Spray polyurea coating using hydrophobic polyol

Since being developed by researchers at Texaco Chemical in the mid-1980s, spray polyurea coatings have gained widespread acceptance in the coatings market. Compared to other coating alternative technologies such as epoxy and acrylic, spray polyurea is uniquely advantageous because of its application properties under extreme conditions. These properties include fast cure and put into use, low temperature cure (less than 0 ° C), moisture insensitivity, low VOC content and excellent physical and mechanical properties. These features, along with improvements in construction equipment, have driven polyurea to become a leading technology in related fields such as secondary sealing, corrosion protection, waterproofing membranes and tank lining.

Polyurea coating chemistry can be divided into two parts: (1) pure polyurea and (2) hybrid polyurea, both based on the chemical reaction of isocyanate curing. Pure polyurea coatings are the result of a one-step reaction between an isocyanate-terminated prepolymer and a cured blend containing only the amine-terminated resin and the chain extender. In another aspect, the hybrid polyurea is a product obtained by reacting an isocyanate-terminated prepolymer with a cured blend comprising a hydroxyl group and a terminal amine-based resin and a chain extender. Although little difference in the final physical properties and mechanical properties of pure polyurea and hybrid polyurea is observed, the addition of a catalyst to the hydroxyl group-containing resin in the hybrid polyurea requires the addition of a catalyst to maintain the same level of reactivity as the pure polyurea. Due to the competitive reaction between the water and the hydroxyl terminated resin and the reactive isocyanate groups, the hybrid polyurea becomes sensitive to moisture, and bubbles are formed when high levels of moisture are present.

The pure polyurea chemical process has always occupied the main market for spraying polyurea, but the recent development of hybrid polyurea spray coating has become a new hot spot. Formulators are taking advantage of the performance advantages of hybrid polyurea to improve certain properties of spray polyurea coatings. These properties include mechanical properties, heat resistance, and chemical resistance. While the availability of terminal amine based resins, such as polyetheramines, is limited in design, hydroxyl terminated resins (e.g., polyols) have a wide range of variability. These polyols may differ in backbone structure, relative molecular mass, and functional groups. These features enable the development of high performance hybrid polyurea coatings whose performance levels are not achievable using typical pure polyurea technology. For example, a recently published article illustrates that hydrocarbon-resistant solvent properties of polyureas can be improved by the addition of polyester polyols to the polymer backbone. By introducing polyester polyols into the formulation, the authors were able to develop coatings with excellent xylene resistance. Xylene is an aggressive chemical commonly encountered in the oil and gas industry. Polyurea can be used for secondary sealing and Container lining.

We recently introduced a new hydrophobic VORAPELTM polyol 3. The use of these polyols has been formulated as a cast polyurethane elastomer which exhibits excellent moisture resistance and good water-resistant acid resistance (e.g., 10% hydrochloric acid and 30% sulfuric acid). As water-soluble acids are used more and more in the fields of sewage treatment, chemical treatment, steel pickling, oil and natural gas recovery, we have expanded the utility of these hydrophobic polyols by developing hybrid polyurea spray coatings. When applied to reinforced concrete, this material provides a mechanically good coating with good adhesion and resistance to high concentrations of acid.

test

The prepolymer was synthesized in a 15 liter glass reactor equipped with a thermometer, an overhead stirrer, a nitrogen inlet and an outlet for continuous flow of nitrogen. In the first step, a polyol was added to the reactor while a few drops of benzoyl chloride were added and heated to a temperature of 50 °C. Once the polyol reached equilibrium, liquid methylene diphenyl isocyanate (MDI) was added to the reactor in two portions over 1 hour. After each aliquot of isocyanate is added, the temperature of the reactor should be carefully monitored to ensure that the temperature does not rise due to the exothermic reaction between the polyol and the isocyanate. After the last portion of the isocyanate was added, the reactor was heated to 70 ° C and maintained at this temperature for 3 hours. The reactor was then cooled to 50 ° C to prevent thermal burns and the prepolymer was packaged in a clean, dry metal can. The prepolymer prepared by this method has a shelf life of up to six months.

