Polyurethane based casts

D6 POLYURETHANE BASED, CASTING RIM/RRIM/SRIM RESINS... 

Polyurethanes based on MDI have the greatest flexibility in the choice of curatives and blends of curatives that can be used to obtained the desired properties. In cast elastomers, the hygroscopic nature of the curatives must be taken into account and proper handling and storage used otherwise, there may be a very high reject rate. Catalysts are also more readily used with the MDI materials. Organic acids such as adipic or oleic acids work better with TDI materials than MDI systems. 

In this chapter we investigate the morphology of a series of polyurethanes based on polycaprolactone polyol (PCP), diphenylmethane diisocyanate (MDI), and butanediol (BDO). Samples of as-batch-reacted and solution-cast polymers were examined by optical microscopy, transmission electron microscopy, electron and x-ray diffraction, and differential scanning calorimetry. Our interest is to provide a mapping of the size and shape of the domains (and any superstructure such as spherulites) and the degree of order as a function of the fraction of each phase present. 

For other recreational surfaces, such as mnning tracks, the installation techniques are quite different. Most are poured-in-place. An interlocking tile technique may be employed for tennis courts. In all cases, adequate provision for weathering and water drainage is essential. In general, the resiHent surfaces are installed over a hard base (see Fig. 4) that contains the necessary curbs to provide the finished level. Outdoors, asphalt is the most common base, and indoors, concrete. A poured-in-place polyurethane surface (14) is mixed on-site and cast from at least two components, an isocyanate and a filled... 

The late 1950s saw the emergence of cast elastomers, which led to the development of reaction injection mol ding (RIM) at Bayer AG in Leverkusen, Germany, in 1964 (see Plastics processing). Also, thermoplastic polyurethane elastomers (TPUs) and Spandex fibers (see Fibers, elastomeric) were introduced during this time. In addition, urethane-based synthetic leather (see Leather-LIKEmaterials) was introduced by Du Pont under the trade name Corfam in 1963. 

Example 2. Two-Shot Cast Elastomer (Prepolymer Method). Synthesis of polyurethane elastomers via the prepolymer method is challenging and requires especial attention to details and techniques. This example is a relatively easy one, using a low-viscosity, 9.6% NCO MDI-based poly(tetramethylene ether) glycol prepolymer. It is adapted from the Bayer Product Information Bulletin for Baytec ME-090 prepolymer. 

Wheels and tires are one of the major uses of cast polyurethane elastomers. We commonly see these on fork lift trucks and shopping carts, where their excellent abrasion resistance, resistance to oil, and good elasticity are valued. In industrial settings we find polyurethane covers on rollers used for paper, steel, and textile conveyor systems. In such applications, their excellent cut and abrasion resistance help prolong their useful life. If used in hot and humid conditions, polyether-based polyurethanes are preferred. 

AF are polyurethane propellants for rockets and ANR is a cast-double-base propellant... 

Thermoset polyurethanes are cross-linked polymers, which are produced by casting or reaction injection molding (RIM). For cast elastomers, TDI in combination with 3,3,-dichloro-4,4,-diphen5lmethanediamine (MOCA) are often used. In the RIM technology, aromatic diamine chain extenders, such as diethyltoluenediamine (DETDA), are used to produce poly(urethane ureas) (47), and replacement of the polyether polyols with amine-terminated polyols produces polyureas (48). The aromatic diamines are soluble in the polyol and provide fast reaction rates. In 1985, internal mold release agents based on zinc stearate compatibilized with primary amines were introduced to the RIM process to minimize mold preparation and scrap from parts tom at demold. Some physical properties of RIM systems are listed in Table 7. 

Based on the numbers in Figures 1 and 2, by 1985 RIM and RRIM will require approximately 50 M lbs. of monomeric MDI, which is about one-third of the monomeric MDI supply in 1985 (Table IX based on 20-25% of 85% nameplate capacity, excluding ARCO capacity, = 137-171 M lbs. monomeric MDI). This will leave about 100 M lbs. of monomeric MDI for cast elastomers, thermoplastic polyurethanes, shoe soles, semi-rigid foams, and some adhesives and sealants, a monomeric MDI supply which should be more than sufficient for these applications. As RRIM grows, a need for capacity expansion can be seen in the late 1980 s. No effects on the market will be seen from PUR-SMC until after 1985, and at the present time meaningful projections are impossible. 

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