Ionomer
Ionomers are thermoplastic resins , the first time in 1964 came on the market. For example, they are sold under the trade name Nafion ( DuPont ).
Ionomers are obtained by copolymerizing a non-polar with a polar monomer . The polar bonds push back the crystallization and lead to an "ionic crosslinking".
Compared to conventional thermoplastics, ionomers have the advantage that both secondary valence forces and ionic bonds are effective in them. These ionic bonds are particularly strong and give the fabric its characteristic properties. In addition, unlike most other plastics, ionoplasts can serve as electrolytes .
Despite the ionic bonds, ionomers are real thermoplastics because they melt at 290-330 ° C. However, the melting process is already connected with the decomposition of the macromolecules. This can produce harmful substances, but in any case the ionomer loses some of its properties.
properties
- high toughness and abrasion resistance
- high impact strength and notched impact strength
- high transparency
- high ionic conductivity
- no electronic conductivity
- good stress cracking resistance
- resistant to acids , alkalis , fats , oils and solvents
- not resistant to oxidizing acids, alcohols , aromatic and chlorinated hydrocarbons
- the weather resistance is similar to that of polyolefins
processing
Processing can be done by injection molding , extrusion , blow molding or thermoforming . Here, however, the functional group that gives the product its ionic conductivity must still be masked. If the ionomer is to become ion-conductive through a sulfonic acid group (-SO 3 H), then the polymer is extruded in its sulfonyl fluoride form (-SO 2 F). The final form -SO 3 H cannot be processed as a melt due to the ionic interaction forces . After the shaping process, the functional group reacts with a strong alkali (NaOH or KOH) to form -SO 3 Na or -SO 3 K. Subsequent action of a strong acid transforms it into -SO 3 H.
- Mold temperature: approx. 200–300 ° C
- Forming temperature: approx. 150 ° C
Another type of production of ionomer membranes is the production of a dispersion from approx. 5-20% by weight SO 3 H ionomer and water-alcohol mixtures. The use of pouring processes creates liquid surfaces from which the solvents then evaporate. What then remains are thin membranes (20–50 micrometers) in -SO 3 H form. Embedded porous materials can increase mechanical strength and dimensional stability.
Applications
- Mercury-free chlor-alkali electrolysis for the production of chlorine and chloride-free sodium hydroxide solution ,
- Electrolyte membranes for polymer electrolyte fuel cells or lithium polymer batteries ,
- Membranes for humidifying or dehumidifying fluid flows,
- solid catalyst for acid catalyzed chemical reactions
- as a cover layer in some golf balls, e.g. B. from Titleist