Two-component polyurea elastomeric coating systems make up the cutting edge protective coating industry. While they both might have some common characteristics, polyurea systems are a unique innovation in itself. Two-component polyurea systems are typically understood for a really fast dry time (normally less than 30 seconds), attained without utilizing a catalyst as in the two-component polyurethane systems. This rapid dry time is extremely consistent over a very broad ambient temperature variety. While the fast reaction/ rapid dry time is practically unaffected by ambient wetness, the presence of moisture on a substrate must be considered when achieving adhesion to that substrate.
This is all made possible by the distinct chemistry of basic materials used to develop the two-component polyurea systems. Two-component fast set polyurea systems usually do not include any solvent or Volatile Organic Compounds (VOC). They are generally processed by specialized plural part equipment, which establishes high pressure and high spray application temperature level. The two parts are combined inside the impingement mix spray weapon, as there usually is not any pre-mixing or hot potting. Because of the introduction of the two-component polyurea technology, a wide range of applications are seen. These include coating/lining applications over concrete, geotextile membranes, various metals for corrosion, ornamental areas, and some plastics. For all of these, the fast dry time of the technology indicates that the application area can be gone back to service rather rapidly. Polyurea systems with a slower/ customized reactivity and set time are likewise discovering use in joint sealant/filler system applications. Here the product is integrated in a low pressure, low temperature by means of "folding" in a static mix tube and applied as a bead of material.
prepolymer, or quasi-prepolymer, can be made from an amine-terminated polymer resin, or a hydroxyl-terminated polymer resin. The resin mix must be made up of amine-terminated polymer resins, and/or amine-terminated chain extenders. The amine-terminated polymer resins will not have any intentional hydroxyl moieties. Any hydroxyls are the result of incomplete conversion to the amine-terminated polymer resins. The resin mix might likewise consist of additives or nonprimary parts. These additives may contain hydroxyls, such as pre-dispersed pigments in a polyol carrier. Generally, the resin mix will not contain a catalyst(s).
Well, that is a mouthful and what does it all mean? This article will attempt to provide a basic summary of the innovation and is not meant to be a complete chemistry innovation lesson on polyureas, hybrids, and polyurethane systems.
A BRIEF HISTORY of POLYUREA DEVELOPMENT:.
The very first actual referral to polyurea can be found in 1948 when some scientists were examining thermal properties/ melting points of various polymer systems. They were comparing polyesters, direct polyethylene, polyurethanes, polyamides, and polyureasand, discovered that the polyureas had far exceptional thermal properties and an extremely high melting point. Remember that these polymers were manufactured in a laboratory environment and were not very conducive to coating/ lining applications. Visual representation of the melting points of different polymers for contrast.
The advantages or special characteristics of polyurea over polyurethane and
polyurethane/polyurea hybrid system in RIM applications consisted of rapid molding/ treatment time which was generally 2-3 seconds set or gel times with a dry time of less than 10 seconds. Also understood was decreased part scrap rate and most notably, the capability to paint the parts using the online Electrophoritic Paint Deposition (ELPO) procedure.
This process included warming the parts to almost 400 ° F( 205 ° C ), a temperature level that was really. harmful to a polyurethane and most hybrid systems. Polyurea systems are kept in mind for their high thermal stability.
The two-component fast set polyurea coating/ lining innovation was first presented to the market in 1988, following the advancement in 1986.4,5 This technology progressed from the requirement to establish a more steady, durable and 100% solids polymer system for coating rigid, spray used polyurethane foam utilized in roofing and other insulation applications.
Some of the very first plural part spray used polyurea formulations had.
get times of 1-- 2 secs, with tack without < 10 secs. The actual very first commercial application of the polyurea elastomeric coating/ lining technology was as a roof system in 1989.
Nevertheless, this was not the first real work with the spray applied two-component polyurea innovation. Earlier work in the 1970's made use of modified polyamines and high levels of plasticizers and solvents to attain a sprayable system for coating work. While this proved successful in laboratory applications, poor field performance was kept in mind and this innovation never ever got acceptance. A distinct, solvent polyurea/ epoxy/ urethane hybrid type system was also utilized in the 1970's for the production of a composite traction system. Other uses included short-lived shelters, roof, and blast defense. This was not a true polyurea system though.
In 1998, the National Association of Corrosion Engineers (NACE) issued a Technical Report on polyurea systems in an effort to provide a preliminary description/ contrast of polyureas to polyurethanes. This document gives a really basic view of technology with limited basic details as to the chemistry included.
POLYUREA CHEMISTRY/ FORMULATION:
Since we, the Polyurea Development Association, are focusing our efforts on defining the technology, we require to identify what part of the technology/ response we are looking to that categorizes whether a polyurea or not. The agreement seems to be that we are looking at a 2-part processed system, whether it was spray, caulk, put or RIM processed.
