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Fractographic study of vinylidene polyfluoride copolymers by scanning electronic microscopy
Composites: Part A 36 (2005) 493–496 www.elsevier.com/locate/compositesa
Fractographic study of vinylidene polyfluoride copolymers by scanning electronic microscopy A. Serdania, Y. Bouzaherb,*, M. Belloumb, A. Djebailib, B. Boutevinc b
a Laboratoire d’Etude des Polymers, LEP., Universite´ de Skikda, Algeria Laboratoire d’Etude des Mate´riaux, LEMO., Universite´ de Batna, Batna 05000, Algeria c Laboratoire d’Etude des Mate´riaux Polyme`res, USTL, France
Abstract This work enabled the observation of the emulsifying effect of a synthesized copolymer. The surface quality of the prepared alloys fracture was analyzed using the SEM. The examination of the stereotypes obtained on various alloys allowed the visualization of the two involved phases system. We observed on the initial mixture a continuous more or less extended PVDF phase, in which polystyrene PS nodules were inserted, forming a heterogeneous system. In addition, with certain films we noticed that, as the emulsifying rate of the mixture increases, the size of the PS nodules formed decreases significantly. Thus, it appears that in these mixtures the emulsifier agent seems to play a major role in the phase size reduction and subsequently in the increase of the dispersion state. On the other hand, it appears that more the concentration of the emulsifying agent increases, more the size of the phases decreases. All these observations confirm the emulsifying effect of our copolymer. q 2004 Elsevier Ltd. All rights reserved. Keywords: B. Adhesion; D. Electron microscopy; D. Mechanical testing; D. Fractography; P.V.D.F
1. Introduction
2. Electronic microscopy
Perfect mixtures of polymers are generally rare, because of a lack of miscibility between these macromolecules. For example, we can consider the case of the NORYL which gives perfect mixtures between polystyrene PS and PPO, or the case of PVC and PMMA leading to single-phase systems [1,2]. The absence of compatibility between the polymers is primarily due to the higher interfacial tensions, which should certainly be decreased to reach the miscibility or at least the compatibility between two different types of polymers. The interfacial properties interest on one hand the preparation of polymers alloys or mixtures [3], but more especially against polymer joining, or the setting in paintings. In all cases, the adhesion of a polymer with a second one is governed by the interfacial tensions between the two polymers, which should be lowered as much as possible [4,5].
Electron microscopy is the most used method for the characterisation of the polymer alloys. As we previously indicated, the emulsifying effect results in a reduction in the size of the phases and in the creation of interfacial interactions which link the various components of the mixture to each other. This can be observed by a simple microscopic examination of the surface of the fractures [6].
* Corresponding author. Tel./fax: C213 33 868 980. E-mail address: [email protected] (Y. Bouzaher). 1359-835X/$ - see front matter q 2004 Elsevier Ltd. All rights reserved. doi:10.1016/j.compositesa.2004.10.018
3. Study of the mixtures PVDF–PS To emulsify a mixture of PVDF–PS, we used a copolymer poly(VDF-g-S) containing 16% of styrene. In order to visualize the effect of emulsifier on the mixtures considered, we prepared a number of test-tubes containing the mixtures of the two homopolymers with or without emulsifier, then we subjected them to mechanical tests and we examined their fractures surfaces by scanning electron microscope.
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A. Serdani et al. / Composites: Part A 36 (2005) 493–496
Table 1 Study of the mechanical characteristics of mixtures PVDF/PS at fluctuating rate in emulsifying agent PVDF/PS %weight
%Emulsifying out of weight
sR!10K6 W/M2
50/50 50/50 50/50 50/50 50/50 50/50
0 2 4 8 10 15
9.8 13.9 16.66 23.6 21.3 17.15
4. Results and discussions
(Table 1, Figs. 1a,b,c). We note that the sample containing 8% of emulsifying agent gives the best characteristics of the mixtures, so this content of emulsifying agent was retained for the continuation of work. It is also noted that when the content of grafted copolymer exceeds this rate, the value of sR decreases notably. We carried out thereafter, a series of measurements of sR value on several mixtures of PVDF–PS at variable proportions. The first observation is that, we obtained a traditional bell shaped curves sRZF (mix design), where the effect of copolymer on the mechanical properties of the mixtures is largely highlighted. In addition, the mechanical properties were strongly improved by the copolymer addition in particular for mixtures of composition close to 50:50 (Table 2, Fig. 2).
