When the paper is saturated with water, due to the destruction of water molecules and the substitution of hydrogen bonds between fibers, the strength of the paper decreases rapidly, reducing to 3% ~ 10% of the original dry strength of the paper. The addition of wet strength agent can improve the retention strength of the wetted paper, and generally can retain 10 ~ 30% or higher of the dry tensile strength. It depends on various process factors in the addition process of wet strength agent. The following are the common factors affecting the wet strength effect of PAE (polyamide polyamide epichlorohydrin) wet strength agent during use.

1. Effect of fiber raw materials on wet strength agent

The wet strength effect of PAE on wood pulp is higher than that of straw pulp and recycled pulp. The higher the effective negative charge of pulp, the more wet strength agents can be adsorbed, so the wet strength effect is better.

2. Effect of beating degree on wet strength agent

The higher the beating degree, the larger the specific surface area of the fiber, which increases the ability of the fiber to adsorb the wet strength agent, so the effect of the wet strength agent is better.

3. Effect of adding location

Wet strength agent shall not be added in advance before the pulp does not reach the required beating degree, so as to avoid further damage to the structure of wet strength agent in the beating process. Therefore, wet strength agent shall be added to the power pump as far as possible. Continuous addition is best close to the headbox, and intermittent addition shall be in the slurry forming tank after slurry grinding.

4. Effect of pH value on the effect of wet strength agent

PH value has a great influence on the ionization state of functional groups such as carboxyl group on the fiber, so it will have an impact on the interaction between negatively charged fiber and positively charged wet strength agent. The wet strength effect of wet strength agent is the best under neutral and slightly alkaline conditions. When the pH value of the system is 4-7, the wet strength effect increases obviously with the increase of pH value. The best choice of pH value is 6-8. At low pH, the reaction activity of wet strength agent will be reduced and the equipment will be greatly corroded.

5. Effect of residual bleach on wet strength agent

The more residual bleach, the worse the wet strength effect, because bleach is a strong oxidant, which will oxidize organic polymers such as wet strength agents.

6. Effect of CMC on wet strength agent

The use of CMC will improve the wet strength effect of wet strength agent.

7. Effect of anionic garbage on wet strength agent

Anionic waste (fillers, fine fibers, dyes, etc.) will adsorb cationic wet strength agent, so as to reduce the wet strength effect of wet strength agent.

8. Effect of hard water on wet strength agent

The existence of calcium and magnesium ions in water will reduce the effect of wet strength agent. Therefore, the higher the hardness of water, the greater the impact on wet strength agent.