Therefore, the determining reaction would be the response that occurs between the 2-the part system, i.e. the response of the polyisocyanate component and the resin blend element. This would be the polymerization/ curing part.
This is a thermoset response
The primary identifying characteristic with the polyurea innovation over polyurethanes is that amine-terminated (- NH2) resins are used rather than hydroxyl ended (- OH) resins, typically described as polyols. The reaction of the amine ended resins with the isocyanate element leads to the development of a urea linkage. Considering that this is a polymer and these units repeat, the term polyurea then applies. A basic illustration of the "polyurea" response is offered below (Figure 3), compared to polyurethane in Figure 4:.
Figure 3: Polyurea Development Reaction.
Figure 4: Polyurethane Formation Response.
It should be kept in mind that "polyurea" is a description of a technology and it in itself is not a coating system. There are a range of solution possibilities to achieve the desired performance, as well as numerous ingredients that might be used. This is enabled by the selection of various basic materials in the formula, much like that for polyurethane chemistry. The choice of appropriate basic materials for the system can be very intricate procedure.
Based upon reactive equivalents between the polyisocyanate part and the resin mix part for the 2-part systems, the following Table I can be established.
From Table II, one can see that for the resin blend part of the 2-part fast set polyurea elastomer systems, the chain extender contributes the most part of the reactive hydrogen equivalents with the isocyanate-reactive equivalents. The chain extender is actually the identifying aspects of what makes a polyurea. There are no polyols, or hydroxyl ended materials, utilized as the main reactive resin in the resin mix part of a two-component polyurea elastomer system. If so, then these would be classified as a polyurea/polyurethane hybrid system.
One might then likewise point to the response of wetness with the polyisocyanate part When wetness enters into the reaction mechanism, the wetness would react with the isocyanate to form a carbamate. This will extremely rapidly dissociate into an amine-terminated molecule, which would then extremely quickly react with an isocyanate speciemoiety to form a urea linkage. For this reason, forth, single component wetness treated urethane.
the system could be thought about as a polyurea system, however not a two-part system. The wetness of the response is the treating mechanism to the response.
There is also some interest and operate in the 2-part systems where part of one element is obstructed, both parts are mixed and reaction/ curing occurs when another element is presented. This other aspect might be heated, as is the case of blocking the isocyanate element (using oximes and phenols). The other would be wetness, as when it comes to obstructed amine resin blends (development of aldimines).
Aromatic Based Polyurea:.
Fragrant based two-component polyurea systems have actually been the workhorse of the two-component polyurea innovation. Aromatic refers to the nature of the chemical backbone of the polymer system. The two-component systems consist of an isocyanate part and a resin mix component. The isocyanate component is usually an isocyanate quasi prepolymer, prepared from methylene diisocyanate.
These are not the only two kinds of chain extenders that might or are currently used; there.
are others that can supply the very same impact. A lot of these are solids at room temperature level.
and might be difficult to mix into the resin blend portion by the maker of the system.
Table IV reveals the relative response rates of an isocyanate component with different amine-terminated materials. The secondary or hindered diamines extend the reactivity of the rapid dry two-component aromatic polyurea elastomer innovation to enable improved processing and much better substrate wetout/ adhesion.
Aliphatic Based Polyurea:.
Following the intro of the fragrant based two-component polyurea elastomer.
systems; the fast dry aliphatic-based products were established.9,10 For these systems, you.
also have an isocyanate element and a resin mix portion. The isocyanate is likewise a.
quasi-prepolymer, like with the fragrant based two-component polyurea systems.
Nevertheless, the isocyanate utilized is a light stable monomer and the "polyol" might in fact be.
the polyoxypropylene diamine. The typical isocyanate used is isophorone diisocyanate.
In general, the standard fast set polyurea spray innovation is comparable to physical properties of polyurethane/polyurea hybrids and polyurethane systems. Simply put these innovations of coatings/ lining systems can be created to accomplish a range of elastomer physical properties.
The genuinely big benefit of polyurea technology is the speed of response and the capability to put the structure or center back into service very quickly. One has to be really careful here though due to the fact that polyurea systems may set and give a preliminary treatment really rapidly that will permit this "go back to service" very rapidly, but not establish supreme elastomer physical properties for 24 hours or more. This all depends upon the specific polyurea system formulation.
The polyurea systems do tend to have much better flexibility at lower temperature levels than to the corresponding polyurethane/polyurea hybrid or polyurethane system.
Moisture and Temperature Sensitivity:.
One of the significant benefits of the polyurea innovation is the relative insensitivity to wetness throughout processing/ application. As the amine-- isocyanate reaction tends to be preferential over the hydroxyl-- isocyanate reaction, foaming of polyurea systems is nearly impossible. However, it can happen, especially if a driver is present. For polyurethane/polyurea hybrids and polyurethane systems, catalysts are utilized to control the reaction. If wetness is present, they may exhibit some foaming which leads to decrease density, porosity and poor performance.
