spinning of equi‐component lignin/polyacrylonitrile blends

Equi‐component blends of polyacrylonitrile (PAN) and lignin, i.e., with a lignin content as large as 50 wt %, were successfully used as precursors to produce carbon fibers. Rheological measurements demonstrated that increasing lignin content in spinning solution reduced shear viscosity and normal stress, indicating a decrease of viscoelastic behavior. This was confirmed by Fourier transform infrared results that show no discernable chemical reaction or crosslinking between PAN and lignin in the solution. However, the resulting carbon fibers display a large I_D/I_G ratio (by Raman spectroscopy) indicating a larger disordered as compared to that from pure PAN. The macro‐voids in the lignin/PAN blend fibers typically generated during wet‐spinning were eliminated by adding lignin in the coagulant bath to counter‐balance the out‐diffusion of lignin. Carbon fibers resulting from lignin/PAN blends with 50 wt % lignin content displayed a tensile strength and modulus of 1.2 ± 0.1 and 130 ± 3 GPa, respectively, establishing that the equi‐component wet‐spun L/P‐based carbon fibers possessed tensile strength and modulus higher than 1 and 100 GPa. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2018 , 135, 45903.     

Effect of maleic anhydride grafted polypropylene on the mechanical and morphological properties of chemically modified short‐pineapple‐leaf‐fiber‐reinforced polypropylene composites

With the rising cost of petroleum‐based fibers, the utilization of plant fibers in the manufacture of polymer–matrix composites is gaining importance worldwide. The scope of this study was to examine the perspective of the use of pineapple leaf fibers (PALFs) as reinforcements for polypropylene (PP). These fibers are environmentally friendly, low‐cost byproducts of pineapple cultivation and are readily available in the northeastern region of India. Here, both untreated and treated pineapple fibers were used. Maleic anhydride grafted polypropylene (MA‐g‐PP) was used as a compatibilizing agent. The polymer matrix of PP was used to prepare composite specimens with different volume fractions (5–20%) of fibers by the addition of 5% of MA‐g‐PP. These specimens were tested for their mechanical properties, and additional assessments were made via observations by scanning electron microscopy, thermogravimetric analysis, and IR spectroscopy. Increase in the impact behavior, flexural properties, and tensile moduli of the composites were noticed, and these were more appreciable in the treated fibers mixed with MA‐g‐PP. PALF in 10 vol % in PP mixed with MA‐g‐PP was the optimum and recommended composition, where the flexural properties were the maximum. The impact strength and the tensile modulus were also considerably high. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

Tensile modulus modeling of carbon‐filled liquid crystal polymer composites

Electrically and thermally conductive resins can be produced by adding conductive fillers to insulating polymers. Mechanical properties, such as tensile modulus, are also important. This research focused on performing compounding runs followed by injection molding and tensile testing of carbon‐filled Vectra liquid crystal polymer. The two carbon fillers investigated were Thermocarb synthetic graphite particles and Fortafil carbon fiber at varying filler amounts. The tensile modulus experimental results were compared to results predicted by several different models. It was found that the Halpin Tsai 2D Randomly Oriented fiber model provided the best fit to the experimental data. The degree of filler‐polymer adhesion was also studied with nanoscratch tests for synthetic graphite and carbon fiber fillers in three polymers: Vectra, nylon 6,6, and polycarbonate. The adhesion trends seen in the nanoscratch tests showed qualitative agreement with the tensile modulus, and should be considered in formulating advanced tensile modulus models. POLYM. COMPOS., 2009. © 2008 Society of Plastics Engineers     

Tensile modulus modeling of carbon‐filled nylon 6,6 and polycarbonate‐based resins

Electrically and thermally conductive resins can be produced by adding conductive fillers to insulating polymers. Mechanical properties, such as tensile modulus, are also important. This research focused on performing compounding runs followed by injection molding and tensile testing of carbon‐filled nylon 6,6 and polycarbonate‐based resins. The three carbon fillers investigated included an electrically conductive carbon black, synthetic graphite particles, and a milled pitch–based carbon fiber. For each polymer, resins were produced and tested that contained varying amounts of these single‐carbon fillers. In addition, combinations of fillers were investigated by conducting a full 2³ factorial design and a complete replicate in each polymer. These tensile modulus experimental results were then compared to results predicted by several different models. For the composites containing only one filler type, the Nielsen model with the modified Ψ term provided the best prediction of the actual experimental values. For the composites containing more than one filler type, a new parameter, which includes the vibrated bulk density (VBD) of the fillers, was incorporated into the Nielsen model with the modified Ψ term. This model with the new VBD parameter provided the best estimate of experimental tensile modulus for composites containing multiple‐filler types. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 90: 1716–1728, 2003     

