Polyester is a hydrophobic fiber. Like its dyeing, non-ionic optical brighteners are required for its whitening. To allow the optical brighteners to diffuse into the fiber, the whitening temperature should be 110-130 degrees in case of an “exhaust dyeing process” or a “carrier” whitening process. With the help of a carrier to transfer the optical brighteners molecules “Ship” with fiber interior. When using a continuous process, to firmly fix the optical brightener molecules on the fiber, the whitening temperature must be as high as 180-210 degrees. Optical brighteners for polyester that meet special requirements for heat resistance and diffusion generally have smaller molecular weights, which allows them to not only diffuse into the fiber through thermal motion but also enter into the fiber through sublimation. When using an intermittent process, it is often carried out in the same bath as bleaching.
Commonly used optical brighteners for polyester include Optical brighteners CI 199, 199:1, 135, 185, 367, 368, 393, etc. Among them, CI199, 368, 378, and 393 can be used to whiten polyester fiber pulp. Polyester staple fiber can use CI 199 and its derivatives.
