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.     

Effect of α-methyl styrene on curing behaviour and interfacial properties of glass fibre-reinforced vinyl ester resins

The curing behaviour of bismethacryloyl derivative of diglycidyl ether of bisphenol A (vinyl ester VE resin) containing styrene and α-methyl styrene (MS) as reactive diluents was studied. Delayed curing was observed in samples containing increasing proportions of MS. Interfacial shear stress of untreated as well as γ-methacryloyloxy-propyl trimethoxy silane (MTS) treated, glass fibre-reinforced VE resin composites were measured by single fibre technique. In comparison to untreated glass fibres, a 30 – 50% increase in interfacial shear stress was observed in composites based on MTS treated glass fibres. Addition of up to 5 wt.-% MS to VE resin did not affect the interfacial shear strength (ILSS). This behaviour was observed by using ILSS measurement of both glass fabric-reinforced composites as well as single fibre specimens. Further increase in MS to 15 wt.-% resulted in an increase in ILSS and bending stiffness as well as flexural strength.     

Verstärkte Thermoplaste – Theorie und Praxis

Reinforced thermoplastics are composites consisting of a viscoelastic plastics matrix of low strength and a material (mostly inorganic) which has a high strength and a high modulus of elasticity, showing purely elastic strain. Globular and fibrous particles can be used for reinforcing. In the first case, the reinforcing action is largely due to an isotropic reduction of the strainability of the thermoplastic. In the second, more important case, the fibres can also accumulate stress from the matrix. In both cases, the elastic and viscous components of strain are pushed closer together. In practice, irregularities in the orientation of the fibres and continually changing patterns of stress cannot be avoided. These give rise to difficulties in checking the theoretical treatment of thermoplastics reinforced with short fibres. The basic element itself, i.e., the individual fibre embedded in the matrix has several variants, i.e., the length of the fibre, the ratio of the fibre length to the diameter, the critical fibre length determined from the interfacial shear strength and fibre strength, and the tensile strength in the transverse direction.     

A Study of the Interphase Region in Carbon Fibre/Epoxy Composites using Dynamic Mechanical Thermal Analysis

We have examined the effect of fibre addition on the glass transition temperature (T_g) of two epoxy resin systems (an amine cured and an anhydride cured epoxy system) using dynamic mechanical thermal analysis (DMTA) and differential scanning calorimetry (DSC). The presence of fibres changes the glass transition temperature (T_g) of an anhydride cured epoxy resin but does not affect that of an amine cured epoxy. The data suggest that two counteracting mechanisms are responsible for these changes: firstly, the presence of fibres causes a restriction of the molecular motion in the resin system, and secondly, the presence of carboxyi and keto-enol groups on the fibre surface inhibit curing of the resin close to the fibre, i.e. in the interphase region. The former increases the T_g and is a long range effect whereas the latter decreases the T_g and is a localised phenomenon. Changes in the dynamic properties of the interphase region are only detected when the samples are loaded in the longitudinal direction and not in the transverse direction where bulk matrix properties dominate. Sizing the fibres before their incorporation into the epoxy resin eliminates the variation in interfacial properties arising from differences in fibre surface chemistry.     

A Study of the Pull‐Out Performance of PPTA Fibres in Composites of Ethylene‐Type Ionomer Matrices/PPTA Fibres

