Civil Engineering Reference
In-Depth Information
Butyl rubber sealants can be obtained using butyl crude rubber,
which can be dissolved in an appropriate organic solvent to give a solvent-
based sealant. Cured butyl rubbers have exceptional resistance to aging by
oxidation, ozone, heat and corrosive chemicals. Hence, butyl rubber is used
for weather seals and gaskets in buildings. However, organic liquids have
a similar swelling action as that of other rubbers and sealants.
Halogenated Butyl.
Butyl elastomers have a low density of
unsaturation, which results in a low cure rate when conventional vulcani-
zation systems are used. Butyl copolymers containing a small amount of
combined chlorine or bromine are vulcanized more quickly than normal
butyl rubber because the halogen atoms provide additional sites for the
cross-linking process. Butyl rubber has poor adhesive properties to metals
and other rubbers because of the lack of polar groups. This is the reason for
using halogenation.
Drying Oil-based Caulks.
The oils used in sealant formulations
are triglyceride esters of long chain unsaturated fatty acids. Oil-based
caulking compounds were employed almost exclusively for sealing joints
in buildings as lining against the infiltration of air, dust, and water during
the first half of the twentieth century.
[3]
Presently, they are supplied in gun grade or knife grade formats.
The gun grade is a viscous semi-liquid, which is suitable for applications by
air or hand-operated guns. The knife grade caulking compounds are more
viscous with a consistency similar to mortar, but used to a lesser extent than
the gun grade.
CH
2
-OOR
1
|
CH-OOR
2
|
CH
2
-OOR
3
triglyceride
where R
1
, R
2
, and R
3
are straight chain hydrocarbons.
There are three main factors to be considered in selecting a sealant:
joint movement, durability, and cost.
[3]
Since most sealants are used in exterior applications, they must be
deformable, have good recovery properties, and should have good overall
elastic properties. Many sealants used in the construction industry are
