The ion exchange resin matrix is made up of hydrocarbon chains held together by crosslinks i.e. a process known as polymerisation. The crosslinking gives the resin polymer a stronger, tougher structure and greater capacity (volume). Most ion exchange resins are made of polystyrene, but some types of resins are made from acrylic acid (acrylonitrile or methyl acrylate). The resin polymer is then chemically treated one or more times to add functional groups to the ion exchange sites throughout the matrix. The functional groups of the ion exchange resin give it the separation capabilities and they can vary a lot from resin type to resin type.
The most common compositions are:
Strong acid ion-exchange resins:
Strong acid cation exchange resins are a polystyrene matrix with sulfonate (SO3-) functional groups that can carry sodium ions (Na2+) for softening applications or hydrogen ions (H+) for demineralisation
Weak Acid Cation Exchange Resins:
Weak acid cation exchange resins are acrylic acid polymers that are hydrolyzed with sulfuric acid or caustic soda to produce carboxylic acid functional groups. The WAC resins are often used to selectively extract the alkalinity-related cations. This is because they are strongly attracted to the hydrogen ions (H+).
