Page 560 - Handbook of Adhesives and Sealants

Sealant Families 481

acetate. They are noted chiefly for their very low cost. Some of these
sealants have been in general use since the early 1900s. Low perform-
ance sealants function mainly as crack fillers to prevent ingress of
dust, rain, and wind in substantially static conditions. However, even
in this application excessive shrinkage, hardening on age, and poor
adhesion severely limit the service. Compatibility issues and chemical
effects must usually be considered with low performance sealants. 3
Low performance sealants see limited use in mainly the consumer
markets.

13.2.1 Oil- and resin based sealants
Oil-based caulks are made from various unsaturated oils, including
linseed and vegetable oil. They have been used for centuries as glazing
sealants and putties. These sealants are 100% solids. The main cure
mechanism is oxidation causing crosslinking of the oil in the presence
of a catalyst. Typical components in an oil-based sealant formulation
are linseed or soy oil, fibrous fillers, calcium carbonate filler, pigment,
gelling agents, and catalyst.
Oil-based sealants with movement capability of only 2% are more
rigid than other sealants. Oil-based sealants continue to cure via ox-
idation while they are in service. After about two years they lose their
pliability and can be considered hard and brittle. Shrinkage of the
sealant in the joint also continues on aging. The service life is only
considered to be several years depending on the application. They are
generally not used in exterior applications where joint movement will
occur. A hand applied linseed oil-based sealant is used as a ‘‘putty’’ for
window sealing. Most oil-based sealants can be applied with an extru-
sion gun.
The rigidity associated with oil-based sealants is often overcome by
the addition of elastomeric resins such as polyisobutylene. These more
elastic formulations are called resin based sealants or caulks. They
are limited in movement to 5%, and their service life is longer than
oil-based sealants. A typical formulation for a resin based caulk is
shown below. 4
Composition Parts by weight

Bodied vegetable oil 100
Kettle-bodied vegetable oil 70
Polyisobutylene 100
Cobalt carboxylate 0.20
Calcium carbonate 483
Thixotropic agent as required for thixotropy
Titanium dioxide 17