METHOD FOR PRODUCING AN IONOMER

Abstract: The invention relates to a method for producing an ionomer comprising of: (i) providing a plastic; (ii) placing an electrically conducting medium in contact with a plastic surface of the plastic; and (iii) applying an electrical field over the plastic surface, such that electrically bonded, ionogenic groups occur in the plastic.

Description: Method for producing an ionomer The invention relates to a method for producing an ionomer. The invention relates more in particular to the producing of an ionomer from a plastic which initially usual¬ ly contains no incorporated ion compounds in addition to the normal organic covalent bonds. This new method for producing ionomers comprises of: i) providing a plastic; ii) placing an electrically conducting medium in contact with a plastic surface of the plastic; and iii) applying an electrical field over the plastic surface. It has been found, namely, that if a plastic is loaded with an electrical field in the presence of an electrically conducting medium, groups are radicalized or ionized from the external and/or internal plastic surface in the direction of the electrical field in the plastic, which groups are con¬ verted as a result for instance of oxidation reactions into for example carboxylic acids and/or sulphonic acids. Under¬ stood by plastic surface is, among other things, an external plastic surface optionally provided with grooves, scratches or other surface defects and walls of cavities in the plastic which may contain contaminants. Under the influence of the electrically conducting medium these oxidized groups will dissociate and in the presence of metal ions form the charac¬ teristic ionogenic, functional groups, i.e. chemically bonded salt groups. Thus formed in the generally amorphous phase of the plastic are hydrophilic channels which are however se i- p rmeable. The electrically conducting medium, for instance water, is mobile in these channels but hydrated ions can only displace in these channels under the influence of the elec- trical field. Depending on the nature and composition of the electrically conducting medium and the applied electrical field an ionomer according to the invention can also be provided with cavities in which salts are entrapped. Both liquids and gases can be used as electrically conducting medium. The latter has the particular objective that the oxidized groups can dissociate and form an ionoge- nic, functional group with the metal ions supplied by the medium. The electrically conducting medium can be an inorga¬ nic medium such as water and ammonia. The electrically con¬ ducting medium can likewise be an organic medium such as alkanols, for instance methanol and ethanol. If the electri¬ cally conducting medium has an inherent insufficient activi- ty, diverse reactive components can be added to the medium and/or to the plastic. One group of reactive components consists of gases such as oxygen, ozone, sulphur oxide, for instance sulphur dioxide. Such gases can sustain and assist the radical-form- ing or ion-forming reactions as well as the oxidation reac¬ tions. Another group of reactive components is formed by salts, particularly salts of multivalent metal ions such as copper, tin and manganese. Such metal ions accelerate the growth of the hydrophilic channels, possibly partly due to a catalytic acceleration of the oxidation reactions. Another group of reactive components is formed by surface-active substances such as a soap. These surface- active substances, for example a stearate, can on the one hand effect the same function as the salts and on the other reduce the surface tension so that the electrically conduct¬ ing, more or less polar medium can penetrate more rapidly into the apolar plastic. Other examples of soaps for use comprise alkyl sulphonates, aryl sulphonates, alkyl(aryl) sulphonates and ethylene oxide adducts optionally in combina¬ tion with alkyl and/or aryl groups. The magnitude of the electrical field applied over the plastic is not limited to a determined value. A first forming of ionogenic, functional groups already takes place from a value of 1 V/mm of plastic. An upper limit for the magnitude of the electrical field is determined by the short-circuit voltage of the plastic, which voltage can change as the iono eric character of the plastic increases. A reasonable speed for the forming of the ionogenic, functional groups occurs with an electrical field of 0.2 to 20 kV/mm. If for instance the plastic consists of polyethylene, optimum speeds for the forming of ionogenic, functional groups are obtained when the electrical field amounts to 0.5 to 10 kV/ m. In general, the strongest possible electrical field will be applied, having in practice a value approximately equal to half the short-circuit voltage. The frequency of the applied field amounts generally to 1 to 10 5 Hz, preferably 10 Hz to 25 kHz. It has been found however that the magnitude of the frequency can influence the properties of the formed ionomers. For instance at lower frequencies of 5 Hz to 10 kHz mainly electrochemical reac¬ tions will occur (oxidation reactions) whereby mainly hydro¬ philic channels are formed. At higher frequencies, for exam- pie from 100 Hz, the ion conduction phenomenon will occur to a greater extent whereby, when the electrically conducting medium contains salts, salts can penetrate into cavities inside the hydrophilic channels and possibly contribute to cavity forming. Once enclosed in these cavities and in the absence of an electrical field, these salts are irreversibly entrapped inside the ionomer. The ionomer produced according to the invention gene¬ rally has the form of a sheet. This sheet form may already be present in the plastic subjected to the method. It is however possible that a for example hollow cylindrical plastic is subjected to a radially oriented electrical field, whereafter an ionomer in the form of a sheet is formed from this hollow cylindrical plastic by means of delamination, optionally by peeling. An optimum method for producing ionomers is obtained if the plastic is placed in contact with the conducting medium on surfaces facing away from each other. A preferred embodiment for performing the method according to the invention comprises the use of a strip-like plastic which is converted into a channel shape, into which channel liquid, electrically conducting medium is introduced. The channel-shaped plastic is guided through a bath of liquid electrically conducting medium. Into both the bath and into the medium present in the channel is inserted an electrode for applying the electrical field over the plastic strip. By subsequently transporting the strip through the bath, wherein the medium present in the channel moves over the channel- shaped internal surface, the method according to the inven- tion can be performed continuously. According to a second embodiment of the method accord¬ ing to the invention for producing an ionomer, the plastic, in this case in the form of a plastic foil, can form a parti¬ tion between two medium chambers each containing for instance gaseous electrically conducting medium (for instance water vapour) and an electrode for generating the electrical field. If a good sealing with the chamber walls is ensured, this method can likewise be converted into a continuous method. Plastics which can be converted into ionomers with the method according to the invention are in principle not limi¬ ted to a specific group of plastics, plastics which can particularly be used comprise polyethylene, polypropylene, polystyrene and polytetrafluoroethylene. The ionomers produced in accordance with the method according to the invention can be applied in very many fie¬ lds. An example which might be quoted is as ion conductor in for instance polymer batteries, in which the ionomer func¬ tions as an electrolyte. The ionomer can also be applied as a semi-permeable membrane with a selective permeability for particular types of molecules and ions, wherein the permeabi¬ lity can moreover be adjusted as a function of the electrical field and/or the temperature. Finally, the ionomers can be used for purifying solutions, dispersions and emulsions of both chemical and medicinal nature. *****

