Polyurea – A Polyurea Overview
Polyurea is a kind of thermosetting elastomer which is derived directly from the chemical reaction between a synthetic polymers polymerizer and an isocyanic acid component during step-growth polymerization. The polyurea can be either aliphatic or aromatic in nature. This thermosetting polymerizes when pressure is applied on the polymerizer. It will harden again once the pressure is released. Polyurea sheets are used in various industries such as chemicals, health care, military applications and aerospace to name a few.
Thermoforming the polyurea into a suitable thermosetting resin is accomplished by compressing it. There are two types of polyureas, thermoform resin and liquid polyurea. Thermoform resin is generally preferred over liquid polymer as it is more elastic and comfortable to work with.
Polyurea coatings are generally prepared by a combination of heat, abrasion and solvent diffusion. Heat treatment is a general term used to describe any of the techniques which influence the thermo-plasticity of a material, usually resulting in changes in physical and/or chemical properties of the material. It is widely accepted that heat treatment plays a major role in the mechanical and structural properties of most polyurea formulations. Abrasion is a technique which involves removing small particles and molecules from a sample in a preparative manner.
After the surface preparation and heat treating, the components are dispersed on a support and the coating is applied. Spray coating is another common term used for the thermosetting of polyurea. A spray coating is generally a premixed formulation containing one or more substances having different compositions for different purposes. It is used as a coating on metals and other solid materials with a high resistance to abrasion, chemical resistance and corrosion.
The formation of polyurethane involves a reaction between polyurethane and one or more of its constituent molecules such as urea, n-type P2O5 and polyimide. This reaction may be partial or complete. Partial reactions may occur when one or more of the polymer components dissolve in the fluid.
A compound which undergoes partial reaction is referred to as isocyanates. Isocyanates have a specific chemical formula which is identical to that of polyurethane. Other isocyanates are referred to as secondary isocyanates. Secondary isocyanates are formed during the drying of the resin blend. In order to prevent the occurrence of isocyanates, a catalyst such as urea or n-type amino acids is added during the heating process of the resin blend.
Polyureas come in various forms including granular, liquid, foam, powder and paste. Some polyureas contain only urea while others contain both urea and N-type PPA. The most popular varieties are those which consist of urea and C-Ene. It should be noted that the most common polyurea component, N-type PPA, does not provide any form of moisture resistance.
Polyureas have been successfully used for coating steel, wood, textiles and other objects. In addition to these applications polyureas have also been found to be useful in treating a variety of oils and waxes. Polyureas have been found to be efficient in absorbing moisture from the atmosphere. They also have the ability to provide a controlled environment for adhesion of adhesives, sealants and adhesion bonding. There are a wide range of polyurea additives available to experiment with and many of them can provide the desired properties.