Influence of fiber wettability on the interfacial adhesion of continuous fiber‐reinforced PPESK composite

Interfacial adhesion between fiber and matrix has a strong influence on composite mechanical performance: better interfacial adhesion can enhance composite transverse properties, flexural properties, and interlaminar shear strength, and so on. To exploit the reinforcement potential of the fibers in advanced composite, it is necessary to reach a deeper understanding on the relation between fiber wettability and interfacial adhesion. In our experiment, we study the influence of fiber wettability on interfacial properties of fiber/PPESK composites by choosing three kinds of fibers with different wettabilities. The relation between fiber wettability and surface free energy was discussed, and the influence of fiber wettability on the interfacial property of fiber/PPESK composites was analyzed. Results indicate that higher surface free energy can enhance the wettability between fiber and matrix, and the humid resistance and interfacial adhesion can be improved at the same time. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 102: 2544–2551, 2006     

Surface modification of PBO fibers by argon plasma and argon plasma combined with coupling agents

The methods of argon plasma and argon plasma combined with coupling agents were employed to modify the poly[1,4‐phenylene‐cis‐benzobisoxazole] (PBO) fiber surface. The interfacial shearing strength (IFSS) of PBO fibers/epoxy resin was measured by the single fiber pull‐out test. The surface chemical structure and surface composition of PBO fibers were determined by FTIR and X‐ray photoelectron spectroscopy respectively. The morphology of the fiber surface was investigated by scanning electron microscopy and the specific surface area of the fibers was calculated by B.E.T. equation. Furthermore, the wettability of PBO fibers was confirmed by the droplet profile analysis method. The results showed that the elemental composition ratio of the fiber surface changed after the modification. The IFSS increased by 42 and 78% when the fibers were treated by argon plasma and argon plasma combined with the coupling agents, respectively. Meanwhile, the specific surface areas of the treated fibers were improved. In addition, compared with the modification of argon plasma, the modification of argon plasma combined with the coupling agents inhibited the attenuation phenomena of the IFSS and the wettability. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 102: 1428–1435, 2006     

Debond behavior of copper fibers in thermoset matrices and their effect on fracture toughening

Single fiber pullout experiments were conducted to determine the adhesion quality, debond behavior and subsequent matrix fracture behavior for a variety of end-modified copper fibers. The matrices were: two different epoxy resins, polyester and polyurethane; the end-modified copper fibers were: straight, flat end-impacted, flat end-impacted with release agent applied and straight end-oxidized. The goal was to determine how the bonding and debonding behavior as well as the pullout behavior of the various fiber-matrix combinations affected the composite fracture toughness increment (ΔG). Results indicate that the greatest improvement in the calculated ΔG occurred with a fiber-matrix combination that had a moderate interface bond strength with an interfacial bond failure, minor matrix damage during fiber pullout and moderate post-debond interface friction. Selective oxidation of the fiber end was performed to determine if chemical anchoring of the fiber end could be as effective as mechanical (end-shaping) anchoring of the fiber into the matrix. Improvement in the adhesion bond strength as a result of the chemical anchoring resulted in a significantly lower ΔG compared to the end-impacted fibers because interfacial failure was not possible. This indicates that for the materials tested, mechanical anchoring of the fiber was better than chemical anchoring in improving ΔG. To decrease the adhesion bond strength and allow the fibers to debond, a release agent was applied to the flat end-impacted fiber prior to embedment into the matrix. This resulted in a significantly lower ΔG compared to straight and flat end-impacted fibers for all matrices tested, because the resulting debonding force and friction were significantly reduced. Pullout curves showed that with release agent applied, the end-shape did not effectively anchor the fiber into the matrix. The reduction in the pullout work indicates that the friction at the fiber-matrix interface plays a crucial role in actively anchoring the end-shaped fiber into the matrix after debonding.     

