Fiber Surface Chemistry Research Articles

Research on Process Parameters for Recycling CF/EP Composites by Thermal Excitation of Oxide Semiconductor

There has a great economic and environmental significance for recycling high performances carbon fibers from the waste carbon fiber reinforced polymers. This paper presented a novel method for recycling carbon fiber (CF)/epoxy resin (EP) composites by thermal excitation oxide semiconductor; the effects of process parameters including the temperature, processing time, concentration and flow of O2 on decomposition rate of resin matrix was analyzed; through some methods of analysis and testing such as micro-morphology, monofilament tensile strength, Raman spectra, the effects of process parameters on morphology, mechanical property and surface chemistry of the recycle carbon fibers were investigated; the components of the gas products were investigated by gas chromatography. The research findings provided theoretical foundations for estimating the process parameters and understanding the general law of resin matrix decomposition.

Effect of fiber surface treatments on the strength of bonding between dyneema® fiber and HDPE matrix

ABSTRACT The focus of this study is to identify the best surface treatment to maximize the bonding between a commercially available Dyneema® fiber and a high-density polyethylene matrix. The effect of a new sol-gel derived organic-inorganic hybrid coating on interfacial shear strength (IFSS) was compared with that of oxygen plasma and chromic acid treatments identified by previous studies. The treated fiber surfaces were examined using Scanning Electron Microscopy (SEM), Fourier Transform Infrared Spectroscopy (FT-IR), X-ray Photoelectron Spectroscopy (XPS) to support the analysis using IFSS. The fiber surface became rough after the treatments, which increased with treatment time. The XPS spectra revealed a similar change in surface chemistry of fibers for sol-gel treatment for 1 min and plasma treatment for 6 min, which resulted in a similar enhancement in IFSS when compared to untreated fiber. Chromic acid treatment for 1 min resulted in the largest change in the percentage of carbon- and oxygen-containing groups on the treated surface when compared to the untreated surface as well as maximum enhancement of the IFSS over untreated fiber.

Activation of electrospun lignin-based carbon fibers and their performance as self-standing supercapacitor electrodes

The production and activation of self-standing carbon electrodes from electrospun lignin fibers was analyzed in this work. Carbon microfibers were prepared at 900 °C from air-stabilized spun cloths by direct carbonization under inert atmosphere and with diluted O2. The modifications of the porosity and surface chemistry of the carbon fibers was also studied by adding H3PO4 in the lignin solution and using different oxygen partial pressures during activation. The presence of phosphoric acid not only increases the porosity development and the preparation yield, but also enhances the gravimetric capacitance of the electrodes. In addition, the activation in presence of oxygen increases the surface area and the generation of wider micropores. Microporous carbon fibers with surface areas as high as 2340 m2 g−1 were obtained using this method. The direct conformation of carbon fibers into binderless electrodes allows to achieve high-power rate capability supercapacitors. Activation in presence of oxygen can enhance up to 50% the energy storage of supercapacitors without compromising the power of the device (8.4 Wh kg−1 and Pmax of 47 kW kg−1). However, at high activation degrees, no further gain in energy density is observed due to the excessive widening of micropores, and the loss of electrical conductivity that increases the cell resistance, limiting the power capability of the device. The optimal results in terms of energy, power and durability are achieved combining low amounts of H3PO4 and mild activation with O2, confirming that electrospinning of lignin is a promising method for sustainable production of self-standing supercapacitor electrodes.

Effect of plasma treatment on chemical composition, structure and sorption properties of lignocellulosic hemp fibers (Cannabis sativa L.)

Hemp fibers with different amount of hemicelluloses and lignin were subjected to atmospheric pressure dielectric barrier discharge under different conditions (40 W and 80 W power of discharge, const. time 120 s) in order to study influence of plasma treatment on their structure and sorption properties. Wettability of plasma treated samples, compared with precursors, increased due to the changes in hemp fiber surface chemistry confirmed by ATR FTIR spectroscopy and increased roughness as a consequence of intensive surface etching, observed by SEM. After plasma treatment, wettability was the highest for hemp fibers with lower content of hemicelluloses (increase up to 9 times), while wettability of raw hemp fibers and fibers with lower content of lignin increased about 5 and 2 times, respectively. This investigation shows that plasma can be successfully used for improvement of raw hemp fibers wettability, even to substitute the chemical treatment for some applications of hemp.

