Slow Reaction with Cellulose
Alkyl ketene dimer (AKD) is considered a relatively low-reactivity sizing agent, particularly compared with alkenyl succinic anhydride (ASA). Its reaction with cellulose hydroxyl groups is comparatively slow, so water resistance develops gradually rather than immediately.
Drying and Curing Matter
AKD is also typically a waxy material. During paper drying, it must melt and distribute over fiber surfaces to develop effective sizing. Insufficient drying or limited curing time can therefore delay water resistance development. Some AKD also undergoes competing hydrolysis, reducing the amount available for effective sizing.
Practical Advice for Papermakers
For papermakers, weak sizing immediately after production does not necessarily indicate insufficient AKD dosage. Drying conditions, AKD retention, and curing time should be evaluated before increasing addition levels.