Polyurethanes:
Polyurethanes are a group of versatile polymers with excellent properties. Therefore, designers and coating industry professionals are well able to use these compounds in a variety of applications. There are several examples of the many applications of these compounds, including clear coatings for single-layer roofing coatings and colors for pedestrian crossings, and more.
Polyurethanes have excellent resistance to impact abrasion and cracking, including fast and complete curing at room temperature. Aliphatic polyurethanes are more expensive than aromatic types. For this reason, aromatic types and epoxy-containing samples are used in esters, base paints and interface coatings. While aliphatics are specific to the final coating. The use of protective coatings to prevent corrosion in steel structures with primers and base coatings of epoxy systems are examples of important applications of polyurethanes. Another case is floor covering systems in which all kinds of base coatings can be used, sometimes the final urethane coating is enough for the final floor layer.
Application of polyurethanes and polyureas in flooring
The types of flooring application technologies are all based on two principles. One of them is thin film technology, in which one or more coatings with a thickness of about 50 to 125 microns are applied on the floor surface. Sealing and dust removal are also among the important steps in this method, the ultimate goal of which is to achieve floors with the following and decorated designs. Resins used in floor coverings are: alkyds, epoxies or epoxy esters based on water and solvents, suspended mixtures, water-based polyurethane mixtures and various types of acrylic polymers. The best case for this type of flooring is that the effect of materials Chemicals or water on the floor surface can be easily removed and no stain will be left. Alkyd coatings are very weak against caustic soda. Another type of coating is thick film technology, in which the minimum thickness of the coating is 200 microns and the maximum is sometimes up to ten millimeters. The purpose of this type of coating is to fill cracks, cavities and level heavily worn surfaces. Thick coatings. Cement and stone materials are mixed with a variety of resins. Epoxies, aromatic polyurethanes (often small oils and MDI di_phenylmethane 4_, 4_ SBR latex isocyanate and acrylic are the most commonly used resins. This is followed by manual troweling or roller application. In some cases, unsaturated esters, vinyl esters and 100% solid epoxies are used in thick floors. MDI-based aromatic polyurethanes are used for coating. Floors are widely used because MDI isocyanate is relatively inexpensive, and it is interesting to note that the MDI molecule and the polymer synthesized from it easily absorb ultraviolet light, causing yellowing of coatings exposed to sunlight. This is the issue.
Polyurea coatings:
In recent years, the technology of polyurea coatings has been developed and applied. One of the main advantages of this type of coating is that it hardens very quickly, which results in access to a high-speed technology. In hexamethylene diisocyanate (TMXDI) based polyurea systems (TMXDI), the coating sprayed on the ice block hardens within 20 seconds. Polyurea coatings are used to cover oil pipelines and the amount of cathodic current required for cathodic protection. They reduce. In many cases, polyurea systems are like two-component polyurethanes. The coating system in conventional polyurethanes consists of a part A consisting of polyurea and, if necessary, a pigment, and a part B, which is often hardener. As mentioned earlier, the reaction rate of polyurea formation is extremely high, so special spraying equipment is required. There was a time when the isocyanate fraction was made up of MDI monomers. These types of polyurea systems are cheap and have good properties. However, later in the early 1990s, aliphatic systems entered the market in the United Kingdom and the United States. In these systems, the optical stability is much better and the reaction speed is lower. However, the rate of the polyurea formation reaction is still so high that it poses a problem for researchers in the laboratory. When polyurea is prepared manually, the system becomes unusable after a few seconds and it will not be possible to mold and prepare a film from it. However, it is possible to prepare samples by spraying, but it is very difficult to move materials when the samples are too cold in the refrigerator.
Flooring with water-based systems:
Significant amounts of volatile organic compounds enter the environment when a large surface is painted with solvent-based paint systems. The increasing use of coatings has created a large market for solvent-free or water-based systems. Polyurethane paints mixed with acrylic varnishes have a large share of the European market. Acrylic emulsion polymers, or latexes, are relatively inexpensive. Acrylic emulsions have been a cost-effective commodity for almost a few years. They are widely used in decorative coatings, especially polyurethane flooring, and are much more resistant to abrasion than acrylics, but these compounds are expensive and new cheap formulas are being developed.
Polyurethane dispersion resins (PUD)
A common method in the manufacture of water-based polyurethane dispersion resins is the preparation of a prepolymer with the final isocyanate group, which modifies the polyol in the chain structure to form the carboxylic acid functional group. Water is dispersed to form ionic centers. In this way, the polymer particles become stable. The presence of a polyamine increases the chain length of the components.