Improved toughness and delamination resistance in continuous fiber reinforced geopolymer composites via incorporation of nano-fillers

Geopolymer matrix composites (GMC) have the potential to bridge the processing performance gap between polymer matrix and ceramic matrix composites. Yet one drawback of GMCs is their extreme brittleness and weak inter-laminar shear strength. The aim of this study was to evaluate the effectiveness of Silicon Carbide Whisker (SCW) nano-filler on the mechanical performance of neat unreinforced geopolymer and unidirectional fiber reinforced GMCs containing variations in fiber surface chemistry. In order to evaluate, neat and SCW populated geopolymer matrices were fabricated for comparison. Nextel 610 fiber reinforced GMCs were also fabricated with SCW for comparison to GMCs without the SCW nano-filler. The effect of the nano-filler was evaluated using three-point flexural methods to obtain strength and fracture toughness (KIC). Results indicate that the addition of SCWs up to 4 vol% improved Mode-I fracture toughness of the baseline geopolymer matrix by 113%. The improvements to the neat matrix also resulted in improved flexural strength, inter-laminar shear strength, and delamination resistance of the continuous fiber reinforced composites.

Differences in adhesion between 1C-PUR and MUF wood adhesives to (ligno)cellulosic surfaces revealed by nanoindentation

The chemical composition of adhesive and adherend involved in a bondline strongly influences the resulting adhesion performance. In this study, nanoindentation was used to mechanically characterize the interface between three chemically different (ligno)cellulosic fiber types and two chemically different adhesives. Regenerated cellulose, virgin wood, and thermally modified fibers were embedded in one-component polyurethane (1C-PUR) and melamine urea formaldehyde (MUF).The results from nanoindentation at the interface between 1C-PUR adhesive and the three fiber types show best adhesion towards the thermally modified fiber surface. In contrast, MUF shows almost identical adhesion behavior for all three fiber type surfaces. Differences in adhesion behavior due to varying fiber surface chemistry seem to be superseded by adhesive penetration into the bulk fiber, which is only expected for MUF adhesive.In addition, chemical surface analysis of the virgin wood and thermally modified fibers was carried out by X-ray Photon Spectroscopy and compared to literature values for regenerated cellulose. Cellulose values show the highest O/C ratio followed by virgin wood fibers and thermally modified fibers. These results are hinting on a higher amount of lignin or hydrophobic extractives on the thermally modified fiber surface. In terms of adhesion performance, these results indicate that the less polar thermally modified fibers surface seems to be favorable for 1C-PUR.

Application of D‐optimal design in the analysis and modelling of dyeing of plasma‐treated wool with three natural dyes

AbstractBoth the dyeing and finishing of textiles with natural compounds are gaining increasing attention because of various environmental and health problems associated with the use of synthetic reagents. In this study, wool fibres were dyed with three natural dyes, namely, Arnebia euchroma, cotton pods and harmal seeds. Alum was used as the mordant, and samples were mordanted by the premordanting method. Oxygen plasma was employed for the surface modification of wool. Plasma treatment time, alum concentration, dyebath temperature and pH were selected as the process variables, and their effects on the K/S of the dyed samples were analysed using D‐optimal design. The surface topography, morphology and chemistry of the wool fibres after plasma treatment were studied by atomic force microscopy (AFM), scanning electron microscopy (SEM) and Fourier Transform–infrared spectroscopy (FTIR), respectively. FTIR confirmed the creation of new oxygen‐containing groups on the surface of wool fibres after plasma treatment. SEM and AFM images confirmed the surface etching and increase in the roughness of plasma‐treated fibres. Increasing the dyebath pH and temperature increased the K/S of the dyed samples. Increasing the amount of alum mordant increased the K/S of samples dyed with cotton pods but decreased the K/S of samples dyed with A. euchroma and harmal seeds. Increasing the plasma treatment time improved the K/S of samples dyed with A. euchroma and cotton pods but had no significant effect on the K/S of samples dyed with harmal seeds.

Bimodal behavior in fabric drying kinetics: An interpretation of modes

Thermo-physiological comfort is an essential property attributed to fabrics. Perceived comfort can be related to the delay in the user experiencing the ambient conditions and the manner in which the fabric manages liquid water. A multitude of material characteristics, ranging from the surface chemistry of the fibers, yarn packing and knit geometry, affect perceived comfort. Standard measures of thermal and evaporative resistance characterize the fabric response at steady state and do not provide insight into the thermal/vapor balance kinetics under dynamic conditions. While investigating an existing dynamic test, International Organization for Standardization 13029:2012, for relating fabric properties to comfort, we observed that the fabric drying kinetics exhibited bimodal behavior. Here, we describe the mechanism that leads to the observed bimodal drying kinetics. While the standard measures the time taken to reach steady state, we use the power profile of the modes to derive quantitative metrics to characterize fabric properties. The derived metrics are based on the observation that the heat of wetting is nearly a constant for a given relative humidity for a material, and that the heat of sorption per unit of absorbed water is identical for a wide range of fabrics. The derived metrics distinguish different fiber types and fabric geometries. The proposed metrics are easily calculated from experimental observations without requiring any modification to the standard test.