The resin blend used to cure the prepolymer is prepared by directly adding the raw material to a clean, dry metal can. Although a specific order of addition is not mandatory, in this case, the order of addition of the raw materials is added from the lowest to the highest in the mass concentration in the formulation. Where a catalyst is used, the catalyst should be carefully weighed on an analytical balance and diluted with 40 to 50 grams of the resin mixture prior to addition. The material was stirred and mixed at a speed of about 1000 rpm with a high speed stirrer and immediately put into use.

The elastomeric coating is prepared using Isotherm PM or other suitable multi-component high pressure spray equipment. The material was dispensed at a static pressure of 2000 psi and sprayed using a Graco Fusion cleaning spray gun or a Probler AP-2 polyurea spray gun. The sample is sprayed onto a low surface energy material, such as polyethylene, and the coating can be peeled off within 20 to 30 minutes after spraying. The sample used for the adhesion test was applied by applying the coating to a 1⁄4 inch thick steel plate which was sandblasted to a roughness of 2 to 4 mm according to the SSPC10 standard. All panels were dried at room temperature for 7 days prior to physical and chemical resistance testing.

The hardness was tested in accordance with ASTM Test Method Standard D2240; tensile strength and elongation at break were tested in accordance with ASTM Test Method Standard D1708 or D412. The tear strength (C die) was measured in accordance with ASTM Test Method Standard D624. By placing a 2 x 2 inch sample (3 mm thick)

The hydrolytic stability was measured by immersion in water for 2 weeks at a test temperature of 95 °C. After soaking, the sample was patted dry, weighed, and stored in a plastic bag to prevent moisture evaporation prior to the tensile test. The chemical resistance was tested in accordance with ASTM Test Method Standard D534-95, and the 2 x 2 inch sample was immersed in the medium required at 25 ° C for 7-21 days for testing. The sample was then rinsed with water, patted dry, and stored in a plastic bag prior to the tensile test. The pull-off adhesion test was carried out in accordance with ASTM test method standard D4541, and the self-calibration (type IV) pneumatic adhesion tester was used for the test. For the sample impregnated with the chemical medium, the test piece was bonded to the surface of the coating after drying the sample at 25 ° C for 1 week.

Results and discussion

The physical and mechanical properties of hybrid sprayed polyurea coatings based on hydrophobic VORAPEL polyols were evaluated and compared to those of pure polyurea coatings. For this study, two methods were used to introduce VORAPEL polyol into the formulation. In the first method, a 16% NCO prepolymer (prepolymer 2) obtained from VORAPEL is cured with a polyamine-containing standard polyurea resin blend. In the second method, the same 16% NCO-terminated prepolymer is cured with a resin blend also comprising VORAPEL polyol. The samples obtained by the two methods contained nearly 25% by mass of VORAPEL (hereinafter referred to as VORASTART M7000 pure polyurea) and 50% (by mass) of VORAPEL (hereinafter referred to as VORAPEL 7000 hybrid polyurea). As shown in Table 1, the addition of the above VORAPEL polyol to the NCO-terminated prepolymer had little effect on the viscosity of the prepolymer. However, when the polyetheramine was replaced with a VORAPEL polyol, the resin viscosity was found to be significantly lowered. From a practical point of view, the lower viscosity facilitates proper mixing of the 1:1 formulation compared to the pure polyurea system, allowing the system to be processed at lower temperatures. The ability to process materials at lower temperatures provides greater flexibility in spray application equipment, using viscosity at a given temperature as a means of controlling the pressure differential between the isocyanate and resin dosing pumps. Maintaining a pressure differential of <100 psi ensures that the material can be sprayed and thoroughly mixed in the desired 1:1 ratio.

The reactivity of all elastomer systems is highly dependent on the choice of resin curing agent blend. As shown in Figure 1, the effective gelation time of the two polyetheramine/DETDA resin blend systems was 3 to 5 seconds, and the surface drying time was between 7 and 10 seconds. The hybrid formulation containing the VORAPEL polyol in the resin blend was extended to 7 seconds and the surface drying time was 20 seconds. Surprisingly, the addition of VORAPEL to the formulation did result in a modest increase in the hardness of the coating. The hybrid polyurea containing only the VORAPEL polyol gave a Shore A hardness of 90, while the pure polyurea had a Shore A hardness of only 85. In general, when a polyetheramine-containing resin blend is used in a pure polyurea material, excellent mechanical properties such as elongation and tear strength can be obtained.

