Strengthening fibre/matrix interphase by fibre surface modification and nanoparticle incorporation into the matrix
Introduction
The combination of various modifications on different hierarchically levels can ideally lead to an increased overall performance of fibre reinforced polymer (FRP) materials.
It is well known, that FRP failure is often determined by matrix behaviour caused by indifferent loading conditions. Studies have shown that nanoscaled particles can improve the matrix properties and are currently the subject of international research that show remarkable improvements in mechanical and thermal characteristics compared with pure resins [1], [2], [18], [19], [24], [25]. The work in this paper was inspired by the idea that nanoscaled particles combined with long CNTs could lead to a strengthened matrix as well as a stronger fibre/matrix interphase. Furthermore, additional strengthening of the fibre/matrix can be achieved by suitably treated carbon fibres [3], [4], [6], [9], [20], [21]. With thus strengthened fibre/matrix interphase FRP materials with considerably improved mechanical properties are accessible.
The fibre/matrix interphase is the transition phase connecting the bulk matrix with the bulk fibre material. The nature of this phase is influenced by the physicochemical nature of both the fibre and the matrix polymer. Kessler et al. have shown that a “strong” interface leads to high resistance to impact and high residual strength [23]. In an extensive literature study Gilliot et al. summed up that a strong fibre/matrix bond increases the damage tolerance as well as the residual strength. A weak fibre/matrix interphase is favouring large-scale delaminations [22]. According to Marginean et al. adhesion of fibre and matrix is based on three effects. Mechanical anchoring of the polymer to the fibre surface, absorption associated with secondary physical bonds and the molecular interaction between the polymer and the matrix [26]. Therefore, an improvement of the fibre/matrix interphase through adhesion is a desired goal for better FRP materials. Carbon fibres show relatively poor adhesion to the matrix leading to a demand for surface treatments to improve the adhesion. Fibres with a larger surface area could lead to better contact with the matrix, thus forming more mechanical interlocking sites.
In this paper, carbon fibres were modified with three different treatments. The treatment of fibres with plasma or oxidation has been widely used as well as other treatments such as using sizing agents or CNT grafting [3], [4], [6], [9], [20], [21]. In this study CNTs, incorporated in a sizing agent, as well as a cryogenic and plasma treatment was used to improve the adhesive properties of carbon fibres. Grafting carbon fibres with CNTs is likely to improve the fibre/matrix interfacial strength, which will strengthen the adhesion and therefore improve the composite delamination resistance. Nanotubes should offer additional benefits as reinforcement radial to the carbon fibres, extending into the surrounding matrix [2]. Plasma can edge the outer layer of carbon fibres in addition to create functionalized surfaces [4]. Zhang et al. has shown that liquid nitrogen can remove the amorphous outer layer of carbon fibres leading to a higher sliding pressure [9].
The mechanical reinforcement of the matrix with the use of nanoparticles is another possibility to improve FRP materials. The application of nanoscaled elements such as carbon nanotubes (CNTs) and boehmite as filler material for the mechanical reinforcement of thermosetting plastics has already been the object of numerous research efforts [14], [16], [18], [19]. Due to their outstanding mechanical properties and a large specific surface area, especially CNTs but also nanoparticles, dispersed in epoxy matrix can be expected to generate significantly improved mechanical characteristics for the nanocomposites (cured matrix material reinforced with nanoscaled elements) as compared to the pure matrix material. The effects can already be observed by small quantities of fillers in the matrix [19]. Nanoscaled particles need to be dispersed properly in order to achieve the desired improvements in the matrix [18], [28].
To determine the effects of these modifications the single fibre pullout test as well as the transverse fibre bundle test was used. The test methods were used in numerous studies to determine the interfacial shear strength or rather the tensile strength between fibre and matrix, respectively [7], [11], [13], [15], [29].
The aim of this study was to develop new hybrid materials with nanoparticles and various fibre treatments as well as to analyse these modifications with two different methods which are used for examining the fibre/matrix bond. To better understand the fracture mechanism of epoxy-based nanocomposites, the morphology of the fractured surface and the corresponding roughness was investigated using scanning electron microscopy (SEM) imaging.
