Aromatic Polyamide Fibers Research Articles

Mechanisms of damage and fracture of aramid fibers: Focus on the role of microfibril cooperativity in fracture toughness

AbstractPushing the limits of synthetic polymers in terms of stiffness and strength, aromatic polyamide fibers–like Kevlar®–are used for demanding applications in the form of fiber assemblies as ropes. The unique mechanical performance of aramid fiber is intimately linked to its hierarchical structure and orientation, induced during the spinning process. Surprisingly, after nearly 60 years of heavy use, very little is known about damage mechanisms and rational explanation of such high resistance. We report an experimental investigation of the fiber damage mechanisms at the single fiber scale (diameter ≅ 10 μm) with the aim to establish a link with the microstructure. Damage mechanisms and crack propagation are observed in situ for the first time and unveil a widespread damage over the entire length of the fiber in the form of a network of transverse and longitudinal cracks. These observations make it possible to draw a novel scenario of fracture that mitigates the small strain failure hypothesis. To shed light on the crucial role of microfibril cooperativity in fracture toughness, a slight twist is applied to the single fiber to promote tortuosity and frictional contacts between microfibrils. Statistical fracture analysis demonstrated the beneficial impact of such torsion on early failure events, since lowest fracture stresses are shifted to higher stresses.

Preparation and properties of an aromatic polyamide fibre derived from a bio-based furan acid chloride

A high-molecular-weight aromatic polyamide resin incorporating furan-rings (f-resin) was prepared by low-temperature solution polycondensation of bio-based 2,5-furandiformyl chloride and 3,4′-diaminodiphenyl ether, in N,N-dimethylacetamide. Further, an aromatic polyamide fibre containing furan-rings (f-fibre) was obtained from the fresin by dry-jet wet spinning, and its structure and properties were investigated. The prepared f-resin showed good solubility and possessed good spinnability in solution. The mechanical, heat-resistance, and flame-retardant properties of the f-fibre were found to be excellent – comparable to or exceeding those of meta-aramid fibre (m-fibre). In addition, the furan acid chloride monomer is bio-based and is derived from abundant resources, unlike petroleum-based monomers. Therefore, f-fibre has good potential and broad application prospects as an environment-friendly and sustainable high-performance material.

Characterization of asphalt mixtures produced with short Pulp Aramid fiber (PAF)

Use of additives and modifiers as an effective alternative to mitigate premature cracking of flexible pavements has been gaining popularity during the past three decades. Several studies have discussed the advantages and disadvantages of using various types of fibers in pavement industry. The objective of this study is to evaluate the impact of using Pulp Aramid Fiber (PAF) in Hot Mix Asphalt (HMA) in terms of mix design and performance. Aramid fibers or aromatic polyamide fibers were the first type of organic fibers found to have sufficient tensile strength and modulus to be used in advanced composites. Although studying the effect of additives on performance of HMA mixes has been the focus of several studies, the extent of work on the use of PAF in HMA mixes using a comprehensive methodology has been limited. A control mix and a PAF modified HMA mix were designed and evaluated with respect to their rutting resistance, fatigue cracking resistance, and low temperature cracking performance. The results indicate that mixes with PAF led to higher demand for bitumen content to achieve the same air void level as compared to the control mix. However, it was concluded that this additional binder content along with the presence of PAF resulted in an enhanced performance, especially with respect to fatigue cracking as well as improved ductility at cold temperatures. In spite of the additional binder content, the PAF modified mix exhibited satisfactory permanent deformation performance at high temperatures while considerably improving the fatigue and low temperature behavior of the mix. The results also indicate that PAF can delay cracking failure in long-term life of asphalt concrete mixes under repeated loading.

Thermal insulation behaviour of Ethylene propylene diene monomer rubber/kevlar fiber based hybrid composites containing Nanosilica for solid rocket motor insulation

AbstractThe current research discusses the properties of an elastomeric heat‐shielding material, based on nano‐silica (NS) filled ethylene propylene diene monomer (EPDM) rubber/Kevlar fiber (KF) hybrid composites. The developed elastomeric insulating material consists of an aromatic polyamide fiber (KF) and silica nanoparticles. An in‐depth analysis of mechanical properties, density, coefficient of thermal expansion, thermal conductivity, thermogravimetric analysis, and heat release rate of the insulating materials ‐was performed. TEM micrograph represents an excellent distribution of nanoparticles in the EPDM matrix. The improvement in the mechanical and the flame retardancy of the NS filled EPDM/KF hybrid composite insulations is based on the fiber/matrix adhesion. Maleic anhydride grafting confers polarity to the nonpolar rubber matrix. The char residues of the insulations inspected by scanning electron microscopy and energy dispersive spectroscopy are depicting a rigid and rough surface by the optimal composites, which can aid in better insulation. The optimal formulation of the hybrid composites exhibited a 220% enhancement in char residue with improved thermal stability and mechanical properties.

