Quantitative surface analysis of hemp fibers using XPS,conventional and low voltage in‐lens SEM

Surfaces of hemp fibers with different treatments: (1) as received; (2) water washed; and (3) treated with NaOH, were examined using a combination of conventional Scanning Electron Microscopy (SEM), lignin staining and a novel low voltage in‐lens detector SEM technique which provides compositional contrast between polymeric materials on the surface. Surface composition determined using quantitative X‐ray photoelectron spectroscopy (XPS) and energy dispersive X‐ray spectroscopy (EDS) showed that the surfaces of the as received fibers and the water washed fibers were predominantly lignin and extractives and only after NaOH treatments was there sufficient oxygen on the surface to allow for the presence of polysaccharides. Using the in‐lens backscattered SEM technique, spatial distribution of polymeric materials on the surface was shown to be highly non‐uniform. The findings have implications for design of natural fiber composites and the interfacial properties between fiber and matrix. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016 , 133, 43023.     

Influence of oxygen plasma treatment on interfacial properties of poly(p‐phenylene benzobisoxazole) fiber‐reinforced poly(phthalazinone ether sulfone ketone) composite

The influence of oxygen plasma treatment on both surface properties of poly(p‐phenylene benzobisoxazole) (PBO) fibers and interfacial properties of PBO fiber reinforced poly(phthalazinone ether sulfone ketone) (PPESK) composite were investigated. Surface chemical composition, surface roughness, and surface morphologies of PBO fibers were analyzed by X‐ray photoelectron spectroscopy (XPS), Atomic force microscopy (AFM), and scanning electron microscopy (SEM), respectively. Surface free energy of the fibers was characterized by dynamic contact angle analysis (DCAA). The interlaminar shear strength (ILSS) and water absorption of PBO fiber‐reinforced PPESK composite were measured. Fracture mechanisms of the composite were examined by SEM. The results indicated that oxygen plasma treatment significantly improved the interfacial adhesion of PBO fiber‐reinforced PPESK composite by introducing some polar or oxygen‐containing groups to PBO fiber surfaces and by fiber surface roughening. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

Application of the microbond technique. IV. Improved fiber–matrix adhesion by RF plasma treatment of organic fibers

The microbond technique is a modification of the single-fiber pullout test for measuring interfacial shear strength. Briefly, a cured microdroplet of material is debonded in shear from a single fiber. Ultra-high modulus polyethylene (Spectra) fibers and aramid fibers (Kevlar) were treated using a radio frequency plasma in order to increase the interfacial bond between the fibers and an epoxy resin. The treated fiber surface was subsequently analyzed by X-ray photoelectron spectroscopy (XPS). Plasma treatment resulted in an increased concentration of oxygen containing functionalities on the fiber surface. The interfacial shear strength as determined by the microbond test increased by 118% for the Spectra fibers and by 45% for the Kevlar fibers with the same epoxy resin. Scanning electron microscopy indicated little change of the surface topography of either fiber following plasma treatment. Effects of friction and surface composition of the plasma-treated fibers is discussed. © 1993 John Wiley & Sons, Inc.     

Surface ammonification of the mutual‐irradiated aramid fibers in 1,4‐dichlorobutane for improving interfacial properties with epoxy resin

The mutual irradiated aramid fibers in 1,4‐dichlorobutane was ammoniated by ammonia/alcohol solution, in an attempt to improve the interfacial properties between aramid fibers and epoxy matrix. Scanning electron microscopy (SEM), X‐ray photoelectron spectroscopy (XPS), dynamic contact angle analysis (DCA), interfacial shear strength (IFSS), and single fiber tensile testing were carried out to investigate the functionalization process of aramid fibers and the interfacial properties of the composites. Experimental results showed that the fiber surface elements content changed obviously as well as the roughness through the radiation and chemical reaction. The surface energy and IFSS of aramid fibers increased distinctly after the ammonification, respectively. The amino groups generated by ammonification enhanced the interfacial adhesion of composites effectively by participating in the epoxy resin curing. Moreover, benefited by the appropriate radiation, the tensile strength of aramid fibers was not affected at all. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017 , 134, 44924.     

