Detailed Explanation of Ultrapure Water Process: Pore Structure of Ion Exchange Resins

The pore structure of ion exchange resins, in general terms, refers to the degree of expansion of the ion exchange resin and the ease with which exchanged ions can enter its interior. It is created by adding porogens such as paraffin wax or solvent gasoline during resin preparation, or by forming gel pores due to slightly larger distances between macromolecular chains. Generally, resins with added porogens have larger pore sizes, becoming macroporous resins; gel pores are smaller, typically below 3 nm. The pore size varies depending on the conditions and environment in which the exchange resin is exposed. When gel resin is in a swollen state, the molecular chains expand, the pores enlarge, and after drying and water loss, the volume shrinks, the micropores close, and at this point, the gel resin has no exchange capacity. The porosity of macroporous resins, caused by porogens, results in a more numerous and larger pore structure than gel resins, allowing them to maintain a certain pore structure even under drying and swelling conditions.

In recent years, a new type of macroporous resin has emerged in gel resins and even beyond. Its presence gives the polymer gel spheres a two-phase structure, with not only gel micropores but also a significant number of macropores within the spheres. The pore size of macroporous resins is much larger than the distance between molecules, ranging from a few nanometers to several thousand nanometers. At the same time, the pore structure of macroporous resins is more stable and less affected by external conditions.