Nonionic polyacrylamide is a water-soluble polymer polyelectrolyte with a molecular weight of 2 to 13 million. Because its molecular chain contains a certain number of polar groups, it can bridge particles by absorbing suspended solid particles in water or condense particles to form large flocs by charge neutralization. Therefore, it can accelerate the settling of particles in the suspension and accelerate the clarification of the solution.
Nonionic polyacrylamide can improve the retention rate of fillers, pigments, etc. in papermaking, so as to reduce the loss of raw materials and pollution to the environment; it can also improve the strength of paper (including dry strength and wet strength). In addition, the use of nonionic polyacrylamide can also improve paper tear resistance and porosity. Actually, nonionic polyacrylamide is rarely used for retention and drainage. When discussing the role of nonionic polyacrylamide, many of the mechanisms that have been discussed so far cannot be applied, such as charge patching, charge retention, and charge recombination.
Studies have shown that high molecular weight is the key to nonionic polyacrylamide as a retention aid. The results are also dependent on many factors, such as temperature, mixing state, mixing time, and various details. The system works well in mechanical pulp, but is not suitable for lignin-free conditions.
In particular, since nonionic polyacrylamide systems do not rely on charge action, they can achieve highly efficient retention effect in very high conductivity or very anionic material systems. Some studies have shown that nonionic polyacrylamide and high-charge cationic additives have better effects when used in combination. For example, adding high-charge cationic starch coagulants to different slurries (including thermomechanical pulp) helps to enhance the effects of retention system of nonionic polyacrylamide.
Nonionic polyacrylamide retention and drainage aids have always attracted much attention in the field of papermaking. Although there have been research results at a certain level at home and abroad, its superior performance is still waiting for further exploration. As an enduring research topic, nonionic polyacrylamide substances have gradually developed from single function to multiple functions, which not only greatly improves the effects of retention and drainage, but also saves costs and reduces pollution emissions. Even though researchers both at home and abroad have begun to explore the field of organic and inorganic composite retention and drainage aids, the research and application of nonionic polyacrylamide retention and drainage aids are still favored by many papermaking researchers.