Prospect of nanoscale interphase evaluation to predict composite properties

For meeting the requirements of lightweight and improved mechanical properties, composites could be tailor-made for specific applications if the adhesion strength which plays a key role for improved properties can be predicted. The relationship between wettability and adhesion strength has been discussed. The microstructure of interphases and adhesion strength can be significantly altered by different surface modifications of the reinforcing fibers, since the specific properties of the interphase result from nucleation, thermal and/or intrinsic stresses, sizing used, interdiffusion, and roughness. The experimental results could not confirm a simple and direct correlation between wettability and adhesion strength for different model systems. The main objective of the work was to identify the interphases for different fiber/polymer matrix systems. By using phase imaging and nanoindentation tests based on atomic force microscopy (AFM), a comparative study of the local mechanical property variation in the interphase of glass fiber reinforced epoxy resin (EP) and glass fiber reinforced polypropylene matrix (PP) composites was conducted. As model sizings for PP composites, γ-aminopropyltriethoxysilane (APS) and either polyurethane (PU) or polypropylene (PP) film former on glass fibers were investigated. The EP-matrix was combined with either unsized glass fibers or glass fibers treated with APS/PU sizing. It was found that phase imaging AFM was a highly useful tool for probing the interphase with much detailed information. Nanoindentation with sufficiently small indentation force was found to be sufficient for measuring actual interphase properties within a 100-nm region close to the fiber surface. Subsequently, it also indicated a different gradient in the modulus across the interphase region due to different sizings. The possibilities of controlling bond strength between fiber surface and polymer matrix are discussed in terms of elastic moduli of the interphases compared with surface stiffness of sized glass fibers, micromechanical results, and the mechanical properties of real composites.     

Surface modification of UHMWPE fibers by means of polyethylene wax grafted maleic anhydride treatment

A novel surface modification method for ultrahigh molecular weight polyethylene (UHMWPE) fibers to improve the adhesion with epoxy matrix was demonstrated. Polyethylene wax grafted maleic anhydride (PEW‐g‐MAH) was deposited on the UHMWPE fibers surface by coating method. The changes of surface chemical composition, crystalline structure, mechanical properties of fiber and composite, wettability, surface topography of fibers and adhesion between fiber and epoxy resin before and after finishing were studied, respectively. The Fourier transform infrared spectroscopy spectra proved that some polar groups (MAH) were introduced onto the fiber surface after finishing. The X‐ray diffraction spectra indicated that crystallinity of the fiber was the same before and after finishing. Tensile testing results showed that mechanical properties of the fiber did not change significantly and the tensile strength of 9 wt % PEW‐g‐MAH treated fiber reinforced composite showed about 10.75% enhancement. The water contact angle of the fibers decreased after finishing. A single‐fiber pull out test was applied to evaluate the adhesion of UHMWPE fibers with the epoxy matrix. After treatment with 9 wt % PEW‐g‐MAH, a pull‐out force of 1.304 MPa which is 53.59% higher than that of pristine UNMWPE fibers was achieved. © 2018 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2018 , 135, 46555.     

UV‐excitable fluorescent poly(lactic acid) fibers

The UV‐excitable fluorescent poly(lactic acid) (PLA) fibers were spun by the traditional melt spinning process, and the effects of the fluorescent powder content (w(FP)) and draw ratio (DR) on the structure and properties of the fluorescent PLA fibers were investigated, respectively. The results showed that the emission spectra of fluorescent PLA fibers were peaked at 530 nm after UV excitation, indicating the PLA fibers would emit green light under UV light. With the increasing of w(FP), the relative fluorescence intensity of PLA fibers increased gradually, whereas more and larger protrusions were formed on the fiber surface due to the agglomeration of fluorescent powder, both the crystallinity and mechanical properties of fluorescent PLA fiber showed the decreasing trend with the increase of w(FP). With the increase of DR, the tensile strength of fluorescent PLA fibers increased gradually, whereas the relative fluorescence intensity of PLA fibers increased firstly and then decreased, and the highest fluorescence intensity was obtained when the DR was 3.6. In addition, the confocal laser scanning microscope can be used well to simulate the 3D distribution of fluorescent powder among the PLA fibers. POLYM. ENG. SCI., 56:373–379, 2016. © 2016 Society of Plastics Engineers     

