Novel Jute/Polycardanol Biocomposites: Effect of Fiber Surface Treatment on Their Properties

In the present study, novel biocomposites with chopped jute fibers and thermosetting polycardanol were prepared using compression molding technique for the first time. Prior to biocomposite fabrication, jute fiber bundles were surface-treated at various concentrations using 3-glycidoxypropyltrimethoxy silane (GPS) and 3-aminopropyltriethoxy silane (APS), respectively. The interfacial shear strength, flexural properties and thermal properties of jute/polycardanol biocomposites reinforced with untreated and silane-treated jute fibers were investigated by means of single fiber microbonding test, three-point flexural test, dynamic mechanical analysis, thermogravimetric analysis and thermomechanical analysis. Both GPS and APS treatments played a role in improving the interfacial adhesion, reflecting that the organofunctional groups located at the end of silane coupling agents may contribute to linking between jute fibers and a polycardanol resin. As a result, it gave rise to increased interfacial shear strength of the biocomposites. Such interfacial improvement also led to increasing the flexural strength and modulus, storage modulus, thermal stability and thermomechanical stability.     

Effect of Fiber Surface Modification on the Interfacial and Mechanical Properties of Kenaf Fiber-Reinforced Thermoplastic and Thermosetting Polymer Composites

The surfaces of kenaf fibers were treated with three different silane coupling agents. 3-glycidoxypropyltrimethoxy silane (GPS), 3-aminopropyltriethoxy silane (APS), and 3-methacryloxypropyltrimethoxy silane (MPS). Among them, the most effective one for the property improvement was GPS when it was applied to the kenaf fiber surfaces at 0.5 wt%. Thermoplastic polypropylene (PP) and thermosetting unsaturated polyester (UPE) matrix composites with chopped kenaf fibers untreated and treated at different GPS concentrations from 0.1 wt% to 5 wt% were fabricated using compression molding technique. The present study demonstrates that the interfacial, flexural, tensile, and dynamic mechanical properties of both kenaf/PP and kenaf/UPE composites importantly depend on the GPS treatments done at different concentrations. The greatest property improvement of both thermoplastic and thermosetting polymer composites was obtained with the silane treatment at 0.5 wt% and the mechanical properties were comparable with E-glass composites prepared the same polymer matrix under the corresponding fiber length and fiber loading. The results also agreed with each other with regard to their interfacial shear strength, flexural properties, tensile properties, storage modulus, with support of fracture surfaces of the composites.     

Improving the adhesion between a aqueous PU and a polyamide fibre with silane

Glycidoxypropyltrimethoxysilane (GPS) and γ-aminopropyltrimethoxysilane (APS) were used to modify the surface chemistry of polyamide fibre. The surface chemistry was characterised using X-ray photoelectron spectroscopy. The silanol functional group was designed to be introduced on the surface of polyamide fibre to increase its chemical activity by N-alkylation of GPS and hydrolysis of APS, and to improve the poor interfacial adhesion between a polyamide 66 fibre and an aqueous polyurethane polymer adhesive. The microbond test was used to measure the interfacial shear strength between the waterborne PU adhesive and the polyamide fibre. It has been found that APS hydrolysis and GPS-alkylated fibre surface can be used to improve the interfacial adhesion of polyamide fibre to PU. The IFSS can be improved by N-alkylation of GPS from 5.0 to 8.4?MPa. After water immersion at 50?°C for 48?h, then drying, the IFSS increased to 8.8?MPa due to the plasticisation of PU in water. Better interfacial adhesion was also observed by the hydrolysis of APS, but not significantly improved by this method due to the relatively weak hydrogen bond at the interface between APS and polyamide fibre.     

Preparation of graphene-glass fiber-resin composites and its electromagnetic shielding performance

The surface of the glass fiber (GF) was modified by silane coupling agent (KH550) and bovine serum albumin (BSA), and then the graphene oxide (GO) was coated onto the modified surface of the glass fiber. Followed by a reduction reaction, the reduced graphene oxide (RGO) coated on glass fiber was obtained. Finally, the reduced graphene oxide-glass fibers (RGO-GF) were combined with unsaturated resins. The interfacial morphology of reduced graphene oxide-glass fibers was investigated by scanning electron microscopy (SEM). The structure of the materials was analyzed by Fourier transform infrared spectroscopy (FT-IR). The crystal phases of the material were identified by X - ray diffraction (XRD). The mechanical properties and electromagnetic shielding effectiveness of the sample were tested. The results showed that the interface between glass fibers and graphene binds more closely after the glass fibers was treated by KH550. The tensile strength of the RGO-GF composites reached 85.05 MPa. Compared with the GF composites, it increased by 51.4% when the glass fibers content was 30%. The shielding effectiveness of the composites reached 21.3 dB at the frequency range of 8.2–12.4 GHz (x-band). Therefore, by coating the surface with reduced graphene oxide, the glass fibers can make a great shielding effect on the electromagnetic wave.     