Effects of fiber extraction,morphology, and surface modification on the mechanical properties and water absorption of bamboo fibers‐unsaturated polyester composites

Bamboo fibers reinforced unsaturated polyester (UPE) composites were prepared by compression molding. Effects of fiber extraction, morphology, and chemical modification on the mechanical properties and water absorption of the bamboo fibers‐UPE composites were investigated. Results showed that the unidirectional original bamboo fibers resulting composites demonstrated the highest tensile strength, flexural strength, and flexural modulus; the 30–40 mesh bamboo particles resulting composites had the lowest tensile strength and flexural strength, but had comparable flexural modulus with that of chemical pulp fibers. The treatment of bamboo fibers with 1,6‐diisocyanatohexane (DIH) and 2‐hydroxyethyl acrylate (HEA) significantly increased the tensile strength, flexural strength and flexural modulus, and water resistance of the resulting composites. Fourier Transform Infrared and X‐ray photoelectron spectroscopy analyses showed that DIH and HEA were covalently bonded onto bamboo fibers. Scanning electron microscopic images of the fractured surfaces of the composites showed that the treatment of bamboo fibers greatly improved the interfacial adhesion between the fibers and UPE resins. The water absorption kinetics of the composites was also investigated; and the results showed that the water absorption of the composites fitted Fickian behavior well. POLYM. COMPOS., 37:1612–1619, 2016. © 2014 Society of Plastics Engineers     

Carbon fibers derived from UV‐assisted stabilization of wet‐spun polyacrylonitrile fibers

A rapid, dual‐stabilization route for the production of carbon fibers from polyacrylonitrile (PAN) precursor fibers is reported. A photoinitiator, 4,4′‐bis(diethylamino)benzophenone, was added to PAN solution before the fiber wet‐spinning step. After a short UV treatment that induced cyclization and crosslinking at a lower temperature, precursor fibers could be rapidly thermo‐oxidatively stabilized and successfully carbonized. Scanning electron microscopy micrographs show no deterioration of the microstructure or hollow‐core formation in the fibers due to UV treatment or presence of photoinitiator. Fast‐thermally stabilized pure PAN‐based carbon fibers show hollow‐core fiber defects due to inadequate thermal stabilization, but such defects were not observed in carbon fibers derived from fast‐thermally stabilized fibers that contained photoinitiator and were UV treated. Tensile testing results confirm that fibers containing 1 wt % photoinitiator and UV treated for 5 min display higher tensile modulus than all other sets of thermally stabilized and carbonized fibers. Wide‐angle X‐ray diffraction results show a higher development of the aromatic structure and molecular orientation in thermally stabilized fibers. No significant increase in interplanar spacing or decrease in crystals size were observed within the UV‐stabilized carbon fibers containing photoinitiator, but such fibers retain a higher extent of molecular orientation when compared with control fibers. These results establish for the first time, the positive effect of the external addition of photoinitiator and UV treatment on the properties of the PAN‐based fibers, and may be used to reduce the precursor stabilization time for faster carbon fiber production rate. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014 , 131, 40623.     

Multifunctional high density polyethylene nanocomposites produced by incorporation of exfoliated graphite nanoplatelets 1: Morphology and mechanical properties

This research explores the potential of using exfoliated graphite nanoplatelets, xGnP, as the reinforcement in high density polyethylene (HDPE). Two kinds of xGnP nanoparticles were used; xGnP‐1 has the thickness of 10 nm and a platelet diameter of 1 μm, whereas xGnP‐15 has the same thickness but the diameter is around 15 μm. HDPE/xGnP nanocomposite were fabricated first by melt blending and then followed by injection molding. The HDPE/xGnP nanocomposite's flexural strength, modulus and impact strength were evaluated and compared with composites filled with commercial reinforcements such as carbon fibers (CF), carbon black (CB) and glass fibers (GF). Polymer nanocomposites from HDPE/xGnP are equivalent in flexural stiffness and strength to HDPE composites reinforced with glass fibers and carbon black but slightly less than that of HDPE/carbon fiber composites at the same volume fraction. However, the Izod impact strength of HDPE/xGnP nanocomposites is significantly greater (∼250%) than all other reinforcements at the same volume fractions. POLYM. COMPOS., 2010. © 2009 Society of Plastics Engineers     