The mean frictional shear stresses of six ionomer resins and sized Kevlar fibre were determined from fibre pull‐out tests. A study of the failure mechanisms occurring during pull‐out revealed that fibre delamination and fibre resin adhesion were factors which increased the measured frictional shear stresses and that there was a definite grouping of high and low frictional shear stress values. The low frictional shear stress values were used to calculate the mean frictional shear stress values, τ_B, because these were uncomplicated by fibre delamination and fibre resin adhesion, since these factors (delamination and adhesion) are certainly not unexpected in an ionomer/Kevlar composite. From these shear stress values, it was determined that critical fibre lengths should be between 35 and 72 mm for the high tensile strength Kevlar fibres within an ionomer matrix, for the composite to be used effectively. The ratio of the debonding force (F_B) to the frictional shear force (F_F), θ, did not vary significantly with the lengths of the embedded reinforcing fibres. Both debonding and frictional forces indicate increasing trends with the interfacial contact areas. The ratio of the interfacial bonding strength (τ_B) to the frictional shear stress (τ_F), ϕ, for the resin PEA‐6 compared to the surface modified poly(p‐phenylene terephthalamide) (PPTA) fibre ranged from 2 to 24. These ratios were grouped into two, viz: those where ϕ > 11 and those with ϕ < 7. Using only the τ_F where ϕ > 11 provided a mean frictional shear stress of 0.94 MPa and a standard deviation, s, of 0.23 MPa (the number of test samples, n, was 9). This value is little different from the frictional shear stresses measured for sized PPTA (0.84 MPa). The decrease in the values of ϕ is attributed to the decrease in τ_B, due to the surface modification reaction, without necessarily affecting the frictional shear stress, τ_F.     

Experimental and numerical investigation into fatigue damage mechanisms in multifibre microcomposites

Abstract

Polarised light microscopy has been used to investigate the influence of stress level, interfibre spacing, and fibre–matrix adhesion on the fatigue micromechanisms in carbon–epoxy model composites consisting of a planar array of five intermediate modulus carbon fibres. It was found that an increase in fatigue stress results in an increase in the number of fibre breaks, a more coordinated fibre fracture pattern as a result of fibre–fibre interaction, and extensive interfacial damage. In addition, it was shown that a smaller interfibre spacing results in a higher level of fibre–fibre interaction. Finally, in the case of surface treated carbon fibres (good fibre–matrix adhesion), a more coordinated fibre failure pattern was observed owing to stronger fibre–fibre interaction, whereas in the case of untreated carbon fibres (poor fibre–matrix adhesion), extensive debonding was observed which resulted in a more random fibre failure pattern. Finally, the experimental results were validated by means of a three-dimensional finite element analysis.     

A Study of the Interphase Region in Carbon Fibre/Epoxy Composites using Dynamic Mechanical Thermal Analysis

We have examined the effect of fibre addition on the glass transition temperature (T _g ) of two epoxy resin systems (an amine cured and an anhydride cured epoxy system) using dynamic mechanical thermal analysis (DMTA) and differential scanning calorimetry (DSC). The presence of fibres changes the glass transition temperature (T _g ) of an anhydride cured epoxy resin but does not affect that of an amine cured epoxy. The data suggest that two counteracting mechanisms are responsible for these changes: firstly, the presence of fibres causes a restriction of the molecular motion in the resin system, and secondly, the presence of carboxyi and keto-enol groups on the fibre surface inhibit curing of the resin close to the fibre, i.e. in the interphase region. The former increases the T _g and is a long range effect whereas the latter decreases the T _g and is a localised phenomenon. Changes in the dynamic properties of the interphase region are only detected when the samples are loaded in the longitudinal direction and not in the transverse direction where bulk matrix properties dominate. Sizing the fibres before their incorporation into the epoxy resin eliminates the variation in interfacial properties arising from differences in fibre surface chemistry.     

The Effect of Low Power Nitrogen Plasma Treatment of Carbon Fibres on the Interfacial Shear Strength of Carbon Fibre/Epoxy Composites

Type II (high strength) carbon fibres have been given a low power nitrogen plasma treatment. It is shown that this plasma treatment has no effect on the fibre diameter, no detrimental effect on fibre strength and can significantly improve fibre/resin adhesion. It is proposed that this improvement is due to chemical interaction via amine/epoxy bonding at the edge sites together with the interaction of the epoxy with activated basal planes present on the fibre surface. This improvement is only achieved if the fibres are immersed in resin before being exposed to air. Exposing the treated fibres to air drastically reduces fibre/adhesion due to the adsorption of moisture from the environment. Heating these latter fibres in a vacuum at 130°C for one hour allows some recovery of the interfacial strength. It is also demonstrated that the interfacial shear strength falls dramatically when the nitrogen-containing functional groups are completely removed from the fibre surface.     

