PA6 Fibers Research Articles

Preparation and Optimization of Electrospun Nylon‐6 Fiber‐Reinforced High Strength and Toughness Thermoplastic Polyurethane Composites for Potential Use in Prosthetic Heart Valves

AbstractThe interfacial aspects of fiber composites are widely favored. Here, three composite strategies based on hot‐pressing, electrospinning, and impregnation of PA6 fibers are presented for the preparation of PA6 fiber‐reinforced thermoplastic polyurethane (PA6/TPU) composites. The morphologies of the electrospun fiber/matrix interface and the mechanical properties of the PA6/TPU composite are investigated. Under the optimal conditions, the tensile strength, Young's modulus, and toughness of the H‐PA6/TPU composite are respectively 29.45 ± 1.477 MPa, 47.28 ± 2.61 MPa, and 38.03 ± 1.996 MJ m−3. The tensile strength, Young's modulus, and toughness of the E‐PA6/TPU composite are 28.03 ± 1.411 MPa, 73.81 ± 4.16 MPa, and 24.12 ± 1.265 MJ m−3, respectively. The tensile strength, Young's modulus, and toughness of the I‐PA6/TPU composite are respectively 29.45 ± 1.477 MPa, 47.28 ± 2.61 MPa, and 38.03 ± 1.996 MJ m−3, and the elongation at break is ≈240%. Moreover, without loss of TPU properties, the impregnation method effectively improves the interface adhesion between the fiber and the matrix, and the mechanical properties of PA6/TPU composite are significantly improved even if the fiber content is low. The impregnation method is simple to operate and can be extended to other thermoplastic polymers and other fiber‐reinforced composites.

Kinetics of radiation-oxidative aging of polyamide fibers and composites based on them

Kinetics of the decrease in the strength of polyamide PA-6 (poly-ε-caprolactam) fibers by X-ray irradiation in air at absorbed dose rates ranging within 0.16–10 Gy/s has been studied. It has been shown that strength of irradiated polyamide PA-6 fibers decreases to a certain limiting value depending on the dose rate and can be described by the kinetics of a reversible pseudo-first-order reaction. The proposed structural-kinetic model of radiation–oxidative aging of fibers takes into account the opposite effects of destruction and crosslinking of tie macromolecules on the strength of the oriented polymer (fiber),and structural features of the oriented polymer. The model agrees well with experiment and allows us to describe the change in the strength of an oriented polymer (fibers PA-6) and a unidirectional composite (impregnated strands) based on them during the simultaneous occurrence of processes of radiation–oxidative degradation and crosslinking of macromolecular chains.

Investigation on mechanical, physico-chemical and thermal properties of recycled polyamide 6 reinforced with continuous glass fibers

The study primarily deals with recycled plastics, mainly polyamide 6 (rPA6), obtained from recycled fishing nets. These plastics are converted into reusable plate-like materials using the compression molding process. Moreover, the material was subjected to compression at different ratios of UD tape (4 wt%, 8 wt% and 12 wt%). In fact, reinforcement was added by incorporating a tape made of PA6 and unidirectional glass fibers, often known as PA6-GF UD tape. This research will investigate the physico-chemical structure, thermal properties, mechanical behavior, and microstructure of recycled Polyamide 6 (rPA6) and its composites, specifically rPA6 reinforced with glass fibers (rPA6GF) at different weight ratios. Besides this research makes a three analytical model (ROM, IROM, Hirsch) to predict the tensile properties of rPA6GF. The study’s findings demonstrate that recycled plastics sourced from fishing nets displayed favorable mechanical characteristics, after the addition of reinforcement materials, such as tensile strength (74.65 MPa), elastic modulus (5.64 GPa), flexural strength (≈155 MPa), impact resistance (143.36 KJ/m2), and hardness (79.5 D). While these improvements have been achieved, the presence of impurities and moisture still pose long-term performance problems that cause the degradation of the material and increased variability associated with it, complicating predictive modeling. Analytical modeling, while useful in explaining fiber reorientation, needs also to include these variabilities in order to improve long-term accuracy and performance prediction. The current study has approved the feasibility of locally reinforced composites with continuous fiber development by thermocompression, hence a promising approach toward the attainment of sustainable and reliable performance for the recycled plastic composites.

