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Peeling and characterisation of the carbon fibre-based radicular adhesive anchorage interface
ARTICLE IN PRESS
International Journal of Adhesion & Adhesives 27 (2007) 629–635 www.elsevier.com/locate/ijadhadh
Peeling and characterisation of the carbon fibre-based radicular adhesive anchorage interface E. Leforestiera,, E. Darque-Cerettib, Ch. Peitib, M. Bollaa a
L.A.S.I.O-UFR Odontologie-Universite´ de Nice 24 Avenue des Diables Bleus 06357 Nice Cedex 4, France b Ecole des Mines de Paris, CNRS UMR 7538, BP 207, 06904 Sophia-Antipolis Cedex, France Accepted 4 September 2006 Available online 29 December 2006
Abstract Carbon fibre plates (20 5 mm) were characterised by scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDS) and X-ray-induced photoelectron spectroscopy (XPS). The 901 peeling test was used (0.5 mm s1) at the carbon fibre Panavia Fs interface. The fracture interfaces were analysed using both SEM and EDS. Panavia Fs was characterised from the rheological point of view using a plate–plate fixture fitted on the Stress Techs Rheometer. The fracture patterns were mixed, cohesive in the adhesive or interfacial between the adhesive and the carbon fibre plates. The presence of Panavia Fs between the carbon fibres was demonstrated on the fracture interfaces (EDS analyses) lending weight to the theory that this adhesive was mechanically retained on composite plates. Even so, the fact that the presence of O¼C bonds was shown opened up the possibility of a chemical bond between the primary and the composite material. r 2007 Elsevier Ltd. All rights reserved. Keywords: Peeling; Carbon fibres; Panavia F; Interfaces
1. Introduction
These are dual component posts:
The purpose of corono-radicular restorations is quite precise (Fig. 1): firstly, protect and make the tooth stronger in spreading all the stresses through the radicular dentin to all the tissues around. Secondly, provide the retention of the material used in order to replace the destroyed coronal tissues [1]. Knowledge about the mechanical behaviour of the pulpless tooth, combined with the progress made in the science of polymer materials, has led to the preparation of carbon fibre radicular anchoring systems or ‘‘carbon fibre posts’’. RTD came up with Composiposts posts in 1988.
Abbreviations: SEM, Scanning electron microscopy; EDS, Energy dispersive X-ray spectroscopy; XPS, X-ray-induced photoelectron spectroscopy Corresponding author. Tel.: +1 33 0 4 93 88 87 19; fax: +1 33 0 4 93 87 73 03. E-mail address: [email protected] (E. Leforestier). 0143-7496/$ - see front matter r 2007 Elsevier Ltd. All rights reserved. doi:10.1016/j.ijadhadh.2006.09.017
Carbon fibres of approximately 7 mm in diameter, even tensioned, unidirectional in the post axis. They account for around 64% by volume of the post. An organic matrix plays the role of a binding agent and accounts for around 36% in volume of the post.
The design of these posts, which has also been used by numerous manufacturers (Composiposts RTD, Pivoclips Odontacryl, Carbonites Harald Nordin sa, Luscents Dentatus, Absolus Spad-Dentsply, Perfects Dental Emco-Dexter), has brought various products of different shapes and diameters onto the market. These latter are all obtained by machining that leads to a surface condition with micro asperities from 5 to 15 mm. According to the designers, this surface condition is favourable to the mechanical adhesion of the luting composite and the crown reconstruction material on the post [2]. The sealing or the luting of the post into its housing is a vitally important stage when performing these
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introduction of these posts into their housings: Panavia Fs from Kuraray. Both Panavia Fs itself and the carbon fibres were previously characterised on the rheological and microstructural levels, respectively. 2. Experimental 2.1. Adhesive material The adhesive used for this work was Panavia Fs (Kuraray). Panavia Fs was first introduced in 1993 and it is a ‘‘dual’’ adhesive, the polymerisation takes place in the absence of oxygen. It salts out cariostatic fluorides and, thanks to its inorganic microcharges (78 wt%), its mechanical properties are excellent: shear bond strength to human enamel is about 40 MPa, to human dentin about 22 MPa, whereas other resin cement offers, respectively, 30 and 15 MPa [11]. The forces of adhesion to enamel and to dentine are very considerable, in the same way as restoration composites, dental amalgam fillings and silanised ceramics. This generation of Panavia offers excellent marginal sealing of restorations and excellent protection against micro-infiltrations. 2.2. Carbon fibres specimen Non-radio-opaque carbon fibre-based composite plates with dimensions of 7 cm 12 cm were used as a substrate. Perfects posts emerged from these same plates. For the purposes of the study, these plates were cut using a disk sander into pieces measuring 5.5 cm 2.5 cm. These were the models that were characterised. 2.3. Rheological characterisation of Panavia Fs
Fig. 1. Components involved in a corono-radicular reconstruction.
