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Durability characteristics of sealants have been assessed by measuring the changes in certain key properties (“performance indices”) after exposure of specimens to natural and to artificial weathering. A major problem in such assessments is the long duration of the cure processes of sealants after specimens are made up: in some cases these extend to 12 months or longer, during which periods continuing changes in sealant properties are observed.
This paper reports the results of a controlled study which attempts to distinguish between those changes in properties due to the continuing cure process, and those caused by changes in the sealant due to exposure to various environments which simulate the effects of weather. The latter included laboratory regimes in which the sealant samples were exposed to elevated temperature (70°C), both with and without UV(B) radiation; to artificial weathering including UV(B) radiation and water condensation; and exposure to weather in the UK, for up to 12 months.
The study involves two phases, in the first of which, reported here, freshly-prepared sealant specimens were exposed to ageing or to weather before tensile testing. In the second phase the same procedures were followed using specimens which had first been stored under standard conditions in the laboratory for 12 months.
Some results of the first phase of this study of cure and durability characteristics are given in this paper, and discussed in relation to the development of test methods for the assessment of the durability of sealants. Modulus values measured on sealant samples after exposure to artificial weathering and to heat ageing in the laboratory show highly-significant correlations with data from naturally-weathered samples.
sealants, durability, cure, weather, accelerated ageing, modulus changes