Multiscale insights into the stretching behavior of Kevlar fiber

Aromatic polyamide fiber becomes the most important material for ballistic protection purposes because of the high modulus and strength from the 1960s. To obtain an insightful understanding of the mechanical deformation of Kevlar, a detailed multiscale model is developed in this paper based on the structures of Kevlar from molecular scale to macroscopic scale. By analyzing the molecular structures of Kevlar, the high modulus of Kevlar fibers can be attributed to the high stiffness of aromatic polyamide chains and the massively distributed hydrogen bonds in the material. The damage initiation and evolution in Kevlar fiber can be captured at the microfibril scale. It can be found that the material strength in the grain boundary regions is only 1.9 GPa, resulting in much lower strength of the whole Kevlar fiber (2.5–3.3 GPa), compared to the theoretical strength of the aromatic polyamide crystals (>30 GPa). The structural parameters of Kevlar fiber (pleated width, misorientation angle and skin thickness) are also studied to understand the contribution of these parameters to the stretching behavior of a Kevlar Bundle, which is significant to the future improvement of aromatic polyamide fibers for reinforcement purposes in advanced equipment.

Evaluation of the durability and the performance of an asphalt mix involving Aramid Pulp Fiber (APF): Complex modulus before and after freeze-thaw cycles, fatigue, and TSRST tests

The main deteriorations of asphalt pavements in cold regions are due to the effect of heavy traffics, water action, low-temperature fluctuations, freeze-thaw cycles and the combination of all these factors together. Fiber additives are mainly used as reinforcement materials in asphalt pavements to improve the tensile properties and increase the strength against low-temperature cracking and potholes. Aromatic polyamide fiber (aramid fiber) is used in advanced composite materials since it has a very high tensile strength, modulus, and high cohesiveness. Whether the addition of Aramid Pulp Fiber (APF) can effectively improve the fatigue life, thermal performance, and durability of asphalt mixture under repeated freeze-thaw cycles are also major problems needed to be investigated properly. In this regard, thermo-mechanical analyses (complex modulus, fatigue, and thermal stress restrained specimen test (TSRST)) have been conducted on the asphalt mix with a nominal maximum aggregate size of 20 mm, known as Grave Bitume (GB20) in Quebec, Canada. The improvement effect of APF incorporation is assessed to compare the stiffness variation before and after 300 rapid freeze-thaw cycles, fatigue behavior, and thermal strength. The results indicate the ability of APF to increase the durability of the GB 20 mix against freeze-thaw cycles. The TSRST and fatigue results also show that the APF additives can increase the performance of the GB 20 mix against low temperature cracking and heavy truckloads.

Preparation of Aromatic Polyamide Particles and Fibers and their Functionalization

Preparation of Aromatic Polyamide Particles and Fibers and their Functionalization

Nanostructural evidence of mechanical aging and performance loss in ballistic fibers

ABSTRACTIt is understood that the ballistic resistance of aromatic polyamide fibers is related to the fiber's ultimate tensile strength, strain‐to‐failure, and Young's modulus. Ideal high‐performance ballistic materials maximize these properties while minimizing material density. Equally important is long‐term mechanical and chemical stability: the fibers should not exhibit performance loss over their lifetime. However, less is known quantitatively about their modes of degradation, and experimental methods to quantify the aging and degradation in these fibers are critical. Multiple variations of next generation high‐performance fibers have been investigated under chemical and mechanical accelerated aging conditions. Performance losses have been empirically correlated to chemical degradation of the polymer chain and nanostructural changes in the fiber morphology through X‐ray photoelectron spectroscopy (XPS). Here, we introduce positron annihilation lifetime spectroscopy measurements as a sensitive method to quantify the early onset of damage in the flexed fibers as quantified through changes in the nanoscale void structure in the material. Published 2017.† J. Polym. Sci., Part B: Polym. Phys. 2017, 55, 1711–1717

Enhancing mechanical properties of aromatic polyamide fibers containing benzimidazole units via temporarily suppressing hydrogen bonding and crystallization

