Aramid Fiber Surface Research Articles

Preparation of highly active aramid fiber and effect on the interface property of aramid/epoxy composites

The smooth surface and the lack of active groups make para-aramid fiber reinforced composites have poor interfacial adhesion property, which limits their applications in various fields. In this study, aramid fiber was coated with nano-coating solution and functional groups such as epoxy and amino groups were introduced to the surface of aramid fiber to enhance the surface activity of the fiber, thereby improving the adhesion between fiber and resin. The surface composition and roughness of the modified fibers were characterized by Fouier transform infrared spectroscopy (FT-IR), X-ray photoelectron spectroscopy (XPS), and scanning electron microscope (SEM), respectively. The effect of functional groups on the interfacial adhesion properties of aramid/epoxy composites was studied by the interfacial shear strength (IFSS) and the flexural strength. aramid fiberter modification, the roughness and the polarity of the fiber were considerably improved. The IFSS reached 45.9 MPa with a significant enhancement by 27.5%; while the flexural strength increased from 240.7 MPa to 302.2 MPa, with a reinforcement of 25.6%, indicating that the study provides an effective method to achieve highiy active aramid fiber.

Multiscale analysis of enclosed nickel metal layer constructed via a palladium-triggered autocatalytic reaction on aramid fiber surfaces

Conductive aramid fibers have been attracting great interest owing to their lightweight, flexibility and metal-specific properties. Revealing the actual growth process of electroless nickel plating on the surface of aramid fibers is conducive to better control the quality of the prepared metal layer. Herein, we have fabricated different samples using the sensitization-activation two-step method and electroless nickel plating. Chemical element and valence analysis confirmed that the Pd, Ni and P uniformly attached to the surface of aramid fibers have zero valence. The chemical phase analysis and microstructure characterization demonstrated that the NiP alloy layer was amorphous as a whole, whereas Pd and Ni were the crystals with the characteristics of face-centered cubic crystals, and both of them could play a catalytic role in the redox reaction of electroless nickel plating. Furthermore, the possible mechanism of NiP growth on the surface of aramid fibers was proposed, which included the principle of closed assembly of the metal layer and three stages of ‘initial growth, high-speed growth and leveling’.

Research on the surface roughness of aramid fibers via the surface modification

The friction among yarns plays an important role in the energy absorption, and in previous research, it has been found that compared to other types of woven fabrics, the aramid angle-interlock woven fabric has shown the weak capability of the energy absorption due to the low friction among yarns. However, the surface of aramid yarn is very smooth, and it is difficult to increase the friction among aramid yarns directly, because of high crystallinity and low chemical activity of the aramid yarn. Therefore, the fiber surface needs to be modified to provide the surface roughness to increase the friction among yarns. In this paper, acetone, calcium chloride, and hydrogen peroxide were used to modify the aramid fiber surface in order to increase the surface roughness, and the effects of which were demonstrated by the infiltration of the fiber. The results showed that the reagent of acetone and calcium chloride, and the reagent of acetone and hydrogen peroxide, had strong capability to increase the surface roughness of the aramid fibers. It was also found that the strength of the aramid fiber treated by the reagent of acetone and calcium chloride achieved an increase of 10.2%, while that by the reagent of acetone and hydrogen peroxide demonstrated a decrease of 4.6%. Therefore, the reagent of acetone and calcium chloride maybe an ideal choice to provide higher surface roughness, with no negative influence on the breaking strength of the aramid fiber, when the aramid fiber is modified to be considered as the ballistic material.

Atomistic simulations of functionalization of aramid fiber‐epoxy nanocomposite

AbstractOwing to its high degree of crystallinity and orientation, the surface of aramid fiber is smooth, causing its low bonding strength with polymer matrix. This has restricted the application of aramid fiber in reinforced polymer materials. Effective methods are by introducing functional groups through surface modification and by increasing its surface roughness thereby greatly improving its bonding strength with the polymer. In this work, molecular dynamics (MD) simulation study fiber functionalized with hydroxyl (OH), carboxyl (COOH), and the silane coupling agent as nanofillers for polymer nanocomposites. The interfacial characteristics and the mechanical behavior of polymer nanocomposites are investigated. The results show that the functionalization can enhance the interfacial shear stress and tensile strength. The functional group not only provides a stronger interface, but also provides additional mechanical interlocking effect, which effectively improves load‐bearing transmission capacity. The analysis of the micro‐mechanism from the energy level also provides new insights for the functionalized design of nanocomposites.