4.1. Mechanical tests 4.2. Fractography We studied the mixtures of polymers starting using standardized test-tubes ISO 1/2. Because of the high rigidity of the PVDF and the PVDF–PS mixtures, we were interested mainly in the measurement of their stress rupture parameters (sR). We compared the values obtained for the simple PVDF–PS mixtures with those obtained for the mixtures added with poly(VDF-g-S) copolymer [7]. Initially, we tried to determine the optimal quantity of copolymer to add to the mixture of polymers in order to obtain the highest sR value. For that we worked on a basic mixture PVDF/PS of composition 50:50 for which we obtained a value of the rupture stress of 9.8!10C6 N/m2. To this mixture we added a variable quantities of emulsifying agent and we measured the mechanical characteristics of the mixtures obtained
The second technique allowing the description of the emulsifying effect of the synthesized copolymer, which consists in visualizing of the surface quality of prepared alloy fractures by the scanning electron microscope. The examination of the stereotypes obtained on various alloys makes possible to visualize the two involved phases system. We observed on the initial mixture a continuous PVDF phase in which polystyrene nodules (more or less lengthened) were inserted, forming a heterogeneous system (Fig. 1a). In addition, we notice on the other stereotypes (Figs. 2 and 3), that while emulsifying in the mixture, as the rate increases, the density and the size of PS nodules decrease appreciably. The role of the emulsifier is translated thus in
Fig. 1. Mix PVDF–PS of composition 50/50. (a) Only; (b) with addition of emulsifier 2%; (c) with addition of emulsifier 8%.
A. Serdani et al. / Composites: Part A 36 (2005) 493–496
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Table 2 Study of the effect emulsifying of copolymer grafted poly(VDF-g-S) on stress the rupture (sR) of mixtures PVDF/PS Stress the rupture sR!10K6 N/m2
Mix design PVDF/PS in % in weight
Without emulsifier
With emulsifier
100/0 80/20 60/40 50/50 40/60 20/80 0/100
37.73 24.50 13.23 9.80 11.76 21.07 30.67
37.73 29.4 25.28 23.62 24.50 25.48 30.67 Fig. 3. Variation of stress the rupture of the mixture PVDF–PS. (a) Without emulsifier; (b) with addition of emulsifier.
these mixtures by a reduction in the size of phase and consequently, by an increase in the state of dispersion. When one passes from a content of emulsifying agent from 2 to 8%, the size of the phases passes from 18 mm to 9 mm, for an initial value in the basic mixture of 23 mm. These measurements clearly demonstrate the emulsifying effect of the (PVDF-g-S) copolymers (Fig. 3). 4.3. Study of the hoping of the PVDF The polyfluoride of vinylidene is known for its excellent resistance to the chemical agents, with the ultraviolet rays like with abrasion. All these qualities confer to this polymer significant application, in particular for materials protection against ageing as in heavy industry, where it is used in corrosive fluids (e.g. acids) conveying tubes. This use of PVDF requires the reinforcement of the material by composites and thus, the use of a transition course of adherence between the composite and the PVDF itself. In this part, we tested our synthesized copolymers: the poly(VDF-g-MAGLY) and the poly(VDF-g-AA) as primary educations of adherence, between the PVDF and an epoxy resin.
