Alkenyl Succinic Anhydride (ASA) is basic or neutral type sizing agent. It is wax like chemicals. ASA is used as internal sizing chemicals for paper. Structurally, it is unsaturated linear chain having five-membered anhydride ring and it is synthesized from Alfa-olefins and maleic anhydride. The anhydride ring has no fixd position in the chain, so it is called that ASA is a mixture of isomers. Physically it is yellowish oily like emulsion chemicals. The waxy solid tiny particles (0.5–2 mm) are dispersed into water and the emulsifications are stabilized usually by the cationic starch or another cationic hydrophilic polyelectrolyte stabilizer. Sometimes some little amount of surfactant is used in emulsification.
The reactive anhydride rings of ASA can easily goes under chemical reaction. At first it is hydrolyzed with the water. Then, it is form covalent bond with the hydroxyl groups of cellulose and forming an ester bond (b-keto esters).
The availability and the reasonably priced of calcium carbonate makes it the popular filler material. But this filler material is unstable in acidic medium; hence the usage of neutral/alkaline sizing agent like ASA is increased.
Alkaline sizing agent improve paper machine runnability, preserve paper’s dimensional stability increase resistance to water penetration, surface conditions of paper and maintain a high frictional coefficient. The Neutral/Alkaline Sizing Agent (ASA) also reduces paper machine breakdown, reduce dusting, reduce picking of vessel segments during offset printing and water recycling difficulties compare to Acidic sizing agent.
It should be followed the manufacturers instruction during storage especially temperature, humidity, water and time since ASA is hydrolyzed.