Synergistic modification by mercapto hyperbranched polysiloxane and functionalized graphene oxide on the surface of aramid fiber

With the purpose of improving the interfacial properties of aramid fibers reinforced rubber composites and enhancing the tensile strength of aramid fibers simultaneously, mercapto hyperbranched polysiloxane (HPSi) and functionalized graphene oxide (GO) were used to modify the surface of aramid fibers. Scanning electron microscopy (SEM), Fourier transform infrared (FTIR) spectroscopy and other characterization methods were performed to confirm the process of synergistic modification. Judging from the results of mechanical property tests, it could be acquired that the tensile strength of modified aramid fiber was increased by 16.8%, which could be ascribed to the wrapping effect of GO sheets. The interfacial properties were assessed by the pull-out tests of composites, and the results showed that the maximum pull-out force after synergistic surface modification was increased by 99.3%, which could be mainly related to additive reaction between double bonds and mercapto groups and the promotion of surface energy. More critically, during pull-out test, aramid fiber bundles might bring a part of shear stress into the grafted GO sheets, namely, GO sheets could convert fracture energy into interfacial energy, which would improve interfacial properties dramatically.

Combined treatments of fiber surface etching/silane-coupling for enhanced mechanical strength of aramid fiber-reinforced rubber blends

This study sought to improve the interfacial bonding force between aramid fiber (AF) and a rubber matrix. We pretreated the aramid fiber with anhydrous calcium chloride (CaCl2) and sodium hydroxide (NaOH) solutions. We then performed a separate modification using two different methods, first, grafting the aramid fiber with silane coupling agent γ-Methacryloxypropyl trimethoxy silane (KH570) and secondly in situ formation of silica on the surface of aramid fiber. In addition, mechanical blending was adopted to prepare natural rubber/cis-1,4-polybutadiene rubber/aramid fiber (NR/BR/AF) composites. Finally, aramid fibers were characterized via Fourier transform infrared spectroscopy (FT-IR), X-ray photoelectron spectroscopy (XPS) and scanning electronic microscopy (SEM), then the mechanical properties of the corresponding composites analyzed. Results revealed that the synergistic action of anhydrous CaCl2 and NaOH solutions caused an increase in surface roughness and the contact area of the aramid fiber. The Sol-gel method allowed successful coating of the secondary modified aramid fiber surface with a layer of in situ-generated silica. Consequently, this improved surface reactivity of the fiber and the rubber matrix, thus promoting their combination. Moreover, we successfully grafted KH570 onto the surface of the aramid fiber through an oxygen-containing group on the surface of the pretreated aramid fiber. Tensile properties of AF composites exhibited a 31.9% increase after secondary modification with KH570 whereas their DIN abrasion performance increased by 16.2%. Notably, a significant improvement in interfacial adhesion was recorded in modified AF prepared NR/BR composites, which further improved the mechanical properties of NR/BR composites.

Development in Additive Methods in Aramid Fiber Surface Modification to Increase Fiber-Matrix Adhesion: A Review

This review article highlights and summarizes the recent developments in the field of surface modification methods for aramid fibers. Special focus is on methods that create a multifunctional fiber surface by incorporating nanostructures and enabling mechanical interlocking. To give a complete picture of adhesion promotion with aramids, the specific questions related to the challenges in aramid-matrix bonding are also shortly presented. The main discussion of the surface modification approaches is divided into sections according to how material is added to the fiber surface; (1) coating, (2) grafting and (3) growing. To provide a comprehensive view of the most recent developments in the field, other methods with similar outcomes, are also shortly reviewed. To conclude, future trends and insights are discussed.

Surface Functionalization of Silver-Coated Aramid Fiber

Silver nanoparticles are deposited on aramid fiber surfaces by a three-step process. Calcium chloride/ethanol coarsening of the aramid fiber is followed by surface functionalization with poly(dopamine) and electroless silver plating. The chemical structure and elemental composition of the aramid fibers are determined by X-ray photoelectron spectroscopy and energy dispersive X-ray spectroscopy, respectively. The surface morphology of the modified aramid fibers is investigated by scanning electron microscopy and atomic force microscopy. The crystalline structure and thermal stability of the modified aramid fibers before and after silver plating are analyzed by X-ray diffraction and thermogravimetric analyses. A four-point probe is used to determine the electrical resistivity of the silver-plated aramid fibers. The results show that after the silver plating of the aramid fiber surface, its electrical resistance was reduced. At 20 g/L AgNO3, the silver layer on the aramid fiber surface is stable and durable with a high electrical resistivity.

