Improvement of Interfacial Adhesion of Glass Fiber/Epoxy Composite by Using Plasma Polymerized Glass Fibers

This study intends to produce plasma polymer thin films of γ-glycidoxypropyltrimethoxysilane (γ-GPS) on glass fibers in order to improve interfacial adhesion of glass fiber-reinforced epoxy composites. A low frequency (LF) plasma generator was used for the plasma polymerization of γ-GPS on the surface of glass fibers at different plasma powers and exposure times. X-ray photoelectron spectroscopy (XPS) and SEM analyses of plasma polymerized glass fibers were conducted to obtain some information about surface properties of glass fibers. Interlaminar shear strength (ILSS) values and interfacial shear strength (IFSS) of composites reinforced with plasma polymerized glass fiber were evaluated. The ILSS and IFSS values of non-plasma polymerized glass fiber-reinforced epoxy composite were increased 110 and 53%, respectively, after plasma polymerization of γ-GPS at a plasma power of 60 W for 30 min. The improvement of interfacial adhesion was also confirmed by SEM observations of fractured surface of the composites.     

Oxygen plasma modification of wool fibre surfaces

A range of oxygen plasma treatments has been used to modify the surfaces of woven and fibrous wool samples. The resulting chemistry and composition have been characterised using X-ray photoelectron spectroscopy (XPS). The extent of oxidation of di-sulphide bonds to sulphur (S^VI), in the form of sulphonic acid groups (?SO₃H), by the plasma is shown to be only about 20–30% compared to 100% using a conventional wet chlorination process. However, the plasma does appear to react with surface carbon of the protein structure, leading to an increase in carbon-oxygen functionalities. Total levels of surface oxygen achieved using the plasma technique are similar to those from the wet process.     

Plasma treatment of polydimethylsiloxane

Plasma treatment of silicone surfaces is a useful way of increasing wettability to improve adhesion and a first step in producing various organosilicon thin-film composites. Despite numerous earlier studies, there is no consensus on the effect of plasma treatment nor on the mechanism of the subsequent hydrophobic recovery. X-ray photoelectron spectroscopy (XPS) and scanning electron microscopy (SEM) were used to study the effect of plasma treatments of polydimethylsiloxane elastomer using four different plasma gases: argon, helium, oxygen, and nitrogen. In each case, the surface was oxidized to produce a thin, wettable, brittle silica-like layer. These surfaces progressively recover their hydrophobicity by diffusion of untreated polymer chains through cracks in the treated layer. Angle-resolved XPS detected the untreated, diffused layer and SEM revealed the common occurrence of cracks in the treated layer, although conditions could be found for each gas where the surface becomes completely wettable by water but is free from cracks.     

X-ray photoelectron spectroscopic studies of carbon fiber surfaces VIII—A comparison of type I and type II fibers and their interaction with thin resin films

Type I (high-modulus HM) and Type II (high-strength HT) carbon fibers electrochemically treated in a variety of electrolytes have been analyzed using X-ray photoelectron spectroscopy. A comparison of the differences in surface functionality and the possible interaction of treated fibers with epoxy resin is reported. The amount of carbon/oxygen functionality is greater for type II for the untreated and electrochemically treated fibers. Carboxylic/ester groups are produced at edge sites in the fiber surface whereas keto-enol groups are produced on the basal planes. Conclusive evidence for a chemical reaction between the fiber surface and 828-resin for fibers polarized in acidic electrolyte is given. It is not possible to conclude whether chemical bonding is responsible for the increased interlaminar shear strength of composites produced from treated fibers.     

Surface Characterization of Plasma Treated Carbon Fibers and Adhesion to a Thermoplastic Polymer

The surface chemistry of IM7 carbon fibers was characterized by x-ray photoelectron spectroscopy (XPS). The fiber surface energetics were determined from a two-liquid tensiometric method. The adhesion between as-received and plasma-treated carbon fibers and polyethersulfone (PES) was measured by the microbond pull-out test.

The surface characterization techniques showed that the effect of any plasma treatment is attained within less than 15 seconds. It was found that both argon and air plasmas increased the oxidation state of the fiber surface and that they reduced the dispersive component (γ_s^d) of the fiber surface free energy considerably. The ammonia plasma treatment resulted in a cleaning of the surface. This plasma treatment was also effective in improving the fiber/matrix adhesion of quenched samples. A similar adhesion enhancement between as-received fibers and PES is obtained by annealing the samples above the Tg of the polymer. The air plasma treatment did not have any significant effect on the fiber/matrix adhesion.     

