Effect of silane treatment on the Curaua fibre/polyester interface

ABSTRACT

Good adhesion at fibre/matrix interface of lignocellulosic fibres is crucial when substituting synthetic fibres in polymer composites. The great variability presented by those fibres requires diverse characterisation studies for better insights on fibre surface treatments and resin systems interactions. In this work, Curaua fibres were treated using silane coupling agents to improve their interfacial properties with polyester. The fibres were pre-treated using 4?wt% solution of NaOH and then treated with 5?wt% solution of (3-aminopropyl) trimethoxysilane (AMPTS) or triethoxymethylsilane (TEMS). Characterisation of the treated fibres was carried out using infrared spectroscopy, X-ray diffraction, thermogravimetric analysis and scanning electron microscopy. Fibre wettability and adhesion towards polyester was investigated using contact angle measurements and pull-out tests, respectively. The AMPTS treatment yielded a significant result of 20.2?MPa in interfacial shear strength (≈2.5 times that of the untreated fibre), attributed to the increase in availability of binding sites with polyester.     

Mechanical properties of maleic anhydride treated jute fibre/polypropylene composites

Abstract

The effect of maleic anhydride (MA) modification of jute fibre on the mechanical properties of jute/polypropylene (PP) composites was studied. Jute fibre, an environmental friendly, low-density renewable material was chemically modified with MA before the incorporation with PP to improve interfacial adhesion between them. Fourier transform infrared (FTIR) study showed that the C=C groups of MA attached to jute cellulose reacted with the PP matrix. Jute fibre/PP composite treated with MA displayed higher Young's modulus and dynamic storage modulus owing to the enhanced interfacial adhesion between the fibre and PP matrix. A scanning electron microscopy (SEM) study showed evidence of the enhanced adhesion and bridging in the interfacial region of the composite as the result of MA modification of jute fibre.     

Effect of alkali treatment on properties of unidirectional isora fibre reinforced epoxy composites

Abstract

Unidirectional isora fibre reinforced epoxy composites were prepared by compression moulding. Isora is a natural bast fibre separated from Helicteres isora plant by retting process. The effect of alkali treatment on the properties of the fibre was studied by scanning electron microscopy (SEM), IR, thermogravimetric analysis (TGA) and differential scanning calorimetry (DSC). Mechanical properties such as tensile strength, Young's modulus, flexural strength, flexural modulus and impact strength of the composites containing untreated and alkali treated fibres have been studied as a function of fibre loading. The optimum fibre loading for tensile properties of the untreated fibre composite was found to be 49% by volume and for flexural properties the loading was optimised at ～45%. Impact strength of the composite increased with increase in fibre loading and remained constant at a fibre loading of 54·5%. Alkali treated fibre composite showed improved thermal and mechanical properties compared to untreated fibre composite. From dynamic mechanical analysis (DMA) studies it was observed that the alkali treated fibre composites have higher E' and low tan δ maximum values compared to untreated fibre composites. From swelling studies in methyl ethyl ketone it was observed that the mole percentage of uptake of the solvent by the treated fibre composites is less than that by the untreated fibre composites. From these results it can be concluded that in composites containing alkalised fibres there is enhanced interfacial adhesion between the fibre and the matrix leading to better properties, compared to untreated fibre composites.     

Experimental techniques for measuring fibre/matrix interfacial bond shear strength

Experimental techniques for directly obtaining some measure of the shear strength of the interfacial bond between fibrous reinforcements and cemetitious matrices are reviewed. These techniques— essentially single- or multiple-fibre pull-out out tests — are classified according to specimen type and configuration and are then evaluated and compared using a set of criteria adapted by the author for this purpose. None of the techniques are found to satisfy completely all of the criteria, but several probably could be modified to do so. The objective of this state-of-the-art review is to provide a basis for discussion of the possible future standardization of a test technique for determining fibre/matrix interfacial bond shear strength in cementitious matrix composite specimens.     