corono-radicular reconstructions. The ideal assembly material should ensure that the post is held in place, prevent breaks by a better distribution of the stresses and also ensure that the filling is sealed [3]. Studies have assessed the surface condition of the various types of post, as well as the interface between these posts and their adhesive system [2,4,5]. To the best of our knowledge, few studies assess the adherence of various adhesive systems on these posts [2,6]. However, with a view to direct clinical application, determining the force with which the material will deadhere from the dental tissues is essential [7–10]. The main objective of this study was to show the potential for applying the 901 peeling type fracture mechanics test on the mechanical characterisation of the carbon fibre interface and a widely used adhesive for the
A ‘‘Stress Techs Rheometer’’ type viscometer fitted with a plate–plate fixture (Fig. 2) was used to characterise the adhesive. Oscillatory rheometry is a mechanical spectrometry method that offers a way of studying the viscoelastic properties of fluids. These experiments provided information about modulus and viscosity expressed in the form of a complex notation according to a frequency. The real part of modulus was called elastic modulus. The imaginary part was called viscous modulus. Our shearing experiment was performed at increasing variable frequency (o) (0.1 Hzofo10 Hz) and different temperature (successively 10, 15, 20, 25 and 37 1C) (Fig. 3). 2.4. Characterisation of carbon fibre composite plates The carbon fibre composite plates were characterised using scanning electron microscopy (SEM) (Jeol) combined with an energy dispersive spectroscopy (EDS) probe (Tracor type system). Analyses of the extreme surface X-ray-induced photoelectron spectroscopy (XPS) was performed using a Riber
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Fig. 4. Diagram of the 901 peeling test.
Fig. 2. Plate–plate rheometer.
Panavia viscosity master curve Tref 25°C 1.0E +06
viscosity Pa.s
1.0E +05 1.0E +04 1.0E +03 1.0E +02 1.0E + 01 1.0E +00 1.0E- 01
Fig. 5. Assembly diagram.
1.0E+00 1.0E+01 1.0E + 02 frequency rd /s
1.0E + 03
37°C viscosity 20°C viscosity 25°C viscosity 15°C viscosity 10°C viscosity Fig. 3. Panavia Fs (Kuraray) viscosity master curve.
Mac 2 spectrometer (source MgKa, 1256.6 eV, internal pressure 107 Pa, source power 250 W). 2.5. Study of the mechanical behaviour of the Panavia Fs/ carbon fibre-based composite plates In this study, characterisation of a Fracture energy Gc (J m2) was performed. It was measured using the 901 peeling-type mechanical adherence test (Fig. 4) where Gc ¼ F/b, F: breaking force (N), b: width of the peeled strip (m) [11]. So, it was possible to compare the different samples. The preparation of the samples was conditioned by the fracture mechanics test. The adhesive/carbon fibre-based composite material interface was investigated here. In order to perform the peeling test, a membrane that allowed us to apprehend the adhesive was introduced into the
assembly. We verified that this membrane was inextensible, and that its flexion modulus was insignifiant. So the F/b value we obtained was typical of our assembling. The carbon fibre plates were pre-treated with ED Primer prior to the introduction of the Panavia Fs. Without application of this ED Primer, the measured peeling strength was useless. So the samples were produced based on the following protocol (Fig. 5):
application of ED Primer on the carbon fibres, drying, introduction of the Panavia, laying of the membrane in the thickness of Panavia, laying of Oxyguard, wait for 15 min.
The tensile testing machine’s (Dartec servo-hydraulic with AST 100 N force sensor) travel speed was 0.5 mm s1. 2.6. Examinations of the interfaces: SEM and EDS analyses Once the mechanical test had been performed, observations of the fracture patterns were done using SEM. EDS
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analyses were then coupled with these observations in order to determine whether the fracture was cohesive or interfacial and at what level of the glue joint was located.
full ranges of carbon fibres without epoxy resin existed, and after application of the ED Primer onto the carbon fibres, the range appeared to have become uniform.
3. Results and discussion 3.1.2.2. Analysis by EDS. The EDS analysis spectrum over a surface area of 50 mm2 for an unused carbon fibre plate did not detect any heavy elements.