Influence of fibre content on the strength of carbon fibre reinforced HfC/SiC composites up to 2100 °C

The influence of carbon fibre content on the mechanical behaviour of HfC/SiC composites was investigated up to 2100 °C for specimens containing 40 or 55 vol% fibres. Silicon carbide was added as a sintering aid during hot pressing. Increasing the fibre content made infiltration more difficult, which resulted in higher porosity in the specimen with 55 vol% fibres. The room temperature flexural strength ranged from 340 to 380 MPa, and it increased to more than 400 MPa at 1800 °C due to stress relaxation. Increasing temperature was accompanied by a decrease in the slope of the load-displacement curve, indicating a decrease in elastic modulus, but plastic deformation was not observed below 2100 °C. At 2100 °C, the specimen containing a higher fibre content underwent significant deformation due to low interfacial strength between the fibre plies, retaining a strength at the proportional limit of 290 MPa and an ultimate strength of 520 MPa.     

The Effect of Low Power Nitrogen Plasma Treatment of Carbon Fibres on the Interfacial Shear Strength of Carbon Fibre/Epoxy Composites

Type II (high strength) carbon fibres have been given a low power nitrogen plasma treatment. It is shown that this plasma treatment has no effect on the fibre diameter, no detrimental effect on fibre strength and can significantly improve fibre/resin adhesion. It is proposed that this improvement is due to chemical interaction via amine/epoxy bonding at the edge sites together with the interaction of the epoxy with activated basal planes present on the fibre surface. This improvement is only achieved if the fibres are immersed in resin before being exposed to air. Exposing the treated fibres to air drastically reduces fibre/adhesion due to the adsorption of moisture from the environment. Heating these latter fibres in a vacuum at 130°C for one hour allows some recovery of the interfacial strength. It is also demonstrated that the interfacial shear strength falls dramatically when the nitrogen-containing functional groups are completely removed from the fibre surface.     

Experimental characterization of interfacial adhesion of an optical fiber embedded in a composite material

The efficiency of an optical sensor embedded in a composite structure strongly depends on the interfacial adhesion between the optical fiber coating and the surrounding solid material. The present paper reports on the study of the interfacial adhesion of an optical fiber embedded in a composite material. A simple system composed of optical fibers embedded in an epoxy vinylester resin was first studied to evaluate the influence of embedded length, curing temperature and curing time. Pull-out tests on optical fibers bonded in epoxy vinylester/glass fiber composite material were carried out to measure the effect of glass concentration on the fiber bonding. The pull-out results showed no effect of both embedded length and curing temperature. However, an increase of the interfacial debonding stress is reported with increased curing time. For the optical fiber/composite system, a linear evolution of interfacial debonding stress with increasing glass fiber concentration is reported.     

Der einfluß von faseroberflächen auf die matrixhärtung bei faserverbundwerkstoffen

The influence of extraction of reinforced fibres on surface properties and the curing reaction of epoxy resin matrix in composites were investigated. With increasing fibre surface polarity, as the result of the extraction, the resin wettability was improved and the reaction rate of curing of the epoxy resin matrix increased. The wettability and the reaction rate oppositely decreased with decreasing fibre surface polarity.     

Experimental Observations of Frictional Heating in Fiber-Reinforced Ceramics

The influence of fatigue loading history and microstructural damage on the magnitude of frictional heating and interfacial shear stress in a unidirectional SiC fiber/calcium aluminosilicate matrix composite was investigated. The extent of frictional heating was found to depend upon loading frequency, stress range, and average matrix crack spacing. The temperature rise attained during fatigue can be significant. For example, the temperature rise exceeded 100 K during fatigue at 75 Hz between stress limits of 220 and 10 MPa. Analysis of the frictional heating data indicates that the interfacial shear stress undergoes an initially rapid decrease during the initial stages of fatigue loading: from an initial value over 20 MPa, to approximately 5 MPa after 25 000 cycles. Over the range of 5 to 25 Hz, the interfacial shear stress was not significantly influenced by loading frequency. The implications of frictional heating in fiber-reinforced ceramics are also discussed.     