The effect of matrix composition on fibre/matrix interfacial bond shear strength in fibre-reinforced mortar

The effects of factors associated with the composition of the matrix, i.e. curing conditions and time and mix proportions, on the shear strength of the interfacial bond between steel fibres and a cementitious mortar matrix have been examined experimentally using a single-fibre pull-out test technique. The experimental results indicate that bond shear strength increases significantly with an increase in matrix curing time and, for specimens with the fibre axis perpendicular to the direction of casting and compaction of the matrix, with a decrease in the proportion of water by weight in the matrix mortar. This latter effect is attributed to bleed water gain under the embedded fibre, as it is not observed in specimens with the fibre axis parallel to the direction of casting and compaction of the matrix. Furthermore, the results indicate that there is no correlation between interfacial bond shear strength and matrix mortar compressive strength.     

Flax fibre reinforced polylactic acid composites with amphiphilic additives

Abstract

Biocomposites were successfully prepared by reinforcing polylactic acid with flax fibres (PF). To improve the interfacial adhesion between the matrix and the fibres, amphiphilic compounds as additives were introduced. Structural and thermal characterisations of the PF were performed by Fourier transform infrared spectra, differential scanning calorimetry and thermogravimetric analysis. The interfacial adhesion between the fibres and the matrix was visually assessed from the SEM images of fractured specimens. Dynamic mechanicalthermal analysis was performed to evaluate the damping behaviour of the composites and thereby to interpret the interfacial adhesion between fibres and the matrix. It was observed that in the case of mandelic acid, particles/spheres were generated, resulting in effective stress transfer from the matrix resins to flax fibres, thereby increasing the storage modulus and impact strength of the composites. Mechanical properties and the water uptake of the composites with amphiphilic additives have also been reported.     

Characterising the time-dependant behaviour on the single fibre level of SHCC: Part 2: The rate effects on fibre pull-out tests

This paper is the second part of a two paper series about the time-dependant behaviour of Strain Hardening Cement-based Composite (SHCC) on the single fibre level. Having dealt with mechanisms of creep in SHCC in the first part, this paper reports single fibre pull-out tests that were done to investigate the effect of the pull-out rate on the mechanical response of the interface between the fibre and the matrix. It was found that not only the pull-out resistance increased with an increase of the pull-out rate but the probability of fibre rupture during pull-out as well. Another important finding was that the interfacial shear resistance and slip-hardening coefficient are not only dependant on the pull-out rate, but also the embedment length.     

Evaluation of micromechanical properties of advanced polymer composites

Abstract

A new methodology for the prediction of stress transfer in the single fibre fragmentation test, known as the plasticity effect model, has been used. A new data reduction technique, known as the cumulative stress transfer function (CSTF technique), which takes the dierent damage events observed during the fragmentation test into account, was used to obtain a measure of fibre–matrix adhesion from the fragmentation test. The effect of carbon fibre surface treatment on the interface of microcomposite properties was studied using the CSTF technique. It was found that the CSTF technique could predict fibre–matrix adhesion in a single fibre fragmentation test more accurately than the conventional data reduction technique. In this study, a commercial resin system was used to produce fragmentation test specimens.     

The Effect of Surface Treatment on the Strength and Adhesion Characteristics of Phoenix dactylifera-L(Date Palm) Fibers