Interfacial adhesion between carbon fibers and nylon 6: Effect of fiber surface chemistry and grafting of nano-SiO2

In this study, the effect of carbon fiber (CF) surface chemistry and grafting of nano-SiO2 on CF surface with respect to the interfacial adhesion of CF-reinforced nylon 6 composites was investigated. CFs were oxidized and reacted with poly(oxypropylene) diamines to modify the surface chemistry. The oxidized CFs were modified with 3-aminopropyltriethoxysilane and then grafted with SiO2 nanoparticles. Fourier transform infrared spectroscopy (FT-IR), X-ray photoelectron spectroscopy (XPS), scanning electron microcopy (SEM), and atomic force microscopy (AFM) were used to characterize the chemistry and topographies of the CF surface. The transverse fiber bundle strength of CF oxidized and grafted nano-SiO2 increased to 31.92 MPa and 39.35 MPa, respectively, from 12.57 MPa for untreated CF. The results indicated that the reaction between the carboxyl group and nylon 6 led to chemical bonding at the interface and it meanwhile was strengthened and toughened by uniformly distributed SiO2 nanoparticles on the CF surface.

Coal Liquefaction Residues Based Carbon Nanofibers Film Prepared by Electrospinning: An Effective Approach to Coal Waste Management

As a major byproduct of direct coal liquefaction, coal liquefaction residue (CLR) waste is environmentally harmful but also valuable. Considering environmental and economic efficiency, exploiting these wastes as electrodes for new generation energy storage devices will increase the economic value and decrease environmental pollution synchronously. In this regard, CLRs are used to prepare carbon nanofibers film for supercapacitors via electrospinning followed by HNO3 preoxidization, air stabilization, and carbonization processes for the first time. The influences of HNO3 preoxidization over the formation of fiber morphology, textural structure, surface chemistry, and electrochemical performance are investigated. Our work demonstrates that HNO3 preoxidization can enhance the content of the heteroatom of the as-spun nanofibers and promote the polymerization of the asphaltene (CLRA) molecular during air stabilization, leading to the changes of the thermal behaviors and thus avoiding the fibers melting success...

Determination of the surface chemistry of ozone-treated carbon fibers by highly consistent evaluation of X-ray photoelectron spectra

Room-temperature ozone treatment is a promising technique for functionalization of carbon materials: it is fast, well controllable, and leads to oxygen uptakes of up to 15 at.% on carbon fiber surfaces. We investigated the surface chemistry of untreated and room-temperature ozone-treated polyacrylonitrile-based carbon fibers using X-ray photoelectron spectroscopy (XPS). By identifying two different nitrogen species (graphitic and pyridine-like) we developed a new constraint for fitting the C 1s spectra. This approach ensured high consistency between measured elemental concentrations and elemental concentrations calculated from fitted functional group peaks. It also revealed a different relative ordering of functional group concentrations than previously reported for ozone-treated carbons. The results of this new fitting procedure were cross-checked with chemical derivatization XPS measurements, resulting in a good correlation for hydroxyl and carbonyl groups. Examination of single fiber cross-sections using energy-dispersive X-ray spectroscopy in a transmission electron microscope showed that even after intense treatments oxygen can mainly be found in the topmost 40 nm–50 nm, stressing the importance of surface sensitive techniques such as XPS. Furthermore, XPS results suggested only a minor surface degradation caused by the ozone treatment. This was corroborated by atomic force microscopy results.

Evaluation of composite interfacial properties based on carbon fiber surface chemistry and topography: Nanometer-scale wetting analysis using molecular dynamics simulation

According to surface chemistry and topography of different high-modulus carbon fiber (HMCF), interfacial properties of various HMCF composite were evaluated, and nanoscale wetting analysis of HMCF were studied using experimental methods and molecular dynamics simulation. Hierarchical amount of active functional groups and nanoscale grooves were detected on the surface of pristine HMCF (p-HMCF), anodic oxidized HMCF (a-HMCF) and sized HMCF (s-HMCF). Remarkable enhancements in interfacial properties of a-HMCF and s-HMCF composites were obtained, which was ascribed to free-void interface from improved surface energy and wettability. Poor interfacial bonding of p-HMCF composites was due to generation of many nanobubbles with pinned contact lines during the wetting of the surface microgrooves with high aspect ratio and chemical inertness. Schematic of interfacial compatibility mechanisms was proposed to illustrate the correlation between surface features of carbon surface and interfacial properties of their composites.

