Discussions

Dyes used in paper applications can be broadly categorized into natural dyes, synthetic dyes, acid dyes, basic (cationic) dyes, and direct dyes.

Natural dyes, such as those derived from plant chlorophyll or flower extracts, are environmentally friendly but suffer from poor lightfastness and batch inconsistency.

Synthetic dyes, derived from petrochemical intermediates, provide stronger color intensity and improved durability. Common examples include methylene blue, methylene red, and methyl orange.

Acid dyes exhibit strong performance on cellulose fibers but require the use of mordants or fixatives.
Basic dyes have high affinity for lignin-rich pulp and are especially effective for coloring unbleached or semi-bleached mechanical pulps.

Direct dyes can be applied without a mordant, forming hydrogen bonds with cellulose, and are widely used in both unbleached and bleached pulp systems.