High Energy Radiation Effects

It is generally considered that polyurethane elastomers are resistant to the effects of damage by high-energy radiation. As dosage increases then 

Time of Tensile Hardness % change immersion strength (IRHD) in weight (days) (MPa) 

Source P. Wright A. P. C. Gumming, Solid Polyurethane Elastomers. Maclaren Sons, London, 1969. 

HYDROLYSIS RESISTANCE OF A TYPICAL COMMERCIAL POLYETHER POLYURETHANE 

Physical properties after water immersion Tensile strength (MPa) after immersion in water at 25°C  

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There have been many studies of high-energy radiation effects upon liquids and solution of organic systems. In many of these, energy transfer by the long-range dipole—dipole interaction may be important to some degree. Since the properties of most of these systems remains uncharacterised, it is difficult to be more definitive, but the articles by Mullin et al. [175], Miyazaki [196], Wada and Hatano [177], Jonah et al. [178], and Katsumura et al. [179] are all of possible interest and concern. 

Simha, R., Wall, L. A., Mechanism of high energy radiation effects in polymers. Journal of Physical Chemistry, 61(4), pp. 425-430 (1957). 

M.S. Sreekala, M.G. Kumaran, M.L. Geethakumariamma, and S. Thomas, Environmental effects in oil palm fiber reinforced phenol formaldehyde composites Studies on thermal, biological, moisture and high energy radiation effects. Adv. Compos. Mater. 13, 171-197 (2004). 

EFFECTS OF THERMAL, PHOTOCHEMICAL AND HIGH-ENERGY RADIATION... 

An effective method of NVF chemical modification is graft copolymerization [34,35]. This reaction is initiated by free radicals of the cellulose molecule. The cellulose is treated with an aqueous solution with selected ions and is exposed to a high-energy radiation. Then, the cellulose molecule cracks and radicals are formed. Afterwards, the radical sites of the cellulose are treated with a suitable solution (compatible with the polymer matrix), for example vinyl monomer [35] acrylonitrile [34], methyl methacrylate [47], polystyrene [41]. The resulting copolymer possesses properties characteristic of both fibrous cellulose and grafted polymer. 

A major complication in applying radiation chemical techniques to ion-molecule reaction studies is the formation of nonionic initial species by high energy radiation. Another difficulty arises from the neutralization of ions, which may also result in the formation of free radicals and stable products. The chemical effects arising from the formation of ions and their reactions with molecules are therefore superimposed on those of the neutral species resulting from excitation and neutralization. To derive information of ion-molecule reactions, it is necessary to identify unequivocally products typical of such reactions. Progress beyond a speculative rationalization of results is possible only when concrete evidence that ionic species participate in the mechanism of product formation can be presented. This evidence is the first subject of this discussion. 

Akhtar et al. [444] have studied the effect of y-irradiation on NR-PE blend. The high-energy radiation at a high dose rate has been found to cause extensive cross-linking in the bulk. The rupmre energy values increase subsequently in the range of 15-25 Mrad and then decrease, as the absorbed dose increases further. 

Section 3 deals with reactions in which at least one of the reactants is an inorganic compound. Many of the processes considered also involve organic compounds, but autocatalytic oxidations and flames, polymerisation and reactions of metals themselves and of certain unstable ionic species, e.g. the solvated electron, are discussed in later sections. Where appropriate, the effects of low and high energy radiation are considered, as are gas and condensed phase systems but not fully heterogeneous processes or solid reactions. Rate parameters of individual elementary steps, as well as of overall reactions, are given if available. 

Re A3. High energy radiation causes some cyclization of the pendant vinyl groups (.29). This should cause a stiffening of the chain and thus an increase in of the free network strands. The modulus should then be decreased by the ratio / (30 ). However, the effect is apparently too small to cause a significant decrease in the modulus. 

Section 2 deals with reactions involving only one molecular reactant, i.e. decompositions, isomerisations and associated physical processes. Where appropriate, results from studies of such reactions in the gas phase and condensed phases and induced photochemically and by high energy radiation, as well as thermally, are considered. The effects of additives, e.g. inert gases, free radical scavengers, and of surfaces are, of course, included for many systems, but fully heterogeneous reactions, decompositions of solids such as salts or decomposition flames are discussed in later sections. Rate parameters of elementary processes involved, as well as of overall reactions, are given if available. 

Recently there has been increasing interest in studies of the effects of high energy radiation on polymers. Some of this interest has arisen because of the use of polymers as resists in the microchip industry, and some through the search for radiation resistant polymers for the aerospace and other high technology industries. 

Polymerization of acrylonitrile adsorbed on polyacrylonitrile" An intimate mixture of polyacrylonitrile solvated by its monomer is obtained if one melts acrylonitrile crystals which have been subjected to high energy radiation at low temperatures. The polymer forms under irradiation within the crystal lattice and upon melting, a gel-like phase is obtained in which the individual polymer molecules do not aggregate, presumably because most of the CN groups are then associated in pairs with the -CN groups of the monomer. Such a polyacrylonitrile solvated by its monomer should indeed be an ideal medium for the matrix effect to operate. 

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