Effect of Antioxidant Activity on Aging Profile of Expansion Joint Sealant

Sealants are usually flexible materials that form an impervious barrier to fluid flow. Expansion joint sealants are largely used in construction industry for large buildings, parking areas, bridges and other structures. These sealants has a unique property that they can expand as necessary to accommodate temperature cycle changes. Modulus. weather ability, durability and hardness are important properties of sealants. Polyurethane expansion joint sealant was prepared by using Hydroxyl terminated polybutadiene (HTPB). Hydroxyl terminated polybutadiene has low glass transition temperature, high tensile strength, good chemical resistance and viscoelastic nature which are desirable properties for a sealant. Unsaturation is present in HTPB, therefore, antioxidants are added to it for protection against oxidation. Oxidation can lead to undesirable properties in sealants like hardening and crack formation. Three different grades of N,N’-Diphenyl para phenylene diamine (DPPD) antioxidant were used in sealant formulations in order to study their effect on aging profile of sealant. These antioxidants were characterized for purity by HPLC. antioxidant activity by DSC and DPPH (radical scavenging) method. The results indicated that sealant prepared with antioxidant of higher antioxidant activity showed less hardness and greater elongation which are desirable properties for a durable expansion joint sealant. The impurities which have radical scavenging properties contribute towards effective antioxidant concentration and thus increase the antioxidant activity, Locally produced DPPD was compared that of Merck. Sealant prepared by using locally produced DPPD Local 02 has longer shelf life as compared to sealant containing DPPD produced by Merck.