Determination of the interfacial properties between modified soy protein resin and kenaf fiber

The kenaf fiber/soy protein resin interface was characterized. The soy protein isolate (SPI) was modified using a polycarboxylic acid, Phytagel^® (PH), to make an interpenetrating network-like (IPN-like structure) structure of the resin. The effects of different PH contents on the interfacial properties were characterized using single fiber composite (SFC) tests and optical microscopy. Kenaf fiber strength was characterized using tensile tests. Kenaf fibers were extracted from nonwoven mats. The length of each kenaf fiber was extended by gluing it to long polyethylene filaments on both sides. After drying the glue, dog-bone shaped SFC specimens were prepared using pure and modified SPI resins. The dried SFC specimens were taken out from the mold and hot-pressed (cured) at 120°C. The interfacial shear strength (IFSS) was calculated using the shear-lag analysis. Single fiber tensile tests at different gauge lengths were performed. The average stresses were computed by fitting the data to Weibull distribution. These values were used in the calculation of the IFSS. After the SFC tests, the specimens were observed under the optical microscope to characterize the fiber fracture modes and the region around the fiber fracture. The SFC tests showed that the IFSS is a function of the PH content which controls the resin shrinkage. It was also seen that the interfacial failure mode is also a function of the PH content. These finding were confirmed by the microbead tests in which E-glass fibers were used with the modified SPI resins.     

The aging of atmospheric plasma-treated ultrahigh-modulus polyethylene fibers

The aging effects of atmospheric plasma treatments on UHMPE fibers are studied. UHMPE fibers are treated for 0.5 and 1 min with He/O₂/air gas and for 2 and 4 min with He/air gas by atmospheric pressure plasma on a capacitively coupled device at a frequency of 5 kHz. The samples are tested for fiber/epoxy interfacial shear strength at time intervals of 0, 3, 15 and 30 days after initial plasma treatment. Scanning electron microscopy shows micro-cracks on each set of treated fibers, which is not affected by aging over the 30 day study. Interfacial shear strengths (IFSS) for plasma-treated fibers are 2–3 times as high as that of the control. The IFSS for the plasma treated fibers remains constant up to 15 days and then decreases afterwards. XPS Analysis shows a slight increase in atomic concentration of oxygen and nitrogen for each plasma-treated sample. For the He/O₂/air plasma-treated samples, XPS analysis shows an observable increase in C–OH bonds, C=O bonds and COOH bonds, while for the He/air plasma-treated samples, there is a slight increase in C–OH and O=C–O bonds. After 30 days, a decrease in oxygen content for all plasma-treated samples is manifested.     

Effect of silane/nano-silica on the mechanical properties of basalt fiber reinforced epoxy composites

The present study explains the role of surface modification of constituent materials on composite material performance. The influence of silane and nano-hybrid coatings on mechanical properties of basalt fibers and composite materials on their base was investigated. Infrared spectroscopy indicated that modification of basalt fiber surface and nano-SiO₂ was successfully applied. The surface modification leads to the significant increase in the tensile strength of basalt fibers compared to the non-coated fibers. The tensile strength of silane-treated fibers was established 23% higher than the non-coated fibers, indicating that silane plays a critical role in the strength retention of basalt fibers. Also it was pointed out that silane coupling agents can be used for the preparation of the nano-hybrid coating. Addition of SiO₂ nanoparticles into the fiber surface was incorporated to enhance the interfacial bonding of basalt fiber reinforced epoxy composite.     

A Fluoropolymer Coating on Carbon Fibers Improves Their Adhesive Interaction with PTFE Matrix

Carbon fibers were treated in a HF glow discharge in tetrafluoroethylene and octafluorocyclobutane in order to improve their adhesion to poly(tetrafluoroethylene) matrix. As the result of the plasma treatment, a thin (20–140 nm) fluoropolymer coating was deposited onto the fiber surface. The structure of this coating was studied by means of IR spectroscopy, XPS, AFM and SEM techniques. The coating material appeared to be similar to PTFE in its chemical composition but distinguished by branched, partially crosslinked, amorphous structure and included unsaturated chemical bonds. The coating thickness of 70 nm was sufficient to effectively screen the field of molecular forces of the initial substrate, thus, decreasing the surface energy of the fibers and improving their compatibility with the PTFE matrix. The adhesive strength in the PTFE–carbon fiber systems, measured by means of the microbond test, more than doubled upon the plasma treatment (the local interfacial shear strength increased from 10.7 to 29.7 MPa, apparent IFSS from 4.3 to 7.8 MPa), and the interfacial frictional stress increased by 70%. The new composite material consisting of 20% short coated carbon fibers in the PTFE matrix showed better mechanical, thermal and tribological characteristics as compared with the composite reinforced with untreated fibers.     

