What is Cationic Polyester?
Cationic Polyester refers to cationic dyed (dyeable) polyester. The abbreviation of cationic polyester is PBT or CDP.
PBT is a specialty or modified polyester, which is produced by charging macromolecules with the cationic dyeable group. As a result, CDP can be dyed with cationic dyes at the temperature of 110℃. The conventional polyester can only be dyed at a temperature of 130℃.
Why need CDP?
Polyester fiber belongs to the hydrophobic synthetic type. It lacks functional groups that can be combined with direct dyes, acid dyes, and basic dyes. Although the ester group can form hydrogen bonds with disperse dyes, the polyester molecular chain structure is tight, and the dye molecules are not easy to enter the inside of the fiber. As a result, it is difficult for regular polyester fibers to be dyed, and their color and luster are very monotonous.
Due to high crystallinity, there is only a small gap beside the polyester fiber. When the temperature is low, the molecular thermal movement changes its position to a small extent. Under wet conditions, the polyester fiber will not increase the gap by violent swelling like cotton fiber, so it is difficult for dye molecules to penetrate into the fiber. Dyeing of polyester fibers is usually done only with disperse dyes and must be under high temperature and pressure or with the help of a carrier.
From the above, we can see regular polyester (polyethylene terephthalate) has the disadvantage of low moisture absorption, poor dyeing performance, easily accumulating static, and easily fuzzing. Cationic polyester is designed to overcome these defects.
How to produce CDP?
Nowadays the commonly used method is adding dimethyl isophthalate with polarity-based SO3Na into the polyester chips. The filament spinning from this way looks similar to the common one. However, thanks to the use of ion modification, this method not only greatly improves the fiber color absorption performance, but also reduces the crystallinity. As a result, the dye molecules are easy to penetrate into the fiber. Then the dyeing property, color absorption, and hygroscopicity are remarkably improved.
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