Mechanical characterisation of basalt fibre reinforced plastic

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Abstract

New perspectives have arisen on basalt fibre applications due to the potential low cost of this material together with its good mechanical performance, in particular at high temperature. The idea to fill these fibres into a polymer matrix is relatively recent and could offer very interesting perspectives that have not yet been sufficiently investigated. In this work, with the principal aim of evaluating the possibility to replace glass fibres in most of their applications, mechanical tests were carried out on comparable E-glass and basalt fibre reinforced plastic laminates. The latter were cut by square plates fabricated through vacuum bag technology. The results obtained on the two laminates were compared showing a high performance of the basalt material in terms of young modulus, compressive and bending strength, impact force and energy. These good properties suggest possible applications of basalt fibres in fields where glass composites are nowadays largely applied. The short-beam strength tests confirmed what above said by denoting an interfacial adhesion similar to that between E-glass and epoxy matrix.

Introduction

In the last years, the increasing interest in environmental issues has promoted the employment of natural fibres in polymer reinforcing [1], [2], [3]. Many types of natural fibres like sisal, kenaf, hem, flax, coconut and banana have been studied and applied. However, vegetal fibres are very sensitive to thermal and hygroscopic load and show limited mechanical properties due to the fibre extraction system, the difficulty in fibre arrangement, the fibre dimension and the interface strength.

A possible solution that takes into account the environmental issues is represented by the use of mineral fibres like basalt. Since deep studies on this material are only recent, in the last 10 years a number of researchers have been investigating properties and behaviour of various composites made of continuous or short basalt fibres [4], [5], [6], [7], [8], [9], [10], [11], [12], [13], [14], [15]. Obviously, a wide field concerning this material performance and its possible applications has not been investigated yet. In addition, some discrepancies among the results obtained by different authors have been observed.

Thanks to the improvements in production technology, a new generation of basalt fibres is now available on market. Spun basalt fibres are obtained at high temperatures from selected melted basalt rocks [16]. The process technology is extremely similar to that used for glass fibres. The rock is first pre-treated and then melted to obtain continuous fibres. The melt flows into one or more bushings containing hundreds of small orifices. The basalt filaments are formed as the molten rock passes through these orifices. The filaments are then pulled over a roller. The advantages of this method are that neither precursor nor additives are necessary in the manufacturing process, with consequent economic gain and reduction of the environmental impact. Of course, on the basis of the specific kind of original rock employed, more than one category of basalt fibres with different chemical compositions can be obtained. As a consequence, not all the basalt fibres show the same mechanical and physical properties.

In general, the positive features of this new generation of basalt fibres include sound insulation properties, excellent heat resistance (better than glass), good resistance to chemical attack and low water absorption [4]. For the latter reason they are suggested for applications requiring thermal insulation as well as for hot fluids transportation pipes. Another important characteristic is represented by the high mechanical performance comparable to that of glass fibre [5], that together with the lower cost could make this material suitable to potentially replace glass fibres in various industrial fields like aerospace, automotive, transportation and shipbuilding.

Cziga´ny [17] asserted that the cheap basalt fibres can be efficiently applied in hybrid composite systems. They had already been adopted and studied as reinforcement in concrete matrix [7], [18], where their high temperature properties such as the high fire resistance were evidenced, or in polymer matrices like epoxy [8], polypropylene [9], [10], [11] or phenol–formaldehyde resin [12], [13].

The most important feature in composites, i.e. the fibre–matrix interface, has been studied in various basalt fibre-polymer matrix systems [6], [7], [8], [14], [15], [19]. In [15], it was demonstrated that the interfacial region of basalt fibre reinforced polymer was more vulnerable than that of glass fibre reinforced composites after salt water immersion and moisture absorption. However, an excellent interfacial shear strength was found and in [6], [19] it was asserted that basalt fibres form a better surface compared to glass fibres. On the other hand, it is known that glass fibres are susceptible to surface damage and suffer from a high sensitivity to alkaline conditions [20], [21], [22], [23] whereas the chemically inert and stiffer carbon fibres present the well known disadvantage of high cost [24]. Basalt products have no toxic reaction with air or water, they are non-combustible and explosion-proof. When in contact with other chemicals they do not produce any chemical reaction that may damage health or the environment. At present no information about the risk related to very low fibre diameters is known. However, according to European law (97/69/Ce and 1907/2006) there should be no risk of toxicity for fibre diameters higher than 6 μm.

In this work, with the aim of verifying the real opportunity to replace glass fibres and to enhance the already available experimental results by providing new data, E-glass and basalt fibre reinforced plastic laminates, with dimensions 300 mm × 300 mm, were obtained by overlapping (0, 90) fabrics through vacuum bag technology. Specimens cut from the square panels by a diamond saw were successively tested in order to characterize the basalt behaviour and compare the results between the two different reinforcements. Mechanical tests like tensile, bending, shear, compression and impact tests were carried out by means of a universal and a drop weight machine. By comparing the performance of the two composites, an overall better behaviour of basalt was evidenced, thus suggesting the possibility to use this material even in fields like the automotive, railway, shipbuilding and aerospace as well as in the chemical industry, where glass composites are already largely applied.

Section snippets

Materials and test procedures

Basalt and glass fibre reinforced plastic laminates with 300 mm × 300 mm in plane dimensions were obtained through vacuum bag technology. The different types of reinforcement employed were: basalt dry fabrics, 200 g/m2, plain-weave (warp 10F/10 mm, weft 10F/10 mm), tex 100, from ZLBM (De), and E-Glass dry fabric, 290 g/m2, plain-weave (warp 5F/10 mm, weft 5F/10 mm), tex 300 (Re 290/50 WEB from Della Betta Group, It). In Fig. 1, the frontal view of both the reinforcements adopted are reported (A, B)

Results and discussion

Basalt and glass fibre reinforced plastic specimens were subjected to tensile, bending and compressive standard tests. The obtained results will be hereafter discussed and the analysed experimental data will be reported and compared in the following figures. The reported data consist of the mean values of five or more tests together with the standard deviations represented by vertical bars. As it can be noted from Fig. 3, in all the carried out tests good results were obtained with the basalt

Conclusions

By comparing the results of the mechanical tests carried out on equivalent basalt and E-glass fibre reinforced plastic laminates, it was possible to figure out the opportunity to replace glass with basalt as filler in the epoxy matrix in applications where glass composites are already largely applied. In fact, basalt composite showed a 35–42% higher Young’s modulus as well as a better compressive strength and flexural behaviour, whereas a higher tensile strength was found for glass material.

Acknowledgements

CIRTIBS Research Centre of University of Naples Federico II is acknowledged for providing the facilities and the financial support to develop the present research work.

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