Role of curing conditions and silanization of glass fibers on carbon nanotubes (CNTs) reinforced glass fiber epoxy composites

Curing behavior of amino-functionalized carbon nanotubes (ACNT) used as reinforcing agent in epoxy resin has been examined by thermal analysis. Experiments performed as per supplier’s curing conditions showed that modification of the curing schedule influences the thermo-mechanical properties of the nanocomposites. Specifically, the glass transition temperature (T_g) of ACNT-reinforced composites increased likely due to the immobility of polymer molecules, held strongly by amino carbon nanotubes. Further, a set of composites were prepared by implementing the experimentally determined optimal curing schedule to examine its effect on the mechanical properties of different GFRP compositions, while focusing primarily on reinforced ACNT and pristine nanotube (PCNT) matrix with silane-treated glass fibers. From the silane treatment of glass fibers in ACNT matrix composition it has been observed that amino silane is much better amongst all the mechanical (tensile and flexural) properties studied. This is because of strong interface between amino silane-treated glass fibers and modified epoxy resin containing uniformly dispersed amino-CNTs. On the other hand, PCNT GFRP composites with epoxy silanes demonstrated enhanced results for the mechanical properties under investigation which may be attributed to the presence of strong covalent bonding between epoxy silane of glass fiber and epoxy–amine matrix.     

Field desorption mass spectroscopic analysis of silane coupling agents hydrolyzed in solution

Aqueous solutions of silane coupling agents used for surface treatment of glass fiber were analyzed using gas chromatography (GC), gel permeation chromatography (GPC), and field desorption mass spectrometry (FD-MS). N-Phenyl-3-aminopropyltrimethoxysilane (AnPS) and 3-aminopropyltriethoxysilane (APS) used were hydrolyzed and condensed in water-ethanol solution. FD-MS analysis was found to be suitable for the evaluation of polymerization of silanes in the process of hydrolysis and condensation in the aqueous solution. FD-MS analysis gave the molecular weight of each silane condensate to evaluate the respective molecular structure.     

Using self-assembled monolayer technology to probe the mechanical response of the fiber interphase-matrix interphase interface

In this paper, a brief review of the fiber-matrix interphase/interface region is given for carbon- and glass-fiber composites. The substructure of the interphase/interface region is discussed in terms of three interphases: (a) the fiber interphase (FI), (b) the sizing interphase (SI), and (c) the matrix interphase (MI), and two interface regions: (a) the FI-SI interface and (b) the SI-MI interface. These substructures are a synthesis of the ideas advanced by Ishida and Koenig and Drzal. The schematic model of interphase deformation behavior originally given by Bascom is reconstructed to include research results from the above researchers. To systematically probe adhesion at the SI-MI interface, functionalized self-assembled monolayers (SAMs) using bonding and non-bonding C₁₁- type trichlorosilanes are prepared using the research of Menzel and Heise, and that of Cave and Kinloch as a guide. Results from this research are compared with short chain bonding and nonbonding silanes prepared by aqueous and non-aqueous deposition processes. The data were interpreted using the mechanisms proposed by Sharpe, Ishida and Koenig, and Drzal and the mathematical equation proposed by Nardin and Ward. For the non-bonding short-chain silane deposited by aqueous deposition, 90% of the adhesion was found to be due to mechanical interlocking, with the remaining adhesion due to physicochemical interactions. For the bonding short-chain silane deposited by aqueous deposition, the interface strength relative to the non-bonding short-chain silane increased by 31%. However the interfacial shear strength (IFSS) of this system was approximately 40% lower than the comparable bonding SAM interface. This difference was interpreted in terms of the propensity of the C₃-alkylamine to form cyclic ring structures in the MI region as described by Ishida, Koenig, et al. The SAM data also indicates that 70-85% of the maximum IFSS is obtained with 25-50% of the surface covered with functional groups. This suggests that steric hindrance, due to the size of the DGEBA molecules, restricts access to the functional groups on the surface. Therefore, only 35% of the surface functional groups are accessible for bonding in the DGEBA/m-PDA epoxy resin system.     