ABSTRACT

There is a growing interest in the use of natural/bio-fibers as reinforcing components for thermoplastics and thermosets. However, they do suffer from a few limitations, such as lower compatibility with relatively hydrophobic polymer matrixes. Thus, improvement of the interface and interphase interactions in natural fiber–polyester composites is essential. In this research date palm (Phoenix dactylifera-L) fibers were modified by surface treatment using chemical method in order to improve their adhesion to polyester matrixes. Alkaline treatment, as an example of dissolution and treatment with silane coupling agents were performed. Furthermore, a combination treatment of alkaline and silane coupling agents was also carried out. Fiber modifications were monitored by Scanning Electron Microscopy (SEM). In addition to that, the improvement of adhesion and strength between date palm–modified fibers and polyester matrix was investigated by single filament pull-out test as well as tensile tests. It was found, from interfacial shear strength values, that substantial improvements in fiber-matrix compatibility have been achieved. According to single filament pull-out test results, interfacial shear strength increased for all treated fibers as compared to non-treated fibers. Particularly, combination of alkaline and silane coupling agents resulted in substantial adhesion improvement to the polyester matrix in comparison to the untreated fibers and fibers treated by alkaline and silane methods only.     

Indirect estimation of fiber/polymer bond strength and interfacial friction from maximum load values recorded in the microbond and pull-out tests. Part I: local bond strength

The techniques aimed at adhesion strength measurement between reinforcing fibers and polymer matrices (the pull-out and microbond tests) involve the measurement of the force, F _max, required to pull out a fiber whose end is embedded in the matrix. Then, this maximum force value is used to calculate such interfacial parameters as the apparent bond strength, τ_app, and the local interfacial shear strength (IFSS), τ_d. However, it has been demonstrated that the F _max value is influenced by interfacial friction in already debonded regions, and, therefore, these parameters are not purely 'adhesional' but depend, in an intricate way, on interfacial adhesion and friction. In the last few years, several techniques for separate determination of adhesion and friction in micromechanical tests have been developed, but their experimental realization is rather complicated, because they require an accurate value of the external load at the moment of crack initiation. We have developed a new technique which uses the relationship between the maximum force and the embedded length ('scale factor') to separately measure fiber-matrix interfacial adhesion and friction. Using the equation for the current crack length as a function of the applied load, based on a stress criterion of interfacial debonding, we modeled the pull-out and microbond experiments and obtained the maximum force value versus the embedded length. By varying τ_d and interfacial friction, τ_f, to fit experimental plots, both interfacial parameters were estimated. The micromechanical tests were modeled for three types of specimen geometries (cylindrical specimens, spherical droplets, and matrix hemispheres in the pull-out test) with different levels of residual thermal stresses and interfacial friction. The effect of all these factors on the experimental results is discussed, and the importance of specimen geometry is demonstrated. One of the most interesting results is that the 'ultimate' IFSS (the limiting τ_app as the embedded length tends to zero) is not always equal to the 'local' bond strength.     

Effect of nitric acid surface treatment on tensile and tribological properties of thermoplastic polyimide composite filled with carbon fibre

Abstract

Polyacrylonitrile based carbon fibres were submitted to nitric acid oxidation treatments to improve the interfacial adhesion of the carbon fibre reinforced polyimide (CF/PI) composite. The carbon fibre surfaces were characterised by X-ray photoelectron spectroscopy. Nitric acid oxidation not only affects the oxygen concentration, but also produces an appreciable change in the nature of the chemical functions, namely the conversion of hydroxy type oxygen into carboxyl functions. Nitrogen concentration of nitric acid oxidation treated carbon fibre is ～1·2 times higher compared with untreated one. The mechanical and tribological properties of the CF/PI composites treated with nitric acid oxidation were investigated. Results showed that the tensile strength of the CF/PI composites improved remarkably due to nitric acid treatment along with enhancement in friction and wear performance.     

Experimental results of a pull-out test performed with single- and multi-fiber samples

Widely-used methods for characterising the fibre/matrix interface in polymeric composites are the fragmentation test and the droplet test as a special kind of the single-fibre pull-out test. A severe disadvantage of these tests is that non-realistic model samples are investigated which contain only one fibre in the matrix. In order to obtain data about the effect of the different residual stress situations for fibres in such samples and in composites, pull-out tests of E-glass fibres in polystyrene and polycarbonate are performed using samples, where the investigated fibre is surrounded by 0 to 3 other near fibres. Neighbouring fibres can increase the pull-out forces by a factor of three and the interfacial toughness by a factor of four. This has to be taken into account, if the tests are performed not only for comparison reasons but for measuring interface properties.     

