Curing polyurethane elastomers

This book is studying the castable family of polyurethanes. The cured polyurethane elastomer is made from three main ingredients that are detailed in Table 2.1. 

The process of curing polyurethane elastomers depends to a large degree on initially having a material with a reasonably low viscosity. This is to allow the flow of the material into the mold and the ability for any entrapped air to rise to the surface. Once the mold has been filled and the air allowed to escape, the increase in viscosity should be rapid to prevent excessive leakage through any parting lines in the mold. 

MDI MEK MOCA (MBOCA) Therefore, a two-part mold would have two master patterns. An abbreviation for diphenylmethane-4,4 -diisocyanate. Methyl Ethyl Ketone Trade name for methylene bischloroaniline, which is a widely used curing agent for hot cure polyurethane elastomers. There are... 

Sulphur- and peroxide-curing polyurethane elastomers usually incorporate olefinic groups as sites for cross-linking. A very suitable reactive group is the allyl... 

Tensile strength and extensibility studies are reported by Smith for cured polyurethane elastomers based on Adiprene L-lOO... 

Butyraldehyde reacts with formaldehyde to produce TMP, which is used to cure polyurethane elastomers. 

Calcium carbide is a feedstock for producing acetylene-phenol tackifying resin. Calcium carbide is a feedstock to make 1,4-butanediol for curing polyurethane elastomers. 

Ethanol is used as a feedstock to produce MDI for curing polyurethane elastomers. Indirect Feedstock Dependency... 

Ethylene is oxidized to ethylene oxide for production of HQEE for curing polyurethane elastomers. 

Ethylene glycol reacts with phosgene to produce ethylene carbonate to make HER for curing polyurethane elastomers. 

Methanol is oxidized to formaldehyde to make RF resins (for RFL dips for cord adhesion to rubber), methylol-terminated PF resins (to cure butyl rubber), RF resins (for HRH rubber-to-metal adhesion system), HMMM (as a methylene donor in HRH rubber-to-metal adhesion system), IMP (to cure polyurethane elastomers), and 1,4-butanediol (to cure polyurethane elastomers). 

Isocyanate-curing polyurethane elastomers incorporate groups containing active hydrogen atoms which serve as sites for cross-linking. The most... 

Metal salts of neodecanoic acid have also been used as catalysts in the preparation of polymers. For example, bismuth, calcium, barium, and 2kconium neodecanoates have been used as catalysts in the formation of polyurethane elastomers (91,92). Magnesium neodecanoate [57453-97-1] is one component of a catalyst system for the preparation of polyolefins (93) vanadium, cobalt, copper, or kon neodecanoates have been used as curing catalysts for conjugated-diene butyl elastomers (94). 

When a thermoplastic polyurethane elastomer is heated above the melting point of its hard blocks, the chains can flow and the polymer can be molded to a new shape. When the polymer cools, new hard blocks form, recreating the physical crosslinks. We take advantage of these properties to mold elastomeric items that do not need to be cured like conventional rubbers. Scrap moldings, sprues, etc. can be recycled directly back to the extruder, which increases the efficiency of this process. In contrast, chemically crosslinked elastomers, which are thermosetting polymers, cannot be reprocessed after they have been cured. 

Dichlorobenzidine is also used with 4,4 -methylenebis (2-chloroaniline) as a curing agent for liquid-castable polyurethane elastomers (HSDB 1996). 

Figure 4.2. Flowsheet of production of cast polyurethane elastomer articles from a prepolymer by the continuous method 1 - vessel to store prepolymer 2 - vessel to prepare prepolymer 3 - reactor for curing agent 4 -transfer pump 5 - metering pump 6 - mixing device 7- mold.

MAJOR USES Used in the manufacture of azo dyes, rubber and plastic, printing ink, textiles, plastics and crayons used as a curing agent for polyurethane elastomers, isocyanate containing polymers and solid urethane plastics used as an intermediate for the detection of gold and production of pigments. 

Isobutyl 4-chloro-3,5-diaminobenzoate Empirical C11H15CIN2O2 Properties M.w. 242.70 Uses Curing agent for polyurethane elastomers crosslinking agent for thermosetting resins Isobutyl cinnamate... 

Table 9.3 Comparison of polyurethane elastomers based on ultra-low monol, low monol and conventional 4000-MW diols (6% NCO MDI prepolymers BDO cured) ...

Table 9.6 Polyurethane elastomers based on 4000-MW, ultra-low monol PPG (MDI prepolymers EDO cured) ...

Attention in this section will be focussed on the thermoplastic polyurethane elastomers. These polymers are based on three monomers (1) an isocyanate source, (2) a macroglycol or carbonate, and (3) a chain extender, or curing agent. The isocyanates can be either aromatic or aliphatic. Although the aliphatic based polyurethanes are more expensive, and inferior in physical properties they do not show the embrittlement, weakening, and progressive darkening of the aromatic equivalents. 

COMMON COMMERCIALLY AVAILABLE DIAMINE CURING AGENTS FOR LIQUID POLYURETHANE ELASTOMERS... 

The physical properties of polyurethane elastomers using these diamine curing agents/chain extenders are given in Tables 5.7(c)-(m). 

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