Table 3 Tests of peeling with 1808 of the systems with and without addition of copolymer (primary of adherence) Hooping of PVDF by a composite verre/e´poxyde Without addition of the copolymer (reference) With condition of the copolymer poly(VDF-g-M)
Force peeling (N) 2300 O5000
Stress the rupture sR!10K4 N/m2 287.5 O625
4.4. Results and discussions The copolymers poly(VDF-g-MAGLY) and poly(VDFg-AA) synthesized, respectively, containing 21 and 12 mol% of corresponding grafts were used like primary educations of adherence during the hooping of PVDF by an epoxy resin. We checked that the operation of hooping was well carried out by subjecting the composites prepared to a test of peeling of 1808 (diagram 1). We compared the values of the stress rupture sR (N/m2) obtained for the composite of reference (composite PVDF–epoxy resin glass fibre) without primary education of adherence with those obtained for the composite laminated with a primary education of adherence. The values obtained for these measurements are gathered in Table 3. This fact exact values of sR (N/m2) cannot be known. We, however, noted a stress the rupture of 287.5!104 N/m2 for the composite of reference and more than 625!104 N/m2 for the systems containing the primary educations of adherence that corresponds to an increase of more than 50% of the breaking load of the system. It thus appears that the grafted copolymers that we prepared present an excellent adhesive strength during the hooping of layer of PVDF by composites glass/resin epoxy.
5. Conclusion Fig. 2. Variation of stress the rupture of the mixture PVDF–PS of composition 50–50 according to the emulsifier PVDP rate-g-S.
In this part, we tested copolymers grafted containing PVDF, either as an agent emulsifying of homopolymers, or
496
A. Serdani et al. / Composites: Part A 36 (2005) 493–496
as a primary education of adherence in the hooping of the PVDF by a composite glass/epoxy. The use of the copolymer poly(VDF-g-S) like emulsifier in mixtures PVDF/PS made it possible to clearly improve the mechanical properties of these mixtures. Indeed, for an alloy PVDF/PS of composition 50:50 in weight, we could increase the value of the rupture stress of 9.8!106–23.6! 106 N/m2.
References [1] [2] [3] [4] [5] [6] [7]
Molau GE. J Polym Sci 1965;A3:4235. Reiss G, Kohler J, Banderet A. Eur Polym J 1968;4:173. Reiss G, Periad J, Banderet A. J Polym Sci 1970;88:109. K.S. Fujio. German patent No. 2 952 457; 1980. Prud’Homme, Belorgey G. J Polym Sci Phys Ed 1982;20:191. S. Nawrot. European patent No. 0 245 159; April 1987. A. Serdani. PhD thesis, USTL, Montpellier; 1990.
Fractographic study of vinylidene polyfluoride copolymers by scanning electronic microscopy A. Serdania, Y. Bouzaherb,*, M. Belloumb, A. Djebailib, B. Boutevinc b
a Laboratoire d’Etude des Polymers, LEP., Universite´ de Skikda, Algeria Laboratoire d’Etude des Mate´riaux, LEMO., Universite´ de Batna, Batna 05000, Algeria c Laboratoire d’Etude des Mate´riaux Polyme`res, USTL, France
Abstract This work enabled the observation of the emulsifying effect of a synthesized copolymer. The surface quality of the prepared alloys fracture was analyzed using the SEM. The examination of the stereotypes obtained on various alloys allowed the visualization of the two involved phases system. We observed on the initial mixture a continuous more or less extended PVDF phase, in which polystyrene PS nodules were inserted, forming a heterogeneous system. In addition, with certain films we noticed that, as the emulsifying rate of the mixture increases, the size of the PS nodules formed decreases significantly. Thus, it appears that in these mixtures the emulsifier agent seems to play a major role in the phase size reduction and subsequently in the increase of the dispersion state. On the other hand, it appears that more the concentration of the emulsifying agent increases, more the size of the phases decreases. All these observations confirm the emulsifying effect of our copolymer. q 2004 Elsevier Ltd. All rights reserved. Keywords: B. Adhesion; D. Electron microscopy; D. Mechanical testing; D. Fractography; P.V.D.F
1. Introduction
2. Electronic microscopy
Perfect mixtures of polymers are generally rare, because of a lack of miscibility between these macromolecules. For example, we can consider the case of the NORYL which gives perfect mixtures between polystyrene PS and PPO, or the case of PVC and PMMA leading to single-phase systems [1,2]. The absence of compatibility between the polymers is primarily due to the higher interfacial tensions, which should certainly be decreased to reach the miscibility or at least the compatibility between two different types of polymers. The interfacial properties interest on one hand the preparation of polymers alloys or mixtures [3], but more especially against polymer joining, or the setting in paintings. In all cases, the adhesion of a polymer with a second one is governed by the interfacial tensions between the two polymers, which should be lowered as much as possible [4,5].
