James Thomason

Micromechanical parameters from macromechanical measurements on glass reinforced polypropylene

Many elegant techniques have been developed for the quantification of composite micromechanical parameters in recent years. Unfortunately most of these techniques have found little enthusiastic support in the industrial product development environment. We have developed an improved method for obtaining the micromechanical parameters, interfacial shear strength, fibre orientation factor, and fibre stress at composite failure using input data from macromechanical tests. In this paper we explore this method through its application to injection moulded glass-fibre-reinforced thermoplastic composites. We have measured the mechanical properties and residual fibre length distributions of glass fibre reinforced polyamide 6,6 containing different levels of glass fibre. These data were used as input for the model. The trends observed for the resultant micromechanical parameters obtained by this method were in good agreement with values obtained by other methods. Given the wealth of microstructural information obtained from this macroscopic analysis and the low level of resources employed to obtain the data we believe that this method deserves further investigation as a screening tool in composite system development programmes.

Thermoelastic anisotropy of a natural fiber

In order to develop structure-property relationships in composite systems, it is often necessary to know the properties of the fiber and matrix constituents. Much research indicates that natural-fibers exhibit a complicated anisotropic structure. Unfortunately, the property anisotropy of most natural fibers has been left undetermined. In this study, dynamic mechanical and thermal mechanical techniques have been employed to measure the elastic and thermal expansion characteristics of a model composite system containing jute fibers over a broad temperature range. The results of these measurements were in turn incorporated into a number of pertinent micro-mechanical models to estimate the thermoelastic properties of the natural fibers. The jute fibers investigated in this study exhibited considerable elastic and thermal expansion anisotropy. The longitudinal Youngs modulus of the fibers has been determined to exceed the transverse fiber modulus by as much as an order of magnitude in certain temperature regimes. The fibers exhibit negative thermal expansion coefficients along their lengths; however, large positive thermal expansion coefficients, similar in magnitude to many polymeric materials, have been estimated in the transverse directions.

The influence of fibre properties of the performance of glass-fibre-reinforced polyamide 6,6

Abstract We discuss the effect of fibre strength and diameter on the balance of mechanical properties of glass-reinforced polyamide 6,6. The results show that the elastic properties of injection-moulded short-glass-fibre-reinforced polyamide 6,6 are not strongly influenced by fibre diameter in the 10–17 micron range. The ultimate properties of these composites (strength and Izod impact behaviour) showed a clear dependence on fibre diameter and were increased by the presence of high-strength S-2 glass fibres. The relationship between the observed mechanical properties and the length, diameter and orientation of the fibres is explored. We have measured fibre length as a function of diameter in composites containing a single glass-reinforcement product and blends of two glass products. The reduction in glass-fibre length from glass-fibre production to final composite moulding has been followed step by step. The final composite mechanical properties, the fibre length, strength, diameter and orientation are all inter-related.

Sizing up the interphase: an insider's guide to the science of sizing

Sizing is a surface coating of organic materials applied to nearly all types of man-made fibres during their manufacture. In the case of glass fibres, sizing is probably the key component influencing the success or failure of most reinforcement products. This is due to the major role played by the sizing in the price, processiblity, and performance of that product. Due to its physical location on the fibre surface, sizing is also a critical component in the formation and properties of the fibre-matrix interphase. Therefore, any attempt to understand the science of the composite interphase must encompass an understanding of the science of sizing. In this paper we will review the role of sizings from fibre manufacture through to performance of composite parts. The review is illustrated by practical examples of sizing development and results from more fundamental studies of sizing application and absorption.

A small angle neutron scattering investigation of block copolymers of styrene and isoprene in the solid state

Abstract Block copolymers of styrene and isoprene have been synthesized using anionic initiation, the weight fraction range of styrene covered being 0.20–0.85. The solid state structure has been examined by electron microscopy and small angle neutron scattering, for two copolymers small angle X-ray scattering measurements have also been made. From the neutron scattering measurements it has been possible to determine the structural arrangement of the domains, the domain morphology and size, the mean square radius of the styrene block in the domain and the interfacial layer thickness. The results have been compared with theoretical models of domain structure and the general theoretical features seem to be confirmed.

The use of XPS for characterisation of glass fibre coatings

We present the results of an investigation of the use of X-ray photoelectron spectroscopy (XPS) as a tool for the rapid characterisation of glass fibre coatings. XPS data have been obtained from a wide range of commercial and experimental glass fibres using three different XPS instruments. By developing a protocol to plot ratios of appropriate atom concentrations, XPS analysis has been shown to give new insights into the in situ nature of the coating on glass. We show how these plots of atom ratios can be used to estimate the surface coverage of the coating on the glass fibres and obtain information on the chemical composition of the coating. Relationships between the XPS data and coated glass fibre parameters are clarified with the aid of a patchy overlayer model. We discuss the use of the XPS Si peak as a glass reference atom in different coverage regimes, and the effect of different XPS detector exit angles. In comparing data from three XPS instruments excellent correlation was obtained after correcting for differences in spectrometer sensitivity factors.

Small-angle neutron scattering measurement of block copolymer interphase structure

Abstract The notion of an interfacial layer at the domain boundary in block copolymers is reviewed and the possibility of its measurement by small-angle X-ray and small angle neutron scattering discussed. Values of the interfacial layer thickness and its volume fraction have been obtained for a range of styrene-isoprene copolymers. Interfacial layer thickness is not strongly dependent on molecular weight whilst the volume fraction shows a dependence more in line with the theory of Helfand.

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.

A technique for the measurement of reinforcement fibre tensile strength at sub-millimetre gauge lengths

The strength of composite reinforcement fibres is normally measured on samples of much greater length than the actual residual fibre lengths found in many composite materials. This is due to a number of limitations of the standard techniques which are employed. We present a description of a technique which enables values for the tensile strength of composite reinforcement fibres at short gauge lengths to be obtained. The technique is based on an adaptation of a micro-mechanical test apparatus for fibre pullout measurements. Data is presented which was obtained at gauge lengths of 180-380 µm on E-glass and S-2 glass® fibres taken from different chopped reinforcement products. The technique can be used at gauge lengths as short as 20 µm. The data indicates that the values of average fibre strength in these products are significantly below the pristine glass strength values.

Micromechanical parameters from macromechanical measurements on glass-reinforced polybutyleneterepthalate

Many elegant techniques have been developed for the quantification of composite micromechanical parameters in recent years. Unfortunately most of these techniques have found little enthusiastic support in the industrial product development environment. We have developed an improved method for obtaining the micromechanical parameters, interfacial shear strength, fibre orientation factor, and fibre stress at composite failure using input data from macromechanical tests. In this paper we explore this method through its application to injection moulded glass-fibre-reinforced thermoplastic composites. We have measured the mechanical properties and residual fibre length distributions of glass-fibre-reinforced polybutyleneterepthalate containing different levels of glass fibre. This data was used as input for the model. The trends observed for the resultant micromechanical parameters obtained by this method were in good agreement with values obtained by other methods. Given the wealth of microstructural information obtained from this macroscopic analysis and the low level of resources employed to obtain the data we believe that this method deserves further investigation as a screening tool in composite system development programmes.