The data indicates that relatively low levels of the additive—that is, 1.7 % in 2EH for one – and two-part urethanes, 6.0 % in MIBK for silane curing polyether sealants—lowers sealant modulus without negatively affecting substrate adhesion. 2EH (alcohol) by itself lowered the pull force but did not increase sealant elongation versus the additive in solvent which did. In separate controls, the additive in MIBK was also evaluated and found to be useful in lowering modulus and increasing sealant elongation in one-part silane curing polyether sealants. In data not shown in this paper, the additive in both 2EH and MIBK lowered the modulus in proportion to the concentration level used while increasing elongation to produce a very interesting product with enhanced joint movement abilities leading to increased sealant durability. In other

Elongation (%)

0 100 200 300 400 500 600 700

FIG. 4—Elongation comparison of two-part, urethane sealant (unprimed) with and without additive.

data not shown in this paper, higher levels of 2EH (alcohol) inhibited cure rate and caused the surface to remain tacky for extended periods. For this reason, MIBK was substituted for 2EH when additive con­centrations above 1.7 % were used. As shown in these tables, lower concentrations of additive were especially useful in one – and two-part urethane formulations in that they had little effect on cure rate or tackiness or adhesion but a significant effect on movement ability and modulus of elasticity. Also, higher concentrations of additive in MIBK were more useful in the silane curing polyether sealants again with little effect on cure rate, tackiness or adhesion but a significant effect on movement ability and modulus.

A key observation is that the melamine type additive, while having a pronounced effect on physical properties, had no detrimental effects on adhesion. These could be very useful in extending the sealants joint movement capabilities into the higher movement (+/-50 %) ranges.

To the extent that joint movement ability, enhanced by lowering sealant modulus and increasing
elongation, is a factor in joint durability, an additive like this could contribute to increased durability and broaden the range of application.