EXPERIMENTAL RESULTS OF A PULL-OUT TEST PERFORMED WITH SINGLE- AND MULTI-FIBER SAMPLES

Widely-used methods for characterising the fibre/matrix interface in polymeric composites are the fragmentation test and the droplet test as a special kind of the single-fibre pull-out test. A severe disadvantage of these tests is that non-realistic model samples are investigated which contain only one fibre in the matrix. In order to obtain data about the effect of the different residual stress situations for fibres in such samples and in composites, pull-out tests of E-glass fibres in polystyrene and polycarbonate are performed using samples, where the investigated fibre is surrounded by 0 to 3 other near fibres. Neighbouring fibres can increase the pull-out forces by a factor of three and the interfacial toughness by a factor of four. This has to be taken into account, if the tests are performed not only for comparison reasons but for measuring interface properties.     

Curing Characteristics and Mechanical Properties of Oil Palm Wood Flour Reinforced Epoxidized Natural Rubber Composites

Abstract

The paper reports on the curing characteristics and mechanical properties of oil palm wood flour (OPWF) reinforced epoxidized natural rubber (ENR) composites. Three sizes of OPWF at different filler loadings were compounded with a two roll mill. The cure (t ₉₀) and scorch times of all filler size decrease with increasing OPWF loading. Increasing OPWF loading in ENR compound resulted in reduction of tensile strength and elongation at break but increased tensile modulus, tear strength and hardness. The composites filled with smaller OPWF size showed higher tensile strength, tensile modulus and tear strength. Scanning electron microscope (SEM) micrographs showed that at lower filler loading the fracture of composites occurred mainly due to the breakage of fibre with minimum pull-out of fibres from the matrix. However as the filler loading is increased, the fibre pull-out became very prominent due to the lack of adhesion between fibre and rubber matrix.     

Interfacial adhesion between embedded fibre optic sensors and epoxy matrix in composites

Fibre optic (FO) sensors are becoming increasingly popular for different applications in structural monitoring. Among their excellent properties, a strong interest for this type of sensors are represented by the possibility of embedding FOs inside composite components. In this case, one of the factors that significantly influence the efficiency of the whole Structural Health Monitoring (SHM) system is the interfacial adhesion between FO sensors and the host material. The main objective of this work is to investigate the interfacial adhesion between embedded fibre optic sensors and epoxy matrix to find the best type of optical fibre to be used in epoxy matrices to produce smart composites. Four types of optical fibres with different diameters and coatings (i.e. polyimide, polyacrylate and ormoceramic) were used. Pull-out tests were carried out and different methods were used to obtain the composite/optical fibre interfacial properties. Finally, an optical microscopy and Scanning Electron Microscopy (SEM) analysis were performed to characterize the fibre/matrix interfaces. It was found that the optical fibre that presented the highest energy required for interface rupture and, consequently, less invasiveness to the host material was the ormoceramic fibre with the smallest diameter.     

Finite element analysis of load transfer at a fibre–matrix interface during pull-out loading

Load transfer ability of the fibre–matrix interface is well known to mainly control the mechanical behaviour of fibre-reinforced materials. This load transfer phenomenon is of great importance in dentistry when a post is used for fixing a ceramic crown on the tooth. The pull-out test has been well accepted as the most important micromechanical test for evaluating the interaction properties between the fibre and matrix. In this study, a finite element model is developed to analyse the pull-out process of a steel fibre from an epoxy matrix. Based on the pull-out force–displacement curves, developed in our previous experimental work, specific load transfer laws at the fibre–matrix interface have been proposed for each stage of the pull-out process, i.e., before and after fibre–matrix debonding. Predicted initial extraction forces for different implantation lengths were fitted to experimental values and an initial interference fit of 4 μm was determined. An interfacial shear strength of 21 MPa was then determined by fitting the predicted debonding forces for different implantation lengths to the experimental values. According to the load transfer laws considered, analysis of the interfacial shear stress indicates that fibre–matrix debonding initiates simultaneously at both the lower and upper extremities of the interface.     

