XPS and AFM Study of Interaction of Organosilane and Sizing with E-Glass Fibre Surface

Organosilanes are often used in commercial sizings for glass fibres to provide wettability with the resin and promote strong interfacial adhesion to the matrix in a fibre reinforced polymer composite. The silane treatment is introduced as part of a complex deposition from an aqueous emulsion immediately at the spinaret and determines the optimum properties of the cured composite. To understand the interaction of organosilanes contained in sizings for glass surfaces, XPS was used to investigate the adsorption of γ-aminopropyltriethoxysilane (APS) from a simple sizing system containing a polyurethane (PU) film former. It has been found that both APS and the sizing (containing APS and PU) deposits on E-glass fibre surfaces contained components of differing hydrolytic stability. The differences observed in the AFM images of APS coated E-glass fibres before and after water extraction also confirmed that the APS deposit contained components with different water solubility.     

XPS analysis of the coverage and composition of coatings on glass fibres

For a fundamental approach to glass fibres for composite applications, it is essential to develop efficient methods to analyse the composition and distribution of the sizing layer on the glass filaments. We have been investigating the use of X-ray photoelectron spectroscopy (XPS) as a tool for the rapid characterization of the sizing and interphase in glass fibre reinforcements. In this report we present and discuss a model, based on a patchy sizing overlayer hypothesis, to assist the data reduction of XPS spectra from glass fibres coated with organic sizings. We show how plots of atomic ratios can be used to estimate the surface coverage of the sizing on glass fibres and to obtain information on the stoichiometry of the sizing. The results generated using this model are in good agreement with previously published data. Using this model, we show that XPS results combined with the weight fraction of the sizing give a quantitative value for the coverage of the fibre surface by the sizing.     

A tof sims study of the incorporation of aluminium into the silane coating on e-glass fibres

Time-of-Flight Secondary Ion Mass Spectrometry (TOF SIMS) in static and scanning mode has been used to study the modification of E-glass fibre surfaces with the silane coupling agent, g-aminopropyltriethoxysilane (APS). Subsequent treatment with the diglycidyl ether of bisphenol S (DGEBS) has been used to simulate the interface in a fibre composite. The formation of chemical bonds between the glass surface, the silane deposit and the resin are discussed. The most important observation is confirmation that aluminium from the glass surface is incorporated integrally into the APS silane coating. On treatment with DGEBS the aluminium signal can still be detected uniformly within the reaction product with the APS deposit.     

Prospect of nanoscale interphase evaluation to predict composite properties

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

Wetting kinetics and adhesion strength between polypropylene melt and glass fibre: influence of chemical reactivity and fibre roughness

A systematic experimental investigation with the purpose of quantifying the effect of the interactions between non-polar (unmodified) and polar (modified) polypropylene melts and treated fibre surfaces during wetting has been performed. The glass fibres were sized by aminosilane (γ-APS), γ-APS/polyurethane film former (γ-APS/PU) and γ-APS/polypropylene film former (γ-APS/ PP). Unsized fibres were used for comparison and were also coated with an azidosilane layer. Zeta potential and contact angle measurements were employed to investigate the surface properties of the treated glass fibres. The surface roughness was characterised using both atomic force microscopy and scanning electron microscopy. A method based on axisymmetric drop shape analysis was employed to determine the surface tension of the polymer melt. The wetting of the fibres by the polymer melt was investigated using the Wilhelmy balance technique. The wetting kinetics was different for different fibre surface treatments. The chemically reactive system based on azidosilane showed a better wetting than the other systems. The aminosilane/polypropylene film former (γ-APS/PP) treated fibre was also characterised by a fast wetting, most probably due to the physical similarity between the polymer and the fibre sizing and, thus, probable compatibility. In the receding case the differences between the reactive systems were smaller than they were for the advancing case. Higher adhesion tension calculated from the wetting measurements correlated well with higher adhesion strength determined from single fibre pull-out tests.     

Swelling and dissolution rates of glass fiber sizings in matrix resin via micro-dielectrometry

Complex fiber-matrix interactions occur in the processing of glass fiber reinforced polymeric composites, because of the proprietary, complex composition of commercial sizings applied to the glass fiber surface. Research involving a vinyl ester resin system and three model commercial glass fiber sizings, having varying levels of solubility in the resin, has shown that micro-dielectrometry can provide important information about interactions and may be useful as a tool in optimizing sizing-matrix resin interactions. Two distinct types of interactions may be monitored by micro-dielectrometry: The initial resin swelling of the sizing, as well as the dissolution of the sizing into the resin. An estimate of the times associated with swelling and dissolution of the sizing into the matrix resin can be made from micro-dielectric measurements to optimize composite processing.     

