Investigation of Chemical and Physical Surface Changes of Thermally Conditioned Glass Fibres

Peter Jenkins,John Watts,Steven Hinder,Liu Yang,James Thomason,Xinyong Chen

doi:10.3390/fib7010007

Abstract

A number of analytical techniques were applied to investigate changes to the surface of unsized boron-free E-glass fibres after thermal conditioning at temperatures up to 700 °C. Novel systematic studies were carried out to investigate the fundamental strength loss from thermal conditioning. Surface chemical changes studied using X-ray photoelectron spectroscopy (XPS) showed a consistent increase in the surface concentration of calcium with increasing conditioning temperature, although this did not correlate well with a loss of fibre strength. Scanning electron microscopy fractography confirmed the difficulty of analysing failure-inducing flaws on individual fibre fracture surfaces. Analysis by atomic force microscopy (AFM) did not reveal any likely surface cracks or flaws of significant dimensions to cause failure: the observation of cracks before fibre fracture may not be possible when using this technique. Fibre surface roughness increased over the whole range of the conditioning temperatures investigated. Although surface roughness did not correlate precisely with fibre strength, there was a clear inverse relationship at temperatures exceeding 400 °C. The interpretation of the surface topography that formed between 400–700 °C produced evidence that the initial stage of phase separation by spinodal decomposition may have occurred at the fibre surface.

Highlights

Glass fibre is the predominate reinforcement material that is used in polymer composites, due its relatively high specific properties, low cost and a versatility, due to the ability for the surface to be chemically tailored for different polymer matrices; the annual consumption of E-glass fibres is in excess of 7 million tons [1]
An increase in the surface concentration of calcium was detected at 600 ◦ C; it did not, correlate with fibre strength loss behaviour
Fibre surface roughness increased significantly with heat treatment temperature, while an inverse trend was found for the depth of topographical features below the z = 0 plane, zmin

Summary

Introduction

Glass fibre is the predominate reinforcement material that is used in polymer composites, due its relatively high specific properties, low cost and a versatility, due to the ability for the surface to be chemically tailored for different polymer matrices; the annual consumption of E-glass fibres is in excess of 7 million tons [1]. A significant challenge facing the glass fibre and composites industries is the relative difficulty associated with the cost-effective recycling of glass fibre-reinforced polymer (GFRP) materials at the end of life. The separation of fibres and matrix in GFRP requires the application of aggressive processes such as pyrolysis, solvolysis or thermal recycling in the presence of oxygen, for example by fluidised bed combustion (FBC) [5]. There is a substantial body of research on the effect of thermal recycling on the properties of the recovered fibres [5,6,7,8,9]. A universal finding of this research is the large decrease in fibre tensile strength following thermal treatments or recycling, as summarised most comprehensively in [10]

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Discussion

Conclusion