Section snippets
Preparation and characterisation of the nanocomposites
The material used in this study is an epoxy resin, diglycidylether of bisphenol A (DGEBA) (Araldite LY556; Huntsman), cured by an anhydride curing agent, 4-methyl-1,2-cyclohexanedicarb-oxylic anhydride (Aradur HY917; Huntsman) and accelerated by an amine, 1-methyl-imidazole (DY070; Huntsman). The carbon fibres used in this study are Toho Tenax HTA40 E13 (Teijin; Japan), with 6000 filaments and a diameter of 7 μm. Two different nanofiller were used in this study. One of the nanoparticles was
Tensile fibre bundle test
The aim of the treatments was to improve the interfacial bonding between the fibre and the matrix and therefore improvement of the fibre/matrix interphase. There are several mechanisms for fibre/matrix bonding, which involve mechanical interlocking, adsorption interaction, electrostatic interaction, and diffusion of polymer chain segments [5].
In this paper, the interfacial bonding between carbon fibres and the epoxy matrix has been studied using a fibre bundle test technique (TFBT). A 10
Conclusion
The present paper investigates possibilities to enhance the fibre/matrix interphase, which could result in improved mechanical properties such as tensile strength, bending strength or shear strength of FRP. By incorporation of nanoscaled particles in the matrix material or by the use of suitably surface-modified fibres, such improvements might be achieved. However, many factors such as the effects of fibre treatments in relation to their mechanical strength have not been investigated, yet. The
Acknowledgements
The author wishes to thank Mr. K. Nagel (Fraunhofer-Institute for Surface Engineering and Thin Films IST in Brunswig, Germany), the Federal Institute for Materials Research and Testing (BAM) in Berlin, Germany, Innomat in Teltow, Germany and Mr. P. Pfeiffer (IfW, TU Brunswig, Germany) for support of the experimental work and the SEM images. We would also like to thank Sasol, Germany or providing the nanoparticles and Sizicyl, Belgium for providing the carbon fibres as well as the sizing agent.
References (28)
- et al.
Effects of ammonia plasma treatment on the surface characteristics of carbon fibres
Surf Coat Technol
(2006) - et al.
Air dielectric barrier discharges plasma surface treatment of 3-dimensional braided carbon fibre reinforced epoxy composites
Surf Coat Technol
(2009) - et al.
Comparison of short carbonfibre surface treatments on epoxy composites I. Enhancement of mechanical properties
Compos Sci Technol
(2004) - et al.
FE macro/micro analysis of thermal residual stresses and failure behaviour under transverse tensile load of VE/CF–fibre bundle composites
Compos Sci Technol
(2006) Why the fibre polymer interface can be stronger than matrix
Compos Sci Technol
(1997)- et al.
Effect of CNT surface functionalization on the mechanical properties
Composites: Part A
(2009) - et al.
Assessment of interfacial bonding between polymer threads and epoxy resin by transverse fibre bundle (TFB) tests
Composites: Part A
(2009) - et al.
Quantitation of the reinforcement effect of silica nanoparticles in epoxy resins used in liquid composite mouling processes
Composites Part A
(2009) - et al.
Effects of plasma oxidation on the surface and interfacial properties of carbon fibres/polycarbonate composites
Carbon
(2001) - et al.
Carbon nanotube grafted silica fibres: characterizing the interface at the single fibre level
Chem Mater
(2010)
Influence of fibre surface oxidation–reduction followed by silsesquioxane coating treatment on interfacial mechanical properties of carbon fibre/polyarylacetylene composites
Compos Part A: Appl Sci Manuf
Epoxy nanocomposites with high mechanical and tribological performance
Compos Sci Technol
Influence of different carbon nanotubes on the mechanical properties of epoxy matrix composites – a comparative study
Compos Sci Technol
Characterization of the surface and interphase of plasma-treated HM carbon fibres
Compos Part A: Appl Sci Manuf
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