Application of surfactants in pulp dispersion

Dispersion mechanism

Dispersion is the distribution of small solid particles as evenly as possible in another incompatible material. For the papermaking process, fibers, fillers and some chemicals are water insoluble, they have a tendency to gather themselves in aqueous solutions, and different materials are often far away from each other because of incompatibility, so it is difficult to get uniform performance, ideal strength paper. The addition of dispersant can form bilayer structure on the surface of solid particles, and the polar end of the outer layer dispersant has a strong affinity with water, which increases the degree of wetting of solid particles by water. The solid particles are separated from each other by electrostatic repulsion to achieve good dispersion effect.

2 Main varieties of dispersant

There are several types of pulp dispersants.

(1) Partially hydrolyzed polyacrylamide This dispersant can be prepared either by the hydrolysis of non-ionic polyacrylamide or by the copolymerization of acrylamide and acrylic acid in a certain proportion. Sodium salts are commonly used as dispersants. Because the molecular chain contains some carboxyl groups, it has a dispersion effect on the negatively charged cellulose fibers. And when the relative molecular mass is about 3 million, it can improve the viscosity of the slurry and is conducive to the suspension of the fiber, so it is a highly efficient dispersant for long fibers.

(2) Polyvinyl oxide (PEO) Polyvinyl oxide (PEO) is the most widely used pulp dispersant at home and abroad. PE0 is a water-soluble polymer obtained by anionic ring-opening polymerization of ethylene oxide.

In addition to its retention and strengthening effects, PE0 has a good dispersion effect on both long and short fibers, and can adapt to a wide range of pH values. In addition, it can improve the softness and smoothness of the paper. Generally used as a dispersant, the relative molecular mass of PE0 is about 2.5 million to 3 million. PEO's molecular chain degradation occurs at high shear and high temperature, resulting in decreased viscosity and dispersion ability.

(3) Gum Many gums (such as spiny sycamore gum, locust bean gum, etc.) have excellent dispersion effect on cellulose fibers. These gums act as protective colloid for the fibers, and their negative charge is evenly distributed across the fibers, preventing them from bonding. Of course, they can also improve the viscosity of the suspended medium, which is not conducive to the cohesion of the fiber.

(4) Sodium alginate This is a sodium salt of alginate extracted from seaweed, a polymer of β-anhydrous d-mannoturonic acid. Sodium alginate is a water-soluble polymer, which has remarkable dispersion ability to fiber and stable viscosity. The molecular chain is not easily degraded under high shear force. The ability of sodium alginate to disperse fiber is particularly excellent, but the price is more expensive.

(5) Other methyl cellulose, carboxymethyl cellulose, hydroxyethyl cellulose, etc., can be used as fiber dispersants.

The above water-soluble polymers are pulp dispersants, which are different from the dispersants added in the coating process, and should be noted in application.