Surface modification of aramid fibers with CaCl2 treatment and secondary functionalization of silane coupling agents

AbstractAramid fibers have excellent mechanical properties as the main reinforcing filler in high‐performance composites. However, the adhesion properties between fibers and most polymer matrices were poor. In this study, aramid fiber (AF) was modified by KH550 through surface coating based on the treatment with CaCl2 solution. The new surface treated with complexing agents could act as an active platform for secondary reactions for further modification. The surface morphology and composition of the treated aramid fibers were tested by scanning electron spectroscopy and X‐ray photoelectron spectroscopy, the interlaminar shear strength and the tensile strength of aramid fiber‐reinforced polymer (AFRP) of were evaluated. The results showed that the silane coupling agent KH550 was successfully grafted onto the surface of aramid fibers after treatment with CaCl2. Interlayer shear strength is greatly improved and the tensile strength of AFRP through further grafting with KH550 on the surface treated with CaCl2 was improved by 48.7%, compared with untreated aramid fiber. In the current scenario, this study is of immense importance because it validates the possibility of secondary modification after fiber complexation modification and useful modification methods, and provides a new direction for the modification of AF.

Surface wettability aging behavior of aramid fiber III after oxygen plasma treatment

Aramid Fiber III was modified by oxygen plasma treatment. The fiber surface wettability before and after different oxygen plasma treatment pressure, and surface wettability aging behavior were observed by Dynamic Contact Angles Analysis (DCAA), respectively. The results showed that aramid fiber surface wettability were increased after oxygen plasma treatment. The total surface free energy increased from 37.78 mJ/m2 for untreated sample to 69.63 mJ/m2 with 40 Pa plasma treated fiber. The fiber surface wettability decreased slowly with storage time in air. The fiber surface wettability decreased from 67.79 mJ/m2 for 20 Pa plasma-treated sample to 63.85 mJ/m2 after 30 days.

A facile method to prepare PEG coatings on the fiber surface by the reconstruction of hydrogen bonds for enhancing the interfacial strength of fibers and resins

A new method for functionalizing the surface of aramid fibers by hydrochloric acid is proposed, and new polyethylene glycol (PEG) coatings are prepared on the surface of the fibers by the reconstruction of hydrogen bonds for improving the bond strength with the resins. The structure and morphology of the aramid fibers are characterized by Fourier transform infrared spectroscopy, X-ray photoelectron spectroscopy, X-ray diffraction instrument, atomic force microscopy, and scanning electron microscopy. Single fiber tensile test and interlaminar shear strength test are carried out to evaluate the mechanical properties of the modified fibers. The results show that the fibers are functionalized after hydrochloric acid treatment. The amino-groups and carbonyl of the aramid fibers are released while both carboxyl and amine groups are produced. In addition, it is also proved that polyethylene glycol has successfully coated the fiber surface, which improves the surface roughness and polarity of the fibers. As a result, the interlaminar shear strength increases by 51.68 %, while the tensile strength of the fibers decreases by 19.61 %.

Preparation of robust aramid composite papers exhibiting water resistance by partial dissolution/regeneration welding

Aramid fibers exhibit impressive mechanical properties, electrical insulation properties, and chemical stability. However, physical properties of the aramid paper are poor because of the chemical inertness and smooth surface of aramid fibers. This study reports a simple and efficient method for substantially improving the performance of the para-aramid/meta-aramid composite paper by introducing the N,N-dimethylacetamide (DMAc)/LiCl solution to induce partial dissolution or by adding the DMAc/LiCl/para-aramid solution to induce regeneration. Experimental results state that the tensile strength, specific strength, folding resistance, and interlayer bonding strength of the aramid paper are increased by 2.17, 2.13, 34.7, and 9.39 times, respectively, because of the dense and compact structure of the paper. Furthermore, the water resistance of the paper was also considerably improved. After immersing the paper samples in water for 24 h, their moisture absorption rate decreased to approximately 54% from approximately 143% for the original paper. Results indicate that partial dissolution/regeneration welding is a viable method for the efficient reinforcement of the aramid composite paper, providing additional possibilities for manufacturing the high-performance aramid paper-based materials.