Characterization of stem phoenix fibres as potential reinforcement of self compacting mortar

In this work, we investigate the effect of different treatment process on stem Phoenix fibres. Underwent different surface modification methods such as alkali treatment with concentration of 10%, epoxy treatment, and combine both of procedures preceded. The treated fibres reinforcement was used in self compacting mortar (SCM) with a length of 20 ± 2 mm and different proportions (0.5, 1, 1.5, 2, 2.5 and 3%) by mortar volume. Flowability of fresh modified self compacting mortar is carried out using two main techniques, including flow table experiments and mini V-funnel flow test. Mechanical performance is derived from bending and compression testing at different curing times. Results show a positive effect of fibre treatment on the rheological and mechanical performances of self compacting mortars. Results show also that optimal formulations need to use fibres treated with (10% NaOH + epoxy resin) by an amount of 3%. These formulations reveal superior mechanical performance compared to all tested mixes after 28 curing days, by 20% in compressive strength and 40% of tensile strength.     

Microstructure control of highly oriented short carbon fibres in SiC matrix composites fabricated by direct ink writing

A novel method is proposed for fabricating highly oriented carbon fibre reinforced SiC ceramic composites (C_f/SiC) by direct ink writing (DIW). For the first time, the control of carbon fibers’ orientation in DIW was studied by numerical simulation. An interfacial layer was prepared by chemical vapor infiltration (CVI). The microstructure and phase composition of C_f/SiC were studied by scanning electron microscopy and X-ray diffraction, respectively. The results showed that fibers of different interfacial thicknesses could be obtained effectively by varying the CVI time. The breakage of short fibres remarkably improved the fracture toughness of the parts. The specimens showed excellent mechanical properties with bending strength of 274 ± 13 MPa and fracture toughness of 5.82 ± 0.25 MPa m^1/2. This method could be extended to the preparation of other resin and ceramic composites.     

Compressive behaviour of rigid rod polymer fibres and their adhesion to composite matrixes

Abstract

The deformation behaviour of the new high performance polymer fibres, poly(p-phenylene benzobisoxazole) (PBO) and polypyridobisimidazole (PIPD) and their adhesion to an epoxy composite matrix have been investigated. Both fibres give well defined Raman spectra, and the deformation micromechanics of PBO and PIPD single fibres and composites were studied from stress induced Raman band shifts. Single fibre stress-strain curves were determined in both tension and compression, thus providing an estimate of the compressive strength of these fibres. It was found that the PIPD fibre has a higher compressive strength (~1 GPa) than PBO (~0·3 GPa) and other high performance polymer fibres, because hydrogen bond formation is possible between PIPD molecules. It has been shown that when PBO and PIPD fibres are incorporated into an epoxy resin matrix, the resulting composites show very different interfacial failure mechanisms. The fibre strain distribution in the PBO-epoxy composites follows that predicted by the full bonding, shear lag model at low matrix strains, but deviations occur at higher matrix strains due to debonding at the fibre/matrix interface. For PIPD-epoxy composites, however, no debonding was observed before fibre fragmentation, indicating better adhesion than for PBO as a result of reactive groups on the PIPD fibre surface.     

Graphite Fibre-Epoxy Matrix Interface Interactions

Studies of fibre-epoxy resin matrix model composites show that the “tensile debond” test is not applicable to carbon or graphite fibres. Fibre fracture occurs under the compression strains involved relieving interface stresses and precluding subsequent debond. Calculated minimum bond strengths for pitch-based graphite fibres are similar to results for boron and glass fibres. Interfacial failure is obtained with the “shear debond” test for low and intermediate modulus graphite fibres, but compression fracture also occurs first with high modulus fibres. Pitch-based graphite fibres show a decreasing adhesive interaction with epoxy resin the more oriented the fibre, but results compare favorably with those of other fibres. Surface characterisation shows that all pitch-based graphite fibres exhibit a surface-oriented skin, although surface roughness increases with fibre modulus. The fibres all exhibit similar apparent surface energy characteristics which suggests that wettability does not play a significant role in determining interfacial bond strengths.     