Claims: CLAIMS 1. Method for producing an ionomer comprising of: i) providing a plastic; ii) placing an electrically conducting medium in contact with a plastic surface of the plastic; and iii) applying an electrical field over the plastic surface, this such that electrically bonded, ionogenic groups occur in the plastic. 2. Method as claimed in claim 1 , wherein the electri¬ cally conducting medium is chosen from liquids and/or gases. 3. Method as claimed in claim 1 or 2, wherein the electrically conducting medium comprises an inorganic medium such as water and ammonia and/or an organic medium such as alkanols, for instance methanol and ethanol. 4. Method as claimed in claims 1-3, wherein the elec- trically conducting medium contains a reactive gas such as oxygen, ozone, sulphur oxide. 5. Method as claimed in claims 1-4, wherein the elec¬ trically conducting medium and/or the plastic contains a salt. 6. Method as claimed in claims 1-5, wherein the elec¬ trically conducting medium and/or the plastic contains a surface-active substance such as a soap. 7. Method as claimed in claims 1-6, wherein the elec¬ trical field is in the order of 1 Volt/mm plastic to the short-circuit voltage of the plastic. 8. Method as claimed in claim 7, wherein the electrical field amounts to 0.2-20 kV/mm plastic. 9. Method as claimed in claim 7 or 8, wherein the plastic is polyethylene and the electrical field amounts to 0.5-10 kV/mm polyethylene. 10. Method as claimed in claims 1-9, wherein the frequency of the electrical field amounts to l-10 5 Hz, prefe¬ rably 10 Hz-25 kHz. 11. Method as claimed in claims 1-10, wherein the plastic is sheet-like. 12. Method as claimed in claims 1-11, wherein plastic surfaces facing away from each other are placed in contact with the conducting medium. 13. Method as claimed in claims 1-12, wherein the plastic has a strip form and is converted into a channel shape, wherein liquid electrically conducting medium is added to the channel. 14. Method as claimed in claims 1-12, wherein the plastic forms a partition between two medium chambers. *****

Inventors: ROSS ROBERT, ROSS, ROBERT
Applicants: KEMA NV, N.V. KEMA
Application year: 1992
Main classification: B01D67
IPC codes: B01D67, B29C59, B29C71, C08J7, H01M2, H01M6