Accelerated ultraviolet aging study of the Vectran fiber

Aging behavior of Vectran fiber exposed to ultraviolet (UV) radiation was investigated. Vectran fiber was subjected to UV‐accelerated degradation environment. Tensile strength of Vectran fiber was determined at room temperature using a two‐parameter Weibull distribution. The average tensile strength loss was 42.75% when the irradiation time reached 186 h. The surface morphology of the degraded fiber was examined using scanning electron microscopy (SEM) and atomic force microscopy (AFM). X‐ray photoelectron spectroscopy (XPS) and ¹³C‐NMR were used to provide a molecular characterization of fibers. SEM and AFM showed that UV exposure result in microvoids on the surface of fibers. The results of the XPS and ¹³C‐NMR indicated that the UV radiation could lead to chain scission of fiber surface layer. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2012     

Silica fiber–polybenzoxazine–syntactic foams; Processing and properties

Polybenzoxazine filled with chopped silica fibers and their syntactic foams of varying composition and densities were processed. The composition and density variations were achieved by regulating the relative concentrations of silica fiber and glass microballoons (MB). The variation of tensile, compressive, and flexural properties with change in composition was investigated. For the silica‐fiber filled materials, the property attained a maximum at about 40% volume content of fiber, and thereafter, the properties showed a diminishing trend. The incorporation of microspheres significantly lowered the strength of silica filled materials. However, the decrease in the specific flexural strength was less pronounced and the strength was unaffected beyond a certain microsphere content. During processing and mechanical testing, a large quantity of fibers was fractured, which reduced the strength of silica filled systems. The diminution in material strength on embedding microspheres is attributed to the presence of stress concentrating loci as evidenced from SEM analysis. The various factors leading to the property variation with composition are discussed with microscopic analyses, like clustering of fibers, crack propagation, fiber pull out, and debonding of fibers from resin phase. Dynamic mechanical analysis revealed an improved damping property for the filled materials in contrast to the unfilled polymer. The T_g (deduced from tan δ maximum from DMTA) decreased in silica fiber containing materials and on incorporating the MB, the values reverted back to that of the neat polymer. Both silica and MB conferred better thermal and thermooxidative stabilities to the polybenzoxazine. However, the degradation mechanism is nonoxidative in nature. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

Surface modification of ultra-high strength polyethylene fibers for enhanced adhesion to epoxy resins using intense pulsed high-power ion beam

The effects of intense pulsed high power ion beam (HPIB) treatment of ultra-high strength polyethylene (UHSPE) fibers on the fiber/epoxy resin interface strength were studied. For this study, argon ions were used to treat Spectra? 1000 (UHSPE) fibers in vacuum. Chemical and topographical changes of the fiber surfaces were characterized using Fourier transform infrared spectroscopy in attenuated total reflectance mode (FTIR-ATR), X-ray photoelectron spectroscopy (XPS), dynamic wettability measurements, and scanning electron microscopy (SEM). The fiber/epoxy resin interfacial shear strength (IFSS) was evaluated by the single fiber pull-out test. The FTIR-ATR and XPS data indicate that oxygen was incorporated onto the fiber surface as a result of the HPIB treatment. The wettability data indicate that the fibers became more polar after HPIB treatment and also more wettable. Although the total surface energy increased only slightly after treatment, the dispersive component decreased significantly while the acid-base component increased by a similar amount. SEM photomicrographs revealed that the surface roughness of the fibers increased following the HPIB treatment. The single fiber pull-out test results indicate that HPIB treatment significantly improved the IFSS of UHSPE fibers with epoxy resin. This enhancement in IFSS is attributed to increased roughness of the fiber surface resulting in mechanical bonding and in increased interface area, increased polar nature and wettability, and an improvement in the acid-base component of the surface energy after the HPIB treatment.     

