Optical brighteners, also known as fluorescent whitening agents (FWAs), are chemical compounds that absorb ultraviolet light and re-emit it as visible blue light, significantly enhancing the whiteness and brightness of paper products.
Optical brightening agents are categorized based on the number of sulfonic groups in their stilbene structure. Each type offers distinct properties and applications in papermaking:
Structure:
Contains 2 sulfonic groups
Properties:
Application:
Wet end addition for internal bonding
Best For:
Mechanical pulp and recycled fiber systems
Structure:
Contains 4 sulfonic groups
Properties:
Application:
Versatile - both wet and dry end
Best For:
Most common type for paper and paperboard grades
Structure:
Contains 6 sulfonic groups
Properties:
Application:
Dry end - surface coating applications
Best For:
High brightness papers, photographic paper, specialty grades
The choice between disulfonated, tetrasulfonated, and hexasulfonated OBAs depends on several factors:
Enhanced whiteness for professional documents and high-quality printing
Improved appearance and consumer appeal for hygiene products
Restoration of whiteness and brightness in recycled paper grades
Added directly to the paper stock for uniform distribution throughout the sheet
Applied at the size press or calender stack for targeted surface enhancement
Dual application for maximum whiteness and brightness optimization