Tertiary nitrogen carbonization and imine cross‐linking facilitated solid‐phase flame retardant for anti‐dripping PA6 fiber

AbstractA developing society requires polycaprolactam (PA6) fibers with flame retardant. Currently, the additive flame retardants commonly used in PA6 fibers cannot solve the molten droplet problem. In this work, (1E,1′ E)‐N,N′‐(6‐phenyl‐1,3,5‐triazine‐2,4‐diyl)bis(1‐(4‐methoxyphenyl) methanimine) (NBM) with triazine ring structure was synthesized. The triazine ring structure was used to expand into carbon and benzoguanimine structure to produce irreversible chemical crosslinking in NBM, thereby achieving anti‐dripping and flame retardant of PA6 fiber. LOI of PA6/NBM8 reaches 30.0 vol.%, UL‐94 reaches V‐0 when the NBM addition amount is 8 wt.%, meanwhile, the residual carbon content is 235.7% higher than that of PA6. The mechanical strength can still reach to 3.22 cN/dTex. From structural design to synthesis, the effects of NBM addition on the flame retardants, rheology, thermal stability and residual carbon morphology of PA6/NBMx were analyzed in detail in this work. It is hoped that in the future work, the structural characteristics and performance requirements can be matched to provide reference for conception and synthesis of flame retardants oriented to other polymers.

“Rooting” engineering strategy for construction of highly stable, scalable, size-customized oxidized graphene/PA6 ultrafine fiber composite nanofiltration membranes for water purification

Nanofiltration membranes based on graphene oxide exhibit substantial potential for practical applications in water treatment, poised to lead the next generation of separation technology. It is noteworthy that the prominent hydration interaction among graphene–graphene oxide nanosheets stands as the primary factor influencing its stability. Simultaneously, the absence of suitable graphene substrates presents challenges to its large-scale production. In this study, our initial endeavor involved constructing a graphene-based selective layer on a PA6 substrate using a quasi-“rooting” strategy. The graphene selective layer was anchored onto the surface of PA6 fibers (with a diameter size of up to 190.0 mm and a selective layer thickness of approximately 5.0 µm). Experimental results reveal that the permeability of the hybrid graphene oxide/PA6 fiber composite nanofiltration membrane consistently maintained within the range of 7.7 to 14.9 L m⁻² h⁻¹ bar⁻1, with a remarkable dye molecule removal rate of 99.06 %. Even under challenging operating conditions (such as strong acid, strong alkali, polar solvent, oxidation, and the coexistence of salt ions), its separation performance remained stable. The permeability of composite membranes was retained between 10.6 and 12.7 L m⁻² h⁻¹ bar⁻1, and the rejection rate of CR dye reached 95.0 % under harsh conditions. Furthermore, the stability and anti-fouling performance of the composite membrane were significantly enhanced. Deposits on the membrane surface could be effectively removed through physical wiping and repeated water rinsing, maintaining membrane integrity even after vigorous ultrasonic cleaning (120 min, 950 W). Additionally, after undergoing 20 cycles of rinsing with deionized water and a 30-day soak in an aqueous solution, the PA6 substrate and graphene selective layer exhibited robust adhesion. No shedding was observed, and the dye rejection rate of the composite membrane consistently exceeded 95 %. This perfectly illustrates the exceptional structural stability and separation durability of the prepared separation membrane. Our work contributes fundamental design principles and theoretical insights for practical applications.

Oligomer composition and content in regenerated PA6 fiber and its effect on properties