3.1. Results 3.1.1. Characterisation of Panavia Fs The results emerging from the study of the rheology of the Panavia Fs gave access to moduli of temperature of 10–37 1C. Based on this, it was possible to build master curves in moduli (Fig. 3). The principle consisted of superimposing all of the experimental points: we ploted [G00 (o, T) vs. G00 (atoTref)] or [Z*(o, T) vs. atZ*(atoTref)], with Tref ¼ 25 1C. The viscosity master curve (Fig. 3) gave information on the behaviour of the material. The experiment corresponding to a low temperature and high frequency gave the viscous behaviour: For a frequency of 1000 rad s1 [12], the viscosity of the material was Z ¼ 3.5 Pa s1. The experiment corresponding a high temperature or low frequency gave the behaviour obtained after cross linking. The variation of the viscosity with the temperature was generally represented by an Arhenius-type law: E 1 1 aT ¼ exp . R T T Ref
3.1.2.3. X-ray photoelectron spectroscopy (XPS). This surface analysis allowed to determine the semi-quantitative concentration of elements present, the nature of the chemical bonds and the composition of the extreme surface. The first lattice layers of the materials were involved in numerous usual processes such as adhesion and corrosion. O–C and O¼C bonds were detected in the 540/524 eV energy interval (Fig. 7). The presence of O¼C, O–C and C–C bonds was detected in the 310/270 eV energy interval (Fig. 8).
When ln aT was represented according to 1/T, the slope on the graph gave the value of the activation energy (E). In the case of Panavia Fs, we found E ¼ 98 kJ mol1 (Fig. 6). 3.1.2. Characterisation of the composite carbon fibre-based plates 3.1.2.1. SEM. These observations showed the heterogeneity of the material:
carbon fibre plates were heterogeneous even within the composite material, fibres were not always unidirectional, ranges with homogenous unidirectional fibres evenly sunk into the resin were present,
activation energy (E) 5
Fig. 7. Photoelectron spectrometry in the 310–270 eV energy interval.
y = 11870x - 38.319 R2 = 0.9884
4
ln at
3 2 1 0 2,0000E-03 -1
4,0000E-03 1/t E/R
Linéaire (E/R)
Fig. 6. Activation energy value.
Fig. 8. Photoelectron spectrometry in the 310/270 eV energy interval.
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3.1.3. Peeling 3.1.3.1. Mechanical results. Fifteen samples were tested. The calculated average energy release rate was 3677140 J m2. A typical sample curve emerging from the peeling test showed that after the part where the force increased according to the movement, a steady state of peeling over a few millimetres occurred until the end of the fissure propagation which corresponded to the end of the test (Fig. 9). 3.1.3.2. Examination of the fracture interfaces. Fibres were observed by optical microscopy. On the carbon fibre-based composite plate side, in order to determine whether the fracture was interfacial or cohesive, once the mechanical test had been performed, observations on the fracture patterns were made using SEM. It was indeed the impression of the membrane that was observed. Fig. 10 showed a mixed fracture: on the left in the figure, cohesive in the adhesive (impression of the membrane) and on the right the carbon fibres were visible, the fracture appeared to be interfacial. At a greater magnification (Fig. 11), cohesive fracture was confirmed, whereas in the carbon fibres, particles of adhesive were held captive in the
Fig. 11. Cohesive failure with the membrane impression.
- Peeling Test N°4 -
- Strength (N) -
6 5 4 3 2 1 0
0
10 5 - Displacement (mm) -
15 Fig. 12. Particles of Panavia Fs held in the hiatuses.
Fig. 9. Typical sample curve emerging from the peeling test.
Fig. 10. Mixed failure.
gaps (Fig. 11). An examination of the cohesive fracture in the adhesive (Figs. 10 and 11) showed the impression of the membrane. Fig. 12 objectified particles inserted between the carbon fibres. In order to confirm the nature of the particles captured in the carbon fibres, the analysis using EDS over a field of 50 mm2 showed peaks of Si and Ba resulting from residues of Panavia Fs. The peeling test had torn off both the membrane and the adhesive. The observations made using the SEM of the layer of ED Primer on the carbon fibres appeared to confirm that the layer of pre-treatment had also disappeared. So, there was a heterogeneous fracture, which was partially cohesive in the adhesive, partially interfacial between the adhesive and the carbon fibres. Within this interfacial fracture, the adhesive had infiltrated into the hiatuses between the carbon fibres, at this level the fracture was also cohesive in the adhesive.
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3.2. Discussion 3.2.1. Regarding the characterisation of the materials 3.2.1.1. The composite carbon fibre-based plates. SEM was used to study carbon fibre-based material for a number of years. The originality of the observations made in this work lied in the results obtained by the XPS analysis. The investigation showed three types of bonds within the material:
the C–C bonds could come from the carbon fibres, the C–O would come from the epoxy resin,
ionomer or a compomer, it was certain that natural bonds may have been created between the dentine and this material. The double carbon fibre–glue–dentine interface was widely studied, cross sections were produced [2,4,14]. The 901 peeling test not only allowed to work using a given interface but also gave an overview of the interface, allowing it to be analysed by analytical methods. Comparing the results of the fracture forces from the mechanical test with the observation of the interfaces had shown:
and for the O¼C bond two hypotheses were proposed:
an electrical hypothesis: the charges and matrix both contained carbon and oxygen with different charge effects that would lead to a double carbon peak, a physical and chemical hypothesis: the O¼C bond that could come from a surface treatment (or from the not fully cross-linked resin).
