Radiation, polyurethane resistance

The undesirable properties of thermoplastic polyurethane elastomer, i.e., softening at high temperatures and flow under pressure, which limit their use at elevated temperamres have been reduced by cross-linking with EB radiation. The cross-linked polyurethane shows good mechanical properties and also displays good resistance to aggressive chemicals, e.g., brake fluid [432 35]. 

The radiation resistance of polyurethanes is better than that of other polymer materials and makes them a good candidate in applications where there is gamma radiation. 

Because of the radiation resistance of polyurethanes, they find use in the nuclear industry. Polyurethanes find an important use in short-run production where parts can be made accurately until more costly molds can be made, without the need for potentially expensive change. Polyurethanes can be used to make molds for casting polyurethane parts. A coat of mold release is required for easy part removal. These molds can be used for short-to-medium production runs. Polyurethane molds can be made from a variety of different materials. Only very low-density wood and high-moisture-containing materials such as plaster of Paris prove to be too difficult to prepare a mold. 

In general, plastics are superior to elastomers in radiation resistance but are inferior to metals and ceramics. The materials that will respond satisfactorily in the range of 1010 and 1011 erg per gram are glass and asbestos-filled phenolics, certain epoxies, polyurethane, polystyrene, mineral-filled polyesters, silicone, and furane. The next group of plastics in order of radiation resistance includes polyethylene, melamine, urea formaldehyde, unfilled phenolic, and silicone resins. Those materials that have poor radiation resistance include methyl methacrylate, unfilled polyesters, cellulosics, polyamides, and fluorocarbons. 

This field has been reviewed by Parkinson [426]. Common hydrocarbon elastomers (with the exception of butyl rubber), nitrile and acrylic rubbers were found to be as resistant to radiation as silicones, fluorocarbon and polyurethane rubbers. 

Ultraviolet Absorbers, Light Stabilizers, and Antioxidants. Ultraviolet absorbers and light stabilizers can be added to urethane coatings in order to increase their resistance to discoloration and to outdoor weathering. UV absorbers are employed to eliminate the radiation in the region of 334 and 411 um that sensitize the polyurethanes and promote an autoxidation process. Light stabilizers on the other hand do not absorb UV radiations but inhibit or control the degradation by other means. 

On account of their insensitivity to solar radiation, some polyester resins are particularly suitable for weather-resistant topcoats (e.g.. facade claddings, blades of shutters and Venetian blinds, vehicle claddings, metal signs). Melamine-formulated paints are economical and have a well-balanced property profile. Polyurethane-formulated paints have an even better processability and weather resistance (colorfastness, chalking resistance) [2.92],... 

Polyurethane ether (PUR-ether) foams are thought to degrade primarily by oxidation, particularly in the presence of light, resulting in discolouration and a loss of mechanical properties. Polyurethanes synthesized from a polyether polyol and an aromatic diisocyanate such as diphenylmethane diisocyanate (MDI) are highly vulnerable to photo-oxidation, whereas polyester-based polyurethanes are more resistant to ultraviolet radiation (Kerr and Batcheller, 1993). Metal ions, particularly copper, aluminium and zinc, form chelates with some polyurethanes imparting increased sensitivity to photo-oxidation (Ranby and Rabek, 1975). 

Urethanes have also been used to toughen vinyl-terminated acrylic adhesives for improved impact resistance. Thus rubber-toughened urethane acrylates [79,80], water-dispersible urethane acrylates [81], and high-temperature-performance urethane-acrylate structural adhesives have been reported [82]. Polyurethanes terminated with acrylic functionality are also used for anaerobic or radiation-cured adhesives with improved toughness [83]. 

Chem. Descrip. Glycerin-1-allylether CAS 123-34-2 EINECS/ELINCS 204-6204 Uses Can be polymerized into polyesters, polyurethanes, polyacetals, and epoxy resins (hydroxyl group) or with acrylates, methacrylates, or styrene (ilyl group) for prod, of PL) rubber and foam printed circuit boards unsat. polyesters used for radiation-resist, coatings copolymers as dispersants for pigments or as corrosion inhibitors Properties Colorless to yish. vise, liq., perceptible odor sol. in water, ethanol, and many org. soivs. dens. 1.07 g/cc vapor pressure 0.004 mbar (20 C) m.p. < C b.p. 245 C (decomp.) flash pt. 135 C pH 7 (5% aq.) 9 /o assay... 

Polyurethanes Properties vary from those of an elastomer to those of hard, rigid cross-linked polymers with mechanical properties showing no reduction after an exposure to 1000 Mrad. (General radiation resistance excellent.)... 

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