AbstractThe preparation process from waste fibers to regenerated fibers is an environmental significance work. In this work, liquid chromatography/time‐of‐flight mass spectrometry, advanced polymer chromatography/multi‐angle laser‐light‐scattering/refractive index detector, and two‐dimensional wide‐angle X‐ray diffractometry were employed to characterize the polycaprolactam(PA6) fibers above oligomers composition and content, molecular weight and distribution, crystallization and orientation, and analyzing the changes in mechanical properties. The total content of oligomers in physical and chemical regenerated PA6 fiber is 2.084 wt% and 1.812 wt%, individually, which is higher than that in waste PA6 fiber. And the oligomer content of C1–C4 (cyclic monomer, cyclic dimer, cyclic trimer, and cyclic tetramer) in the regenerated PA6 fiber is higher than that of waste PA6 fiber. The regenerated PA6 fiber sample contains more low‐molecular‐weight substances, making it easier to form crystal nuclei and crystallize. During the dyeing process of the regenerated PA6 fiber, the γ crystal transformed into α crystal. The tensile strength of physical and chemical regenerated PA6 fiber is lower than that of waste PA6 fiber. And after dyeing, the oligomers content of regenerated PA6 fiber is significantly decreased, especially in C1–C4 oligomer. However, the crystalliniy and orientation of regenerated PA6 fibers were improved, which also leads to the fracture strength increased by about 20% compared to undyed fibers.

Micro-Scale Model of rCF/PA6 Spun Yarn Composite

Recycling carbon fibers (rCF) for reuse is one approach to improve the sustainability of CFRP. However, until now, recycled carbon fiber plastics (rCFRP) had limited composite properties due to the microgeometry of the fibers, which made it difficult to use in load-bearing components. The production of hybrid yarns from rCF and PA6 fibers allows the fibers to be aligned. The geometric properties of the yarn and the individual fibers influence the mechanical properties of the composite. An approach for the modeling and simulation of hybrid yarns consisting of recycled carbon fibers and thermoplastic fibers is presented. The yarn unit cell geometry is modeled in the form of a stochastic fiber network. The fiber trajectory is modeled in form of helical curves using the idealized yarn model of Hearle et al. The variability in the fiber geometry (e.g., length) is included in form of statistical distributions. An additional compaction step ensures a realistic composite geometry. The created model is validated geometrically and by comparison with tensile tests of manufactured composites. With the validated model, multiple parameter studies investigating the influence of fiber and yarn geometry are carried out.

Effect of Copper Selenide Modification on the Conductivity of PA6, PA66, PAN, and PES Fibers.

Textile production has been steadily increasing for a few decades and, as a result, the amount of industrial textile waste is also increasing. This waste can be reused as raw material to produce new functional composites. Such materials can be used for special purposes with varying combinations of physical and chemical properties by using polymers modified with thin semiconductive or electrically conductive layers of binary inorganic compounds. In this paper, a study of the possibilities of altering the properties of synthetic fiber conductivity by modification with copper selenide is presented. A two-step adsorption/diffusion method was used for the copper selenide layer forming on the surface of the fibers. The treatment process was repeated cyclically. To evaluate the morphological properties of CuxSe treated fibers, scanning electron microscopy (SEM) and energy dispersion X-ray (EDX) were performed. The study showed that the chosen modification method is more suitable for PA and PAN fibers. Dense layers of copper selenides were successfully formed on their surface, which significantly reduced their electrical resistance.

Microporous Formation Mechanism of Biaxial Stretching PA6/PP Membranes with High Porosity and Uniform Pore Size Distribution.

The low porosity and wide pore size distribution of biaxial stretching PP microporous membranes continue to be the primary impediments to their industrial application. To solve this problem, there is a critical and urgent need to study the micropore-forming mechanism of PP membranes. In this research, the interfacial micropore formation mechanism of PA6/PP membranes during biaxial stretching was investigated. PA6/PP membranes containing spherical PA6 and fibrillar PA6 were found to exhibit different interfacial micropore formation mechanisms. Numerous micropores were generated in the PA6/PP membranes, containing PA6 spherical particles via the interface separation between the PP matrix and PA6 spherical particles during longitudinal stretching. Subsequent transverse stretching further expanded the two-phase interface, promoting the breakdown and fibrosis of the PP matrix and forming a spider-web-like microporous structure centered on spherical PA6 particles. In PA6/PP membranes with PA6 fibers, fewer micropores were generated during longitudinal stretching, but the subsequent transverse stretching violently separated the PA6 fibers, resulting in a dense fiber network composed of PA6 fibers interwoven with PP fibers. Crucially, the PA6/PP biaxial stretching of microporous membranes presented an optimized pore structure, higher porosity, narrower pore size distribution, and better permeability than β-PP membranes. Furthermore, this study explored a new approach to the fabrication of high-performance PA6/PP microporous membranes, with good prospects for potential industrial application.

