Elastomeric Sealants (Polyurethane Sealants)

3.Polyurethane Sealants

There are 2 types of polyurethane sealants:

• The single-component sealants which are terminated by isocyanate groups -NCO and react with the ambient humidity,

• The 2 components sealants where part A is a polymer with -NCO terminal groups and Part B a polymer with hydroxyl -OH terminal groups, these 2 groups reacting together in several well-known modes and reactions.

By varying polymer composition, NCO/OH ratio, catalyst, a wide range of products and properties may be obtained.


General Properties of Polyurethane Sealants

All PU sealants have:

• Good elongation at break: 250 to 600%,

• Low to high modulus: 0.25 to 1 MPa

• Excellent elastic recovery higher than 90%

• Excellent abrasion resistance and tear strength, their resistance to indentation makes them the best sealants for floor joints,

• Service elongation range from 12 to 25% according to formulations

• Excellent adhesion to a wide variety of substrates: concrete, metals (preferably with a primer), wood, PVC

• Fair resistance to water (some formulation may be sensitive to hydrolysis), excellent aging resistance, a 20 years durability can be achieved or expected

The only drawbacks include:

• Slow cure (skin over time 5 to 20 minutes at 20°C and 50% RH, complete cure after 2 to 7 days at a speed of 2 mm/day)

• Resistance to UV is only fair

• Moderate resistance to chemicals, oils, solvents, acids and alkalis, and moderate resistance to hydrolysis

Some Uses of Polyurethane Sealants in Construction

• Pourable sealant for floor joints

• One component sealant for curtain walls joints

• One component sealant for concrete prefabricated panels

• Other utilization for one component PU sealants are: installation of wood and metal windows into the masonry, sealing roofs, expansion joints in masonry.