Microstructure of interface between fibre and matrix in 10-year aged GRC modified by calcium sulfoaluminate cement

Time-dependent property changes in glass fibre reinforced cement (GRC) mainly result from a combination of the alkalinity of the matrix and densification of the matrix (e.g. due to calcium hydroxide precipitation) within and around the glass fibre strands. The microstructure of the interface between matrix and fibres in GRC has a significant impact on its durability. This paper describes a study of two GRC formulations (with OPC, and OPC plus calcium sulfoaluminate based matrices) aged for 10 years at 25 °C. Thin-section petrography (TSP) and SEM are used to compare the microstructure of both polished surfaces and fractured surfaces. The aged OPC/GRC demonstrates significantly brittle behaviour with substantial densification of C–S–H/CH intermixture occurring around glass fibres. In contrary, the aged composite made with the OPC plus calcium sulfoaluminate shows greatly retained toughness, accompanied by considerably flexible interfacial and interfilamentary areas around the glass fibres.     

Application of the surface free energy concept in polymer processing

The surface characteristics of variously treated carbon and glass fibres have been determined by contact angle measurements (using a capillary rise technique), inverse gas chromatography, and zeta potential measurements. The contact angles of water and methylene iodide were used to calculate the dispersive and non-dispersive components of the fibre surface free energy by applying the geometric mean approach, and the approach by Fowkes to estimate the acid-base term of the thermodynamic work of adhesion. The results obtained correlate with those of inverse gas chromatographic and zeta potential measurements. The non-polar surface character of the carbon fibre can be altered by oxidizing, or finishing the fibres with an epoxy resin. The acid-base term of the thermodynamic work of adhesion, W^ab _a, and the non-dispersive component of the surface free energy, γ^p _s, are increased drastically by these treatments. Treatment of the 'high-energy' glass fibre surface with an aminosilane results in a relatively low surface free energy with basic surface groups. When epoxy dispersions were used for sizing the glass fibres, the surface free energy increased without changing the basic surface character. A direct correlation between the surface-energetic properties of the fibres and the mechanical behaviour of the fibre-reinforced polyamide composites was not generally found.     

Functional interphases with multi-walled carbon nanotubes in glass fibre/epoxy composites

The interphase between reinforcing fibre and matrix is a controlling element in composite performance. We deposited multi-walled carbon nanotubes (MWCNTs) onto electrically insulating glass fibre surfaces leading to the formation of semiconductive MWCNT-glass fibres and in turn multifunctional fibre/polymer interphases. The deposition process of MWCNTs onto glass fibre surfaces involved both electrophoretic deposition (EPD) and conventional dip coating methods. The EPD coating method produces a more homogeneous and continuous nanotube distribution on the glass fibre surface compared with the dip coating. According to fragmentation test results, the interphase with a small number of heterogeneous MWCNTs in the EPD fibre/epoxy composites, mimicking a biological bone structure, can remarkably improve the interfacial shear strength. We found that the semiconductive interphase results in a high sensitivity of the electrical resistance to the tensile strain of single glass fibre model composites. This material provides a possible in situ mechanical load sensor and early warning of fibre composite damage.     

The influence of silane coupling agent composition on the surface characterization of fiber and on fiber-matrix interfacial shear strength

It is well known that the fiber-matrix interface in many composites has a profound influence on composite performance. The objective of this study is to understand the influence of composition and concentration of coupling agent on interface strength by coating E-glass fibers with solutions containing a mixture of hydrolyzed propyl trimethoxysilane (PTMS) and n -aminopropyl trimethoxysilane (APS). The failure behavior and strength of the fiber-matrix interface were assessed by the single-fiber fragmentation test (SFFT), while the structure of silane coupling agent was studied in terms of its thickness by ellipsometry, its morphology by atomic force microscopy, its chemical composition by diffuse reflectance infrared Fourier transform (DRIFT), and its wettability by contact angle measurement. Deposition of 4.5 ‐ 10 m 3 mol/L solution of coupling agent in water resulted in a heterogeneous surface with irregular morphology. The SFFT results suggest that the amount of adhesion between the glass fiber and epoxy is dependent not only on the type of coupling agent but also on the composition of the coupling agent mixture. As the concentration of APS in the mixture increased, the extent of interfacial bonding between the fiber and matrix increased and the mode of failure changed. For the APS coated glass epoxy system, matrix cracks were formed perpendicular to the fiber axis in addition to a sheath of debonded interface region along the fiber axis.     

