Urea plastics

Urea plastics Group of plastics whose resins are derived from the condensation of urea and aldehydes. 

Which of the following could be a nonpetrochemical plastic (a) Bakelite (b) urea plastics or (c) melamine plastics ... 

Many of the properties of urea plastics are similar to those of the phe nolics, but, unlike phenolics, the urea plastics are not dark and are characterized by pastel and translucent colors as well as slightly superior insulating electric properties. Urea is tetrafunctional. As shown in Figure 15.5, linear and cross-linked network products are readily produced. 

The principal filler used for the production of light-colored urea plastics is alpha cellulose, which has an index of refraction similar to that of the urea ... 

A typical cellulose-filled urea plastic has a tensile strength of 55,000 kPa, an Izod impact strength of 16 cm N/per centimeter of notch, and a coefficient of linear expansion of 3 X 10 3 cm/cm C. Urea-formaldehyde plastics have good electric insulating properties. Unlike phenolic plastics, urea plastics do not carbonize when an electric arc is placed on their surfaces. They also have a high dielectric strength. 

There is no sharp dividing line between plastic mortars and sealants, but the former are usually in situ-polymerized, highly-filled, rigid composites while the latter are usually in sltu-polymerized, flexible polymers. Since plastic mortars do not require expensive molds, the phenolic and urea plastic motars were the pioneer plastics. The Interest in these readily fabricated, labor-intensive, plastics decreased as automated molding processes were developed. However, because of their excellent properties and the need to conserve energy, there is an renewed interest in these materials. 

Formaldehyde was essential not only for the production of Bakelite, but also for some of the important plastics introduced, in part, because of the difficulty of producing water-white sheet material from phenolic resinoids [Bakelite]. This had led to the development of urea plastics in 1924 and later vinyl, styrol, and acrylic resins. In... 

PEG-3 dicaprylate/caprate Stearyl nitrile plasticizer, starch Hydroxypropylglycerin plasticizer, starch adhesives Dicyandiamide Urea plasticizer, starch pastes PEG-180... 

Melamine plastics. Together with urea plastics, these are the most important representatives of the amino plastics. Their properties (water and chemical resistance, thermal stability) are superior to those of urea plastics. 

Urea plastics. One of the most important representatives of amino plastics, besides the melamine plastics. 

Its principal use, however, is as an adhesive for wood. In this application, resorcinol-formaldehyde has the unique property of setting at room temperature. The bond becomes completely waterproof in 24 h, and in another 2-4 days the bond is stronger than wood itself. Resorcinol resins also find application in bonding cellulose acetate, molded urea plastics, nylon, and various plastic laminates to wood core. They also bond to porous materials such as paper, textiles, leather, and fiberboard. 

Chen et al. [156] produced nanocomposite foams by melt processing TPS using urea as plasticizer and ammonium-treated montmoriUonite (NH MMT). They noticed that the use of urea also enhanced the dispersion of NH MMT in the TPS, making exfoHated TPS-clay nanocomposites possible. Synergistic effects of the urea plasticizer with ammonium treatment of the clay enhanced clay dispersion and foaming due to ammonia production. 

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