We know that protein molecules are composed of many chemical monomers with the same composition. Molecules with structures like this are called macromolecules. There are also two cases of the structure of the reproduced monomer that constitutes the macromolecule. One is that the monomer only includes one type of molecule, and this compound is called a polymer. If a monomer includes several molecular structures, it is called a copolymer. Generally, polymers include more than 1,000 chemical monomers, and the molecular weight is more than 10,000.
According to the dissociation of macromolecules in water, they can be divided into three categories: anionic polyacrylamide, cationic polyacrylamide and non-ionic polyacrylamide.
When the groups on the monomer dissociate in water, leaving a negatively charged site on the monomer, the entire molecule becomes a large negatively charged ion, and this polymer is called an anionic polymer. When the groups on the monomer dissociate in water, a positively charged site is left on the monomer, so the entire molecule becomes a large positive ion, and this polymer is a cationic polymer.
Polymers without dissociative groups are called non-ionic polymers. Sometimes the monomer of a high polymer often has cationic and anionic polymer groups at the same time, and the entire high polymer has both positive and negatively charged parts. At this time, the algebraic sum of positive and negative charges represents the polymer ionic type charge.
Many high polymer substances such as glue, starch, cellulose, protein and so on have agglomeration effect. The coagulation effect of the high molecular polyamine coagulant is closely related to the groups it carries, the degree of dissociation of the groups and the molecular weight. At present, their agglomeration effect is roughly explained as two functions, one is the neutralization of the charge of the colloid nucleus and the adsorption of fine colloidal particles by the charged part. belong to this role. Therefore, adsorption is also a method of destabilizing colloids, which is different in nature from compressing the electric double layer. The other is the bridging effect of entanglement after many fine particles are adsorbed by the long chain action of macromolecules.
In order to play the role of bridging and adsorption, the chain of the polymer must be extended to the maximum length, and at the same time, the ionizable groups must reach the maximum degree of ionization. There are two reasons, one is to generate the most charged sites, which is conducive to adsorption; the other is that the repulsion of these charged sites with the same charge can extend the polymer chain to the maximum length. This increases the chance of collision and adsorption with other particles, which is beneficial for bridging. The alkalization of polyacrylamide is a typical example. Polyacrylamide itself is a non-ionic polymer, which can be used alone as a coagulant, and has achieved good results in the treatment of high turbidity water in Northwest China.