Cast elastomers polyurethane

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. 

Turner, S. Richard, 1 Two-component (2-K), nonsagging, polyurea structural adhesive, preparation of, 255-256 Two-component (2-K) systems, 238-241 Two-component (2-K) waterborne polyurethane coatings, 206 preparation of, 254-255 Two-shot cast elastomer, preparation of, 249-250... 

Rigid polyurethane foams account for 80% of MDI use, especially for construction (about half of this use), refrigeration, packaging, and tank and pipe insulation. Other uses are reaction-injection molding (RIM) applications (13%) and cast elastomers (2%). 

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. 

Castable Polyurethane Elastomers is a practical guide to the production of cast-able polyurethane articles. These articles can be as simple as a doorstop to items used in nuclear and military industries. The book shows the progression from the raw materials needed to produce prepolymers to the production of prepolymers. This will include both the chemistry and the practical side of the production processes. 

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. 

TABLE III. COMPOSITION AND PROPERTIES OF POLYURETHANE CAST ELASTOMERS COMPOSITION ... 

Adhesives and sealants, cast elastomers, microcdWar products, polyurethane stretch fibers (Spandex fibers i, surface coatings, thermoplastic elastomers and Billable gums—... 

Lnpraphcn. [BASF AG] Polyester poly for die prod, ci ptdyurethane, dwmioplastic grmules, textfie coating systems, finished parts made of polyurethane and casting elastomers for foe auKunotive, machine and equfo. construction industries. 

Uses Eunctional polyol for formulation of polyurethane for flexible coatings, adhesives, and cast elastomers Trade Names Lexorez 1640-35 Lexorez 1640-55R Lexorez 1640-150 Lexorez 1640-320... 

A drawback to the cast elastomers is limited shelf-life and a need to store them in the absence of moisture. As a result, millable elastomers were developed. These are produced by first forming hydroxy-terminated linear polyurethanes through reactions of linear aliphatic polyesters or polyethers with diisocyanates. The prepolymers are rubber-like gums that can be compounded on rubber mills with other ingredients and crosslinked. Crosslinking is accomplished by adding either more diisocyanates, or sulfur, or peroxides. Diisocyanates dimers that dissociate at about 150 °C are often used ... 

Polyurethane, cast elastomer Tetrafluoroethylene/propylene copolymer diaphragm cells Asbestos... 

Polyurethane, cast elastomer formaldehyde condensates m-Phenylenediamine formaldehyde donor MDM hydantoin 2-Nitro-2-ethyl-1,3-propanediol formaldehyde mfg. 

Acetal copolymer Acetal homopolymer Polyethylene, ultrahigh m.w. high-density Polyurethane, cast elastomer pPDI-PTMEG rollers, abrasion-resistant Polyurethane elastomer, thermoplastic roofing... 

Polyurethane, cast elastomer seals, water pump... 

The influence of the high MW diols present in the HER chain extenders on the transition behavior of cast elastomers was studied by DSC analysis. Figure 8.3 compares the DSC curves of HQEE, HER-HP and different HER-TG extended polyurethanes. The transitions, which are observed to occnr above room temperature, are associated with the melting of... 

Loss compliance quantifies the heat generated during dynamic loading in applications like tyres, wheels and rollers. Polyurethane elastomers with lower loss compliance values will experience less heat build up and, consequently, may suffer fewer field failures [14]. Figure 8.8 shows the graph of loss compliance as a function of temperature for the cast elastomers made with HER extended materials. The results are summarised in Table 8.5. 

Polyurethane elastomers are known for their high elongation, tensile strength and modulus properties. The combination of these properties provides toughness and durability in fabricated parts. Cast elastomers extended with butanediol can maintain these tensile properties when the use temperature is about 80 C. When these elastomers are subjected to higher temperatures, reduction in the tensile properties are observed due to the weakening of physical bonds in the elastomer. 

In this chapter, the dramatic effect that monol content or polyol functionality has on processability and properties of polyurethane cast elastomers is discussed. This effect is shown for elastomers prepared by both the prepolymer and one-shot processes. Further improvements in elastomer processability and formulating latitude can be achieved by incorporating oxyethylene moieties into the polyol backbone. For one-shot elastomer processes, ultra-low monol PPG polyols capped with ethylene oxide have been commercialised. 

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