Influence of Fiber Surface Treatment on Mechanical Properties of CF/PET Composites

Carbon fiber (CF) / poly (ethylene terephthalate) (PET) composites were prepared with various contents (2–15wt%) of short carbon fibers. To investigate the effect of surface treatment of the CF on the mechanical properties of the composites, three specimens were prepared; those with short carbon fibers (called SCF), short carbon fibers oxidized with nitric acid (called NASCF) and the fibers oxidized with nitric acid and treated with silane coupling agent (called SCSCF). Flexural, tensile and impact tests were performed to observe mechanical behavior of the specimens. The morphology of the specimens was also studied with a scanning electron microscope (SEM). SCSCF composite had better mechanical properties than the other composites with the same content of carbon fibers since the coupling agent resulted in better interfacial adhesion between the fiber and the matrix.     

The Effect of ZrO2 Interphase on Interfacial Frictional Stresses in SiC/ZrO2/SiCf Composites

Two types of SiC fiber tows (Hi-Nicalon? and Hi-Nicalon S?) were coated with stabilized ZrO₂ and composited using preceramic polymer impregnation pyrolysis to form SiC/SiC_f minicomposites. Properties of the fiber/matrix interface in composites were investigated using the indentation method in which a pyramidal indenter was used to push on an individual fiber and cause sliding at the interface. The interfacial frictional stresses were determined from the force–displacement relation. The composites reinforced by the ZrO₂-coated fibers have smaller interfacial frictional stresses than composites reinforced by the initial fibers and show fibers sliding relatively more easily with respect to the SiC matrix.     

Interfacial evaluation of single Ramie and Kenaf fiber/epoxy resin composites using micromechanical test and nondestructive acoustic emission

Interfacial shear strength (IFSS) of environmentally friendly natural fiber reinforced polymer composites plays a very important role in controlling their overall mechanical performance. The IFSS of various Ramie and Kenaf fiber/epoxy composites was evaluated using the combination of micromechanical test and nondestructive acoustic emission (AE) to find the optimal conditions for desirable final performance. Dynamic contact angle was measured for Ramie and Kenaf fibers and correlated the wettability properties with interfacial adhesion. Mechanical properties of Ramie and Kenaf fibers were investigated using single-fiber tensile test and analyzed statistically by both unimodal and bimodal Weibull distributions. The effect of clamping on the real elongation for both Ramie and Kenaf fibers was evaluated as well. Two different microfailure modes, axial dedonding and fibril fracture, coming from fiber bundles and single fiber composites (SFC) were observed under tension and compression. They were evaluated optically and also determined by AE and their FFT analysis nondestructively.     

Henequen/poly(butylene succinate) biocomposites: electron beam irradiation effects on henequen fiber and the interfacial properties of biocomposites

Henequen natural fiber-reinforced poly(butylene succinate) biocomposites were prepared through a resin microdroplet formation on a single fiber and also fabricated by a compression molding technique using chopped henequen fibers, surface-treated with electron beam irradiation (EBI) at various dosages. The effect of EBI treatment on the surface characteristics and dynamic mechanical properties of henequen fibers was investigated using SEM, XPS and DMA methods, respectively. Also, the interfacial behavior of biocomposites was explored through a single fiber microbonding test and fracture surface observations. The result indicates that the interfacial shear strength (IFSS) of biocomposites greatly depends on the EBI treatment level on the henequen fiber surface. This study also suggests that appropriate modification of natural fiber surfaces at an optimum EBI dosage significantly contributes to improving the interfacial properties of biocomposites.     

Novel Route to Control Interfacial Properties of Glass Fiber-Reinforced Polystyrene Composites via a Photo-Cross-Linkable Block Copolymer Coupling Agent

A diblock copolymer of polystyrene–block–poly(2-hydroxyethyl acrylate) (PS-b-PHEA) was synthesized via atom transfer radical polymerization (ATRP) and reacted with cinnamoyl chloride in triethylamine to yield PS-b-(PCEA-co-PHEA) copolymer with photo-cross-linkable poly(2-cinnamoylethyl acrylate) (PCEA) moieties. Then the triblock copolymer of polystyrene–block–poly(2-cinnamoylethyl acrylate-co-2-hydroxyethyl acrylate)–block–poly(γ-methacryloxypropyltrimethoxysilane) (PS-b-(PCEA-co-PHEA)-b-PMPS) was synthesized viaATRP from PS-b-(PCEA-co-PHEA) copolymer. Using as-prepared triblock copolymer as a macromolecular coupling agent to modify glass fibers, via microbond tests, the interfacial bond strength between pretreated glass fiber and polystyrene was compared before and after copolymer photo-crosslinking. The partially crosslinked block copolymer coupling agent greatly improved the interfacial adhesion of glass fiber-reinforced polystyrene.     

