Studies of the Effects of Sub-Zero Storage Temperatures on the Properties of Pre-Mixed Polysulphide Sealants

摘要

Pre-mixed polysulphide sealants were stored at -20, -30 and -40 C for selected intervals and then tested for conformity for the requirements of the appropriate MIL-specification in regard to cure rate or hardness, application time, tack-free time and peel strength. For Pro-Seal 899 and PR-1750 sealants, no significant change in hardness or peel strength occurred after prolonged storage at temperatures of -20 C and below; a minor decline in peel strength occurred with PR-1422. Application properties were also maintained for extended periods and at -40 C tests terminated only due to consumption of samples after storage times ranging from 7 to 16 weeks. These storage lives far exceed manufacturers' limits. Batch variations and stricter observation of class requirements could influence recommended storage times but at -40 C even materials such as PR-1750, which have a close tolerance in application life rating, may be pre-mixed and be safely stored for at least 10 weeks. Both class A and B sealants may be stored in pre-mixed form provided their application lives are at least 2 hours. Thawing is most conveniently and efficiently achieved by allowing the frozen sealant to equilibrate at room temperature. (Author)