ABSTRACTThe copolymerization modified poly(p‐phenylene terephthalamide) containing 2‐(4‐aminophenyl)−5‐aminobenzimidazole (PABZ) units in the main chain was synthesized and the corresponding poly‐p‐phenylene‐benzimidazole‐terephthalamide (PBIA) fibers were prepared by wet spinning. The HCl, the by‐product released during polymerization, can complex with PABZ units to prevent the formation of hydrogen bonding between PABZ units, resulting in amorphous PBIA fibers and a lower glass transition temperature (Tg). Therefore, for the purpose of gaining strong hydrogen bonding and high orientation degree at the same time in PBIA fibers, two‐step drawing–annealing processing was adopted. The as‐spun PBIA/HCl complex fibers were drawn first at 280°C, higher than the Tg of the PBIA/HCl complex fibers and lower than the decomplexed temperature of HCl, which temporarily suppresses the formation of hydrogen bonding and crystallization. Subsequently, the fibers were annealed to reform hydrogen bonding between PABZ units and crystallization via decomplexation of HCl at 400°C. However, when the drawing is above the decomplexed temperature of HCl, the decomplexation of HCl begins to occur which leads to the reform of hydrogen bonding and crystallization, and the tensile strength of the drawn‐annealed PBIA/HCl complex fibers decreases with a decrease in the HCl content of fibers. The tensile strength of two‐step drawn‐annealed fibers increased by approximately 15% compared to that of one‐step drawn PBIA/HCl complex fibers. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015, 132, 42482.

Fabrication of the Colored PMIA Fibers by Wet Spinning: Effect of Spinning Parameters on the Coagulation Process

The poly (m-phenylene isophthalamide) (PMIA) fiber, which can be prepared by wet spinning, is a kind of aromatic polyamide fiber. The spinning parameters could influence the performance and structure of the colored PMIA fiber such as the diffusion coefficient and coagulation bath. In this study, the PMIA spinning solutions doped with Color Inde purple 120 were first commixed in a pressurizer and then spun into a coagulation bath under a pressure about 0.3 MPa. In the coagulation bath, the pure or dope-dyed PMIA fibers were prepared by wet spinning at 323 K, and then the as-spun fibers were extracted by an ultrasonic oscillation method. The effects of jet stretch ratio, temperature, and concentration of the coagulation bath on the ratio of diffusion coefficient of solvent to coagulator were analyzed during the spinning process of dope-dyed PMIA fibers. The properties and structures of the colored PMIA fibers were characterized by SEM. Finally the most optimized spinning technology of the dope-dyed PMIA fiber was obtained and the dope-dyed PMIA fibers were successfully fabricated through wet spinning.

Crosslinked Aromatic Polyamides: A Further Step in High‐Performance Materials

This work aims to improve the outstanding thermal and mechanical properties of commercialized wholly aromatic polyamide fibers (i.e., aramids), by crosslinking the materials. The introduction of a reactive azide group into the polymer structure leads to functional aramids. Crosslinking processes can be easily performed using an inexpensive thermal treatment after fiber spinning with current spin production facilities. image

Study of Diffusion Performance and Preparation Technology of the Coloured PMIA Fibre

Poly(m-phenylene isophthalamide) (PMIA) fibre is a kind of aromatic polyamide fibre, which can be prepared by a wet-spinning method. In this work, the process conditions of spinning influenced the performance and structure of the coloured PMIA fibre, and these conditions included spinning speed, coagulation bath, etc. Because the diffusion coefficient was associated with the performance and structure, the ratio of solvent to coagulant could explain the reason of influence of the coagulation bath on the fibre. In this study, PMIA spinning dopes with Colour Inde Blue 60 were first commixed in a pressurizer and then spun into a coagulation bath under a pressure of around 0.3 MPa. At a coagulation bath temperature of 50 °C, pure or dope-dyed PMIA fibres were prepared by wet spinning, and then the spun fibres were extracted by an ultrasonic oscillation method. The effect of the jet stretch ratio and the temperature and concentration of coagulation bath on the ratio of diffusion coefficient of solvent to coagulator were analysed during spinning process of dope-dyed PMIA fibres. The properties and structures of coloured PMIA fibres were characterized by SEM. Finally the optimized spinning technology of the dope-dyed PMIA fibre was obtained.

Uv Spectroscopy in Monitoring of Biological Treatment of Washing Waters from Aromatic Polyamide Fibre Production

Aromatic polyamide fibre production wastes — aqueous solutions consisting of a mixture of dimethylacetamide and isobutyl alcohol, initial and treated with microorganisms for different times — were analyzed. Monitoring solutions with absorption in the UV region and COD allowed following biological treatment and modeling its components of the solutions. The possibility of monitoring biological treatment by UV spectroscopy was demonstrated.

The Influence of Temperature on the Tensile Properties and Residual Strain Following Stress-relaxation Processes of Armos and Terlon Aramid Yarns

Aromatic polyamide fibres occupy a unique position among synthetic fibres due to their superior mechanical and thermal properties. Armos and Terlon are of particular interest as initial raw material for the production of high-strength, high-modulus and heat-resistant aramid fibres and yarns. This study investigates the influence of temperature on the strength and deformation properties of these yarns. It is found that the characteristics of tensile stress– strain properties and the accumulation of residual deformation are temperature dependent, especially in the case of Armos. The mechanical properties are strongly influenced by the level of moisture which is associated with intermolecular interaction such as hydrogen bonds and Van der Waals forces.