The second hypothesis appeared more likely given that three clear peaks were objectified on the spectrum emerging from the XPS analysis. With the electrical hypothesis, there would have been only two peaks. The presence of this double bond on the extreme surface of the material was an element that needed to be taken into account in order to discuss the various hypotheses on the adhesion of glues to this material. 3.2.1.2. The characterisation of Panavia Fs. The various experiments showed the formation of abnormal networks, proving that the material was a highly complex polymer. A study of the rheological behaviour of Panavia Fs showed that it only began to cross link between 10 and 20 s after having being placed into an anaerobic environment. Even though this material was considerably more viscous than other adhesives, of the Prime & Bond NTs type [13], it was possible that in the few seconds that elapsed between the introduction of the product into an anaerobic environment and the start of the cross-linking allowed Panavia Fs to penetrate the surface irregularities of the carbon fibres and especially between these latter and the matrix. 3.2.2. Regarding the breaking forces from the peeling tests and the examinations of the interfaces In this study, it was fiber/PanaviaFs interface that was studied. The Panavia Fs dentine interface was totally absent from this study. In fact, the examination of the interfaces performed by other authors [14,15] always comprised two interfaces: dentine/glue plus glue/carbon fibres. In the case of a mechanical test performed on a post+glue assembly in a root, the forces applied during the test were reflected on the double carbon fibre–glue and glue–dentine interface. Except in the case of the glue–dentine interface, if the adhesive used was a glass cement
that the highest fracture values corresponded to predominantly cohesive fractures in the adhesive. In this case, it was the cohesion of the adhesive that was measured, that the lowest fracture values corresponded to fractures at the Panavia Fs carbon fibre interface. These zones corresponded to a detachment of the membrane, the adhesive and the ED Primer.
The results of the mechanical tests performed showed the very considerable adherence resulting from this luting (367 J m2). This order of magnitude was found in the literature for polymer/polymer or metal/polymer interfaces [16]. These values obtained were a great deal higher than those obtained by Attal and Degrange [17]. But with the method of ‘‘the coin’’ he worked on a dentine/adhesive interface whereas this work was located on a polymer/ polymer interface. As the cleavage method belongs to mechanics fractures it is possible to compare the results from the coin and the peeling test. 5. Conclusions A few authors observed the surfaces of machined posts [2,4,5]. They noted that this machining and the presence of particles of barium lead, respectively, to fractures of fibres and heterogeneities within the material that helped to increase the retention of mechanical origin. Using SEM, these authors observed axial sections of the adhesive–post interfaces and drew conclusions about the more or less homogenous continuity of these interfaces depending on the posts and glues used. The application of the peeling and the observations of the fracture interfaces resulting from this test allowed us to:
do without the glue–dentine interface and work only on the glue–carbon fibre interface, calculate an energy release rate using this interface, observe fracture patterns over the whole of the peeled surface, confirm that Panavia Fs penetrated the carbon fibres, thus ensuring a mechanical retention of this adhesive on the plates as appears in the literature. We were unable to characterise these interfaces from the mechanical point of view without the earlier application of
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ED Primer onto the carbon fibres. This appeared to play an essential role in ensuring that the interface offered good adherence:
by ensuring a chemical bond between itself and the Panavia Fs, by facilitating the penetration of the Panavia Fs into the uneven areas on the surface of the carbon fibre based composite plates. We supposed that it increased the surface energy of these latter (the HEMA contained in the Ed Primer probably had a role to play in this stage).
Finally, the way was paved with the highlighting of the O¼C bond on the surface of the carbon fibres. The possibility of a chemical bonds between the adhesive and the treated carbon fibres was possible but still remains to be demonstrated. It would then be a physical and chemical bond between the glue and the carbon fibres, ensuring continuity between these two materials, a key element in the proper distribution of constraints at the radicular level.