Synthesis and characterization of a rigid-rod dihydroxy poly(<Emphasis Type="Italic">p</Emphasis>-phenylene benzobisoxazole) fiber with excellent surface and axial compression properties

A series of dihydroxy poly(p-phenylene benzobisoxazole) (DHPBO) were prepared by introducing binary hydroxyl polar groups into poly(p-phenylene benzoxazole) PBO macromolecular chains and the effects of hydroxyl polar groups on surface wettability, interfacial adhesion and axial compression property of PBO fiber were investigated. Contact angle measurement showed that the wetting process both for water and for ethanol on DHPBO fibers were obviously shorter than that on PBO fibers, implying DHPBO fibers have a higher surface free energy. Meanwhile, single fiber pull-out test showed that DHPBO fibers had higher interfacial shear strength than that of PBO fibers. Scanning electron microscope proved that there was more resin remained on the surface of DHPBO fibers than on PBO fibers after pull-out test. Furthermore, axial compression bending test showed that the introduction of binary hydroxyl groups into macromolecular chains apparently improved the equivalent bending modulus of DHPBO fibers.     

Effect of ultrasound on wettability between aramid fibers and epoxy resin

Good wetting of reinforced fiber by resin was a main factor in the improvement of the interface adhesion of their composites. Ultrasound with a frequency of 20 kHz was used to improve the wettability between aramid fibers and epoxy resin during the winding process of the composites. The effects of ultrasound on the viscosity and surface tension of epoxy resin and on the surface characteristics of aramid fibers were investigated. The wettability of aramid fibers and treated epoxy resin under different conditions and of aramid fibers and epoxy resin under ultrasonic online treatment were compared. The results indicated that the main action of ultrasound was to force epoxy resin to impregnate aramid fibers, in addition to the influence of ultrasound on the properties of epoxy resin and aramid fibers. The results of microdebond testing showed that the interfacial shear strength (IFSS) of aramid/epoxy composites could be 26% higher than that of untreated composites because of the improved wettability between aramid fibers and epoxy resin subjected to ultrasonic online treatment. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci, 2006     

Softness evaluation of keratin fibers based on single‐fiber bending test

The evaluation of single‐fiber softness by bending is an ingenious and vital approach for the basic investigation of both the fiber bending properties and the textile softness. The bending behavior and bending modulus of wool, alpaca and silk fibers have been measured by an axial‐buckling method developed by the authors, which uses the fiber compression bending analyzer (FICBA). The bending properties of single fibers were quantified by calculating the equivalent bending modulus and the flexural rigidity by measuring the protruding length and diameter of fiber needles and the critical force, P_cr, obtained from the peak point of the force‐displacement curve. The measured data showed that the equivalent bending modulus of the alpaca fiber is higher than that of wool fiber, and even the rigidity is 10 times as high as wool, but its friction coefficient is lower than that of wool, which means that the soft handle of alpaca fabrics is mainly due to the smooth surface and low friction coefficient of alpaca fibers in contrast to that of wool fiber. For the silk fiber, despite high equivalent bending modulus, the smoother handle of silk should be mainly due to the thin fiber diameter in contrast to that of keratin fibers. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 101: 701–707, 2006     

Solvent‐free acetylation of lignocellulosic fibers at room temperature: Effect on fiber structure and surface properties

