Temperature cycling, effect adhesives

These low-temperature environmental effects can be significant factors that contribute to an adhesive system s durability and life. This section discusses the characteristics of epoxy adhesive joints exposed to low temperatures and to thermal cycling and suggests formulations for improving the resistance of adhesives and sealants to these conditions. 

Basically, there are two major considerations when one is formulating or selecting adhesives or sealants for low-temperature applications. The first is the effect of the low temperature on the bulk properties of the polymer, and the second is the effect of thermal cycling and resulting internal stresses on the joint interface. 

Thermal shock resistance. Cured coating or adhesive can withstand, without fracturing, the expansion and contraction movements encountered during thermal cycling. A correctly formulated system can withstand the effects of thermal cycling over a wide temperature range, from -55°C to 85°C. 

Austin, L. G. "Studies on Slag Deposit Formation in Pulverized Coal Combustors. 5. The Effect of Flame Temperature, Thermal Cycling of the Steel Substrate, and Time on the Adhesion of Slag Drops to Oxidized Boiler Steels" Fuel, accepted. 

The adhesion of specimens subjected to environmental exposure tests was evaluated prior to and subsequent to the contact. Wet thermal shock testing consisted of five cycles each for IS minutes in boiling water and 2 minutes in ice water. The maximum transfer time between the two baths was 30 seconds. Thermal and temperature/humidity exposures were performed in controlled atmosphere chambers for 200 hours. Simulated solder tests comprised immersing the test. specimen in a silicone oil followed by solder flotation. The solder temperature varied from 232 to 288 C and the contact time was S or 10 seconds. In some cases, two flotations were performed on the same sample. The effect of a heat treatment at 135 C prior to solder testing was examined the heat treatment time varied from 0 to 16 hours. ... 

A simple joint test sample is subjected to temperature and humidity cycles before transverse tensile loading at a constant loading rate of (10 1) kN/min up to failure (Fig. 3). The objective is to evaluate the effect on bond strength of the damage to wood hbres caused by the action of acids from the adhesive during the climatic cycle. Thus, it must be achieved only if either the adhesive mixture or one of the adhesive components when apphed separately, show an acid pH value lower than 4.0. 

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