Electrochemical studies of the interaction between a modified activated carbon surface and heavy metal ions

Cyclic voltammetric studies of the influence of surface chemistry on the electrochemical behaviour of powdered activated carbon electrodes (PACE) in the presence of selected heavy metal ions (Pb²⁺, Hg²⁺, Cd²⁺) in bulk solution and pre-adsorbed on carbon were carried out. The variety of surfaces was achieved via the modification of carbon samples by heat treatment under vacuum and in an oxygen/ammonia atmosphere, as well as oxidation with conc. nitric acid. The chemical structures of the modified carbon surfaces were characterised by XPS and standard pH-titration. The adsorption capacities of the modified carbon samples towards the heavy metal ions in question were estimated. The mechanisms of adsorption processes of metal species on carbon surfaces were analysed and described on the basis of their electrochemical behaviour. The nature of the interactions between the modified carbon surfaces and adsorbed cations is discussed.     

Surface Characterization of Plasma Treated Carbon Fibers and Adhesion to a Thermoplastic Polymer

The surface chemistry of IM7 carbon fibers was characterized by x-ray photoelectron spectroscopy (XPS). The fiber surface energetics were determined from a two-liquid tensiometric method. The adhesion between as-received and plasma-treated carbon fibers and polyethersulfone (PES) was measured by the microbond pull-out test.

The surface characterization techniques showed that the effect of any plasma treatment is attained within less than 15 seconds. It was found that both argon and air plasmas increased the oxidation state of the fiber surface and that they reduced the dispersive component (γ_s ^d) of the fiber surface free energy considerably. The ammonia plasma treatment resulted in a cleaning of the surface. This plasma treatment was also effective in improving the fiber/matrix adhesion of quenched samples. A similar adhesion enhancement between as-received fibers and PES is obtained by annealing the samples above the Tg of the polymer. The air plasma treatment did not have any significant effect on the fiber/matrix adhesion.     

Hydrophobic recovery of repeatedly plasma-treated silicone rubber. Part 1. Storage in air

Silicone rubber is used for a wide variety of biomedical and industrial applications due to its good mechanical properties, combined with a hydrophobic surface. Frequently, however, it is desirable to alter the surface hydrophobicity of silicone rubber. Often this is done by plasma treatments but the effects are usually transient. In this study, surfaces of medical grade silicone rubber have been repeatedly modified by means of oxygen, argon, carbon dioxide, and ammonia RF plasma treatments with a 24 h time interval in between treatments. Treated samples were stored in air prior to surface characterization by water contact angle measurements, X-ray photoelectron spectroscopy (XPS), streaming potential measurements, and profilometry for surface roughness. The carbon percentage of the surfaces decreased after plasma treatment, while the silicon and oxygen percentages increased irrespective of the plasma used. The formation of Si-O-Si bridges between siloxane chains after plasma treatment was demonstrated by the appearance of a new component in the Si_2p peak but the degree to which this occurred differed per gas. Streaming potential measurements in a 10 mM potassium phosphate buffer indicated a more negatively charged surface for treated samples compared to untreated samples (-23.3 mV at pH 7.0). Surface roughness increased slightly for repeatedly plasma-treated samples from R_A = 0.35 μm to R_A = 0.46 μm, while scanning electron microscopy showed the presence of several 'cracks' spanning the surface after repeated treatment. Argon, carbon dioxide, and ammonia plasmas significantly reduced the advancing water contact angle from 115° to 58°, 72°, and 85°, respectively, on a more permanent basis (especially when the treatments were repeated after recovery). Oxygen plasma effects on water contact angles generally disappeared within 5 h, also after repeated treatment.     