Cellulose-Based Natural Fiber Topography and the Interfacial Shear Strength of Henequen/Unsaturated Polyester Composites: Influence of Water and Alkali Treatments

In the present work, the effect of surface treatment methods on the henequen fiber topography and how the surface treatment influences the interfacial shear strength of henequen/unsaturated polyester composites were studied. Two different surface treatment methods were used: soaking method and ultrasonic method. Two different treatment media were used: normal tap water and sodium hydroxide. The result showed that the topography of henequen fiber surfaces was greatly changed, strongly depending on the treatment method and media used. It was demonstrated from the single fiber microbonding test result that the interfacial shear strength (IFSS) between the natural fibers and the matrix of henequen/unsaturated polyester composites was significantly improved by the surface treatments of henequen prior to composite preparation. The topological and interfacial results were quite consistent with each other.     

Effects of Regenerated Cellulose and Natural Fiber on Interfacial Adhesion,Rheology and Crystallization Property in ε-Polycaprolactone Compounds

Regenerated cellulose fiber (RN) and natural fiber (pine wood fiber (PW)) filled ε-polycaprolactone (PCL) compound, PCL/RN (90/05 and 75/25 wt%) and PCL/PW (90/05, 75/25 and 50/50 wt%), are investigated with regard to interfacial adhesion, rheological properties, morphology, nucleation and mechanical properties. The interfacial adhesion of the RN filled PCL compounds shows better values than that of the PW filled ones. As the concentration of the RN and the PW particles is increased, the dynamic viscosity, the crystallization temperature and the elongation modulus are increased; however, the elongation strain is decreased. The viscosity of the RN filled compounds is higher than that of the PW ones at the same loadings. Striking differences are observed in elongation yield stress measurements. As the concentration of the particles is increased, while the elongation yield stress of the RN compounds is significantly increased, that of the PW compounds does not show significant improvement. More spherulites are locally developed on the RN surface than on the PW surface. We conclude the interfacial adhesion of the RN surface with the PCL is better than that of the PW surface with the PCL.     

Hydrolytically Stable Interphase on Alumina and Glass Fibers via Hydrosilylation

The poor hydrolytic stability of silane interphase greatly limits the use of fiber reinforced composites (FRC) in demanding applications in which the FRC part is permanently exposed to a moist environment such as in prosthetic dentistry and orthodontics. To improve hydrolytic stability of the interphase between the matrix composed of a blend of triethyleneglycol dimethacrylate (TEGMA) and bisphenol A glycidylmethacrylate (Bis–GMA) monomers and glass or alumina oxide fibers, a two-step hydrosilylation procedure was employed. The process consisted of creating hydride intermediate on the fiber surface followed by hydrosilylation reaction attaching the unsaturated organic monomer (Bis–GMA) forming stable –Si–C bonds. Infrared spectroscopy (FTIR) confirmed formation of the hydride intermediate on the surface and then, attachment of the appropriate organic compound in the second step. The amount of deposited interphase and its stability was significantly enhanced compared to standard silanization treatment. Fracture surfaces were observed by scanning electron microscopy (SEM) before and after environmental exposure proving that the most stable interfacial bond was obtained with the two-step treated fibers. It was concluded that hydrosilylation provides a viable alternative to silanization for both glass and ceramic fibers in composites intended for applications requiring enhanced hydrolytic stability of the composite parts.     

Fixation of silane coupling agents to glass fiber in silane treatment process

Fixation of silane coupling agents to glass fiber was quantitatively determined using pyrolysis-GC/FT-IR to explore the formation of chemical-bonded and physisorbed silanes. The silane coupling agent used was N-phenyl-1-aminopropyltrimethoxysilane (AnPS). In silane treatment, E-glass fiber was dipped into acetic acid solution containing AnPS and was cured under different temperature and time. The fixation of silane was obtained by determining the amount of AnPS at the glass surface after and before washing the treated fiber with methanol. The silane fixation increased with decrease in the silane concentration, but it fell significantly below a lower silane concentration. The change of fixation in curing temperature gave an optimum temperature for the fixing. The dependence of curing time on the fixing ratio showed that the fixation was depressed below the curing temperature of 100°C. These results suggested that more than a specific amount of AnPS deposit on glass fiber was necessary to form silane networks fixed to glass fiber through siloxane bonds. The networks formation was interpreted in terms of the competitive reaction of the silanol group of silane to hydroxyl of glass fiber and to other silane molecules.