Acetylation is one of the most interesting chemical treatments to improve the affinity of lignocellulosic fibers with polymeric matrices for the elaboration of several types of composites. In this paper, the acetylation of flax and wood pulp (bleached softwood Kraft pulp and thermomechanical pulp) fibers was carried out at room temperature in a solvent‐free system with acetic anhydride in the presence of sulfuric acid as catalyst. The effect of acetylation on the fine structure of fibers was investigated by spectroscopic methods, while the extent of acetylation was quantified by weight percent gain. The effect of reaction time on fiber morphology was studied at macro‐ and microscale using scanning electron microscopy, optical microscopy, and fiber quality analysis. The evolution of the hydrophobic/hydrophilic character of fibers was determined by contact angle measurements. The wettability of fibers by liquid epoxy resin was also evaluated to confirm the improvement of the affinity of acetylated fibers with the epoxy matrix. It was found that the hydrophilic character of fibers decrease with increasing reaction time, whereas the trend was less pronounced beyond specific reaction times. Acetylated fibers can therefore be potential candidates for replacing nonbiodegradable reinforcing materials in composite applications. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 42247.     

Wetting properties of human hair by means of dynamic contact angle measurement

The interaction between human hair and water occurs continuously in atmospheric air, and even more so, during application of shampoo and conditioner. For this reason the wettability of hair, and how hair care products affect the wetting properties, is of interest to hair care science. In this study, the Wilhelmy balance method is used to measure dynamic contact angle of both conditioner‐treated hairs and those left untreated to study the interaction of hair with water. The method uses a microbalance to measure the force exerted on a single fiber when it is immersed into the wetting liquid of interest. This measured force is related to the wetting force of the liquid on the fiber, and the dynamic contact angle can be calculated. The contact angles of chemically damaged, mechanically damaged, virgin (undamaged) as well as conditioner‐treated hairs and those left untreated are measured and compared. These samples were measured dry, and then also allowed to soak in water before being measured to determine whether a wet environment affects the wetting properties of the hair surface. Additionally, wettability of hairs from subjects of different ethnicities are measured and compared. Further, the mechanisms driving a significant directionality dependence are studied and discussed. The results are also used to explain tribological properties found in previous studies. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 102:5255–5265, 2006     

Magnetically active composite cellulose fibers

A process has been developed for manufacturing magnetically active composite fibers of cellulose using N‐methylmorpholine‐N‐oxide as a direct solvent for this natural polymer. Owing to its elasticity and stability, the process made it possible to add considerable quantities of modifier (up to 50% of fiber weight) to spinning solutions. The incorporation of powdered hard ferrites (barium ferrite) into the polymer solution resulted in fibers with magnetic properties, which exhibited a uniform distribution of the modifier. The results of testing the magnetic properties of the fibers obtained have shown that the coercive force of fibers do not depend on the modifier content, while the residual magnetism increases with the content of the ferromagnetic material. The value of fiber remanence is a fraction of the value of magnetic material remanence, corresponding to its volume content in fibers. This may indicate that the modifier used is chemically stable in the spinning solution medium. The thermal analysis of the fibers (DSC and TGA) has shown no negative effect of the modifiers on the fibers' thermal stability. An undesirable influence of the ferromagnetic compound on the fibers is the deterioration of their mechanical properties. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 101: 1529–1534, 2006     

Improvement of interfacial adhesion between PBO fibers and cyanate ester matrix

Poly(p‐phenylene benzobisoxazole) (PBO) fibers were activated by the horseradish peroxidases (HRP) and then treated by 3‐Glycidoxypropyltrimethoxysilane (KH‐560) to improve the wettability and the interfacial adhesion between PBO fibers and cyanate ester matrix. The chemical compositions of PBO fibers were characterized and analyzed by FTIR and XPS. Surface morphologies of PBO fibers were examined by SEM. The wettability of PBO fibers was evaluated by the dynamic contact angle analysis test. The mechanical properties were evaluated by tensile strength and interfacial shear strength, respectively. The results demonstrated that hydroxyl groups and epoxy groups were introduced onto the surface of PBO fibers during the treatments. These treatments can effectively improve the wettability and adhesion of PBO fibers. The surface free energy of PBO fibers was increased from 31.1 mN/m to 55.2 mN/m, and the interfacial adhesion between PBO fiber and cyanate ester resin was improved to 10.77 MPa. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014 , 131, 40204.     