635
References [1] [2] [3] [4] [5] [6] [7] [8] [9] [10] [11] [12] [13] [14] [15] [16] [17]
Bolla M, Bennani V. Guide clinique, 1999; 90p. Moyen O, Armand S. Cah Prothe`se 1999;27(106):7–18. Gonthier S, Cheylan J-M, et al. Cah Prothe`se 2001;29(113):35–47. Purton D-G, Payne J-A. Clinic 1996;17(5):275–9. Torbjo¨rner A, Karlsson S, et al. Europ J Oral Sci 1996;104:605–11. Duret B, Reynaud M, et al. J Biomater Dent 1992;7:45–57. Iost A, Claisse A, et al. Tribol Dent 1997;5:17–24. Rueggeberg F-A. Dent Mater 1991;7:2–10. Sano H, Shono T, et al. Dent Mater 1994;10:236–40. Steinbrecher G, Buchman A, et al. Int J Adhes Adhes 2006; 26:644–50. Leforestier E, Darque-Ceretti E, et al. J Biomat Dent 2003;18:50–8. Leforestier E, Darque-Ceretti E, et al. Int J Adhes Adhes 2002; 22:23–35. Leforestier E, Darque-Ceretti E, et al. J Biomat Dent 2002;17: 114–8. Dietschi D, Romelli M, et al. Int J Prosthodont 1997;10(6): 498–507. Moyen O, Cheleux N, et al. Cah Prothe`se 2001;29(116):43–50. Hagemeyer A, Hibst H, et al. J Adhes Technol 1991;8(1):29–40. Attal J-P, Degrange M. J Biomat Dent 1997;12:145–62.
International Journal of Adhesion & Adhesives 27 (2007) 629–635 www.elsevier.com/locate/ijadhadh
Peeling and characterisation of the carbon fibre-based radicular adhesive anchorage interface E. Leforestiera,, E. Darque-Cerettib, Ch. Peitib, M. Bollaa a
L.A.S.I.O-UFR Odontologie-Universite´ de Nice 24 Avenue des Diables Bleus 06357 Nice Cedex 4, France b Ecole des Mines de Paris, CNRS UMR 7538, BP 207, 06904 Sophia-Antipolis Cedex, France Accepted 4 September 2006 Available online 29 December 2006
Abstract Carbon fibre plates (20 5 mm) were characterised by scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDS) and X-ray-induced photoelectron spectroscopy (XPS). The 901 peeling test was used (0.5 mm s1) at the carbon fibre Panavia Fs interface. The fracture interfaces were analysed using both SEM and EDS. Panavia Fs was characterised from the rheological point of view using a plate–plate fixture fitted on the Stress Techs Rheometer. The fracture patterns were mixed, cohesive in the adhesive or interfacial between the adhesive and the carbon fibre plates. The presence of Panavia Fs between the carbon fibres was demonstrated on the fracture interfaces (EDS analyses) lending weight to the theory that this adhesive was mechanically retained on composite plates. Even so, the fact that the presence of O¼C bonds was shown opened up the possibility of a chemical bond between the primary and the composite material. r 2007 Elsevier Ltd. All rights reserved. Keywords: Peeling; Carbon fibres; Panavia F; Interfaces
1. Introduction
These are dual component posts:
The purpose of corono-radicular restorations is quite precise (Fig. 1): firstly, protect and make the tooth stronger in spreading all the stresses through the radicular dentin to all the tissues around. Secondly, provide the retention of the material used in order to replace the destroyed coronal tissues [1]. Knowledge about the mechanical behaviour of the pulpless tooth, combined with the progress made in the science of polymer materials, has led to the preparation of carbon fibre radicular anchoring systems or ‘‘carbon fibre posts’’. RTD came up with Composiposts posts in 1988.
Abbreviations: SEM, Scanning electron microscopy; EDS, Energy dispersive X-ray spectroscopy; XPS, X-ray-induced photoelectron spectroscopy Corresponding author. Tel.: +1 33 0 4 93 88 87 19; fax: +1 33 0 4 93 87 73 03. E-mail address: [email protected] (E. Leforestier). 0143-7496/$ - see front matter r 2007 Elsevier Ltd. All rights reserved. doi:10.1016/j.ijadhadh.2006.09.017
Carbon fibres of approximately 7 mm in diameter, even tensioned, unidirectional in the post axis. They account for around 64% by volume of the post. An organic matrix plays the role of a binding agent and accounts for around 36% in volume of the post.
The design of these posts, which has also been used by numerous manufacturers (Composiposts RTD, Pivoclips Odontacryl, Carbonites Harald Nordin sa, Luscents Dentatus, Absolus Spad-Dentsply, Perfects Dental Emco-Dexter), has brought various products of different shapes and diameters onto the market. These latter are all obtained by machining that leads to a surface condition with micro asperities from 5 to 15 mm. According to the designers, this surface condition is favourable to the mechanical adhesion of the luting composite and the crown reconstruction material on the post [2]. The sealing or the luting of the post into its housing is a vitally important stage when performing these
ARTICLE IN PRESS 630
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introduction of these posts into their housings: Panavia Fs from Kuraray. Both Panavia Fs itself and the carbon fibres were previously characterised on the rheological and microstructural levels, respectively. 2. Experimental 2.1. Adhesive material The adhesive used for this work was Panavia Fs (Kuraray). Panavia Fs was first introduced in 1993 and it is a ‘‘dual’’ adhesive, the polymerisation takes place in the absence of oxygen. It salts out cariostatic fluorides and, thanks to its inorganic microcharges (78 wt%), its mechanical properties are excellent: shear bond strength to human enamel is about 40 MPa, to human dentin about 22 MPa, whereas other resin cement offers, respectively, 30 and 15 MPa [11]. The forces of adhesion to enamel and to dentine are very considerable, in the same way as restoration composites, dental amalgam fillings and silanised ceramics. This generation of Panavia offers excellent marginal sealing of restorations and excellent protection against micro-infiltrations. 2.2. Carbon fibres specimen Non-radio-opaque carbon fibre-based composite plates with dimensions of 7 cm 12 cm were used as a substrate. Perfects posts emerged from these same plates. For the purposes of the study, these plates were cut using a disk sander into pieces measuring 5.5 cm 2.5 cm. These were the models that were characterised. 2.3. Rheological characterisation of Panavia Fs
Fig. 1. Components involved in a corono-radicular reconstruction.