Surface potential tailoring of PMMA fibers by electrospinning for enhanced triboelectric performance

Triboelectric generators rely on contact-generated surface charge transfer between materials with different electron affinities to convert mechanical energy into useful electricity. The ability to modify the surface chemistry of polymeric materials can therefore lead to significant enhancement of the triboelectric performance. Poly(methyl methacrylate) (PMMA) is a biocompatible polymer commonly used in medical applications, but its central position on the triboelectric series, which empirically ranks materials according to their electron-donating or electron accepting tendencies, renders it unsuitable for application in triboelectric generators. Here, we show that the surface potential of PMMA fibers produced by electrospinning can be tailored through the polarity of the voltage used during the fabrication process, thereby improving its triboelectric performance, as compared to typically spin-coated PMMA films. The change in surface chemistry of the electrospun PMMA fibers is verified using X-ray photoelectron spectroscopy, and this is directly correlated to the changes in surface potential observed by Kelvin probe force microscopy. We demonstrate the enhancement of triboelectric energy harvesting capability of the electrospun PMMA fibers, suggesting that this surface potential modification approach can be more widely applied to other materials as well, for improved triboelectric performance.

Role of surface chemistry of fibres additives on rheological behavior of ceramic particle based Shear Thickening Fluids

Influence of surface chemistry and size (fineness) of fibres as additives on the rheological behavior of ceramic particle (silica) based Shear Thickening Fluid (STF) has been investigated in this research work. Two different types of fibres, Kevlar microfibres (KMF) and chemically modified cellulose nanofibres (M-CNF) were used for tuning the rheological characteristics of STFs. The extraction of both the fibres, was carried out using supermasscollider. The CNFs were then chemically modified with vinyl silane to impart hydrophobic character to the nano-fibres. The characterization was done by TEM-EDX and contact angle analyzer. Ultrasonication was used to obtain the fibres reinforced STFs. In both STFs, reduction in peak viscosity in comparison to virgin STFs was observed with increasing concentration of fibres in STFs. Interaction between additive fibres, silica and media (PEG) was assessed by dynamic state rheological analysis. The crossover point between storage (G′) and loss modulus (G″) for both cases (KMF & M-CNF) shifted towards lower frequency as concentration of fibres additives in STFs increased. It is postulated that presence of fibres with hydrophobic characters reduces the interaction between hydrophilic particles and fibres leading to decrease in peak viscosity and increase in critical shear rate.

Wet-peel: a tool for comparing wet-strength resins

Abstract We propose that a testing procedure we call wet-peel significantly augments conventional wet paper testing when comparing wet-strength resin efficacy or the influence wood pulp fiber surface treatments on wet paper strength. A thin layer of wet-strength resin is sandwiched between a pair of thin, wet regenerated cellulose membranes to form a laminate, which is a physical model for fiber-fiber joints in paper. In the wet-peel method, the ninety-degree wet-delamination force gives a direct measure of adhesion in the wet cellulose-cellulose joint. Wet-peel measurements offer: 1) comparisons of wet-strength polymers at the same content of polymer in the laminate joint without the influences of varying fines contents, formation or paper density; 2) measurements of both the wet-strength of cured, dried joints, and the strength of never-dried joints (i. e. analogous to wet-web strength); 3) demonstrations of the influence of fiber surface chemistry modifications including oxidation and the presence of firmly bound polymers; and, 4) the evaluation of more exotic joint structures including layer-by-layer assemblies, microgels and colloidal polyelectrolyte complexes.

Large-area fabrication of low- and high-spatial-frequency laser-induced periodic surface structures on carbon fibers

The formation and properties of laser-induced periodic surface structures (LIPSS) were investigated on carbon fibers under irradiation of fs-laser pulses characterized by a pulse duration τ = 300 fs and a laser wavelength λ = 1025 nm. The LIPSS were fabricated in an air environment at normal incidence with different values of the laser peak fluence and number of pulses per spot. The morphology of the generated structures was characterized by using scanning electron microscopy, atomic force microscopy and Fast-Fourier transform analyses. Moreover, the material structure and the surface chemistry of the carbon fibers before and after laser irradiation was analyzed by micro Raman spectroscopy and X-ray photoelectron spectroscopy. Large areas in the cm2 range of carbon fiber arrangements were successfully processed with homogenously distributed high- and low-spatial frequency LIPSS. Beyond those distinct nanostructures, hybrid structures were realized for the very first time by a superposition of both types of LIPSS in a two-step process. The findings facilitate the fabrication of tailored LIPSS-based surface structures on carbon fibers that could be of particular interest for e.g. fiber reinforced polymers and concretes.