The difference in stress-strain properties of pure polyurea materials is also reflected in their heat rheology curves, which are obtained by DMTA analysis from a temperature range of -100 ° C to 200 ° C. Track the tan δ and storage modulus (G') of each system, as shown in Figure 1. The VORASTAR 7000 pure polyurea material has a much higher storage modulus (about 80 MPa) at room temperature compared to the hybrid polyurea (25 MPa). Polymers with high storage modulus require greater force (stress) to stretch the material (strain), thus resulting in greater ultimate tensile strength and elongation properties. On the other hand, high hardness polymers, such as VORAPEL hybrid materials, require less force to stretch the material, which is a preferred choice for applications like waterproofing. The high temperature stability of the VORASTAR 7000 hybrid polyurea also showed modest improvement. The tan delta curve indicates that the two pure polyurea materials can withstand a melt transition of about 150 ° C, while the melting temperature of the hybrid polyurea exceeds 200 ° C.

To evaluate the ability of polyol VORAPEL to alter the overall hydrophobicity of elastomer samples, our initial efforts focused on measuring hydrolytic stability. Since polyurea is known to exhibit excellent hydrolytic stability under normal environmental conditions, we have chosen a more stringent set of conditions to test our materials. The data in Table 2 represents the change in mass and mechanical properties after 14 days of immersion in deionized water at 95 °C. The samples were evaluated for changes in tensile strength, elongation, hardness and quality after impregnation. All VORAPEL-containing materials have excellent hydrolytic aging properties compared to pure polyurea samples. When the VORAPEL polyol was simultaneously added to the prepolymer and the resin component, the loss of tensile strength was reduced from 57% to only 35%, and almost complete elongation and hardness retention were observed. The improved hydrolytic stability of the VORAPEL 7000 hybrid formulation may be due to the significantly lower mass increase of the sample after immersion. Pure polyurea absorbs about 5% of its own mass in water, while VORAPEL 7000 hybrids only absorb <1% of water. By minimizing the absorption of water in the polymer matrix, the plasticizing effect of water (lower hardness) and the hydrolytic cleavage of urethane/urea bonds (lower tensile strength) are all reduced. The results of the high temperature hydrolysis aging study showed a delicate balance between the treatment of the sprayed polyurea and the long-term performance of the polyurea. Although it is a fact that the hybrid polyurea is often sensitive to atmospheric humidity during the curing process, greatly improving the overall hydrolysis performance of the polymer can be achieved by careful selection of the polyol component; in particular, the environmental conditions can be controlled during the construction process. In case of humidity, for example.

Many industrial uses of polyurea coatings have been discovered which protect steel and concrete surfaces from corrosive effects in the presence of water soluble acids such as hydrochloric acid and sulfuric acid. These industries include steel processing, oil and gas production, mining and wastewater treatment. Although there are some polyurea coatings on the market that are resistant to low concentrations of water-soluble acids, there is still a need for a polyurea coating that demonstrates its ability to withstand high concentrations of water-soluble acids over extended periods of exposure. The resistance in these types of applications is best defined as the ability of the coating to retain its original rigidity and flexibility, and its ability to withstand swelling (increased size and mass). To achieve this goal, we decided to evaluate the performance of VORAPEL-containing polyurea coatings for these applications. The effect of immersing the polyurea coating in 28% HCl and 50% H2SO4 is shown in Table 3. After 7 days of immersion in 28% hydrochloric acid at 25 ° C, the loss of tensile strength of the two pure polyurea coatings was close to 90% and the flexibility decreased by 50%. Although the addition of VORAPEL (55% vs. 85%) in polyurea showed a modest improvement in mass increase, it had little effect on the decline in mechanical properties. When the hydrophobic polyol VORAPEL was simultaneously added to the isocyanate and resin blend, the coating still had 91% of its original tensile strength and the mass increase was reduced to <2%. The Global Coatings Network also found a similar trend for coatings that were immersed in 50% H2SO4 for 7 days. In this case, however, only the VORASTAR hybrid system survived the exposure test. After the exposure period, the sample retained 60% tensile properties, retained an initial flexibility of greater than 90%, and only a 23% increase in mass. The surface shows slight discoloration and surface defects. Two pure polyurea samples showed extreme swelling with an increase in mass of 135% and 90%, respectively (based on VORAPEL). The degree of surface deformation is so severe that the material cannot be tested for mechanical properties.