Figure 14 shows the impact of wetness/ humidity during processing of both a fast set spray polyurea and spray polyurethane systems. As the INDEX boosts, ratio of isocyanate equivalents to reactive hydrogen equivalents, the density of a polyurea system remains consistent while the polyurethane system shows a decline in elastomer density.
The non-polyurea system foamed due to the catalyzed response of isocyanate with the moisture in the air. This reduction of density/ foaming would result in total efficiency concerns for the polyurethane system. Comparable outcomes have likewise been shown with a polyurethane/ polyurea hybrid technology.
While polyurea systems might show insensitivity to moisture, that does not suggest they can be applied over a wet substrate. The polyurea will react over the water, but the used system will not bond to the substrate because area.
The ambient temperature and substrate temperature level might have little affect on the response and treatment of a polyurea system as compared to the others. But, the real important concern is substrate temperature level and dew point. Market basic coating practices need to likewise be.
followed with polyurea systems and application because the substrate temperature level must be 5 ° above humidity and increasing. If not, moisture will condense on that substrate and cause adhesion concerns with the polyurea innovation, similar to other coating/ lining systems.
Polyurea systems in general show comparable chemical resistance properties as that of similar formulated polyurethane/ polyurea hybrids and polyurethanes. This is due mainly to the reality that all have the polyether backbone in the elastomer. The urea linkage discovered in the polyurea along with the hybrid system is more resistant to hydrolysis.
than the urethane linkage. Polyurea systems do tend to have much better resistance to alkali high pH, than the hybrids or polyurethane systems. Aromatic polyurea systems are subject to chemical oxidation.
There are some more recent innovations of polyurea systems that are showing considerably higher chemical resistance with respect to extremely acidic environments. Remember that chemical resistance/ efficiency can be straight related to processing conditions of the polyurea systems. Those that do not attain total mix and include porosity will have lower chemical resistance performance than those processed at the optimum conditions. This would consist of appropriate processing temperatures and pressures as well as.
the correct mix setup in the spray gun.
One extremely interesting note about the rapid dry two-component aromatic and aliphatic polyurea elastomer systems is the resultant thermal properties of the polymer films.
Two-Component polyurea elastomer systems are amorphous in nature, not crystalline like polyurethane systems. This amorphous nature is similar to that of epoxy type systems other than that two-component polyurea system do not have a real glass transition temperature level. Rather, 2 unique Tg's can be noted, one corresponding to the melting point of the soft-block in the polymer and the other corresponding to the melting point of the hard-block in the polymer.
From Dynamic Mechanical Spectroscopy examinations of typical two-component polyurea elastomer systems, a low temperature Tg is noted at about -50 ° to -60 ° C with a high. temperature Tg of about 230 ° to 260 ° C for the fragrant based systems. The twocomponent aliphatic polyurea systems have a low temperature level Tg about the like the " Polyurea Coatings:
two-component fragrant polyurea however have a heat Tg of about 110 ° to. 120 ° C. 10 The response curve between these 2 points remains relatively flat. This would be the efficiency variety, temperature smart, for a polyurea elastomer system. In lay terms, the polyurea elastomer systems would tend to show some substantial stiffening at temperature levels less than -50 ° C with some polymer softening, or possible decomposition,.
at the upper temperatures Tg's Figure 15: Dynamic Mechanical Spectroscopy of Aromatic Polyurea Spray.
Because the formation of the elastomeric polyureas is based upon a thermoset response, some direct shrinkage during remedy will take place. This is not thermal growth/ contraction due to temperature level modifications. The total quantity of shrinkage will depend upon the reactive constituents of the isocyanate and resin mix components, even though the elastomeric system might have elongation values greater than 200%. These direct shrinking forces might be strong enough to curl the corners or edges of the used work and might cause disbondment or damage to the substrate. The elastomeric polyurea systems utilized must be developed for the particular coating/ lining application work.
Aliphatic polyurea systems have outstanding resistance to degradation by ultraviolet light and are utilized for a variety of exterior and interior atmospheric services.
Two-component polyurea elastomeric coating/ lining systems may be rather of a newcomer to the market, however it has revealed a good deal of versatility and application usage.
The quick dry time attributes offers an exceptionally excellent cost and time-effective option to a variety of coating/ lining applications over traditional technologies. With the severe efforts for commercial rehab and increasing requirement to abide by ecological, economic and time restrictions, the speed and sturdiness of the twocomponent polyurea technology hold fantastic guarantee.
The two-component polyurea technology must be dealt with as other coating type systems with regard to correct and total surface area preparation. The originality of the technology is not a cause to restrict and even remove proper, industry accepted surface preparation standards. The substrates should be clean, dry and free of contaminants.