Flame versus air atmospheric gliding arc plasma treatment of polypropylene-based automotive bumpers: Physicochemical characterization and investigation of coating properties

In this research, the polypropylene (PP) sheets used for automotive bumper surface were treated using two methods: air atmospheric gliding arc plasma and flame modifications. Atomic force microscopy was applied to study the morphology of surfaces before and after treatment processes. While calculating the surface free energy (SFE), contact angle of the surfaces was measured, and the chemical composition of the PP surface was analyzed using X-ray photoelectron spectroscopy. Surface modifications by gliding arc plasma increased the ratio of the oxygen and nitrogen atoms on the surface by 100%, indicating that polar chemical functionalities form on the surface. The surface morphology was highly affected by gliding arc plasma treatments, which triggered an impact on roughness and etching. It was also found that the SFE was drastically increased by certain modifications. Noticeable improvement was also observed in wettability by the gliding arc plasma technique. In the next stage, polyurethane paints were coated on the treated and untreated PP surfaces. Then, we examined the flame and gliding arc plasma treatments' effect on coating properties of PP bumper, adhesion analysis, water immersion resistance, and sulfuric acid resistance. Finally, high-pressure carwash test and gloss analysis were conducted on the treated and untreated coated sheets, respectively.     

Molecular structure of interfaces between plasma-polymerized acetylene films and steel substrates

Plasma-polymerized films of acetylene were deposited onto steel substrates in an inductively coupled reactor by exciting the plasma in an argon carrier gas and then injecting the monomer into the afterglow region. The molecular structure of the film/substrate interface was determined using reflection–absorption infrared spectroscopy (RAIR) and X-ray photoelectron spectroscopy (XPS) to characterize the films as a function of thickness. RAIR showed that thick (∼ 900 Å) as-deposited plasma-polymerized acetylene films had a complicated molecular structure and contained methyl and methylene, mono- and disubstituted acetylene, vinyl, and cis- and trans-disubstituted olefin groups. Evidence of oxidation resulting from the reaction of trapped radicals with atmospheric oxygen and moisture to form O—H and C=O groups was also obtained. The molecular structure of thin films (∼ 60 Å) was similar although evidence was obtained to indicate that acetylide groups (H—C≡C⁻) were present at the film/substrate interface. Results obtained using angle-resolved XPS analysis showed that carbonaceous contamination was removed from the substrate and that oxides and hydroxides on the substrate surface, especially FeOOH, were chemically reduced during deposition of the films. XPS also confirmed that plasma-polymerized acetylene films deposited on steel substrates contained groups. Preliminary results also showed that films deposited in an inductively coupled reactor were good primers for rubber-to-metal bonding, whereas films deposited in a capacitively coupled reactor were not. The differences may be due to the wide variety of functional groups found in the former type of films but not in the latter. © 1998 John Wiley & Sons, Inc. J. Appl. Polym. Sci. 70: 1283–1298, 1998     

Properties of carbon/graphite fibers modified by plasma polymerization

Carbon fibers and pyrolytic graphite blocks were treated with plasma of acrylonitrile (AN) and styrene (ST) monomers, using an induction-coupled, RF-plasma reactor. Both substrates were stable towards plasma, leading to a deposition of thin, coherent coatings of 400Å∼1000Å thickness. Both monomers produced surfaces which are substantially more polar (γ_c=54 dynes/cm for AN and 40 dynes/cm for ST) than the untreated surfaces (γ_c=32 dynes/cm). ESCA and IR studies indicate that the plasma polymers contain a high concentration of oxygen (12 percent in PPAN and 17.8 percent in PPST), in the form of CO, COOH, C O C, and OH groups. Also, treated fibers exhibited slightly higher tensile strengths than the untreated counterparts, suggesting that the plasma coatings effectively heal some of the surface flaws of the fiber. The abundant surface polar groups combined with the improved tensile properties of the plasma treated fibers make them attractive reinforcements for advanced composite materials.     

Characterization of Oxidized Polymer-Derived SiBCN Fibers

The oxidation behavior of a developmental amorphous SiBCN fiber was investigated. Fibers were heat-treated in stagnant laboratory air at temperatures of 1300°–1500°C for 1 or 2 h. The oxidized SiBCN fibers contained three distinct concentric layers, each increasing in oxygen concentration from the core to the outer surface. The unreacted fiber core retained its amorphous nature. The first oxidation layer next to the core consisted of a mixture of amorphous SiBCNO and turbostratic BN, which evolved into a more oxygen-rich glass with hexagonal and turbostratic BN grains dispersed throughout nearer the surface. The second layer consisted of essentially pure silica glass with no detectable B, C, or N present. The outermost layer in the fiber oxidized at 1500°C had devitrified to cristobalite. The fiber suffered significant strength degradation after oxidation.     