Caffeine Encapsulation in Metal Organic Framework MIL-53(Al) at Pilot Plant Scale for Preparation of Polyamide Textile Fibers with Cosmetic Properties.

Currently in the marketplace, we can find clothing items able to release skin-friendly ingredients while wearing them. These innovative products with high-added value are based on microencapsulation technology. In this work, due to its lightness, flexibility, porosity, chemical affinity and adsorption capacity, metal–organic framework (MOF) MIL-53(Al) was the selected microcapsule to be synthesized at a large scale and subsequent caffeine encapsulation. The synthesis conditions (molar ratio of reactants, solvents used, reaction time, temperature, pressure reached in the reactor and activation treatment to enhance the encapsulation capacity) were optimized by screening various scaling-up reactor volumes (from lab-scale of 40 mL to pilot plant production of 3.75 L). Two types of Al salts (Al(NO3)3·9H2O from the original recipe and Al2(SO4)3 as commercial SUFAL 8.2) were employed. The liporeductor cosmetic caffeine was selected as the active molecule for encapsulation. Caffeine (38 wt %) was incorporated in CAF@MIL-53(Al) microcapsules, as analyzed by TGA and corroborated by GC/MS and UV–vis after additive extraction. CAF@MIL-53(Al) microcapsules showed a controlled release of caffeine during 6 days at 25 °C (up to 22% of the initial caffeine). These capsules were incorporated through an industrial spinning process (with temperatures up to 260 °C) to manufacture PA-6 fibers with cosmetic properties. Up to 0.7 wt % of capsules were successfully incorporated into the fibers hosting 1700 ppm of caffeine. Fabrics were submitted to scouring, staining, and washing processes, detecting the presence of caffeine in the cosmetic fiber.

All-Nanofiber Network Structure for Ultrasensitive Piezoresistive Pressure Sensors.

Sensing materials with fiber structures are excellent candidates for the fabrication of flexible pressure sensors due to their large specific surface area and abundant contact points. Here, an ultrathin, flexible piezoresistive pressure sensor that consists of a multilayer nanofiber network structure prepared via a simple electrospinning technique is reported. The ultrathin sensitive layer is composite nanofiber films composed of poly (3,4-ethylenedioxythiophene):poly (styrenesulfonate) and polyamide 6 (PEDOT:PSS/PA6) prepared by simultaneous electrospinning. PEDOT:PSS conductive fibers and PA6 elastic fibers are interwoven to form a multilayer network structure that can achieve ultrahigh sensitivity by forming a wealth of contact points during loading. In particular, gold-deposited PA6 fibers as upper and lower flexible electrodes can effectively increase the initial resistance. Due to this special fiber electrode structure, the sensor is able to generate a large electrical signal variability when subjected to a weak external force. The devices with different sensing properties can be obtained by controlling the electrospinning time. The sensor based on the PEDOT:PSS/PA6 nanofiber network has high sensitivity (6554.6 kPa-1 at 0-1.4 kPa), fast response time (53 ms), and wide detection range (0-60 kPa). Significantly, the device maintains ultrahigh sensitivity when cyclically loaded over 10,000 cycles at 5 kPa, which makes it have great prospects for applications in human health monitoring and motion monitoring.

Study on Preparation of PA6 / PDMS Blended Fibers and Fabric Properties

PA6 fibers and fabric properties were studied by adding PDMS, and PA6 / PDMS blend fibers were prepared by melt spinning. The experiment found that the addition of PDMS can significantly promote the rheology of the PET / PDMS blend melt. DSC tests show that the addition of PDMS has basically no effect on its crystallization and melting characteristics. With the increase of PDMS content, the contact angle of water on the blended fabric surface increased. KES-FB was used to evaluate fabrics made from PA6 / PDMS blended fibers. It was found that with the increase of PDMS content, the softness and elasticity of the fabrics were improved, and the stain resistance experiments showed that the modified fabrics had good resistance dirty performance.

