Amphoteric polyacrylamide generally refers to a water-soluble polymer containing both positive and negative charge groups on the macromolecular chain. It has good water solubility, and the anionic group plays a protective role on the cationic group, which can repel "impurity anions" present in the pulp system.
Amphoteric polyacrylamide can prevent the cationic group from reacting or being neutralized prematurely. At the same time, compared with water-soluble cationic or anionic polyacrylamide containing only one charge, it not only has the comprehensive properties of both, but also has better properties. It has the characteristics of obvious "reverse polyelectrolyte effect" and a wide range of pH values. The distribution and content of the anions and cations contained in the molecule in the molecular chain have a great influence on the curled shape of the molecular chain, thereby affecting its flocculation and drainage effect.
The cations in the amphoteric polyacrylamide (PAM) can capture negatively charged organic suspended solids, and an appropriate amount of anionic units and neutral units can promote the sedimentation of inorganic suspended solids and play the role of flocculation aids.
Amphoteric polyacrylamide compensates the charge balance of anions and cations, and is suitable for papermaking systems with a wide pH range and high closed cycle. At the same time, different uses can be achieved by adjusting the range of molecular weight and changing the synthesis technology. In terms of molecular weight, those with a molecular weight of less than 100,000 are used as dispersants, those between 250,000 and 500,000 are used as reinforcing agents, those used for retention and drainage need to be greater than 1 million, and those used for flocculation need to be greater than 7 million.
The factors affecting the retention and drainage effects of amphoteric polyacrylamide include the amount of aluminum sulfate, the amount of reinforcing agent, the amount of EDTA added, the molecular weight, the stirring speed, the amount of emulsifier, the reaction time, the amount of initiator, the concentration of monomer, the temperature, the pH value, etc.
The research shows that the reaction temperature has a great influence on the retention and drainage effects of the amphoteric polyacrylamide, mainly because the reaction temperature has a great influence on the molecular weight and retention rate of the amphoteric polyacrylamide. With the increase of reaction temperature, the retention rate of paper material will decrease gradually, and the beating degree will increase gradually, which indicates that with the increase of reaction temperature, the retention and drainage effects of amphoteric polyacrylamide on secondary fibers become worse. The main reason may be that the molecular weight of the amphoteric polyacrylamide and the stability of the emulsion decrease with the increase of the reaction temperature, and the decrease of the molecular weight affects the retention and drainage effects of the amphoteric polyacrylamide. However, a very low polymerization temperature cannot be selected. If the temperature is too low, it is not easy to initiate polymerization and the conversion rate is very low; if the temperature is not too high, the retention and drainage effects of the amphoteric polyacrylamide will decrease.