Influence of oxygen plasma treatment parameters on the properties of carbon fiber

This study is focused on the impact of oxygen plasma treatment on properties of carbon fibers and interfacial adhesion behavior between the carbon fibers and epoxy resin. The influences of the main parameters of plasma treatment process, including duration, power, and flow rate of oxygen gas were studied in detail using interlaminar shear strength (ILSS) of carbon fiber composites. The ILSS of composites made of carbon fibers treated by oxygen plasma for 1 min, at power of 125 W, and oxygen flow rate of 100 sccm presented a maximum increase of 28% compared to composites made of untreated carbon fibers. Furthermore, carbon fibers were characterized by scanning electron microscopy (SEM), tensile strength test, attenuated total reflectance Fourier transform infrared (ATR-FTIR), and Raman spectroscopy analyses. It was found that the concentration of reactive functional groups on the fiber surface was increased after the plasma modification, as well the surface roughness, which finally improved the interfacial adhesion between carbon fibers and epoxy resin. However, high power and long exposure times could partly damage the surface of carbon fibers and decrease the tensile strength of filaments and ILSS of treated fiber composites.     

Influence of surface treatment of carbon fibers on interfacial adhesion strength and mechanical properties of PLA‐based composites

In the present study C/PLA composites with different fiber surface conditions (untreated and with nitric acid oxidation for 4 h and 8 h) were prepared to determine the influence of surface treatment on the interfacial adhesion strength and mechanical properties of the composites. A chemical reaction at the fiber–matrix interfaces was confirmed by XPS studies. Nitric acid treatment was found to improve the amount of oxygen‐containing functional groups (particularly the carboxylic group, —COOH) on carbon fiber surfaces and to increase the surface roughness because of the formation of longitudinal crevices. The treated composites exhibited stronger interface adhesion and better mechanical properties in comparison to their untreated counterparts. There was a greater percentage of improvement in interfacial adhesion strength than in the mechanical properties. The strengthened interfaces and improved mechanical performance have been mainly attributed to the greater extent of the chemical reaction between the PLA matrix and the carbon fibers. The increased surface roughness also has had a slight contribution. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 80: 367–376, 2001     

Effect of Atmospheric Plasma Treatment on Carbon Fiber/Epoxy Interfacial Adhesion

In this work the effect of atmospheric plasma treatment on carbon fiber has been studied. The carbon fibers were treated for 1, 3 and 5 min with a He/O₂ dielectric barrier discharge atmospheric pressure plasma. The fiber surface morphology, surface chemical composition and interfacial shear strength between the carbon fiber and epoxy resin were investigated using atomic force microscopy (AFM), X-ray photoelectron spectroscopy (XPS) and the single fiber composite fragmentation test. Compared to untreated carbon fibers, the plasma treated fiber surfaces exhibited surface morphological and surface composition changes. The fiber surfaces were found to be roughened, the oxygen content on the fiber surfaces increased, and the interfacial shear strength (IFSS) improved after the atmospheric pressure plasma treatment. The fiber strength showed no significant changes after the plasma treatment.     

A study of the effect of oxygen plasma treatment on the interfacial properties of carbon fiber/epoxy composites

In this work, effects of the interface modification on the carbon fiber‐reinforced epoxy composites were studied. For this purpose, the surface of carbon fibers were modified by oxygen plasma treatment. The surface characteristics of carbon fibers were studied by X‐ray photoelectron spectroscopy (XPS), atomic force microscopy (AFM), dynamic contact angle analysis (DCAA), and dynamic mechanical thermal analysis (DMTA), respectively. The interlaminar shear strength (ILSS) was also measured. XPS and AFM analyses indicated that the oxygen plasma treatment successfully increased some oxygen‐containing functional groups concentration on the carbon fiber surfaces, the surface roughness of carbon fibers was enhanced by plasma etching and oxidative reactions. DCAA and DMTA analyses show that the surface energy of carbon fibers increased 44.9% after plasma treatment for 3 min and the interfacial bonding intensities A and α also reached minimum and maximum value respectively. The composites exhibited the highest value of ILSS after oxgen plasma treated for 3 min. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

Dynamic oxidation mechanism of SiC fiber reinforced SiC matrix composite in high-enthalpy plasmas

