Our primary product for the pulp & papermaking industry is alum. The largest use of alum in papermaking is as a mordant for rosin sizing under acidic conditions.  In the case of traditional soluble soap rosin size, (where approximately 25 to 30 lb/ton of alum is added), alum reacts with the rosin size forming insoluble aluminum rosinate, and the positively charged aluminum ions attach the size complex firmly to the negatively charged fiber surface. For liquid dispersed (insoluble) acid rosin size, (where approximately 5 to 10 lb/ton of alum is used), the alum and rosin each attach to the fiber independently and the alum rosinate reaction occurs later during the drying section of the paper machine.  

Alum is also widely used with the traditional alkaline sizes such as alkyl ketene dimer (AKD) and alkenyl succinic anhydride (ASA) to improve sizing efficiency and precipitate hydrolyzed size onto fibers, thereby reducing deposition on the paper machine leading to increased runnability.   Standard alum addition rates for alkaline sizing systems are in the 3 to 5 lb/ton range.  Another significant use for alum on the paper machine is as retention and drainage aid.  It is used as a stand alone product or as part of more complex multi component retention aid program, depending on the grade that is being manufactured.  Mills typically use about 3 lb/ton of alum for retention and drainage improvements.

To summarize, alum has many benefits when used in papermaking, including:
— Improved efficiency of both rosin and synthetic sizing agents
— Improved drainage and retention of fines, fillers and other microparticulates
— Improved control of pitch and other resin deposits
— Improved retention of dyes and chemical additives