When used in polyurethane, Diethyl toluene diamine (DETDA) can improve the strength and hydrolytic resistance of products, significantly enhance the productivity of products, and make it possible to industrialize polyurethane products with large sizes and complex structures. The rapid reaction speed of DETDA with isocyanate vinegar is also particularly suitable for solvent-free, fast-curing coatings. In addition, it can also be used as a curing agent of epoxy and alkyd resin antioxidant of rubber oil, dye, and pesticide intermediate.
Diethyl toluene diamine (DETDA) is a liquid steric aromatic diamine chain extender curing agent for polyurethane elastomers and epoxy resins. It is used for pouring, coatings, rim, and adhesives. It is also a chain extender for polyurethane and polyurea elastomers.
DETDA is a sterically hindered aromatic diamine. The steric hindrance of ethyl and methyl makes its activity much lower than that of toluene diamine (TDA). Its reaction speed with polyurethane prepolymer is several times faster than DMTDA and about 30 times faster than MOCA. It is mainly used in RIM polyurethane and polyurethane (urea) elastomer coating systems. It has the advantages of fast reaction speed, short demolding time, high initial strength, hydrolysis, and heat resistance. In addition, the product can also be used as an elastomer, chain extender of reactive injection molding polyurethane, curing agent of polyurethane coating, epoxy resin, and alkyd resin. Lubricants, pesticides, dye intermediates, plastics, rubber, oil antioxidants, and chemical synthesis intermediates.
The product is matured in an oven at 120 ℃ for 12h and placed at room temperature for seven days. According to the West German standard DNI53504, the performance of the product is equivalent to that of imported products:
|Item||Self produced DETDA||Imported DETDA|
|Tensile strength (MPa)||18.52||16.9|
|Elongation at break (%)||300||280|
|Flexural modulus (MPa)||208.5||210.8|
|Bending strength (MPa)||10.63||10.98|
Two kinds of liquid amine chain extenders are commonly used: diethyl toluene diamine (DETDA) and dimethyl lthio-toluene diamine (DMTDA). The reaction speed of liquid amine chain extender DMTDA with prepolymer is lower than that of liquid amine chain extender detda. When mixed with detda, it can give elastomer good surface leveling performance and has little effect on mechanical properties. However, because its molecule contains methylthio (- sch3), it is easy to change color and yellowing when used outdoors and cannot be used on occasions with high requirements for color retention.
A sterically hindered secondary amine chain extender, such as N, N'- dialkyl ethylenediamine, can be used. Its structural formula contains an unstable H and an alkyl group, equivalent to an internal plasticizer in the molecule. Compared with other aromatic amine chain extenders, the reaction speed of N, N'- dialkyl ethylenediamine with isocyanate is slow, and a better surface state can be obtained. When mixed with detda, it can adjust the gel time and improve the adhesion and surface state.
Polyurea formula DETDA contains five components: isocyanate, (active) thinner, polyether amine, chain extender detda, additives, and pigments.
|NO.||Relative molecular mass||Functionality||Viscosity, typical value at 25 ℃ / mPa・s|
|Relative Molecular Mass||Functionality||Viscosity, typical value / mPa・s|
|Chain extender1||178||2||280 at 20 ℃|
|Chain extender2||214||2||691at 20 ℃|
|Chain extender3||310||2||8 at 38 ℃|
|Chain extender4||379||2||Solid at 20 ℃|
The corresponding additives, pigments, and fillers are added to the pending on the application field. The addition of pigments and fillers is limited because the viscosity of the two-component must be controlled at the construction temperature. When the fillers and reinforcing fillers added to the system are high, they may be used as the third component.
The most crucial step in the treatment of polyurea coatings is mixing. Good mixing will be obtained using the appropriate mixing mode of mechanical purification and impact. The product's operating pressure and temperature also help optimize the mixing efficiency. Due to polyurea's high curing rate and short mixing time, the product is better prepared with a fixed 1:1 volume mixing ratio by impact mixing under high pressure. The pressure is 150 ~ 250 bar, the ideal product viscosity at the construction temperature needs to be <100 MPa • s, and the viscosity of the two components needs to be at the same viscosity level. Figure 3 shows the viscosity of MDI prepolymers at different temperatures, and table 2 lists the properties of these prepolymers. The viscosity of the resin mixture is about 900 MPa · s at 25 ℃ and drops below 100 MPa · s at construction temperature. Experiments have proved that the film properties of polyurea formed at 65 ℃, 70 ℃, and 80 ℃ are different and increase with the temperature increase. The new spraying equipment can set different temperatures for the two components to ensure optimal mixing on the nozzle.
Some things could be improved in the application formula of polyurea at the initial stage. There is still an illusion about polyurea technology as before. Some of these problems may be due to the need for more experience in introducing this technology. Some may be due to the need for sufficient construction equipment and the fact that this new technology cannot be constructed like the existing coating system. When polyurea was first proposed, it began to be misunderstood because it seemed almost impossible to construct. Polyurea is a fast-drying coating that can be used immediately after construction. As long as a few hours, the layer can achieve the best performance. It is insensitive to water or temperature and easy to prepare and produce. The following lists some unsuccessful tests and solutions of general concern.
Polyurea plays a unique role in the coating industry and polyurethane coating industry. The new raw materials and construction equipment development has expanded its application fields. The main advantages of polyurea spray coating are its activity, water insensitivity, low-temperature curing, and its unique physicochemical properties. Polyurea coating still cannot replace all other coating systems, but it plays an essential role in the coating market. Cost-performance cost of raw materials, polyurea coating, is still an inevitable and specialized project with the best cost-performance system. Polyurea may be the best or even the only suitable way if one or more unique performance requirements are met, depending on the required final performance and construction conditions. For a project, the absolute success of a polyurea system often depends on four key aspects: raw material suppliers, equipment manufacturers, system sites, and constructors.
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