The effect of contact with PTFE tape on the moisture cure of an alkoxysilicone sealant

PTFE tape can be placed in contact with silicone glazing sealants, before they cure by reaction with water vapour from the atmosphere. Upon removal of the tape after cure, a smooth and tack free silicone surface remains. This phenomenon has been investigated by surface analysis (X-ray photoelectron spectroscopy and contact angle measurement) measurement of tack and weight changes of the tape, and it is concluded that what is involved is the rapid entry of liquid components from the silicone into pores in the PTFE. Cure depths have been measured at various times for sealant exposed at 25°C and 75.4% relative humidity, both with and without the PTFE tape. The tape has no effect on the rate of cure.