The effects of surface treatments of fibers on the interfacial properties in single-fiber composites

The interfacial properties between fibers and the matrix contribute to the overall properties in high performance composites. Plasma treatments (Ar, O₂, CF₄/O₂, N₂/H₂) have been performed on carbon fibers to improve the fiber-matrix interaction. The treatment efficiency was checked by the single-fiber technique, while the surface chemistry and morphology were characterized by X-ray photoelectron spectroscopy (XPS), static secondary ion mass spectroscopy (SSIMS), and scanning electron microscopy (SEM). The O₂- and N₂/H₂-plasma treatments proved most effective both for introducing oxygen-containing functionalities at the fiber surface and for improving the interfacial shear strength of carbon fiber/epoxy composites. A relationship between the oxygen concentration at the fiber surface and the interfacial shear strength is demonstrated.     

Fracture behavior of vinylester resin matrix composites reinforced with alkali‐treated jute fibers

Jute fibers were treated with 5% NaOH solution for 4 and 8 h, respectively, to study the mechanical and impact fatigue properties of jute‐reinforced vinylester resin matrix composites. Mechanical properties were enhanced in case of fiber composites treated for 4 h, where improved interfacial bonding (as evident from scanning electron microscopy [SEM]) and increased fiber strength properties contributed effectively in load transfer from the matrix to the fiber; but their superior mechanical property was not retained with fatigue, as they showed poor impact fatigue behavior. The fracture surfaces produced under a three‐point bend test and repeated impact loading were examined under SEM to study the nature of failure in the composites. In case of untreated fiber composites, interfacial debonding and extensive fiber pullout were observed, which lowered the mechanical property of the composites but improved their impact fatigue behavior. In composites treated for 4 h under repeated impact loading, interfacial debonding occurred, followed by fiber breakage, producing a sawlike structure at the fracture surface, which lowered the fatigue resistance property of the composites. The composites with fibers treated with alkali for 8 h showed maximum impact fatigue resistance. Here, interfacial debonding was at a minimum, and the fibers, being much stronger and stiffer owing to their increased crystallinity, suffered catastrophic fracture along with some microfibrillar pullout (as evident from the SEM micrographs), absorbing a lot of energy in the process, which increased the fatigue resistance property of the composites. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 85: 2588–2593, 2002     

Grafting starch nanocrystals onto the surface of sisal fibers and consequent improvement of interfacial adhesion in sisal reinforced starch composite

Starch nanocrystals (SNCs) were obtained by the hydrolysis of waxy starch and used to improve the interfacial adhesion of a composite of sisal fibers and starch. Sisal fibers were first treated with acrylic acid (AA), and the modified fibers were then reacted with SNCs to form ester groups. The grafted fibers were characterized by Fourier transform infrared spectroscopy (FTIR), X-ray photoelectron spectroscopy (XPS), and scanning electron microscopy (SEM). The FTIR and XPS results showed that the SNCs were successfully grafted onto the surface of SF-AA, and an ester linkage was formed during the reaction of AA with the SNCs. The SEM analysis showed that the SNCs were distributed over the fiber surface. Tensile tests and pull-out tests were also performed utilizing a two-parameter Weibull distribution analysis to study the effect of the grafted SNCs on the mechanical and interfacial properties. Compared to the untreated fibers, the interfacial shear strength of the grafted SNCs fibers increased by 79.3%. Therefore, the structural similarity between starch and the SNCs contributed towards their compatibility and improved interfacial properties, with the introduction of SNCs being used as an alternative material for fiber surface modification. © 2018 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2019 , 136, 47202.     