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     

Methodology for characterisation of glass fibre composite architecture

Abstract

The present study outlines a methodology for microstructural characterisation of fibre reinforced composites containing circular fibres. Digital micrographs of polished cross-sections are used as input to a numerical image processing tool that determines spatial mapping and radii detection of the fibres. The information is used for different analyses to investigate and characterise the fibre architecture. As an example, the methodology is applied to glass fibre reinforced composites with varying fibre contents. The different fibre volume fractions (FVFs) affect the number of contact points per fibre, the communal fibre distance and the local FVF. The fibre diameter distribution and packing pattern remain somewhat similar for the considered materials. The methodology is a step towards a better understanding of the composite microstructure and can be used to evaluate the interconnection between fibre architecture and composite properties.     

THE INFLUENCE OF SILANE COUPLING AGENT COMPOSITION ON THE SURFACE CHARACTERIZATION OF FIBER AND ON FIBER-MATRIX INTERFACIAL SHEAR STRENGTH

It is well known that the fiber-matrix interface in many composites has a profound influence on composite performance. The objective of this study is to understand the influence of composition and concentration of coupling agent on interface strength by coating E-glass fibers with solutions containing a mixture of hydrolyzed propyl trimethoxysilane (PTMS) and γ-aminopropyl trimethoxysilane (APS). The failure behavior and strength of the fiber-matrix interface were assessed by the single-fiber fragmentation test (SFFT), while the structure of silane coupling agent was studied in terms of its thickness by ellipsometry, its morphology by atomic force microscopy, its chemical composition by diffuse reflectance infrared Fourier transform (DRIFT), and its wettability by contact angle measurement. Deposition of 4.5 ×10 -3 mol/L solution of coupling agent in water resulted in a heterogeneous surface with irregular morphology. The SFFT results suggest that the amount of adhesion between the glass fiber and epoxy is dependent not only on the type of coupling agent but also on the composition of the coupling agent mixture. As the concentration of APS in the mixture increased, the extent of interfacial bonding between the fiber and matrix increased and the mode of failure changed. For the APS coated glass epoxy system, matrix cracks were formed perpendicular to the fiber axis in addition to a sheath of debonded interface region along the fiber axis.     

Physico-Chemical and micromechanical analysis of the interface in a poly(phenylene sulfide)/glass fiber composite—a microbond study

The glass fiber/PPS composite has excellent thermal and chemical properties. The main disadvantage of the composite is its poor mechanical resistance to impact. To improve this property, the fibers were coated with a new type of sizing. The equired characteristics for this sizing is to create strong interactions between the PPS matrix and the glass fiber surface. The ability of the sizings to improve the glass/PPS adhesion has been assessed by the microbond technique. An inconvenience of this technique is the difficulty in defining a parameter that is characteristic of the interfacial adhesion. The objective of this publication is to demonstrate that a plastic flow of the PPS matrix around the fiber leads to a uniform shear strength. The adhesion between these two materials can therefore be obtained by the mean interfacial shear strength.     

Moisture absorption and wet-adhesion properties of resin transfer molded (RTM) composites containing elastomer-coated glass fibers

Transient water sorption studies were carried out at constant temperature (45 °C) to assess the hydrolytic stability and wet-adhesion properties of glass fiber/epoxy composites having different sizings. Lower effective diffusivity values correlated with improved overall mechanical performance in relation to the control (unsized) samples, and revealed the importance of changing the surface energy characteristics of glass fibers by using distinctively hydrophobic pure polymers. Admicellar polystyrene and styrene-isoprene coatings formed over the inorganic reinforcement appear to create an interface with much higher resistance to moisture attack than the organosilane/matrix interface in composites with commercial sizing. This fact was corroborated by comparing their effectiveness in property retention, which showed the mechanical property (e.g. ultimate tensile strength, stiffness and interlaminar shear strength) increased with respect to the uncoated composites in the dry state as well as after water saturation. Poor wet-adhesion properties of commercial sizings in humid conditions could perhaps be attributed to higher contents of inert material present in these coatings. Fractography analysis was consistent with the previous observations regarding catastrophic failure in composites without coating, and suggested that interfacial debonding, extensive fiber pullout and matrix crazing were the major contributors to the overall failure mechanism. Failed surfaces of both commercial and elastomer-coated composites also showed areas with fiber pullout, but in this case, matrix residues remained on the fiber surfaces, yielding a much rougher appearance. Good fiber-matrix adhesion, particularly in admicellar-coated composites, was also revealed by the presence of hackles and more tortuous failure paths.     