Thermal degradation behaviour of aromatic polyamide fiber blended with cotton fiber

The flammability behaviour of a blend fabric cannot be predicted from the flammability characteristics of its component fibers because of the physical or chemical interaction of the thermal degradation products of the blend during heating or combustion. In order to consider the design of flame retardant fabrics from blends of cotton as a flammable fiber and aromatic polyamide fiber as a nonflammable fiber, the thermal degradation of each and blends of fiber has been studied using a conventional dynamic thermogravimetric technique in a flowing air atmosphere at several heating rates. Quantitative data are presented which pinpoint how the thermal degradation behaviour of this blend differs from that of the components. Comparison of the thermogravimetric curves and calculated kinetic parameters indicates that interactions occur faintly between the cotton and aromatic polyamide components in the blends. The thermogravimetric analysis data show three degradation stages in an air atmosphere.

Quantum Chemical Calculation of the Character of Structural Organization and H-Bond Energy in the Benzimidazole Fragment of Fibres of the Armos Type

A quantum chemical calculation of the character of the structure in the benzimidazole fragment of aromatic polyamide fibres of the Armos type is performed. It is shown that the fragments form duplicate H bonds with imidazole rings. The experimental and calculated values of the position of the long-wave band maxima in the UV spectra of model benzimidazole compounds are compared.

Determination of the Concentration of Polymers in Spinning Solutions for Production of Aromatic Polyamide Fibres

A method was developed for finding the concentration of fibre-forming polymers in spinning solutions based on extraction and subsequent titrimetric determination of the solvent. It was found that the solvent is totally extracted from the spinning solution in most cases only during titration. When an extractant is added to the solution, two related equilibria are established between polymer and solvent and between solvent and extractant. The acid-base interaction between solvent and titrant shifts the equilibrium toward extraction of the solvent from the polymer solution.

Surface modification of high-strength aromatic polyamide fibres

A modifying (finishing) composition for aromatic polyamide fibres which improves their properties in use was developed, extending the area of application of these fibres. The optimum composition of the finish was determined: an aqueous emulsion of oligoethyl hydride siloxane with SnCl 2 catalyst. The finish is fixed and reacts with the fibre primarily in the surface layer, causing certain structural changes.

Short fiber reinforced thermoplastic polyurethane elastomer composites

AbstractMechanical properties of thermoplastic polyurethane elastomer (TPE) reinforced with short fibers were studied. Two types of fibers were used as the discontinuous phase: an aromatic polyamide (Twaron, diameter: 12 μm) and carbon fiber (FCI 140/90‐R33—diameter: 8–10 μm). Because of processing limitations, the maximum length of both fibers, after incorporation in the composites, was reduced to 3 mm. The TPE (continuous phase) was a polyol‐polyester type [Elastollan—glass transition of short fiber segments: −42°C (1)]. Both types of composites had fiber concentration of 10, 20, and 30 phr. Component interaction is discussed, as well as the application of a third power polynomial to establish a relationship between the amount of fiber added and stress at break data. Stress‐strength, tear resistance, shore A and B hardness, abrasion resistance, and compression set tests were performed. Composites reinforced with aromatic polyamides showed higher values in most of the tests, except in the abrasion resistance test, in which a smaller material loss was observed.

Moisture sorption mechanism of aromatic polyamide fibers. V: Growth of crystallites in as-spun wet poly(p-phenylene terephthalamide) fiber during dehydration

Wide-angle x-ray diffraction studies were performed for as-spun wet poly(p -phenylene terephthalamide) fiber. The effects of sorbed water on the equatorial diffractions from the (110) and (200) crystal planes and on the meridional diffractions from the (002),(004), and (006) crystal planes were analyzed during desorption and absorption. There was no significant change in the d-spacing from the respective crystal plane irrespective of the moisture (water) regain. The ratio of the diffracted intensity from the (110) diffraction to that from the ( 200 ) diffraction remarkably increased by removing the sorbed water. The crystallite size estimated from the (110) diffraction, L 110 , also increased as the moisture regain decreased, while the L 200 did not increase. The longitudinal size of paracrystallite, D 001 , also remarkably increased with the decrease in moisture regain with the lattice distortion factor, g II , kept unchanged. These results strongly suggested the growth of the crystallite via hydrogen bonds in the lateral (b-axis) direction. The growth of the lateral size of crystallite also accompanied the longitudinal growth of crystallite during desorption.