Electron microscopy is the most used method for the characterisation of the polymer alloys. As we previously indicated, the emulsifying effect results in a reduction in the size of the phases and in the creation of interfacial interactions which link the various components of the mixture to each other. This can be observed by a simple microscopic examination of the surface of the fractures [6].
* Corresponding author. Tel./fax: C213 33 868 980. E-mail address: [email protected] (Y. Bouzaher). 1359-835X/$ - see front matter q 2004 Elsevier Ltd. All rights reserved. doi:10.1016/j.compositesa.2004.10.018
3. Study of the mixtures PVDF–PS To emulsify a mixture of PVDF–PS, we used a copolymer poly(VDF-g-S) containing 16% of styrene. In order to visualize the effect of emulsifier on the mixtures considered, we prepared a number of test-tubes containing the mixtures of the two homopolymers with or without emulsifier, then we subjected them to mechanical tests and we examined their fractures surfaces by scanning electron microscope.
494
A. Serdani et al. / Composites: Part A 36 (2005) 493–496
Table 1 Study of the mechanical characteristics of mixtures PVDF/PS at fluctuating rate in emulsifying agent PVDF/PS %weight
%Emulsifying out of weight
sR!10K6 W/M2
50/50 50/50 50/50 50/50 50/50 50/50
0 2 4 8 10 15
9.8 13.9 16.66 23.6 21.3 17.15
4. Results and discussions
(Table 1, Figs. 1a,b,c). We note that the sample containing 8% of emulsifying agent gives the best characteristics of the mixtures, so this content of emulsifying agent was retained for the continuation of work. It is also noted that when the content of grafted copolymer exceeds this rate, the value of sR decreases notably. We carried out thereafter, a series of measurements of sR value on several mixtures of PVDF–PS at variable proportions. The first observation is that, we obtained a traditional bell shaped curves sRZF (mix design), where the effect of copolymer on the mechanical properties of the mixtures is largely highlighted. In addition, the mechanical properties were strongly improved by the copolymer addition in particular for mixtures of composition close to 50:50 (Table 2, Fig. 2).
4.1. Mechanical tests 4.2. Fractography We studied the mixtures of polymers starting using standardized test-tubes ISO 1/2. Because of the high rigidity of the PVDF and the PVDF–PS mixtures, we were interested mainly in the measurement of their stress rupture parameters (sR). We compared the values obtained for the simple PVDF–PS mixtures with those obtained for the mixtures added with poly(VDF-g-S) copolymer [7]. Initially, we tried to determine the optimal quantity of copolymer to add to the mixture of polymers in order to obtain the highest sR value. For that we worked on a basic mixture PVDF/PS of composition 50:50 for which we obtained a value of the rupture stress of 9.8!10C6 N/m2. To this mixture we added a variable quantities of emulsifying agent and we measured the mechanical characteristics of the mixtures obtained
The second technique allowing the description of the emulsifying effect of the synthesized copolymer, which consists in visualizing of the surface quality of prepared alloy fractures by the scanning electron microscope. The examination of the stereotypes obtained on various alloys makes possible to visualize the two involved phases system. We observed on the initial mixture a continuous PVDF phase in which polystyrene nodules (more or less lengthened) were inserted, forming a heterogeneous system (Fig. 1a). In addition, we notice on the other stereotypes (Figs. 2 and 3), that while emulsifying in the mixture, as the rate increases, the density and the size of PS nodules decrease appreciably. The role of the emulsifier is translated thus in
Fig. 1. Mix PVDF–PS of composition 50/50. (a) Only; (b) with addition of emulsifier 2%; (c) with addition of emulsifier 8%.
