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Utility of the Poly(alkylene oxide)s
Published in F. E. Bailey, Joseph V. Koleske, Alkylene Oxides and Their Polymers, 2020
F. E. Bailey, Joseph V. Koleske
The primary amine (with either TDI or MDI) reacts with more isocyanate to form urea linkages that will coalesce or aggregate to form polyurea domains in the rising foam that, at this stage, is still largely liquid-phase reactants. Near full rise of the foam, urethane formation becomes the dominant reaction to produce the elastomeric network of the foam. The solid phase of the fully cured foam can be described as a segmented block urethane-urea copolymer. The continuous phase of the elastomeric foam is polyether urethane reinforced by polyurea domains that form the discontinuous, high-softening, reinforcing phase of the elastomer network. At the full rise-height of the foam, the walls of the gas cells, which have been expanding due to heat of reaction, break open in the case of an open-cell, flexible foam. The cell-opening process is complicated and depends not only on the surfactant used and its concentration but also on the process of aggregation of the polyureas as these domains form. The actual supramolecular architecture of the foam is determined first by the polyureas, which form a gel of hydrogen-bonded structures. The urethane reaction chemically gels the elastomer network in the final form.
Smart Delivery Systems for Personal Care and Cosmetic Products
Published in Munmaya K. Mishra, Applications of Encapsulation and Controlled Release, 2019
A different approach to manufacture submicron encapsulation particles through interfacial polymerization was reported by Zeng et al at the Dow Chemical Company.22 As described in the patent application, the aqueous phase contains partially hydrolyzed polyvinyl alcohol and a cosmetically acceptable non-ionic surfactant, while the personal care active includes UV absorbers such as avobenzone, homosalate, octocrylene, octyl methoxycinnamate, etc. Examples of the non-ionic surfactant include fatty alcohol ethoxylates and alkoxylates of fatty acid esters. A polyurea shell formed by interfacial reaction of a multifunctional isocyanate and a multifunctional amine was used in the example. It is also worthy of mention that the homogenizing step can be carried out under ambient pressure. In comparison with the micron-sized UV absorber capsule, the submicron UV absorber capsule provides an even better in vitro SPF boost in sunscreen formulation.
Reactive Hot Melt Conformal Coating Materials
Published in Ralph D. Hermansen, Polymeric Thermosetting Compounds, 2017
One-component, moisture-curing polyurethane coatings have been com-mercially available for decades and are principally used as coatings. They typically are isocyanate-terminated prepolymers, prepared by reacting a diisocyanate with a diol or triol. The molecular weight of the prepolymer can be predetermined by adjusting the ratio of NCO to OH groups. The formulated coating may contain organic solvents to reduce viscosity and other additives to produce a smooth level coating. For outdoor applica-tions, UV absorbers and antioxidants may be added to the coating formu-lation to extend its life. These coatings are typically applied only a few mils thick. Moisture, absorbed into the coating from the air, causes the prepolymer to link with itself via urea linkages. The water molecule con-verts an isocyanate group into a primary amine, which, in turn, reacts with a second isocyanate group to form the urea linkage. Technically speaking, the moisture-cured prepolymer is now both a polyurethane and a polyurea polymer.
Thermal-vibration aging of fiber-reinforced polymer cylindrical shells with polyurea coating: Theoretical and experimental studies
Published in Mechanics of Advanced Materials and Structures, 2023
Hui Li, Zhao Siqi, Xianjie Shi, Haihong Wu, Qin Zhaoye, Lu Pengxu, Xiangping Wang, Guan Zhongwei
Fiber-reinforced polymer (FRP) shell structures have been extensively implemented across wide ranges such as aerospace, marine and civil engineering [1–4] owing to their excellent mechanical performances and lightweight properties [5–9]. The aging or degradation issue of vibration resistant behaviors [10–12] in a thermal environment is one of the major concerns for various FRP shells. Polyurea coating (PC) has already been proved to be a promising surface treatment technology for improving structural blast resistance, damping, thermal protection [13–17], etc. However, few people have focused on the thermal-vibration aging issue of composite shells attached with polyurea coating. Particularly, it remains an open a question that how to quantitatively describe the suppression contribution of coating material on aging behaviors of the PC- FRP shells with different environmental temperatures. Therefore, it is critical to investigate the corresponding aging modeling, experimentation, and evaluation of such coated shell structures.
Buckling of helically wound composite cylinders under uniform external pressure
Published in Ships and Offshore Structures, 2023
Xinlong Zuo, Jian Zhang, Wenxian Tang, Ming Zhan, Yongsheng Li
The two ends of each specimen were carefully ground to fit 304 steel flanges, which were used to close each cylinder under a hydrostatic test (Figure 2). The flanges were bonded to the two ends of each specimen by using Araldite 2015. The Poisson’s ratio and Young’s modulus of the flanges were 0.33 and 190 GPa, respectively, and the main dimensions of the specimens are listed in Table 2. The two ends of the composite cylinder were enclosed by heavy flanges, which imposed rigid boundary conditions on the cylinder’s ends. To prevent water absorption, each specimen was varnished with Polyurea Coatings GDJN001 (Ross et al. 2011). Polyurea Coatings films of three layers have a total thickness of 0.25 mm. Each layer of the Polyurea Coatings film was applied after a 5-hour interval in an environment below 30 °C. The specimens used in the hydrostatic test are depicted in Figure 3.
Effects of prolonged saline water exposure on the peel strength of polyurea/monel 400 interface
Published in The Journal of Adhesion, 2022
Irine Neche Chenwi, Thomas Ramotowski, James LeBlanc, Arun Shukla
Elastomeric coatings are widely used in the marine industry to increase the survivability of structures and hardware. Polyurea is an elastomer with excellent adhesion to most surfaces and exceptional physical and mechanical properties such as high flexibility, hardness, tear strength and tensile strength. This elastomer has shown considerable promise as a coating material on marine structures to mitigate blast loadings and to provide corrosion and abrasion resistance. For over two decades, research efforts have focused on the use of polyurea to enhance corrosion resistance and the failure resistance of materials subjected to blast and ballistic loading.[1] More recent work has focused on the use of polyurea coatings on metallic and composite plates and cylinders for blast mitigation.[2–7] The emphasis in these studies was the location of the polyurea that optimizes blast and ballistic mitigation through energy absorption. The energy absorption capacity of polyurea is closely related to its mechanical behavior under high strain rates. Under both compressive and tensile loads, polyurea exhibits strain rate dependency.[8–10] This is attributed to its ability to transition from rubbery to leathery-regime behavior as the strain rate increases, thus leading to more energy absorption under dynamic loading conditions. Other research focuses on the influence of pressure and temperature on the mechanical behavior of polyurea.[11] Recently, the constitutive compressive behavior of polyurea after exposure to saline water and UV radiation has been investigated.[12] Findings showed a drastic decrease in the elastic modulus and strain energy after exposure to saline water, and an increase in the elastic modulus and strain energy after exposure to UV radiation.