In-situ polymerization and covalent modification on aramid fiber surface via direct fluorination for interfacial enhancement

Poor adhesive performance is considered to be a major disadvantage of aramid fibers in the fabrication of aramid fiber reinforced polymer composites, and it's a main drawback to restrict its wide application. In this paper, fluorine-related free radicals induced by direct fluorination were detected by Electron Paramagnetic Spectrum (EPR), which were considered as active spots to initiate copolymerization between acrylic acid (AA) and divinylbenzene (DVB), and the copolymer was chemically grafted onto AF surface, thus aramid fiber was covalently decorated by plenty of –COOH groups. Furthermore, amine-functionalized carbon nanotubes were devised to undergo the condensation reaction with the –COOH groups on fiber surface so that high density of carbon nanotubes could be chemically grafted on aramid fiber surface. Testing of mechanical properties showed that there was almost no damage to the mechanical property of aramid fibers, and interfacial shear strength of modified fiber increased by 53.1% and 69.1% after grafting polyacrylic acid-divinylbenzene copolymer and carbon nanotubes in sequence, respectively. Mathematical analysis for the changes and relationships between surface energy, surface roughness of fibers and their IFSS revealed that specific surface energy made a greater contribution to the enhancement of IFSS than surface roughness, which proved that surface energy was more helpful to the interfacial properties of the composites. Additionally, electric conductivity of organic aramid fiber improved obviously with a conductivity of 0.48 S/m.

Reinforcing effect of aramid fibers on fatigue behavior of SBR/aramid fiber composites

This paper investigates the correlation between fatigue performance and static tensile behavior of fiber reinforced rubber materials and presents change of fiber reinforced effect during fatigue process. A rough aramid fiber (AF) surface, which is helpful for combining AF and rubber matrix, was achieved by etching AF in NaOH/CH3CH2OH solution via the hydrolysis of amide bonds on the fiber. Then, the treated fiber was coated with an epoxy-functionalized silane (γ-propyltrimethoxysilane, KH560) and was used to prepare AF/carbon black/styrene-butadiene rubber (AF/CB/SBR) composites. The results showed that the interfacial adhesion between the complex-modified AF and the rubber matrix was further enhanced and the mechanical properties of the composite were further improved compared with those of the composite which was prepared by unhydrolyzed AF coated with KH560. The hysteresis reinforcing effect of the fiber was found after 30,000 cycles of strain-controlled fatigue, and the reinforcing effect of AF was reduced with increasing average fatigue strain. Moreover, the relative debonding energy (RDE) was calculated to evaluate the reinforcing effect of the fiber, and the RDE value sharply decreased after 30,000 cycles of strain-controlled fatigue. When the AF was treated with the NaOH/CH3CH2OH solution and then coated with KH560, the rubber composite had a high RDE value, and the fatigue life of the composite under the stress-control condition was increased approximately 4 times. The results from the characterization of the fracture appearance after 30,000 cycles of fatigue showed that the composite with the complex-modified AF could maintain better interface bonding during the fatigue process.

Growing Nano-SiO2 on the Surface of Aramid Fibers Assisted by Supercritical CO2 to Enhance the Thermal Stability, Interfacial Shear Strength, and UV Resistance.

Aramid fibers (AFs) with their high Young′s modulus and tenacity are easy to degrade seriously with ultraviolet (UV) radiation that leads to reduction in their performance, causing premature failure and limiting their outdoor end use. Herein, we report a method to synthesize nano-SiO2 on AFs surfaces in supercritical carbon dioxide (Sc-CO2) to simultaneously improve their UV resistance, thermal stability, and interfacial shear strength (IFSS). The effects of different pressures (10, 12, 14, 16 MPa) on the growth of nanoparticles were investigated. The untreated and modified fibers were characterized by Fourier transform infrared spectroscopy (FT-IR), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS) and scanning electron microscopy (SEM). It was found that the nano-SiO2-decorated fibers exhibited improvement of thermal stability and mechanical properties, and the IFSS of the nano-SiO2 modified fibers increases by up to 64% compared with the untreated fibers. After exposure to 216 h of UV radiation, the AFs-UV shows a less decrease in tensile strength, elongation to break and tensile modulus, retaining only 73%, 91%, and 85% of the pristine AFs, respectively, while those of AFs-SiO2-14MPa-UV retain 91.5%, 98%, and 95.5%. In short, this study presents a green method for growing nano-SiO2 on the surface of AFs by Sc-CO2 to enhance the thermal stability, IFSS, and UV resistance.

