Polyurea is a type of elastomer derived from the reaction product of an isocyanate component and a synthetic resin mixture component through a step growth polymerization. Isocyanates may be aromatic or aliphatic. May be monomers, polymers, or various isocyanate reactions, quasi-prepolymers or prepolymers. Prepolymers, or quasi-prepolymers, may be prepared from amine-terminated polymer resins, or polymer resins ending in hydroxyl.
The resin mixture may comprise an amine-terminated polymer resin, and/or an extension of the amine-terminated chain. The amine-terminated polymer resin has no intentional hydroxyl group. Each hydroxyl is the result of an incomplete conversion to an amine-terminated polymer resin. The resin mixture may also contain additives or non-primary components. These additives may contain hydroxyl, such as pre-dispersion pigments in a polyol carrier. Typically, the resin mixture does not contain a catalyst (s).
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Polymer structure
The word polyurea comes from the Greek word ???? - - poly - meaning "many"; and ?????? - oÃÆ' Â »ron means" urinate "(referring to urea, found in urine). Urea or carbamide is an organic compound with the chemical formula (NH 2 ) 2 CO. This molecule has two amine groups (-NH 2 ) that join the carbonyl functional group (C = O). In the monomer units of the polyurea, alternand of isocyanates and amines react with each other to form urea relationships. Urea can also be formed from isocyanate and water reactions that form carbamic acid intermediates. This acid quickly decomposes by breaking down carbon dioxide and leaving the amine. The amine then reacts with another isocyanate group to form a polyurea link. This two-step reaction is used to make polyurethane foam foams commonly called improper. The carbon dioxide released in this reaction is the main blowing agent (bubbly) especially in many polyurethane foams which more precisely should be called polyurethane/urea foam.
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Usage
Polyurea and polyurethane are copolymers used in the manufacture of spandex, which was discovered in 1959.
Polyurea was originally developed to protect the edges of the table leading to the development of two polyurethane polyurethane spray components and elastomers occurring in the 1990s by Mark S Barton and Mark Schlichter ( US 5534295 patent). Rapid reactivity and relative humidity insensitivity make it useful for coating on large surface area projects, such as secondary retaining layers, manhole and tunnels, tank liners, and truck liners. Excellent adhesion to concrete and steel is obtained with precise primers and surface treatments. They can also be used for spray and armor printing. Some polyureas achieve 6000psi (40MPa) tensile strength and more than 500% elongation makes it a difficult layer. Fast healing time allows many coats to be built quickly.
By 2014, polyurea-based elastomer material proves self-healing, combining itself after half-cut. This material also includes commercially sold free compounds. Elastomeric molecules are tweaked, making the bonds between them longer. The resulting molecules are more easily separated from each other and are better able to rebond at room temperature with almost the same strength. The rebellion can be repeated. Paints that dissolve self-healing and other coatings have recently taken a step closer to common usage, thanks to research conducted at the University of Illinois. Scientists there have used the "off-the-shelf" component to create a reintegrated polymer after half-cutting, without the addition of other chemicals.
Polyurea has become the preferred long-term solution for narrow boats. The traditional bitumen coating, known as "blacking" is replaced by the practice of polyurea coatings. The most obvious advantage is that there is no need to reattach the mantle every 3-4 years. It is estimated that the polyurea layer lasts 25-30 years.
References
Source of the article : Wikipedia
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