Characterization of the electrical behavior of a discontinuous hybrid yarn textile made of recycled carbon and PA6 fibers during Joule heating

The Joule heating of carbon fiber-based textiles enables an energy- and cost-efficient processing of carbon fiber reinforced thermoplastic parts. This article introduces a new method to pass direct current into a dry, not pre-consolidated hybrid yarn textile based on recycled carbon fibers and polyamide 6 fibers. The aim is to melt polyamide fibers, subsequently impregnate carbon fibers, and finally consolidate the material to form a composite part in a single process step. To increase the reliability of this technology, the electrical properties and the behavior of the material during the heating process must be thoroughly investigated. It will be addressed how the material is characterized during the process and how the changing resistivity of the textile affects the current flow between the electrodes to generate intrinsic heat. Moreover, a method to determine the effective material resistivity by finite element simulation on the fiber scale based on a CT scan is presented. Thus, a validated material model with respect to the temperature development in the textile based on ρ = ρ (Τ) was established.

Nano‐modified HDPE/PA6 microfibrillar composites: Effect of aminated graphite platelets coupling

ABSTRACTModification of microfibrillar composites (MFCs) by nanofillers shows important effects of its localization on performance. This work deals with control of migration/localization of amine‐modified graphite nanoplatelets (GNPAs) in the HDPE/PA6 system through their in situ coupling. GNPA/HDPE linking also leads to complex morphology of PA6 fibers. Although such control of GNPA localization and migration in MFC is limited, marked variations of properties, including decrease with high draw ratio, occurs. This is in spite of the fact that structure and crystallinity are comparable with that of the polymer/GNPA adduct. The reason is a more pronounced negative effect of presence of the GNP adducts in the fiber surface layer on HDPE crystallinity, in comparison with neat GNP, that is, formation of “soft” interface. The negative effects were markedly eliminated by pre‐blending and coupling of GNPA in both polymer phases. Results confirm more effective control of MFC performance by in situ coupling of GNPA with polymer components in comparison with a nonreactive system. © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2019, 136, 47660.

Study on the anti‐biofouling effects of the grafted polyamide 6 fibers by several vinyl chemicals

ABSTRACTThe biofouling is any non‐desirable accumulation and growth of living matters on the material surfaces. Four grafting agents, Acrylic acid (AA), 2‐hydroxyethyl methacrylate (HEMA), 2‐dimethyl amino ethyl methacrylate (DMAEMA), and Methyl acrylate (MA) were grafted on a polyamide fiber (PA6) with two techniques “simultaneous UV irradiation and grafting” (SUVIG) and “pre‐UV irradiation (PUVI). It revealed that all used grafting chemicals grafted on the PA6 fiber surface efficiently. The SEM micrographs showed that the surface of the ungrafted PA6 fiber was relatively smooth, but for the grafted fibers, they were coarse and the grafted chemicals distributed on the PA6 surface heterogeneously. The grafting of the used grafting agents on the PA6 fiber surface increased the glass transition temperature of the PA6 fiber. The grafting of the PA6 fiber altered its crystallinity depending on the type of the grafting agent. With except of the MA, the hydrophilicity of the grafted PA6 fibers was higher than the ungrafted PA6 fiber. The grafting efficiency percentages and degrees were remarkably higher for the PUVI technique when compared with the SUVIG technique. The results of the biological tests showed that the MA was a suitable grafting agent for increasing anti‐biofouling property of the PA6 fiber. © 2018 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2018, 135, 46760.

Fracture Failure Mechanisms of Long Single PA6 Fibers.

The present study investigates the failure mechanisms of industrial fiber materials, using a custom designed fiber cutting performance test bench. The fracture morphologies of single PA6 fibers are examined by scanning electron microscopy. The analysis reveals that fiber cutting can be distinguished according to four distinct stages of fiber failure represented by shearing, cutting, brittle fracture, and tensile failure, which are the result of different mechanisms active during the processes of crack initiation, extension, and fracture. The results of fractographic analysis are further verified by an analysis of the blade assembly speed with respect to time over the entire fracture failure process based on high-speed camera data. The results of fractographic analysis and blade assembly speed are fully consistent.