Influence of new thermoplastic sizing agents on the mechanical behavior of poly(ether ketone ketone)/carbon fiber composites

In this study, unidirectional poly(ether ether ketone)/carbon fiber (CF) composite sheets were elaborated with unsized, epoxy‐sized, and thermoplastic‐sized CFs by hot‐press molding. The thermoplastic sizings that we used were poly(ether imide) (PEI) and poly(ether ketone ketone) oligomer aqueous dispersions. Scanning electron microscopy observation of the composites freeze fractures showed that unlike unsized or epoxy‐sized CFs, the thermoplastic sizings improved the interaction between the fibers and the matrix. A comparative study of the mechanical relaxations by dynamic mechanical analysis was carried out on the different composites before and after immersion in kerosene. At low temperature, the PEI sizing had a significant influence on the β relaxation, particularly after kerosene immersion. The thermoplastic sizings did not modify the glass‐transition temperature but improved the kerosene resistance on the composites. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 42550.     

Development of novel silk/wool hybrid fibre polypropylene composites

Recycling and reusing fibrous waste is one of the most important environmental tasks that face the world, to reduce environmental loading and promote the most effective use of resources. In this study, the shuttle-less loom silk selvedge waste and wool fibres were used to produce functional composites. First, the silk selvedge waste was opened and converted into fibrous form. The opened silk fibres were mixed with wool and polypropylene staple fibres in the proportions of 35/15/50, 35/35/30 and 15/35/50. The functional composites were produced by compression moulding technique with optimum process conditions. The effect of silk and wool fibre content on the mechanical properties of silk/wool hybrid fibre polypropylene composites was studied by measuring the tensile strength, flexural strength and impact strength of the resultant composite material. The thermal conductivity and water uptake properties of the composites were also studied. The morphology of silk/wool hybrid fibre polypropylene composites was analyzed by scanning electron microscopy technique. It was found that the composite containing 35/15/50 silk/wool/polypropylene showed the best performance in mechanical properties. The tensile, flexural and impact strengths of 35/15/50 silk/wool/polypropylene composite sample were found to be 30.21 MPa, 19.88 MPa and 0.713 J, respectively. The results also showed that the thermal conductivity was the least while the silk and wool fibre contents were the most in the composite. The water absorption study showed that the composite containing more fibre content possessed maximum water uptake properties. The study strongly suggests that the silk/wool hybrid fibre polypropylene composite materials are quite capable of serving as a potential cost effective, technologically viable, and attractive substitute to the conventional glass epoxy composites used as electrical insulating materials in printed circuit boards.     

Silane coupling agents in basalt-reinforced polyester composites

A new reinforcing mineral fibre, comparable in strength (3 MPa) and modulus (90 MPa) with E-glass fibres, has recently been produced from naturally-occurring basalt rock. Following earlier studies of basalt fibre/polymer matrix interactions by single fibre pull-out tests, the interfacial interaction in basalt/polyester composite systems has now been investigated. The effect of silane coupling agents applied under various conditions is reported here. The controlling effects of silane hydrolysis, condensation, orientation on the basalt surface and chemical bonding on the surface are revealed in corresponding variations in flexural strengths.     

Glass fiber 'sizings' and their role in fiber-matrix adhesion

Silane coupling agents are but one of the many ingredients in commercial sizings that are applied to glass fibers. The action of epoxy-compatible silane coupling agents alone is to increase the fiber-matrix adhesion; however, the action of a silane coupling agent-containing sizing system is not well understood. Research has been conducted in order to determine to what degree an epoxy-compatible glass fiber sizing alters the adhesion between fiber and matrix, as well as to what degree it changes the mechanical properties of the resulting composite. By using blends of epoxy-compatible sizing with bulk matrix, it has been possible to model the properties of the fiber-matrix interphase formed when the sizing interacts with the matrix during composite processing and fabrication. It has been shown in this case that the sizing's interaction with the matrix produces a material with a higher modulus, a greater tensile strength, but a lower toughness. The level of fiber-matrix adhesion increases along with a change in failure mode of the composite caused by the presence of the lower toughness interphase. The results from this study show that a chemical interaction theory of adhesion is not sufficient to explain the effect of fiber-matrix adhesion on composite properties. An interphase-based theory in which the mechanical properties of the interphase are considered along with the chemical interactions between the fiber surface and the sizing offers the best approach for developing these relationships.     

Mechanical properties of polypropylene composites reinforced with long glass fibres and mineral fillers

Abstract

The mechanical behaviour of long discontinuous glass fibre (LGF) reinforced polypropylene (PP) composites filled with talc or calcium carbonate fillers was studied. Sample specimens were processed by injection moulding, after which tensile and impact properties were analysed. In addition, scanning electron microscopy was used to analyse the morphology of the fracture surfaces. The results showed that the use of talc as a hybrid filler in LGF reinforced PP leads to a better tensile strength and toughness than in a corresponding hybrid composite based on calcium carbonate. Furthermore, it was observed that the matrix had a dominant role at low fibre content, whereas at high fibre loading, the effect of fibres was more evident.