Grafting of a liquid crystal polymer on carbon fibers

Covalent grafting of mesogenic chains on carbon fiber surfaces was attempted as part of a study on composite materials containing liquid crystal polymer matrices. Grafting in these composite systems is viewed not only as a mechanism to achieve interfacial bonding but also as an approach to modify the interphase physical structure. The synthetic approach to grafting involved the in-situ polymerization of monomers in the presence of functionalized fibers in order to grow chains covalently attached to the fibers. The chemical mechanism may be viewed as the “transesterification of car boxy lated fibers” with acetylated monomers. The monomers used were pimelic acid, p-acetoxybenzoic acid and diacetoxy hydroquinone which are known to yield upon condensation a chemically aperiodic nematic polymer. Evidence for grafting was obtained from X-ray photoelectron spectroscopy (XPS) and scanning electron microscopy (SEM) analysis on fibers retrieved from composite samples. Interestingly, SEM micrographs of fractured composite specimens containing the mesogen-grafted fibers reveal excellent wetting and interfacial bonding of a liquid crystalline matrix on the carbon surfaces. Based on theoretical considerations for end-adsorbed macromolecules and the nematogenic nature of the grafted chains we infer that dense layers of adsorbed polymer may form at the interfaces studied. From a materials point of view the in situ growth of liquid crystal polymer chains on fibers may offer mechanisms to control composite properties through both bonding and molecular orientation in interfacial regions.     

Improvement of interfacial properties of carbon fiber‐reinforced poly(phthalazinone ether ketone) composites by introducing carbon nanotube to the interphase

This article aims to improve interfacial properties of carbon fiber‐reinforced poly(phthalazinone ether ketone) (PPEK) composites by means of preparing carbon nanotube (CNT)/carbon fiber hybrid fiber. XPS was used to characterize the chemical structure of unsized carbon fiber and SEM was used to observe the surface topography of carbon fibers. Specific area measurement, dynamic contact angle, and interfacial shear strength (IFSS) testing were performed to examine the effect of CNT on the interfacial properties of carbon fiber/PPEK composites. By the introduction of CNT to the interphase of carbon fiber‐reinforced PPEK composites, an enhancement of IFSS by 55.52% was achieved. Meanwhile, the interfacial fracture topography was also observed and the reinforcing mechanism was discussed. POLYM. COMPOS., 36:26–33, 2015. © 2014 Society of Plastics Engineers     

Mechanical properties and morphology of flax fiber reinforced melamine‐formaldehyde composites

The mechanical performance of natural fiber reinforced polymers is often limited owing to a weak fiber‐matrix interface. In contrast, melamine‐formaldehyde (MF) resins are well known to have a strong adhesion to most cellulose containing materials. In this Paper, nonwoven flax fiber mat reinforced and particulate filled MF composites processed by compression molding are studied and compared to a similar MF composite reinforced with glass fibers. Using flax instead of glass fibers has a somewhat negative effect on tensile performance. However, the difference is relatively small, and if density and material cost are taken into account, flax fibers become competitive. Tensile damage is quantified from the stiffness reduction during cyclic straining. Compared to glass fibers, flax fibers generate a material with a considerably lower damage rate. From scanning electron microscopy (SEM), it is found that microcracking takes place mainly in the fiber cell walls and not at the fiber‐matrix interface. This suggests that the fiber‐matrix adhesion is high. The materials are also compared using dynamic mechanical thermal analysis (DMTA) and water absorption measurements.     

Kevlar fiber–epoxy adhesion and its effect on composite mechanical and fracture properties by plasma and chemical treatment

Kevlar 49 fibers were surface-modified by NH₃-, O₂-, and H₂O-plasma etching and chlo-rosulfonation and subsequent reaction with some reagents (glycine, deionized water, eth-ylendeiamine, and 1-butanol) to improve the adhesion to epoxy resin. After these treatments, the changes in fiber topography, chemical compositions of the fiber surfaces, and the surface functional groups introduced to the surface of fibers were identified by SEM, XPS, and static SIMS. Interlaminar shear strength (ILSS) and T-peel strenght between the fiber and opoxy resin, as measured by the short-beam test and T-peel test, were remarkedly improved by gas plasma and chlorosulfonation (0.1% and 0.25% CISO₃H at 30 s). However, from the results of similar G_IC values of the treated and untreated fiber composites, it is clear that the fiber/matrix interfacial bond strength is only a minor contributor to G_IC. SEM was also used to study the surface topography of the fracture surfaces of composites in T-peel test. It could be seen from SEM observations that the improvement of fiber/matrix interfacial bond strength often accompanied a change in fracture mode from the interface of fiber/epoxy resins to the fiber fibrillation and the resins. © 1996 John Wiley & Sons, Inc.     