Effect of Aramid Fiber Surface State on Properties of Epoxy Resin Composites

The surface state of aramid fiber was modified by coupling agent to characterize the change of the state. The fiber / epoxy resin composites were prepared to study the mechanical and electrical properties and the internal mechanism of how different surface states affect. The results show that, after the treatment with the coupling agent, the surface roughness of the aramid fiber is increased，and the content of Si on the surface reach 5.8%, thus the surface activity is enhanced. At the same time, the treatment makes the properties of composites further improved. When the filling amount of aramid fiber reaches 30 strands, the tensile strength increase by 38.4% due to the coupling agent. In the test of two-layer samples, the breakdown field strength of the composites before and after treatment with coupling agent increased by 15.9% and 20.2%, respectively.Key words: aramid fiber; coupling agent; surface state; mechanical properties; electrical properties

Surface modification mechanism of aramid fiber by AACH nanowire recasting and its enhanced modification of TPU

In order to improve the interfacial adhesion with matrix resin, the surface of aramid fibers was recast by surface growth of NH4[Al(OOH)HCO3] (AACH) nanowires. The morphology of aramid fibers before and after treatment was observed by scanning electron microscopy. The infrared and thermal stability of the fibers were tested and the mechanism of surface modification reaction was speculated. The effect of recasting modification on the mechanical properties and thermal stability of TPU resin was further studied. The results show that the roughness of aramid fibers increases obviously after surface recasting, but the thermal stability decreases and the thermal decomposition temperature decreases from 560 °C to 480 °C. At the same time, the interfacial state between surface recasted aramid fibers and TPU resin matrix was significantly improved and the mechanical properties of the composites were further improved. Compared with pure TPU resin, the tensile strength and modulus of the composites increased as 34.3% and 384.0%, respectively, but the elongation at break decreased from 1180.0% to 787.0%.

Enhanced interfacial strength of aramid fiber reinforced composites through adsorbed aramid nanofiber coatings

Aramid fibers are well-known for their excellent tensile properties and low density but are limited in composite applications due to their inert surface which leads to poor interfacial properties. One method that has shown promise in recent years is the application of nanoscale reinforcements to the surface of the fibers to improve mechanical interaction with the matrix. With aramid fibers, it is ideal to perform an interfacial reinforcement utilizing the dense hydrogen bonding which is responsible for the fibers strength. Here, it is demonstrated that recently developed aramid nanofibers (ANFs) can adsorb onto the surface of macroscale aramid fibers to enhance the interfacial properties through mechanical interlocking with the matrix. A simple and rapid dip-coating process is used to deposit the ANFs on the aramid fiber surface. These ANFs bond with the fiber through physisorption and hydrogen bonding, yielding a 70.27% increase in interfacial shear strength and a 25.6% increase in short beam shear strength in composites prepared by dip-coating unidirectional tape into a solution of ANFs. Notably, the interfacial gains are made while fully preserving the strength of the aramid fiber following the treatment, therefore ensuring in-plane properties of the composite are maintained. This work shows that the introduction of an ANF interphase may present a novel and convenient method to improve the interfacial strength of aramid reinforced composites, enabling cost-effective and simplified production of stronger structural materials.

Amino graphene oxide/dopamine modified aramid fibers: Preparation, epoxy nanocomposites and property analysis

Dopamine modified aramid fiber (AF) surface was grafted with amino functionalized graphene oxide to improve the interfacial adhesive performance. The self-polymerized polydopamine (PDA) coating and subsequent amino GO grafting on the AF surface attributed to the increase in its surface roughness and surface-active groups. The functional groups, chemical composition and surface topography of unmodified and modified AF was investigated by Fourier transform infrared (FTIR) spectroscopy, X-ray photoelectron spectroscopy (XPS) and Scanning electron microscopy (SEM). The interfacial properties were analyzed by measuring interfacial shear strength (IFSS) of unmodified and modified AF embedded epoxy matrix. Further, the properties were tuned by optimizing the reaction temperature and concentration of ethylenediamine. The IFSS of AF/epoxy composites was increased by 34% after grafting amino graphene oxide.

Cu (II) coordination modification of aramid fiber and effect on interfacial adhesion of composites

In this article, active groups were introduced to the surface of aramid fiber by building a Cu2+ bridge between the aramid fiber and polyethyleneimine (PEI) to improve adhesion in composites between the aramid fiber and the matrix such as epoxy resin. The changes in the structure and properties of the aramid fiber were verified with Fourier transform infrared (FTIR) spectroscopy, X-ray photoelectron spectroscopy (XPS), scanning electron microscope (SEM), and the single-fiber pull-out test. The FTIR and XPS results show a significant change in the structure and morphology of the aramid fiber after modification. The results of the single-fiber pull-out test show that the interfacial shear strength (IFSS) of epoxy composites reinforced with PEI-grafted aramid fiber increases by 48.8% compared with the IFSS of epoxy composites reinforced with untreated fiber. Thus, the proposed method can improve the interfacial bonding of composites by creating a copper ion bridge between the aramid fiber and PEI.