A. Serdani et al. / Composites: Part A 36 (2005) 493–496
495
Table 2 Study of the effect emulsifying of copolymer grafted poly(VDF-g-S) on stress the rupture (sR) of mixtures PVDF/PS Stress the rupture sR!10K6 N/m2
Mix design PVDF/PS in % in weight
Without emulsifier
With emulsifier
100/0 80/20 60/40 50/50 40/60 20/80 0/100
37.73 24.50 13.23 9.80 11.76 21.07 30.67
37.73 29.4 25.28 23.62 24.50 25.48 30.67 Fig. 3. Variation of stress the rupture of the mixture PVDF–PS. (a) Without emulsifier; (b) with addition of emulsifier.
these mixtures by a reduction in the size of phase and consequently, by an increase in the state of dispersion. When one passes from a content of emulsifying agent from 2 to 8%, the size of the phases passes from 18 mm to 9 mm, for an initial value in the basic mixture of 23 mm. These measurements clearly demonstrate the emulsifying effect of the (PVDF-g-S) copolymers (Fig. 3). 4.3. Study of the hoping of the PVDF The polyfluoride of vinylidene is known for its excellent resistance to the chemical agents, with the ultraviolet rays like with abrasion. All these qualities confer to this polymer significant application, in particular for materials protection against ageing as in heavy industry, where it is used in corrosive fluids (e.g. acids) conveying tubes. This use of PVDF requires the reinforcement of the material by composites and thus, the use of a transition course of adherence between the composite and the PVDF itself. In this part, we tested our synthesized copolymers: the poly(VDF-g-MAGLY) and the poly(VDF-g-AA) as primary educations of adherence, between the PVDF and an epoxy resin.
Table 3 Tests of peeling with 1808 of the systems with and without addition of copolymer (primary of adherence) Hooping of PVDF by a composite verre/e´poxyde Without addition of the copolymer (reference) With condition of the copolymer poly(VDF-g-M)
Force peeling (N) 2300 O5000
Stress the rupture sR!10K4 N/m2 287.5 O625
4.4. Results and discussions The copolymers poly(VDF-g-MAGLY) and poly(VDFg-AA) synthesized, respectively, containing 21 and 12 mol% of corresponding grafts were used like primary educations of adherence during the hooping of PVDF by an epoxy resin. We checked that the operation of hooping was well carried out by subjecting the composites prepared to a test of peeling of 1808 (diagram 1). We compared the values of the stress rupture sR (N/m2) obtained for the composite of reference (composite PVDF–epoxy resin glass fibre) without primary education of adherence with those obtained for the composite laminated with a primary education of adherence. The values obtained for these measurements are gathered in Table 3. This fact exact values of sR (N/m2) cannot be known. We, however, noted a stress the rupture of 287.5!104 N/m2 for the composite of reference and more than 625!104 N/m2 for the systems containing the primary educations of adherence that corresponds to an increase of more than 50% of the breaking load of the system. It thus appears that the grafted copolymers that we prepared present an excellent adhesive strength during the hooping of layer of PVDF by composites glass/resin epoxy.
5. Conclusion Fig. 2. Variation of stress the rupture of the mixture PVDF–PS of composition 50–50 according to the emulsifier PVDP rate-g-S.
In this part, we tested copolymers grafted containing PVDF, either as an agent emulsifying of homopolymers, or
496
A. Serdani et al. / Composites: Part A 36 (2005) 493–496
as a primary education of adherence in the hooping of the PVDF by a composite glass/epoxy. The use of the copolymer poly(VDF-g-S) like emulsifier in mixtures PVDF/PS made it possible to clearly improve the mechanical properties of these mixtures. Indeed, for an alloy PVDF/PS of composition 50:50 in weight, we could increase the value of the rupture stress of 9.8!106–23.6! 106 N/m2.
References [1] [2] [3] [4] [5] [6] [7]
Molau GE. J Polym Sci 1965;A3:4235. Reiss G, Kohler J, Banderet A. Eur Polym J 1968;4:173. Reiss G, Periad J, Banderet A. J Polym Sci 1970;88:109. K.S. Fujio. German patent No. 2 952 457; 1980. Prud’Homme, Belorgey G. J Polym Sci Phys Ed 1982;20:191. S. Nawrot. European patent No. 0 245 159; April 1987. A. Serdani. PhD thesis, USTL, Montpellier; 1990.