Effect of corona discharge on the stability of the adhesion of thin silicone-organic coating to polyamide fiber surface made by the sol\u2013gel method

This paper presents the effect of pretreatment of polyamide (PA6) nonwoven with corona discharge on the stability of the adhesion of thin hydrophobic silicone-organic coating based on vinyltriethoxysilane, made by the sol–gel method. This pretreatment with corona discharge causes a change in the physicochemical properties of the PA6 fiber surface. These changes include, among others, an increase in the fiber surface roughness, wettability, and surface free energy. At the same time, XPS and EDS investigations have shown an increase in the degree of oxidation and the formation of functional polar groups on the fiber surface (C–O–, C–OH, and O=C–O–). As a result of the changes in the surface properties of pretreated PA6 fibers, a higher degree of the sol deposition was obtained compared with that for untreated nonwoven surface. The assessment of the stability of the adhesion of thin hydrophobic coating to the fiber surface was carried out on the basis of changes in the content of silica deposited on fibers and the kinetics of water contact angle after washing and abrasion processes. In the end, the PA6 nonwoven, pretreated with corona discharge, shows a higher stability of the adherence of the thin silicone-organic coating and a higher degree of hydrophobicity than the untreated nonwoven.

Strength properties of fine aggregate concretes reinforced by polyamide fibers

Reinforcing concrete with fiber is one of the most effective methods to improve the properties of cement-based materials. In this study, the effect of using two different polyamide fibers (i.e. PA6 and PA66) as reinforcement in fine aggregate concretes was investigated. The effects of the fiber length and type of supplementary cementitious materials (SCM) were also studied. Three-point bending test, pullout, and compression tests were carried out on the cementitious composites. The effect of embedment length was also investigated on pullout behavior. Pseudo-strain hardening behavior was obtained in the fiber-reinforced concretes. Although there was no significant difference in the flexural properties of composites containing PA66 and PA6 fibers, the pullout load and energy which were obtained by PA66 fibers were 36% and 45% higher than PA6 fibers, respectively. It was found that an increase in PA66 fiber embedment length up to 10 mm leads to an increase in pullout energy. The compressive strength of more than 90 MPa was obtained using PA66 fibers, which were considerably higher than ordinary concrete and PVA fiber-reinforced concrete.

Electrospun nanofiber-reinforced polypropylene composites: Nucleating ability of nanofibers

Electrospun nanofibers of 10 semi-crystalline polymers were obtained. The nucleating abilities of these nanofibers toward isotactic polypropylene (iPP) were investigated. Conventional PTFE and PBO fibers were also examined for comparison. The tested fibers were embedded in the iPP matrix to induce the transcrystalline layer and their nucleating abilities were characterized by optical microscopy. However, due to the limitation of optical resolution the increasing number of iPP nuclei on the tiny electrospun fibers was too difficult to trace for determining the surface nucleating rate. To address this problem, the variation of depolarized light intensity under a constant cooling rate was monitored. The induction temperature (Ti) for fiber-surface nucleation was determined to characterize the nucleating ability of fibers; that is, the higher the Ti, the better the nucleating ability of the fibers. Our results indicated that the nucleating ability of fibers can be classified into four categories: strong for the PBT and PTFE fibers; medium for the PTT, PET, iPS, PVA, PA6 and PBO fibers; weak for the sPS fiber; and inactive for the PA46, and PMP fibers. All active fibers induced the α-form of iPP crystals except the iPS fibers, which induced the β crystals through the α-to-β growth transition mechanism.

Occurrence and morphology of bead-on-string structures in centrifugal forcespun PA6 fibers

This research aimed at investigating the morphology and frequency of bead-on-string occurrences on forcespun nano- and sub-micron fibers. The formation of bead-on-string structures was observed on a range of fiber samples forcespun in varied conditions from PA6 solutions of different concentrations. Bead-on-string structures were characterized for morphology using SEM micrographs, and were counted on all samples. Two major factors appeared to affect both the morphology and the bead count, namely spinning solution concentration, i.e. viscosity, and spinning needle gage or diameter. Low viscosity solutions resulted in large numbers of mostly spherical beads. Solutions with higher viscosity appeared to suppress the fluid jet instability thus resulting in significantly fewer beads with exclusively elongated spindle-like shapes. Spinning needle diameter also had a significant impact on beading behavior, with the larger diameter exhibiting higher bead counts. A significant interaction between the two factors was detected and its impact on the competition between the fluid jet visco-elastic relaxation and the Rayleigh instability is discussed.