corono-radicular reconstructions. The ideal assembly material should ensure that the post is held in place, prevent breaks by a better distribution of the stresses and also ensure that the filling is sealed [3]. Studies have assessed the surface condition of the various types of post, as well as the interface between these posts and their adhesive system [2,4,5]. To the best of our knowledge, few studies assess the adherence of various adhesive systems on these posts [2,6]. However, with a view to direct clinical application, determining the force with which the material will deadhere from the dental tissues is essential [7–10]. The main objective of this study was to show the potential for applying the 901 peeling type fracture mechanics test on the mechanical characterisation of the carbon fibre interface and a widely used adhesive for the
A ‘‘Stress Techs Rheometer’’ type viscometer fitted with a plate–plate fixture (Fig. 2) was used to characterise the adhesive. Oscillatory rheometry is a mechanical spectrometry method that offers a way of studying the viscoelastic properties of fluids. These experiments provided information about modulus and viscosity expressed in the form of a complex notation according to a frequency. The real part of modulus was called elastic modulus. The imaginary part was called viscous modulus. Our shearing experiment was performed at increasing variable frequency (o) (0.1 Hzofo10 Hz) and different temperature (successively 10, 15, 20, 25 and 37 1C) (Fig. 3). 2.4. Characterisation of carbon fibre composite plates The carbon fibre composite plates were characterised using scanning electron microscopy (SEM) (Jeol) combined with an energy dispersive spectroscopy (EDS) probe (Tracor type system). Analyses of the extreme surface X-ray-induced photoelectron spectroscopy (XPS) was performed using a Riber
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Fig. 4. Diagram of the 901 peeling test.
Fig. 2. Plate–plate rheometer.
Panavia viscosity master curve Tref 25°C 1.0E +06
viscosity Pa.s
1.0E +05 1.0E +04 1.0E +03 1.0E +02 1.0E + 01 1.0E +00 1.0E- 01
Fig. 5. Assembly diagram.
1.0E+00 1.0E+01 1.0E + 02 frequency rd /s
1.0E + 03
37°C viscosity 20°C viscosity 25°C viscosity 15°C viscosity 10°C viscosity Fig. 3. Panavia Fs (Kuraray) viscosity master curve.
Mac 2 spectrometer (source MgKa, 1256.6 eV, internal pressure 107 Pa, source power 250 W). 2.5. Study of the mechanical behaviour of the Panavia Fs/ carbon fibre-based composite plates In this study, characterisation of a Fracture energy Gc (J m2) was performed. It was measured using the 901 peeling-type mechanical adherence test (Fig. 4) where Gc ¼ F/b, F: breaking force (N), b: width of the peeled strip (m) [11]. So, it was possible to compare the different samples. The preparation of the samples was conditioned by the fracture mechanics test. The adhesive/carbon fibre-based composite material interface was investigated here. In order to perform the peeling test, a membrane that allowed us to apprehend the adhesive was introduced into the
assembly. We verified that this membrane was inextensible, and that its flexion modulus was insignifiant. So the F/b value we obtained was typical of our assembling. The carbon fibre plates were pre-treated with ED Primer prior to the introduction of the Panavia Fs. Without application of this ED Primer, the measured peeling strength was useless. So the samples were produced based on the following protocol (Fig. 5):
application of ED Primer on the carbon fibres, drying, introduction of the Panavia, laying of the membrane in the thickness of Panavia, laying of Oxyguard, wait for 15 min.
The tensile testing machine’s (Dartec servo-hydraulic with AST 100 N force sensor) travel speed was 0.5 mm s1. 2.6. Examinations of the interfaces: SEM and EDS analyses Once the mechanical test had been performed, observations of the fracture patterns were done using SEM. EDS
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analyses were then coupled with these observations in order to determine whether the fracture was cohesive or interfacial and at what level of the glue joint was located.
full ranges of carbon fibres without epoxy resin existed, and after application of the ED Primer onto the carbon fibres, the range appeared to have become uniform.