The structure of γ‐glycidoxypropyltrimethoxysilane on glass fiber surfaces: Characterization by FTIR,SEM, and contact angle measurements

The purpose of this article is to determine the structure of γ‐glycidoxypropyltrimethoxysilane (γ‐GPS) on glass fiber surfaces. The interfacial adhesion of glass fiber–polymer can be improved by the silane treatment of the glass fiber. To change the composition of the glass and regenerate to the hydroxyl groups, activation pretreatment of heat cleaned woven glass fabric was performed using a 10% (v/v) hydrochloric acid aqueous solution for different durations before silane treatment. The treatment of silanization of heat cleaned and acid activated glass fibers with (γ‐GPS) were conducted at various time intervals. These fibers would be used to quantify the relationship between contact angle of glass fiber surface and the interfacial shear strength of the fiber–polymer interface. The effect of acid activation on glass surface and the interaction between glass fibers and silane coupling agent were examined using Fourier transform infrared spectroscopy. The experiments, in conjunction with electron photomicrographs of glass surfaces treated with coupling agent, are interpreted in an attempt to explain the stability of coupling agent‐glass interfaces. From SEM analysis, it was clearly observed that agglomerations of silane agent in the cavities among the heat cleaned fibers are available. However, this case was not observed for the silanization of acid activated glass fibers. In addition, contact angle measurements on glass fibers were performed to evaluate surface structure. POLYM. COMPOS., 2009. © 2008 Society of Plastics Engineers     

Interfacial evaluation of epoxy/carbon nanofiber nanocomposite reinforced with glycidyl methacrylate treated UHMWPE fiber

Interface interactions of fiber–matrix play a crucial role in final performance of polymer composites. Herein, in situ polymerization of glycidyl methacrylate (GMA) on the ultrahigh molecular weight polyethylene (UHMWPE) fibers surface was proposed for improving the surface activity and adhesion property of UHMWPE fibers towards carbon nanofibers (CNF)‐epoxy nanocomposites. Chemical treatment of UHMWPE fibers was characterized by FTIR, XPS analysis, SEM, and microdroplet tests, confirming that the grafting of poly (GMA) chains on the surface alongside a significant synergy in the interfacial properties. SEM evaluations also exhibited cohesive type of failure for the samples when both GMA‐treated UHMWPE fiber and CNF were used to reinforce epoxy matrix. Compared with unmodified composite, a ～319% increase in interfacial shear strength was observed for the samples reinforced with both 5 wt % GMA‐grafted UHMWPE and 0.5 wt % of CNF. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016 , 133, 43751.     

Characterization of three‐dimensional braided polyethylene fiber–PMMA composites and influence of fiber surface treatment

Three‐dimensional (3D) braided polyethylene (PE) fiber‐reinforced poly(methyl methacrylate) (PMMA), denoted as PE_3D/PMMA, composites were prepared. Mechanical properties including flexural and impact properties, and wear resistance were tested and compared with those of the corresponding unidirectional PE fiber–PMMA (abbreviated to PE_L/PMMA) composites. Both untreated and chromic acid‐treated PE fibers were used to fabricate the 3D composites in an attempt to assess the effect of chromic acid treatment on the mechanical properties of the composites. Relative changes of mechanical properties caused by fiber surface treatment were compared between the PE_3D/PMMA and PE_L/PMMA composites. The treated and untreated PE fibers were observed by scanning electron microscopy (SEM) and analyzed by X‐ray photoelectron spectroscope (XPS). SEM observations found that micro‐pits were created and that deeper and wider grooves were noted on the surfaces of the PE fibers. XPS analysis revealed that more hydroxyl (? OH) and carboxyl (? COOH) groups were formed after surface treatment. The physical and chemical changes on the surfaces of the PE fibers were responsible for the variations of the mechanical properties of the PE/PMMA composites. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 99: 949–956, 2006     