Effects of carbon fillers on tensile and flexural properties in polypropylene‐based resins

A potential application for conductive resins is in bipolar plates for use in fuel cells. The addition of carbon filler can increase the electrical and thermal conductivities of the polymer matrix but will also have an effect on the tensile and flexural properties, important for bipolar plates. In this research, three different types of carbon (carbon black, synthetic graphite, and carbon nanotubes) were added to polypropylene and the effects of these single fillers on the flexural and tensile properties were measured. All three carbon fillers caused an increase in the tensile and flexural modulus of the composite. The ultimate tensile and flexural strengths decreased with the addition of carbon black and synthetic graphite, but increased for carbon nanotubes/polypropylene composites due to the difference in the aspect ratio of this filler compared to carbon black and synthetic graphite. Finally, it was found that the Nielsen model gave the best prediction of the tensile modulus for the polypropylene based composites. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

Effect of fiber modification with a novel compatibilizer on the mechanical properties and water absorption of hemp‐fiber‐reinforced unsaturated polyester composites

Hemp‐fiber‐reinforced unsaturated polyester (UPE) composites were prepared by compression molding. The treatment of hemp fibers with N‐methylol acrylamide (NMA) and sulfuric acid as a catalyst significantly increased tensile strength, flexural modulus of rupture and flexural modulus of elasticity, and water resistance of the resulting hemp–UPE composites. Fourier transform infrared (FTIR) spectra revealed that some NMA was covalently bonded to hemp fibers. Scanning electronic microscopy graphs of the fractured hemp–UPE composites revealed that treatment of hemp fibers with NMA greatly improved the interfacial adhesion between hemp fibers and UPE. The chemical reactions between hemp fibers and NMA as well as the mechanism of improving the interfacial adhesion were proposed and discussed. POLYM. ENG. SCI., 2012. © 2012 Society of Plastics Engineers     

Properties of bio‐based polymer nylon 11 reinforced with short carbon fiber composites

In this work, micro‐composite materials were produced by incorporating 3‐mm long reclaimed short carbon fibers into bio‐based nylon 11 via melt compounding. A systematic fiber length distribution analysis was performed after the masterbatching, compounding and an injection moulding processes using optical microscopy images. It was found that the large majority of the fibers were within the 200–300 μm in length range after the injection moulding process. The mechanical (flexural and tensile), thermo‐mechanical, and creep properties of the injection moulded materials are reported. We found that an enhancement in flexural and Young's modulus of 25% and 14%, respectively, could be attained with 2 wt% carbon fiber loading whilst no significant drawback on the ductility and toughness of the matrix was observed. The creep resistance and recovery of the nylon 11, tested using dynamic mechanical thermal analysis at room temperature and 65°C, was significantly improved by up to 30% and 14%, respectively, after loading with carbon fiber. This work provides an insight into the property improvement of the bio‐based polymer nylon 11 using a small amount of a reclaimed engineered material. POLYM. COMPOS., 36:668–674, 2015. © 2014 Society of Plastics Engineers     

Flexural properties of S‐2 glass and TR30S carbon fiber‐reinforced epoxy hybrid composites

A study on the flexural properties of hybrid composites reinforced by S‐2 glass and TR30S carbon fibers is presented in this article. Test specimens were made by the hand lay‐up process in an intraply configuration with varying numbers of glass/epoxy laminas substituted for carbon/epoxy laminas. These specimens were then tested in the three point bend configuration in accordance with ASTM D790‐07 at a span to depth ratio of 32. The failed specimens were examined under an optical microscope, and the results show that the dominant failure mode is at the compressive side. The flexural behavior was also simulated by finite element analysis (FEA). Based on the FEA results, the flexural modulus and flexural strength were calculated. Good agreement is found between the experiments and FEA. It is shown that flexural modulus decreases with increasing percentage of S‐2 glass fibers, positive hybrid effects exist by substituting carbon fibers for glass fibers, and applying a thin layer of S‐2 glass fiber‐reinforced polymer on the compressive surface yields the highest flexural strength. The modeling approach presented will pave a way to the effective design of hybrid composites. POLYM. COMPOS., © 2012 Society of Plastics Engineers     

Mechanical properties of injection‐molded short‐fiber thermoplastic composites. Part 1: The elastic moduli and strengths of glass‐filled poly(butylene terephthalate)