Modelling method based on idealised fibre bundles

Abstract

In the fibrous structures such as textiles and composites there are fibre assemblies exhibiting statistical bundle like behaviour. This paper presents a modelling method and software FibreSpace, based on a system of structuralised statistical fibre bundles, so called fibre bundle cells. These fibre bundle cells introduced before represent different idealised and typified fibre properties such as fibre shape, state of deformation, gripping as a connection with the vicinity, and the characteristic of force-transmitting and damage. With the help of the weighted parallel connection of the fibre bundle cells the mechanical behaviour and the damage process of real fibrous systems can be modelled as well as some structural properties or the strength data of single fibres can be determined by a fibre bundle cells model identified on the basis of measurements. The applicability of the fibre bundle cells method and modelling program developed is demonstrated by modelling the load and damage process of real textile structures and unidirectional composites during tensile or flexural test.     

The effect of fibre sizing and compatibilizer of polypropylene/poly(butylene terephthalate) blends on the mechanical and interphase properties of basalt fibre reinforced composites

The effect of basalt fibre sizing on the mechanical and interphase properties of fibre‐reinforced composites was studied. Two different chemical preparations of the fibre surface (PBT‐compliant and PP‐compliant) were used. The polymer matrix was prepared from polypropylene/poly(butylene terephthalate) (PP/PBT) immiscible polymer blend and the effect of different compatibilizers on the composite properties was evaluated. SEM hints at improved fibre adhesion to the polymer matrix when a PP‐compliant sizing is applied. SEM also reveals improved compatibilization effects when block copolymer instead of multiblock copolymer is used for the PP/PBT blend preparation. The pull‐out test was applied to quantitatively evaluate the interface adhesion between the fibres and matrices. It showed a high value of the interfacial shear strength between basalt fibres modified with PP‐compliant sizing and polymer blend compatibilized by block copolymer, thus confirming good adhesion. One possible explanation of such good mechanical properties can be related to the chemical interactions between functional groups, mainly maleic anhydride on basalt fibres and the polyolefin component (PP) of the polymer matrix. © 2017 Society of Chemical Industry     

Autogenous healing of fibre/matrix interfacial bond in fibre-reinforced mortar

Autogenous or self-healing of the interfacial bond between steel fibres and a cementitious mortar matrix has been examined experimentally using water-cured, single-fibre pull-out specimens. The test results indicate that the extent of the interfacial bond healing which occurs is greater than that observed for fractured plain mortar or concrete similarly cured.     

Effect of hygrothermal conditioning on the energy release rate and failure mechanism of metal only adherend-glass fibre prepreg co-cured single lap joints

Abstract

Fibre-reinforced composite materials are extensively used in repair and rehabilitation of oil and gas metal infrastructures which are largely exposed to water and hydrocarbon. An important aspect to this is applying adequate surface preparation to the metal to ensure a durable bond between the composite and metal substrate. In this paper, mild steel surface was prepared using grit blasting and single lap joint (SLJ) test specimens were manufactured and tested to investigate the adhesion in terms of total energy release rate (G_T) of the interface between mild steel adherend and glass fibre prepreg. An out-of-water usable epoxy resin primer was incorporated to join mild steel adherend with glass fibre prepreg by curing at a temperature of 55 °C for 48 h. Upon durability testing of the SLJ specimens using hygrothermal conditioning at a temperature of 55 °C for 1000 h, the experimental G_T values were seen to reduce significantly. Comparatively lower amount of cohesive failure and increased amount of swelling or delamination of the adhesive was observed for conditioned SLJ specimens when compared to controlled SLJ specimens. Furthermore, the experimental G_T values were found to correlate well with an analytical adhesive interface model.