A plasma wind tunnel was utilized to explore the dynamic oxidation mechanism of SiC fiber reinforced SiC matrix composite in high-enthalpy plasmas. The results suggest the occurrences of active and passive oxidations on SiC fiber/matrix with atomic oxygen at 900～1600 °C and 1～6 kPa. Increasing plasma pressure could retard the active oxidation and promote the passive oxidation. Severe corrosion of SiC fibers due to active oxidation is highlighted. The as-formed SiO₂ layers cannot fully seal the open porosities and the interfacial gaps formed by oxidation of pyrocarbon interphases. This led to penetration of oxidized species and failure of fiber bundles directly exposed to heat flows. In addition, the spatial heat flux and temperature distributions were not homogeneous on the oxidized surface, which triggered early ‘temperature jump’ at ≈1600 °C (≈4.5 kPa) and severe localized ablation. If sealing the composite surface with SiC coating, the ablation resistance was significantly improved.     

Oxidation of BN/Nicalon Fiber Interfaces in Ceramic-Matrix Composites and Its Effect on Fiber Strength

Microstructural changes at the interface were analyzed in two Nicalon-fiber ceramic-matrix composites with a dual BN/SiC coating on the fibers after thermal exposure at different temperatures (in the range 800°-1400°C) and in different environments (air and argon). The outer SiC coating acted as a barrier to oxygen, which penetrated into the composite via pipeline diffusion along the BN/fiber interfaces. Oxygen penetration led to the formation of an SiO₂ layer by oxidation of the fiber surfaces. The in situ fiber strength at different temperatures, as determined from the radius of the mirror region on the fiber fracture surface, indicated that this SiO₂ layer severely degraded the fiber strength. Oxidation was highly dependent on the nature of the BN/fiber interface. The presence of a thin carbon-rich interlayer, which burned out rapidly at high temperature, favored the entry of oxygen and accelerated oxidation of the fibers.     

Surface and Interfacial Studies of Plasma-Modified Composite Surfaces

Model epoxy and bismaleimide compounds in thin film form were used to simulate epoxy and bismaleimide composite surfaces, in order to study compositional changes and interfacial reactions induced by oxygen plasma treatment. X-ray photoelectron spectroscopy (XPS) and infrared reflection-absorption spectroscopy (IR-RAS) were used to probe chemical changes which occurred. XPS and IR-RAS were found to be complementary techniques in determining the nature of functional groups incorporated into surfaces by plasma treatment. IR-RAS analysis of the model surfaces following exposure to a liquid epoxy resin revealed that while adsorption of the liquid epoxy occurred on both plasma-treated and nonplasma-treated surfaces, the oxygen plasma-treated surface alone was capable of initiating ring-opening reactions in the epoxy. However, this effect was not observed unless immediate contact was made between the plasma-treated surface and the liquid epoxy resin, illustrating the short-lived reactivity of the functional groups on the plasma-treated surface.     

Atomic force microscopy,X-ray diffraction,X-ray photoelectron spectroscopy and thermal studies of the new melamine fiber

This paper reports the characterization of unaged and aged melamine fibers using various characterization techniques including atomic force microscopy (AFM), X-ray photoelectron spectroscopy (XPS), X-ray diffraction (XRD), scanning electron microscopy (SEM) and thermal analysis. Since melamine fiber is a relatively new fiber, very few studies on its characterization have been made. Morphological studies of the fiber surface using SEM display die lines running along the filament surface, which are characteristics of synthetic fibers and generally occur during spinning of the molten prepolymer through the spinnerets. AFM studies show that the surface of a melamine fiber filament contains a large number of hills and valleys, which are triangular in shape. AFM roughness analysis shows that melamine fiber surface is considerably rough which may aid in adhesion of the fiber with polymeric matrices. Ageing causes an increase in the surface roughness with simultaneous increase in the crystallinity of the fiber from 19.4% to 22.6%. In XPS studies, high concentrations of carbonyl and hydroxyl groups on the filament surface have been detected. Ageing causes a reduction in the hydroxyl group concentration and an increase in the carbonyl group concentration due to surface oxidation. The reduction in the surface hydroxyl groups due to ageing has also been detected in the Fourier-Transform infrared (FT-IR) spectra of the aged fibers. Thermogravimetric (TG) studies reveal a high thermal stability of the melamine fiber even in an oxidative environment such as air.