The effects of processing and part geometry on the local mechanical properties of injection‐molded, 30 wt% short‐fiber‐reinforced filled poly(butylene terephthalate) (PBT) are characterized by mechanical tests on specimens cut from rectangular plaques of different thicknesses injection molded at several different processing conditions. Stiffness data from tensile tests at 12.7‐mm intervals on 12.7‐mm‐wide strips cut from injection‐molded plaques—both along the flow and cross‐flow directions—and flexural tests on these strips show consistency of plaque‐to‐plaque local properties. Also, in addition to the well‐known anisotropic properties caused by flow‐induced fiber orientation, injection‐molded short fiber composites exhibit in‐plane and through‐thickness nonhomogeneity—as indicated by in‐plane property variations, by differences between tensile and flexural properties, and by the flexural strength being significantly higher than the tensile strength. The sensitivity of these mechanical properties to process conditions and plaque geometry have also been determined: the flow‐direction tensile modulus increases with fill time, the differences between flow and cross‐flow properties decrease with increasing thickness, and both the flow and cross‐flow flexural moduli decrease with increasing plaque thickness. While the flexural modulus is comparable to the tensile modulus, the flexural strength is significantly higher than the tensile strength. POLYM. COMPOS., 26:428–447, 2005. © 2005 Society of Plastics Engineers     

Influence of fly ash cenospheres on performance of coir fiber‐reinforced recycled high‐density polyethylene biocomposites

Recycled high‐density polyethylene (RHDPE)/coir fiber (CF)‐reinforced biocomposites were fabricated using melt blending technique in a twin‐screw extruder and the test specimens were prepared in an automatic injection molding machine. Variation in mechanical properties, crystallization behavior, water absorption, and thermal stability with the addition of fly ash cenospheres (FACS) in RHDPE/CF composites were investigated. It was observed that the tensile modulus, flexural strength, flexural modulus, and hardness properties of RHDPE increase with an increase in fiber loading from 10 to 30 wt %. Composites prepared using 30 wt % CF and 1 wt % MA‐g‐HDPE exhibited optimum mechanical performance with an increase in tensile modulus to 217%, flexural strength to 30%, flexural modulus to 97%, and hardness to 27% when compared with the RHDPE matrix. Addition of FACS results in a significant increase in the flexural modulus and hardness of the RHDPE/CF composites. Dynamic mechanical analysis tests of the RHDPE/CF/FACS biocomposites in presence of MA‐g‐HDPE revealed an increase in storage (E′) and loss (E″) modulus with reduction in damping factor (tan δ), confirming a strong influence between the fiber/FACS and MA‐g‐HDPE in the RHDPE matrix. Differential scanning calorimetry, thermogravimetric analysis thermograms also showed improved thermal properties in the composites when compared with RHDPE matrix. The main motivation of this study was to prepare a value added and low‐cost composite material with optimum properties from consumer and industrial wastes as matrix and filler. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 42237.     

Processing,structure, and properties of gel spun PAN and PAN/CNT fibers and gel spun PAN based carbon fibers

Polyacrylonitrile (PAN) and PAN/carbon nanotube (PAN/CNT) fibers were manufactured through dry‐jet wet spinning and gel spinning. Fiber coagulation occurred in a solvent‐free or solvent/nonsolvent coagulation bath mixture with temperatures ranging from ?50 to 25°C. The effect of fiber processing conditions was studied to understand their effect on the as‐spun fiber cross‐sectional shape, as well as the as‐spun fiber morphology. Increased coagulation bath temperature and a higher concentration of solvent in the coagulation bath medium resulted in more circular fibers and smoother fiber surface. as‐spun fibers were then drawn to investigate the relationship between as‐spun fiber processing conditions and the drawn precursor fiber structure and mechanical properties. PAN precursor fiber tows were then stabilized and carbonized in a continuous process for the manufacture of PAN based carbon fibers. Carbon fibers with tensile strengths as high as 5.8 GPa and tensile modulus as high as 375 GPa were produced. The highest strength PAN based carbon fibers were manufactured from as‐spun fibers with an irregular cross‐sectional shape produced using a ?50°C methanol coagulation bath, and exhibited a 61% increase in carbon fiber tensile strength as compared to the carbon fibers manufactured with a circular cross‐section. POLYM. ENG. SCI., 55:2603–2614, 2015. © 2015 Society of Plastics Engineers