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Adhesives Ingredients
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Adhesives Ingredients

Polyurea Adhesives and Sealants - All You Need to Know

Edward M. Petrie – Jul 31, 2020

Polyurea Adhesives and SealantsPolyurea adhesives and sealants offer fast-curing systems with interesting properties. Polyurea chemistry has been well developed for high-performance maintenance coatings. However, polyureas are not as well-known as adhesives or sealants except in applications that require exceptionally fast cure, such as high-volume assembly (e.g. RFID chips or fast-setting construction sealants).

Let’s review the chemistry of polyureas used in adhesive and selant formulations. This article assesses the advantages and disadvantages of these interesting polymers in current and future applications. To achieve adhesive and sealant products that have a fast cure with properties that are equivalent or superior to conventional polyurethane and epoxy systems, updated formulation principles will also be provided here.

Chemistry of Polyureas Versus Polyurethanes

Polyureas are similar to polyurethanes but they are based on reacting an isocyanate with a multifunctional amine rather than with a polyol (see figure below). The polyurea chemical reaction occurs quickly in a single step without added catalysts. This type of reaction offers advantages, such as:

  • It provides good bonding and physical properties within a few seconds to minutes at room temperature.
  • This unique “auto-catalytic” nature is one of the most notable characteristics of polyurea products.

Chemistry of Polyurea and Polyurethane
Chemical Reaction for a Polyurethane (Top) and Polyurea (Bottom)

With a conventional 2K polyurethane adhesive, the base chemicals consist of an isocyanate and a polyol with a mixing ratio of approximately 1:1. The 2K polyurea adhesives consist of isocyanate and an amine, also mixed at a ratio of approximately 1:1. The high reaction speed of a polyurea often requires dedicated mixing and dispensing technology.

Current developments in the industry have aimed at controlling (slowing) the gelation of polyurea without sacrificing performance properties.

The Polyurea Development Association (PDA) is the official trade association for the polyurea industry. Polyurea is defined by the PDA as a material derived from the reaction product of an isocyanate component and a resin component.

  • The isocyanate can be aromatic or aliphatic in nature. It can be a monomer, polymer, or any variant reaction of isocyanates, quasi-prepolymer, or a prepolymer.
  • The prepolymer or quasi-prepolymer can be made of an amine-terminated polymer resin or a hydroxy-terminated polymer resin.

The table below defines the differences between a polyurea, polyurethane, and polyurea/polyurethane hybrid.

Chemistry Characteristics
  • A polyurea provides a chemical backbone containing amine linkages.
  • Polyurea has been used as an industrial coating and sealant in severe environments with good chemical resistance.
  • For example, it is resistant to hydrocarbons and hydrogen sulfide gas and immersed sewage application.
  • Usually these formulations have no amines in the polymer backbone.
  • All functionality is considered to be hydroxyl.
  • Polyurethanes show good longevity and are relatively inexpensive.
  • This hybrid is the result of a chemical reaction between an isocyanate and a mixture of polyol and amine reactants.
  • Hybrid formation can display some of the negative problems associated with polyurethane chemistry (less resistance to immersion or extreme application temperature conditions).

Characteristics of Polyurea, Polyurethane, and Polyurea/Polyurethane Hybrids

The classic water/isocyanate reaction used with most moisture-cured polyurethane adhesives and sealants also produces urea groups at the end of the process. However, this reaction should not be considered a polyurea reaction since the mechanism is a two-step process. It is a much slower reaction and produces carbon dioxide as a byproduct.

The properties of polyurea, polyurethane, and polyurea/polyurethane products can be made comparable since there is a great degree of freedom in the formulation. The unique characteristics of polyurea systems are described below.

 » Continue reading to learn more about the properties, formulation refinements, applications and recent developments of polyureas in adhesives and sealants versus other polymers.

2 Comments on "Polyurea Adhesives and Sealants - All You Need to Know"
Joseph S Aug 10, 2020
Excellent article
Sheila M Aug 6, 2020
Dear all, Can I use this same approach to overprint varnish on flexible food packaging? Thanks and regards, Sheila

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