Moisture sorption on the wetting behavior of poly(p-phenylene terephthalamide) fibers in water and epoxy resin

The moisture sorption of poly(p-phenylene terephthalamide) (PPTA) fibers and the effects of moisture on the wetting behavior of these fibers in water and in an epoxy resin were studied. The moisture regains in the Kevlar 149 fibers followed a third order polynomial dependency on increasing relative humidity at 23°C. When preconditioned at 0% relative humidity (R.H.), water wettability of Kevlar 49 fibers was superior to that of Kevlar 149 fibers. Resin wettability of the dried Kevlar 49 fibers, on the other hand, was lower than that of Kevlar 149 fibers. Wettability in water and resin of these two fiber types was affected differently by moisture. Exposure to 97% R.H. moisture level significantly lowered water wettability of Kevlar 49 fibers but did not affect the wettability of Kevlar 149 fibers in water. Resin wettability of Kevlar 49 fibers was improved upon exposure to moisture, but the opposite was observed on Kevlar 149 fibers.     

Surface characterization of hollow fiber membranes used in artificial kidney

The internal and external curved surfaces of polysulfone hollow fiber membranes were characterized by atomic force microscopy (AFM), contact angle measurement (CAM), and scanning electron microscopy (SEM) with the aim of improving the membrane surface properties for blood compatibility. Novel approaches were applied to evaluate a number of properties, including the roughness, pore size, nodule size, and wettability of the surfaces of the hollow fibers. CAM studies were carried out by directly observing the liquid meniscus at the surfaces of hollow fibers. Observation of the meniscus and measurement of the contact angle became possible by using an imaging system developed in our laboratory. AFM and SEM studies were also conducted on the surfaces of the hollow fiber membranes by cutting them at an inclined angle. The effect of the molecular weight of poly(ethylene glycol) (PEG) in the polymer blend on the surface properties of the hollow fibers was studied. Increasing the PEG molecular weight increased the average pore size whereas it decreased the contact angle. The contact angle depended on the microscopic surface morphology, including nodule size and roughness parameters. The theoretical prediction along with the experimental data showed that the measured contact angle would be greater than the value intrinsic to the membrane material because of the formation of composite surface structures. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 101: 4386–4400, 2006     

Evaluation of Fracture Surfaces in Carbon Fiber/Epoxy Composites

We have investigated carbon fiber/resin debonding mechanisms using wetting force scanning to examine the fracture surfaces. The wettability of the site of a resin microdroplet (50-150 μm long) on a fiber after debonding is compared with that of the original fiber surface by scanning along the fiber with an appropriate probe liquid. For an HMS/Epon828 system, debonding seems to involve removal of a layer of carbon fiber, while for an AS4/Epon828 system, there is evidence for adhesive failure as well as cohesive failures in both fiber and resin. These contrasting failure mechanisms are consistent with the morphological structures of the carbon fibers studied.     

Fabrication and characterization of electrospun polybutadiene fibers crosslinked by UV irradiation

Crosslinked electrospun polybutadiene (BR) fibers were made using electrospinning and UV curing methods. The crosslinked BR fibers were obtained by irradiating UV light on the electrospun BR fibers containing a photoinitiator and a crosslinker. Although uncrosslinked electrospun BR fibers did not retain the fiber morphology at room temperature due to a cold flow resulting from the very low glass transition temperature (T_g) of BR (below ?80°C), the crosslinked electrospun BR fibers retained the fiber morphology. The crosslink density increased with increase of the content of crosslinking agent. The crosslinked BR fibers had higher T_g than the raw BR. Tensile strength, modulus, and elongation at break of the electrospun BR fiber mats increased with increase of the crosslinker content. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 101: 2233–2337, 2006     

Surface wettability of human hair. I. Effect of deposition of polymers and surfactants