In some mixtures, the molar ratio of NCO to OH groups is exactly 2: 1. At a molar ratio of about 1: 1, the viscosity becomes very high and the preparation of polyurethane dispersion resins becomes difficult. There is also a risk of untimely jelly. But if this ratio is less than 1.5 to 1, the possibility of such a risk is less. Ice is used to quickly lower the temperature while preparing polyurethane mixtures. As a result, the reaction rate between the water and the isocyanate group decreases. It is best for the prepolymer to react with the NCO terminal group with the amino chain enhancer. However, dispersing the prepolymer in water, especially in an industrial unit, takes some time. In any case, adverse reactions occur between water and isocyanate. By cooling the neutral mixture to below 0 ° C, adverse reactions are minimized.
Adhesion modifiers
There are many ways to improve the properties and performance of polyurethane dispersion resins. One of the methods of correction is conventional technology. Polyurethane dispersion resins are prepared in the presence of other polymers. In other words, they are mixed with them and must be modified before the new polymer polyurethane used to make the polyurethane dispersion resin is dispersed. By inserting an epoxy modifier into the prepolymer structure, the adhesion strength of polyurethane dispersion resins can be increased. For example, propylene oxide based on diglycidyl ether with a molecular weight of more than 700 reacts with diethanolamine at a molar ratio of one to one at C60 to form a combination with the epoxy terminal group and the three OH groups. With NMP as an auxiliary solvent, viscosity can be controlled. Before adding isocyanate, the intermediate compound is added to the polyol and DMPA mixture. The epoxy end group does not react with isocyanate or polyamine chain enhancer groups, as the reaction with isocyanate and amine is very slow, especially when the temperature is low. Modified polyurethane dispersion resins can be used to coat a variety of plastics used in the automotive industry, or these mixtures can be used in combination with a water-based aerosol. In this case, a substance such as dimethyl ether is needed. One way to reduce prices is to mix polyurethane dispersion resins with acrylic polymers. For a long time in Europe, water-based pigment coatings containing a 50:50 mixture of suspended polyurethane and acrylic emulsion resins have been used in the preparation of flooring. Becomes. When dry, these coatings create a semi-glossy white surface that is very suitable for covering concrete floors or decorating wooden floors, especially in cases where resistance to alcohol or water is important. One of the most important advantages of water-based polyurethane suspended mixtures is the completion of the reactions during this period of the systems, so that at the end of the reaction no free isocyanates are left. In the long run, with the move of the coating industry to isocyanate-free systems, this is considered a serious advantage.
Cement-based systems
A number of companies have recently used modified polyurethane cements in their flooring. Among the important properties in this composition, we can mention the low carbon dioxide gas, good flattening and its working time of about 30 minutes. All three components affect the properties of the floor covering based on polyurethane-modified cement. In this type of polyurethane systems, the reaction of the components with water, urea and carbon dioxide gas is caused by the presence of MDI in the formula. MDI reacts with hydroxy groups in castor oil, a type of fatty alcohol triglyceride. The cement-polyurethane mixture forms a hard coating that can be applied to a variety of liquid coatings for decoration. The lime in the composition absorbs water and the hardening rate of the cement is controlled in this way. Lime also absorbs some of the carbon dioxide from the MDI reaction and water. The reactions of lime with carbon dioxide and water are as follows:
CaO+CaCO3 —–> CaCO3
Ca(OH)+ CO2 —-> CaCO3+H2O
In modern technology, mortar is a part of the paint dyeing system. Mortar is a mixture of special resins and pigment components that consists of cement and fibers. The fibers provide the necessary flexibility to the coating and control the growth of cracks, while improving the tensile strength. Tensile strength of cementitious compounds, like most ceramic materials, is low, but their compressive strength is high. By adding fibers with some polymers, crack growth properties in the coating can be controlled. When cement is mixed with water. OH ions are formed in large numbers and the pH rises sharply. If this type of coating is used to coat steel surfaces, the alkaline environment of the steel protects against corrosion. Just like what happens in flat concrete with steel rebars. This type of coating can be easily used on vertical surfaces such as oil pipelines. The result is inexpensive corrosion-resistant systems that are highly flexible, robust and durable.
Conclusion
The use of polyurethanes, polyureas and polyurethane dispersion resins and the materials involved in their reactions is constantly growing and developing. These materials are most used in covering various surfaces. New environmental issues and regulations are driving new coating technology to solvent-free, solid-state systems and water-based systems. In the future, isocyanate-free coating systems will be used more. Of course, this depends on the intelligence, ingenuity and efforts of researchers and designers of all types of polymers and industrial resins. There are also interesting new designs for cement systems modified with polymers to protect the floor and steel surfaces. With the arrival of new systems in the market, the old ones will become obsolete and a bright future is ahead for the new systems.