Radiation polyurethanes

Polymers. The molecular weights of polymers used in high energy electron radiation-curable coating systems are ca 1,000—25,000 and the polymers usually contain acryUc, methacrylic, or fumaric vinyl unsaturation along or attached to the polymer backbone (4,48). Aromatic or aUphatic diisocyanates react with glycols or alcohol-terrninated polyether or polyester to form either isocyanate or hydroxyl functional polyurethane intermediates. The isocyanate functional polyurethane intermediates react with hydroxyl functional polyurethane and with acryUc or methacrylic acids to form reactive p olyurethanes. 

Coating materials may be based on short or medium-oil alkyds (e.g. primers for door and window frames) nitrocellulose or thermoplastic acrylics (e.g. lacquers for paper or furniture finishes) amino resin-alkyd coatings, with or without nitrocellulose inclusions, but with a strong acid catalyst to promote low temperature cure (furniture finishes) two-pack polyurethanes (furniture, flat boards) unsaturated polyester resins in styrene with free-radical cure initiated by peroxides (furniture) or unsaturated acrylic oligomers and monomers cured by u.v. radiation or electron beams (coatings for record sleeves paperback covers, knock-down furniture or flush interior doors). 

Treatment of TR with UV radiation has been shown to be successful in increasing its adhesion to polyurethane adhesive. A low-pressure mercury vapor lamp (main emission at 254 nm power = 20 mW/cm ) has been used. The UV treatment of TR improves the wettabUity, produces the formation of C—O, C=0, and COO moieties, and ablation is also produced. The extended UV treatment produces greater surface modifications, as well as the incorporation of nitrogen moieties at the surface. Peel strength values increase after UV treatment of TR, in a greater extent by increasing the treatment time. 

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]. 

Paraffin gauze dressing Perforated film absorbent dressing Polyurethane foam Burns, scaids, grafts Postoperative wounds Burns, ulcers, grafts. Any combination of dry heat, gamma-radiation and ethylene oxide... 

The following mechanism has been proposed to explain the kinetics of the radiation curing process for elastomeric polyurethanes and polythio ethers. 

The conversion versus time profiles were recorded by RTIR spectroscopy for a polyurethane acrylate (PUA) formulation (Actilane 20/HDDA in a 1/1 weight ratio) exposed to UV radiation of various intensities (I0). It can be seen in Figure 3 that, after a short induction period due to the inhibitory effect of the oxygen dissolved in the formulation, the rate of polymerization rises rapidly up to a maximum value,... 

The routes give, using well-known condensation and radical reactions, bakelites (I), polyazophenylenes (II), polyimides (III), polyurethanes (IV), nitro compounds and polyamides (V), aromatic polyethers and polyesters (VI), polychalcones (VII), polyphenylene sulfides (IX), ammonia lignin (X), carbon fibers (XI), silicones (XII), and phosphorus esters (XIII). In addition, radiation and chemical grafting can be used to obtain polymers of theoretical interest and practical use. Although the literature on the above subject is very large, there are comprehensive summaries available (1,28,69). 

Hannig et al. (3) prepared carbodiimide- and uretoni mine-modified polyisocyanates using microwave radiation. These oligomeric isocyanates were subsequently used to prepare polyurethane articles. 

Radiation-Induced Graft Polymerization of Flexible Polyurethane Foam... 

Flexible polyurethane foam pre-irradiated with ionizing radiation in the presence of air can be readily grafted with vinyl monomers. Relatively low radiation doses (3 to 10 megarads) are required to graft various polar vinyl monomers. Grafting of as little as 2% by weight of acrylamide, methacrylamide, or acrylic acid converts the normally hydro-phobic polyurethane foam into a water-wettable sjjonge. 

This paper describes a method for improving hydrophilicity by using radiation-induced grafting of flexible polyurethane (polyether) foam with polar vinyl monomers. By this procedure, the normally hydrophobic material can be converted into a remarkably water-wettable sponge. 

The need to maintain elasticity of rubber is of paramount importance under any serious and severe environmental conditions. The most stable rubbers in radiation environments are polyurethanes and phenyl silaxanes which are usable at well above 108 rads (106 Gy). Butyl rubber liquefies and neoprene evolves hydrochloric acid at similar dose levels. Most polyurethane rubber foams can be used at a dose level of 109 rads (107Gy) in vacuum at temperature levels of between -85°C to +250°C. Silicone and polysulphide sealants are probably less tolerant to ionizing radiation in a nuclear plant where chemical processes are being carried out. A schematic graphical representation of the tolerance of rubbers to ionizing radiation in nuclear plant is shown below in figure 7.4. 

Odian et a1 (Refs 113,133 150) showed that the deflagration rates of many composite AP solid propints were affected by gamma doses of 5 x I07 R. Two poly sulfide-based proplnts (Thiokol TP-L-3014 and TP-L-3014a) showed rate decreases, polyurethane (Thiokol TP-6-3129), polyacrylate (Hercules HES-6420) and polyacrylonitrile (HES-6648) based proplnts showed increases, while hydrocarbon (Thiokol TP-H-3062) and cellulose acetate (Hercules HES-5808) proplnts showed no changes in deflagration rate. Since the composite propint formulations contain various additives besides the binder and oxidizer, an effort was made to determine the effect of radiation on the deflagration rates of binder and oxidizer separately and independent of additives... 

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. 

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