Monitoring the wetting force exerted on a single fiber while the fiber is slowly and continuously immersed in a liquid and then withdrawn can provide several kinds of information about the physicochemical heterogeneity of the fiber surface. This method for scanning the fiber surface with an appropriate liquid has been found useful for studying the distribution of materials deposited on the surface of human hair to improve hair assembly properties, such as cationic polymers used in hair conditioners. It is shown how wetting force vs. immersion depth curves can reflect not only the average distribution of the material on the surface, but also the degree of uniformity of the deposit; further, wetting force curves for multiple immersions of the same treated fiber indicate the ease of desorption of the surface material. The results for the systems studied, which include mildly oxidized hair and smooth nylon fibers for comparison, show how the relation between the critical surface tension of the fiber and the surface tension of the treating solution influences distribution and substantivity. Finally, data on the difference between advancing and receding wettability indicate how this hysteresis is related to the nature of the surface and to surface coverage by treating agents.     

RETRACTED ARTICLE: Surface modification of aramid fibers with novel chemical approach

Friedel–Crafts Reaction as a simple and convenient approach to the surface modification of aramid fiber was introduced in this paper. Epoxy chloropropane was chosen as the treatment reagent to modify aramid fibers surface via Graft reaction. After the modification, the interfacial properties of aramid/epoxy composites were investigated by the single fiber pull-out test (SFP), and the mechanical properties of aramid fibers were investigated by the tensile strength test. The results showed that the interfacial shear strength (IFSS) value of aramid/epoxy composites was enhanced by about 50%, and the tensile strength of aramid fibers had no obvious damage. The crystalline state of aramid fibers was determined by X-ray diffraction instrument (XRD), and the results showed that there were not any distinct crystal type varieties. The surface elements of aramid fibers were determined by X-ray photoelectron spectroscopy (XPS), the analysis of which showed that the oxygen/carbon ratio of aramid fiber surface increased obviously. The possible changes of the chemical structure of aramid fibers were investigated via Fourier transform infrared spectrum (FTIR), and the analysis of which showed that the epoxy functional groups were grafted into the molecule structure of aramid fibers. The surface morphology of aramid fibers was analyzed by Scanning electron microscope (SEM), and the SEM results showed that the physical structure of aramid fibers was not etched or damaged obviously. The surface energy of aramid fibers was investigated via the dynamic capillary method, and the results showed that the surface energy was enhanced by 31.5%, and then the wettability degree of aramid fiber surface was enhanced obviously too. All of the results indicated that this novel chemical modification approach not only can improve the interfacial bonding strength of aramid/epoxy composites remarkably, but also have no negative influence on the intrinsic tensile strength of aramid fibers.     

A comparative study on the mechanical and degradation properties of plant fibers reinforced polyethylene composites

Coir and abaca fiber‐reinforced linear low density polyethylene (LLDPE) composites (30 wt% fiber) were prepared by compression molding. Coir and abaca fibers were treated with methyl methacrylate (MMA) using ultraviolet radiation to improve the mechanical properties of the composites. Concentration of MMA and radiation dose was optimized. It was found that 30% MMA in methanol along with photoinitiator Darocur‐1173 (2%) and 15th pass of radiation rendered better performance. Chemically treated fiber‐reinforced specimens yielded better mechanical properties compared to the untreated composites, whereas coir fiber composites had better mechanical properties than abaca fiber reinforced ones. For the improvement of the properties, optimized coir (coir fiber treated with 30% MMA) and abaca (abaca fiber treated with 40% MMA) fibers were again treated with aqueous starch solution (2%–8%, w/w) for 2–7 min. Composites made of 3%‐starch‐treated coir fiber (5 min soaking time) showed the best mechanical properties than that of abaca‐fiber‐based composites. Water uptake and soil degradation tests of the composites were also performed. POLYM. COMPOS., 2011. © 2011 Society of Plastics Engineers