When different methods are used, the types of fluorescent whitening agents selected are also different. There are three application methods:

　　1.Whitening of pulp: (The dosage is generally about 0.05%~0.2% of dry pulp weight, pH value is 7~8).

　　Neutral or alkaline papermaking should use disulfonic acid varieties, such as C.I. fluorescent brighteners 28, 85, 134, etc.; Acidic papermaking requires that the fluorescent whitening agent be stable to acid and aluminum sulfate. It is preferred to use tetrasulfonic acid varieties such as C.I. Fluorescent whitening agent 24, 220;Since the affinity of the hexasulfonic acid species to the pulp fiber is too small, such as C.I. Fluorescent Brightener 264 is not suitable for pulp whitening.

　　2.Whitening of surface coating: (usually 0.01%~0.2% of coating dosage, pH 7~8.5)

　　Two, four or six sulfonic acid groups can be used, among which the four and six sulfonic acid groups have better effects, such as C.I. fluorescent brighteners 220, 264, 357 etc.

　　3.Surface sizing whitening: (The dosage is generally 0.2%~1.0% of the coating amount, pH value is 8~9)

　　Due to the water-soluble polymer often containing cations in surface sizing, the disulfonic acid group is sensitive to cationic compounds and is not suitable for use in surface sizing. It is recommended to use tetra- or hexasulfonate varieties such as CI fluorescent whitening agent. 24, 220, 264, 336, 353, 357.