Improvement of interfacial properties in bismaleimide composites using functionalized graphene oxide grafted carbon fiber

A hierarchical reinforcement, which was used to improve the interfacial properties of bismaleimide (BMI) composites, was prepared by grafting functionalized graphene oxide (GO) onto a carbon fiber surface. The GO and carbon fibers were first functionalized separately to create interactional functional groups on their surfaces. The grafting process was then realized by an amidation reaction of the amine and acyl chloride function groups formed on GO and carbon fibers, respectively. The surface groups of functionalized GO and carbon fibers were identified by an X‐ray photoelectron spectroscopy (XPS). The resulting reinforcement was further characterized by scanning electron microscopy (SEM), atomic force microscopy (AFM) and dynamic contact angle analysis. Experimental results showed that the functionalized GO were successfully grafted onto the carbon fibers surfaces and significantly increased the surface energy of carbon fibers. The study also indicated that the prepared hierarchical reinforcement could significantly improve the interfacial adhesion of resulting BMI composite. POLYM. ENG. SCI., 58:886–893, 2018. © 2017 Society of Plastics Engineers     

Surface modification of ultra high modulus polyethylene fibers by an atmospheric pressure plasma jet

To improve their adhesion properties, ultra high modulus polyethylene (UHMPE) fibers were treated by an atmospheric pressure helium plasma jet (APPJ), which was operated at radio frequency (13.56 MHz). The surface properties of the fibers were investigated by X‐ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM), and contact angle measurement. The surface dyeability improvement after plasma treatments was investigated using laser scanning confocal microscopy (LSCM). The adhesion strengths of the fibers with epoxy were evaluated by microbond tests. In addition, the influence of operational parameters of the plasma treatment including power input and treatment temperature was studied. XPS analysis showed a significant increase in the surface oxygen content. LSCM results showed that the plasma treatments greatly increased fluorescence dye concentrations on the surface and higher diffusion rate to the fiber center. The tensile strength of UHMPE fiber either remained unchanged or decreased by 10–13.6% after plasma treatment. The contact angle exhibited a characteristic increase in wettability, due to the polar groups introduced by plasma treatment. The microbond test showed that the interfacial shear strengths (IFSS) increase significantly (57–139%) after plasma treatment for all groups and the optimum activation is obtained at 100°C and 5 W power input. SEM analysis showed roughened surfaces after the plasma treatments. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 2008     

Temperature effect on graphene‐filled interface between glass–carbon hybrid fibers and epoxy resin characterized by fiber‐bundle pull‐out test

The overall mechanical performance of glass–carbon hybrid fibers reinforced epoxy composites depends heavily upon fiber–matrix interfacial properties and the service temperatures. Fiber‐bundle pull‐out tests of glass (GF) and/or carbon fiber (CF) reinforced epoxy composites were carried out at room and elevated temperatures. Graphene nanoplatelets were added in the interfacial region to investigate their influence on the interfacial shear strength (IFSS). Results show that IFSS of specimens with fiber‐bundle number ratio of GF:CF = 1:2 is the largest among the hybrid composites, and a positive hybridization effect is found at elevated temperatures. IFSS of all the specimens decreases with the increasing of test temperatures, while the toughness shows a contrary tendency. As verified by scanning electron microscopy observations, graphene nanoplatelets on fiber surface could enhance the IFSS of pure glass/carbon and hybrid fibers reinforced epoxy composites at higher temperatures significantly. © 2018 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2018 , 135, 46263.