3. Results and discussion 3.1.2.2. Analysis by EDS. The EDS analysis spectrum over a surface area of 50 mm2 for an unused carbon fibre plate did not detect any heavy elements.
3.1. Results 3.1.1. Characterisation of Panavia Fs The results emerging from the study of the rheology of the Panavia Fs gave access to moduli of temperature of 10–37 1C. Based on this, it was possible to build master curves in moduli (Fig. 3). The principle consisted of superimposing all of the experimental points: we ploted [G00 (o, T) vs. G00 (atoTref)] or [Z*(o, T) vs. atZ*(atoTref)], with Tref ¼ 25 1C. The viscosity master curve (Fig. 3) gave information on the behaviour of the material. The experiment corresponding to a low temperature and high frequency gave the viscous behaviour: For a frequency of 1000 rad s1 [12], the viscosity of the material was Z ¼ 3.5 Pa s1. The experiment corresponding a high temperature or low frequency gave the behaviour obtained after cross linking. The variation of the viscosity with the temperature was generally represented by an Arhenius-type law: E 1 1 aT ¼ exp . R T T Ref
3.1.2.3. X-ray photoelectron spectroscopy (XPS). This surface analysis allowed to determine the semi-quantitative concentration of elements present, the nature of the chemical bonds and the composition of the extreme surface. The first lattice layers of the materials were involved in numerous usual processes such as adhesion and corrosion. O–C and O¼C bonds were detected in the 540/524 eV energy interval (Fig. 7). The presence of O¼C, O–C and C–C bonds was detected in the 310/270 eV energy interval (Fig. 8).
When ln aT was represented according to 1/T, the slope on the graph gave the value of the activation energy (E). In the case of Panavia Fs, we found E ¼ 98 kJ mol1 (Fig. 6). 3.1.2. Characterisation of the composite carbon fibre-based plates 3.1.2.1. SEM. These observations showed the heterogeneity of the material:
carbon fibre plates were heterogeneous even within the composite material, fibres were not always unidirectional, ranges with homogenous unidirectional fibres evenly sunk into the resin were present,
activation energy (E) 5
Fig. 7. Photoelectron spectrometry in the 310–270 eV energy interval.
y = 11870x - 38.319 R2 = 0.9884
4
ln at
3 2 1 0 2,0000E-03 -1
4,0000E-03 1/t E/R
Linéaire (E/R)
Fig. 6. Activation energy value.
Fig. 8. Photoelectron spectrometry in the 310/270 eV energy interval.
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3.1.3. Peeling 3.1.3.1. Mechanical results. Fifteen samples were tested. The calculated average energy release rate was 3677140 J m2. A typical sample curve emerging from the peeling test showed that after the part where the force increased according to the movement, a steady state of peeling over a few millimetres occurred until the end of the fissure propagation which corresponded to the end of the test (Fig. 9). 3.1.3.2. Examination of the fracture interfaces. Fibres were observed by optical microscopy. On the carbon fibre-based composite plate side, in order to determine whether the fracture was interfacial or cohesive, once the mechanical test had been performed, observations on the fracture patterns were made using SEM. It was indeed the impression of the membrane that was observed. Fig. 10 showed a mixed fracture: on the left in the figure, cohesive in the adhesive (impression of the membrane) and on the right the carbon fibres were visible, the fracture appeared to be interfacial. At a greater magnification (Fig. 11), cohesive fracture was confirmed, whereas in the carbon fibres, particles of adhesive were held captive in the
Fig. 11. Cohesive failure with the membrane impression.
- Peeling Test N°4 -
- Strength (N) -
6 5 4 3 2 1 0
0
10 5 - Displacement (mm) -
15 Fig. 12. Particles of Panavia Fs held in the hiatuses.
Fig. 9. Typical sample curve emerging from the peeling test.
Fig. 10. Mixed failure.
gaps (Fig. 11). An examination of the cohesive fracture in the adhesive (Figs. 10 and 11) showed the impression of the membrane. Fig. 12 objectified particles inserted between the carbon fibres. In order to confirm the nature of the particles captured in the carbon fibres, the analysis using EDS over a field of 50 mm2 showed peaks of Si and Ba resulting from residues of Panavia Fs. The peeling test had torn off both the membrane and the adhesive. The observations made using the SEM of the layer of ED Primer on the carbon fibres appeared to confirm that the layer of pre-treatment had also disappeared. So, there was a heterogeneous fracture, which was partially cohesive in the adhesive, partially interfacial between the adhesive and the carbon fibres. Within this interfacial fracture, the adhesive had infiltrated into the hiatuses between the carbon fibres, at this level the fracture was also cohesive in the adhesive.