Interaction between carbon fibers and polymer sizing: Influence of fiber surface chemistry and sizing reactivity

Different aspects of the interaction of carbon fibers and epoxy-based polymer sizings are investigated, e.g. the wetting behavior, the strength of adhesion between fiber and sizing, and the thermal stability of the sizing layer. The influence of carbon fiber surface chemistry and sizing reactivity is investigated using fibers of different degree of anodic oxidation and sizings with different number of reactive epoxy groups per molecule. Wetting of the carbon fibers by the sizing dispersion is found to be specified by both, the degree of fiber activation and the sizing reactivity. In contrast, adhesion strength between fibers and sizing is dominated by the surface chemistry of the carbon fibers. Here, the number of surface oxygen groups seems to be the limiting factor. We also find that the sizing and the additional functionalities induced by anodic oxidation are removed by thermal treatment at 600 °C, leaving the carbon fiber in its original state after carbonization.

Fiber surface chemistry in relation to the efficiency of chlorine dioxide bleaching

Relationships between fiber surface chemical components and the efficiency of chlorine dioxide bleaching were studied using chemical analysis in combination with attenuated total reflectance-Fourier transform infrared spectrscopy (ATR-FTIR) and X-ray photoelectron spectroscopy (XPS). The amount of surface lignin decreased quickly at the beginning of the bleaching, and the brightness increased during the bleaching. Surface oxidation took place immediately, and the amount of lignin on the fiber surface decreased during the bleaching, especially in the first 5 min. The ratio of aromatic carbons to aliphatic carbons also decreased, which indicated that the lignin was degraded and new aliphatic carbons formed that might noticeably deposit on the surface of the fiber. The aliphatic carbons reacted with the in-situ formed hypochlorous acids, and thus affected the bleaching efficiency. Further bleaching led to the deposition of more acidic functional groups on the fiber surface with increased acidity-basicity ratios, which also affected the whole efficiency of bleaching.

The influence of polymer adsorption, and fiber composition, on the rheology of aqueous suspensions of aspen, cotton, and corn stover pulps

The mechanisms governing the ability of water-soluble polymers (WSP) to alter the rheological properties of lignocellulosic biomass to achieve processing advantages are investigated. Lignocellulosic fiber surface chemistry is found to be an important factor in the efficacy of WSPs as rheological modifiers, and a strong correlation between the amount of adsorbed polymer at fiber surfaces and the yield stress of the fiber suspension indicate that adsorption of polymer is important for rheological modification. Three fiber suspensions of varying physical chemistry were produced from Aspen wood chips, and a number of additional fiber suspensions with chemically functionalized surfaces were generated from cellulose pulp. Polymer adsorption and suspension rheology are found to correlate in every case examined, but the amount of adsorbed polymer alone cannot be used to predict the efficacy of a WSP as a rheological modifier, suggesting that there are contributions from additional variables such as adsorbed-polymer conformation.

Debonding mechanism of polymeric fibers in reinforced cementitious composites as a function of crystallinity degree of fibers

Engineered cementitious composites containing polymeric fibers such as poly(vinyl alcohol) show high tensile ductility and toughness. The aim of the current study was to evaluate the effect of crystallinity degree of poly(vinyl alcohol) fibers on fiber debonding from cementitious matrix in the bending test. In this work, two types of poly(vinyl alcohol) fibers and one grade of polypropylene fiber were separately incorporated in cementitious composites. The chemical structure, surface chemistry, roughness, and microstructure of fibers were examined by Fourier transform infrared, attenuated total reflection, atomic force microscopy, and wide-angle X-ray diffraction tests, respectively. The compression and flexural behaviors of cementitious composites were also assessed. Attenuated total reflection results were indicative of similar surface chemistry for both poly(vinyl alcohol) fibers, while the main difference was observed in the case of degree of crystallinity, which plays an important role in the Poisson’s ratio. Finally, the way in which the degree of crystallinity and Poisson’s ratio of fibers can lead to premature debonding was described and confirmed by scanning electron microscopic images.