A potential disadvantage when developing a specific set of chemically resistant and solvent resistant hybrid coatings is that the sample is increasingly susceptible to other types of chemical media. For example, hydrophobic polymers designed to be water resistant are generally susceptible to attack from non-polar media. In order to understand the water and non-polar media capabilities of the VORAPEL system, we investigated the effect of diesel on the mechanical properties of elastomers. As shown in Table 4, there was almost no difference in the addition of VORAPEL polyol to the prepolymer formulation (VORASTAR 7000 Pure Polyurea) compared to the pure polyurea formulation. The change in tensile and elongation properties was similar and only a small difference in mass increase percentage (9% to 13%) was found. When a higher content of VORAPEL was added to the polymer (hybrid polyurea), it was found that the decrease in mechanical properties and the increase in mass were almost twice that of the pure polyurea sample containing the polyetheramine resin as a curing agent. Surprisingly, after all samples were immersed in diesel, there was no change in appearance and the hybrid polyurea material maintained excellent adhesion (Table 5).

Chemical media aging and adhesion

Polyurea coatings can often fail due to detachment of the coating from the substrate. Coating peeling may be the result of impact forces or chemical attack on the polymer. Excellent ability to maintain the original mechanical properties and low mass increase is an important feature of the coating, that is, its ability to adhere to the surface and maintain good adhesion after chemical exposure is extremely important. Based on its impressive performance after long-term immersion testing, VORASTAR hybrids require further adhesion testing. The ability to maintain the original adhesion of the coating after being fully immersed in 28% HCl and diesel can be tested by pull-on adhesion. Table 5 gives data for the pull-off adhesion test for two different coated samples. Excellent adhesion was observed after immersion in 28% hydrochloric acid for 21 days, and the adhesion was reduced by only 100 to 150 lbs. It is worth noting that these tests yield cohesive failure of specific surfaces of the material. This may indicate that any acid-induced damage occurs only on the surface of the coating and thus weakens the portion with little effect on the substrate coating interface. The mechanical properties of the coatings impregnated in diesel (Table 4) indicate that the VORASTAR hybrid coating is slightly more susceptible than the pure polyurea coating. However, adhesion tests after 21 days showed that these coatings maintained excellent adhesion, even after exposure. These samples retained an initial adhesion of greater than 80%.

in conclusion

In summary, spray-on polyurea coatings based on hydrophobic VORAPEL polyols provide end users with excellent physical and mechanical properties of typical spray polyurea coatings while improving the resistance to moisture and water-resistant concentrated acids. Although the performance was found to be moderately improved by adding the polyol VORAPEL to the isocyanate-terminated prepolymer, the VVORAPEL polyol was added to the resin curing agent blend to obtain 28% hydrochloric acid and 50% H2SO4. Coating. VORAPEL 7000 hybrid polyurea coating has excellent adhesion to steel and maintains good adhesion after long-term immersion test. Sprayed polyurea coatings with such performance levels have a wide range of uses, for tank and container liners, for interior wall coatings, and as concrete protective coatings.

[Follow the WeChat public number "Jiuzheng Paint Network"; pay attention to surprises, scan code to view "If your husband is selling paint" Jiuzheng coating network exchange group]

FeMn Electrode Paste Cylinders

Femn Electrode Paste Cylinders,Self-Baking Electrode Paste Cylinders For Femn,Electrode Paste Cylinders For Femn,Femn Electrode Paste Cylinder

Pingluo Zhongxing Carbon Co.,Ltd , https://www.ztecarbon.com