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3.2. Discussion 3.2.1. Regarding the characterisation of the materials 3.2.1.1. The composite carbon fibre-based plates. SEM was used to study carbon fibre-based material for a number of years. The originality of the observations made in this work lied in the results obtained by the XPS analysis. The investigation showed three types of bonds within the material:
the C–C bonds could come from the carbon fibres, the C–O would come from the epoxy resin,
ionomer or a compomer, it was certain that natural bonds may have been created between the dentine and this material. The double carbon fibre–glue–dentine interface was widely studied, cross sections were produced [2,4,14]. The 901 peeling test not only allowed to work using a given interface but also gave an overview of the interface, allowing it to be analysed by analytical methods. Comparing the results of the fracture forces from the mechanical test with the observation of the interfaces had shown:
and for the O¼C bond two hypotheses were proposed:
an electrical hypothesis: the charges and matrix both contained carbon and oxygen with different charge effects that would lead to a double carbon peak, a physical and chemical hypothesis: the O¼C bond that could come from a surface treatment (or from the not fully cross-linked resin).
The second hypothesis appeared more likely given that three clear peaks were objectified on the spectrum emerging from the XPS analysis. With the electrical hypothesis, there would have been only two peaks. The presence of this double bond on the extreme surface of the material was an element that needed to be taken into account in order to discuss the various hypotheses on the adhesion of glues to this material. 3.2.1.2. The characterisation of Panavia Fs. The various experiments showed the formation of abnormal networks, proving that the material was a highly complex polymer. A study of the rheological behaviour of Panavia Fs showed that it only began to cross link between 10 and 20 s after having being placed into an anaerobic environment. Even though this material was considerably more viscous than other adhesives, of the Prime & Bond NTs type [13], it was possible that in the few seconds that elapsed between the introduction of the product into an anaerobic environment and the start of the cross-linking allowed Panavia Fs to penetrate the surface irregularities of the carbon fibres and especially between these latter and the matrix. 3.2.2. Regarding the breaking forces from the peeling tests and the examinations of the interfaces In this study, it was fiber/PanaviaFs interface that was studied. The Panavia Fs dentine interface was totally absent from this study. In fact, the examination of the interfaces performed by other authors [14,15] always comprised two interfaces: dentine/glue plus glue/carbon fibres. In the case of a mechanical test performed on a post+glue assembly in a root, the forces applied during the test were reflected on the double carbon fibre–glue and glue–dentine interface. Except in the case of the glue–dentine interface, if the adhesive used was a glass cement
that the highest fracture values corresponded to predominantly cohesive fractures in the adhesive. In this case, it was the cohesion of the adhesive that was measured, that the lowest fracture values corresponded to fractures at the Panavia Fs carbon fibre interface. These zones corresponded to a detachment of the membrane, the adhesive and the ED Primer.
The results of the mechanical tests performed showed the very considerable adherence resulting from this luting (367 J m2). This order of magnitude was found in the literature for polymer/polymer or metal/polymer interfaces [16]. These values obtained were a great deal higher than those obtained by Attal and Degrange [17]. But with the method of ‘‘the coin’’ he worked on a dentine/adhesive interface whereas this work was located on a polymer/ polymer interface. As the cleavage method belongs to mechanics fractures it is possible to compare the results from the coin and the peeling test. 5. Conclusions A few authors observed the surfaces of machined posts [2,4,5]. They noted that this machining and the presence of particles of barium lead, respectively, to fractures of fibres and heterogeneities within the material that helped to increase the retention of mechanical origin. Using SEM, these authors observed axial sections of the adhesive–post interfaces and drew conclusions about the more or less homogenous continuity of these interfaces depending on the posts and glues used. The application of the peeling and the observations of the fracture interfaces resulting from this test allowed us to:
do without the glue–dentine interface and work only on the glue–carbon fibre interface, calculate an energy release rate using this interface, observe fracture patterns over the whole of the peeled surface, confirm that Panavia Fs penetrated the carbon fibres, thus ensuring a mechanical retention of this adhesive on the plates as appears in the literature. We were unable to characterise these interfaces from the mechanical point of view without the earlier application of
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ED Primer onto the carbon fibres. This appeared to play an essential role in ensuring that the interface offered good adherence:
by ensuring a chemical bond between itself and the Panavia Fs, by facilitating the penetration of the Panavia Fs into the uneven areas on the surface of the carbon fibre based composite plates. We supposed that it increased the surface energy of these latter (the HEMA contained in the Ed Primer probably had a role to play in this stage).
Finally, the way was paved with the highlighting of the O¼C bond on the surface of the carbon fibres. The possibility of a chemical bonds between the adhesive and the treated carbon fibres was possible but still remains to be demonstrated. It would then be a physical and chemical bond between the glue and the carbon fibres, ensuring continuity between these two materials, a key element in the proper distribution of constraints at the radicular level.
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