Electrolysis: processes – compositions used therein – and methods – Electrolytic coating – Coating predominantly nonmetal substrate
Reexamination Certificate
2000-04-03
2001-12-04
Wong, Edna (Department: 1741)
Electrolysis: processes, compositions used therein, and methods
Electrolytic coating
Coating predominantly nonmetal substrate
C205S317000
Reexamination Certificate
active
06325911
ABSTRACT:
The present invention relates to a process for manufacturing composites by electrochemically coating a carbon-based substrate with a polymer.
The field of composites has become particularly widespread, given the range of their applications in sectors of activity as different as the aerospace industry, the automobile industry (means of transportation in general), the sports industry, etc.
The use of carbon fibres in such materials is not only due to their low density but their high mechanical properties. However, the use of carbon fibres not pretreated on their surface results in composites with a low interlaminar shear strength. This has been attributed to poor adhesion—a weak bond between the fibres and the matrix. In order to improve this interfacial bond, the surface of these carbon fibres is generally subjected to an oxidizing or non-oxidizing treatment.
Such processes for the manufacture of carbon/polymer-based composites has formed the subject of many articles in the literature, as indicated below:
1) R. Subramanian and J. Jakubowski (Polymer Engineering, 1978, Vol. 18, No. 7, 590-600) claim the electrochemical grafting of various polymers such as methyl acrylates and styrene, but the grafting takes place, according to a mechanism which remains unknown, starting from surface impurities on the carbon. The potential required for this type of grafting is not specified.
2) Another method of indirectly initiating the polymerization is known: electrochemically formed species and radicals (anions and cations) are capable of causing polymerization reactions; J. Iroh, J. Bell and D. Scola (Journal of Applied Polymer Science, 1993, Vol. 49, 583-592) use the appearance of H radicals to electropolymerize N,N-dimethylacrylamide in aqueous H
2
SO
4
solutions. The choice of potential is not a key factor. In this type of polymerization, grafting of the polymer onto the carbon has never been able to be proved: there is precipitation on the carbon electrode and the carbon/polymer adhesion is based on a simple physical phenomenon.
3) J. Pinson, J. M. Saveant at H. Rachid (French Patent 91/01172) form functional aryl radicals on the surface of the carbon by the electrochemical reduction of diazonium salts: an aromatic group thus modifies the carbon surface to which it is fixed. According to this process, other modifications of the composite thus formed ought also to be possible. In this process, the potential conditions are fixed by the fact that the reduction potential of the diazonium salt is less cathodic than the reduction potential of the radical initially produced.
4) S. Shkolnik and C. Barash (Polymer, 1993, Vol. 34, No. 1, 2921-2928) describe the electrocopolymerization of glycidyl methacrylate (GMA) and methyl methacrylate. The oxirane ring of the GMA should be involved in the formation of a bond between the polymerized layer and the graphite surface. This technique implies no control of the potential.
5) We should point out that, in 1983, N. Tsubokawa, A. Yamada and Y. Stona (Polymer Bulletin, 1983, Vol. 10, 63-69) demonstrated the grafting of polyesters, resulting from the copolymerization of GMA with phthalic anhydride, onto carbon. Nevertheless, mention should be made, in this case, of the presence of COOK groups on the surface of the carbon which would react with the epoxy group of the GMA.
Tsubokawa and H. Ueno (Journal of Applied Polymer Science, 1995, Vol. 58, 1221-1227) follow a similar approach: the polymerization of vinyl monomers is also initiated by the COOK functional groups on the surface of the carbon. In this case there is nothing more than a chemical polymerization, but one which starts from a carboxylate group. It should be pointed out that, in the abovementioned studies, the density of the grafted chains is fixed and limited by the surface density of the functional groups.
These same authors also describe the possibility of grafting, directly on the carbon substrate, preformed polymer chains, (polydimethylsiloxane-azobiscyanopentanoate or polyethylene glycol-azobiscyanopentanoate) carrying a chemical functional group capable of decomposing in order to form a radical (“azopolymers”). This macroradical would react with the aromatic rings available on the surface of the carbon.
6) T. Lipatova, V. Matyushova and J. Donnet (Carbon, 1985, Vol. 23, No. 1. 59-64) also claim the electrochemical grafting of a polymer, such as, for example, poly(2-ethylhexyl acrylate) onto carbon fibres. No control of the current or of the potential is specified. As regards the grafting mechanism, this has not been clearly established and, according to the authors, would involve reactive centres lying in surface microheterogeneities of favourable energy. The grafting would only take place at these heterogeneities and would result in an inhomogeneous surface coating.
One of the essential aims of the present invention is to provide a process making it possible to produce carbon-based composites in which the polymer is fixed directly to the carbon without recourse to any intermediate chemical molecule or element normally used for fixing the polymer to the carbon.
According to the invention, a composite is obtained in which the polymer is fixed, by grafting onto the carbon substrate, by a carbon-carbon chemical bond which forms an integral part of the polymer itself. There is therefore continuity between the carbon and the polymer.
This has proved to allow a composite to be obtained which has very good mechanical and chemical properties compared with the prior art mentioned above.
For this purpose, the process according to the invention is characterized in that use is made of a reaction system comprising (a) at least one monomer able to form a polymer on the abovementioned substrate, (b) an aprotic solvent and (c) an electrolyte giving the organic medium thus obtained an electrical conductivity sufficient to lead to electrolysis therein, in which the carbon substrate forms the cathode, by applying an electric potential or an electric current bringing the reaction system into the passivation region corresponding to a first inhibition peak revealed in voltammetry, so as to form a polymer grafted onto the aforementioned substrate.
Advantageously, use is made of a monomer/solvent pair chosen from the group formed by acrylonitrile/acetonitrile, acrylonitrile/propylene carbonate, acrylonitrile/dimethylformamide, acrylon itride/dimethacrylamide, acrylonitrile/pyridine, ethyl acrylate/dimethylformamide, ethyl acrylate/pyridine, silylated 2-hydroxy-ethyl methacrylate/dimethylformamide, methyl methacrylate/dimethylformamide, glycidyl methacrylate/dimethylformamide, n-butyl acrylate/dimethylformamide, tert-butyl acrylate/dimethylformamide and allyl methacrylate/dimethylformamide systems.
REFERENCES:
patent: 4130465 (1978-12-01), Arai et al.
patent: 5232560 (1993-08-01), Bell et al.
patent: 5567297 (1996-10-01), Mertens et al.
patent: 0 106 352 A1 (1984-04-01), None
patent: 0 665 275 A1 (1995-08-01), None
patent: 2 672 307 A1 (1992-08-01), None
Jerome Robert
Martinot Lucien
Mertens Marc
Cipari, SA
Laff, Whitesel & Saret, Ltd.
Whitesel J. Warren
Wong Edna
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