1-己烯共聚拉伸缠绕膜专用树脂的开发

开发了一种1-己烯共聚拉伸缠绕膜专用树脂DFDA-9030。采用专用催化剂,优化工艺参数,在气相法流化床工艺的聚乙烯装置上实现了DFDA-9030的稳定生产,产品具有优良的耐穿刺和拉伸性能,落镖冲击强度达到110 g,拉伸屈服应力达到11 MPa,拉伸断裂应力达到28 MPa。采用该产品加工的薄膜横向、纵向拉伸强度均衡,能够满足缠绕包装膜的加工及使用要求。     

Surface modification of boron fibres for improved strength in composite materials

When boron fibres are combined with an organic matrix, such as an epoxy resin, a high-performance composite structure is created. This study investigates the surface chemistry of plasma- and organosilane-treated boron fibres with the key aim to improving the adhesion properties between the boron fibre and the epoxy matrix. Optimisation of this interfacial region plays a critical role in influencing the mechanical behaviour of composite materials and has considerable industrial applications in the aerospace and manufacturing industries. The surface chemistry of a model boron surface and boron fibres was monitored using a combination of X-ray photoelectron spectroscopy (XPS) and time-of-flight secondary ion mass spectrometry (TOF-SIMS). Initial investigation of the as-received fibres showed the presence of silicone contamination on the fibre surface, which would affect adhesion. Removal of this contaminant through solvent cleaning and plasma oxidation provided an ideal surface for attachment of the organosilane adhesion promoter. A model for the interaction of the organosilane with a boron surface is proposed. The pull-out strength of boron fibres, with different surface treatments, embedded in the epoxy resin was measured using a custom designed adhesiometer. Compared with as-received boron fibres, a 6-fold improvement in the apparent interfacial shear strength was achieved for the organosilane treated fibres. Optical microscopy was used to determine the failure mechanisms between the fibre and epoxy resin. Typically, as the surface treatment improved adhesion, the locus of failure changed from the boron–epoxy interface to failure within the epoxy and ultimately fibre breakage.     

Stress Transfer Function for Interface Assessment in Composites with Plasma Copolymer Functionalized Carbon Fibres

Radio-frequency-induced plasma copolymerization of acrylic acid/1,7-octadiene was used to produce a range of functionalized plasma copolymer coatings with controlled degree of adhesion. The single-fibre fragmentation test was used to characterize the adhesion of plasma copolymer coated fibres to epoxy resin. The cumulative stress transfer function (CSTF) and Kelly-Tyson approaches were used to evaluate the degree of adhesion. By continuous monitoring of the fragmentation process, it was found that the mechanical performance of a composite material could be evaluated using the CSTF methodology at strain well below saturation. The degree of debonding was a good measure of relative interface/interphase adhesive strength. The trend in the CSTF is consistent with the propagation of interfacial debonds during the test. For a completely debonded fibre a normalized CSTF value, referred as stress transfer efficiency (STE), was found to provide a more consistent analysis that was able to differentiate between fibres with similar degrees of debonding. The calculated values of interfacial shear strength (IFSS) were only valid for a fully debonded fibre (1,7-octadiene plasma homopolymer coating) where the assumption of a constant shear stress, as in the Kelly-Tyson model, applied. However, IFSS did not provide the same ranking. Where debonding does not occur, the stress transfer efficiency also provides a sensitive measure of the interface/interphase performance. Improved adhesion over the untreated-unsized carbon fibre was observed for both of the plasma copolymer-coated and commercially treated carbon fibres. Since there is a concentration dependence of carboxyl groups on adhesion, the mechanism appears to relate to covalent bond formation with the epoxy group. Plasma copolymer coatings on carbon fibres also causes an increased tensile strength and Weibull modulus.