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Resin, originally known as the gum like gum released from crown wood, was later known as "resin" with some properties similar to resin, such as epoxy resin, phenolic resin, ion exchange resin and so on. Ion exchange resin is a kind of synthetic polymer compound whose properties are determined by manufacturing process, raw material formula, polymerization temperature, cross-linking agent and functional group. Its main properties can be seen from physical and chemical aspects

  1、 Physical properties
   1) appearance. Resin is a kind of transparent or translucent material, but it has different varieties and different colors. In general, there are more impurities or cross-linking agents in raw materials, and the color of resin is darker. During the operation of the resin, the color sometimes changes for various reasons. The shape of resin is spherical, and the ball ratio is required to be more than 90%.
   2) granularity. The size of resin particles will affect the exchange rate, pressure loss and backwash effect. The particle size of ion exchange resin for water treatment should be 20-40 mesh. The particle size should not vary too much. Particle size is represented by effective particle size and nonuniformity coefficient.
   3) density. It is related to water treatment process and resin loading. The expression of density is: thousand true density (generally 1. 6 g / cm3), wet true density (generally 1. 04~1. Between 30), wet density (generally 0. 60-0. 80).
   4) water content. The higher the moisture content of the resin, the higher the porosity and the smaller the crosslinking degree.
5) swelling rate. The swelling of resin in water is related to the degree of crosslinking, the exchange capacity of active group, the density of electrolyte in water and the properties of exchangeable ions. The resin will swell and shrink in the process of exchange and regeneration, and multiple expansion and contraction will make the resin prone to embrittlement.
   6) wear resistance. Reflecting the mechanical strength of resin, it should ensure that the amount of loss due to mechanical wear does not exceed 7% every year.
   7) solubility. When there are oligomers in the resin, they will dissolve and affect the water quality in the process of use.
   8) heat resistance. Generally, the temperature resistance of cation resin is about 100 ℃, that of strong base anion resin is 60 ℃, and that of weak anion resin is 80 ℃. When the temperature is lower than 0 ℃, it will be broken due to freezing.
    9) conductivity: dry resin does not conduct electricity, wet resin can conduct electricity.

2、 Chemical properties
1) The exchange reaction of ion exchange resin is reversible, so it can be exchanged, regenerated and reused.
2) It is acid and alkaline. The properties of H positive ion exchange resin and oh negative ion exchange resin are the same as that of electrolyte acid and base, and H positive and oh negative can be ionized in water.
3) It has neutralization and hydrolysis properties. Due to the nature of electrolyte, it can neutralize with acid or base and hydrolyze.
4) Ion exchange resin can absorb different ions with different abilities and selectivity.
5) Switching capacity. It is often used in design and operation management. It can be expressed by full switching capacity, working switching capacity, balanced switching capacity, etc. The unit is MMR / L or MMR / g, etc