Irradiation toughness

The question of the independent validation of the irradiated toughness methodology and its comparison with actual data was raised in the early 1990s because of two factors ... 

UV and gamma irradiation, toughness strength, flame spread, hydrolytic Q ... 

FIGURE 36.26 Topaz. Examples of Irradiated tough, natural imperial topaz and a huge natural single crystal. 

A method that would enable detection and classification of the bone content in 100% of the incoming frozen fish blocks in real time without delaying the production line was desired. An obvious solution to this was the use of X-ray inspection. X-ray inspection however requires the integration of a highly sensitive inspection equipment with the corrosive atmosphere associated with food processing as well as the tough restrictions imposed by the health authorities regarding irradiation of food. 

Sulfur dioxide was the major volatile product and was used as a probe to correlate the radiation resistance with polymer structure. The use of biphenol in the polymer reduced G(SO ) by 60% compared with bisphenol A based systems (Bis-A PSF). Surprisingly, the isopro-pylidene group was shown to be remarkably radiation resistant. The ultimate tensile strain decreased with dose for all polysulfones investigated and the rate of decrease correlated well with the order of radiation resistance determined from volatile product measurements. The fracture toughness (K ) of Bis-A PSF also decreased with irradiation dose, but the biphenol based system maintained its original ductility. 

Ultimately, it is the retention of mechanical properties after irradiation which will determine the suitability of a polymer for use in a radiation environment. Since the potential applications for this class of polymer require high modulus and toughness over... 

Fracture toughness may correlate with the 0 relaxation temperature for the polymer. After irradiation, the 0 relaxation temperature increases with a corresponding broadening and decrease in intensity which can be seen in Figure 1. This result is consistent with the results of Hinkley et. al. (13) who observed the same phenomenon for polyether sulfone irradiated with electron beam irradiation above Tg. 

The increase in the modulus for Bis A PSF and Hq/Bp PSF with irradiation indicated that crosslinking predominated for both polymers and that the crosslink structures were probably basically similar. Hq/Bp(50) PSF was considerably more radiation resistant than Bis-A PSF, as shown by the rate of decrease in the elongation at failure. For both polymers, there was an initial rapid decrease in the elongation at failure followed by a slower decrease. This effect was also demonstrated by the variation in the fracture toughness (KI(.) with irradiation for Bis-A PSF. This work with cobalt-60 gamma radiation complements earlier studies of these materials using high dose rate electron beam irradiation (6). 

J. O Donnell, H. Huthmann, and A. A. Tavassoli, The Fracture Toughness Behavior of Austenitic Steels and Weld Metal Including the Effects of Thermal Aging and Irradiation , Int. J. Pres. Ves. Piping, 65 (1996), 209-220. 

A material, such as (a) a terpolymer of propylene, ethylene and butene-1, (b) a polyolefin composition, which includes about 31 to 39% of a copolymer of propylene and ethylene and about 58 to 72% of a terpolymer of propylene, ethylene and butene-1 or (c) a polyolefin composition, which includes about 30 to 65% of a copolymer of propylene and butene-1 and about 35 to 70% of a copolymer of propylene and ethylene, is irradiated and extruded through a die in the presence of a physical expanding agent and a cell nucleating agent to produce a structure having a density, which is at least 10 times less than the initial density of the material. The foam articles exhibit improved flexibility and low temperature toughness compared to conventional propylene polymer materials. 

EVA reins can be conveniently crosslinked by both peroxide or irradiation to enhance the mechanical properties and the heat resistance. It is the crosslinking, coupled with the inherent rubbery nature of the polymer, which makes EVA suitable for production of tough and abrasion resistant foams, especially suitable for footwear applications. Crosslinked EVA foams can be manufactured by two methods (8) ... 

For host/guest systems, tri(acryloxyethyl)trimelletate (7), a liquid trifunctional monomer was employed. This compound is easily and rapidly crosslinked to a tough solid by photopolymerization in the presence of a suitable sensitizer and activator, for example 8 and 9. This particular initiator system is useful because the sensitizer 8 is partially bleached out during irradiation, which allows the light to penetrate the sample as polymerization proceeds. 

Table 9.13 summarizes the effect of the kind of reductant on the photochromic behavior of thionine dye. All reductants afforded transparent films upon irradiation and complete color recovery in the dark. The greatest photosensitivity was obtained with TEA as the reductant. The reversibility decreased in the order, tri->di->mono-ethanolamine. The difference cannot be explained by an electron-donating character such as the basicity of the reductant (P A a value of their ammonium salt tri-mono-ethanolamine). A potential explanation is that TEA(bp, 335.4°C/760mmHg) is so hygroscopic that the moisture absorbed in TEA and TEA itself acts as a plasticizer, providing tough films that afford higher color reversibility, as mentioned earlier. 

Spontaneous Crosslinking. In the absence of TCPA, evaporated solutions of XVIII can be completely redissolved in fresh solvent in a few minutes. And solutions of 0.05 M XVIII containing 0.007 M TCPA in acetonitrile are stable indefinitely (at least three weeks) at room temperature. However, on evaporation of the solvent under vacuum, the mixture forms a very tough film that is insoluble in acetonitrile or hot DMF, does not melt up to 300°, and is resistant to attack by chromic acid. The IR spectrum is identical to that of XVIII crossiinked BF3 or by irradiation in the presence of TCPA. Apparently as the solution becomes highly concentrated, crosslinking occurs by thermal excitation of charge-transfer complexes of TCPA and XVIII. The IR evidence and the insolubility behavior appear to discount an alternative possibility of simple association of polymer chains facilitated by the presence of the acceptor compound. The spontaneous crossiinking is also observed with the acceptors chloranil and 1,3,5-trinitrobenzene, and presumably would occur with others. 

In Fig. 4 the Young moduli of the irradiated blends are reported. All values are slightly lower than the modulus value of PMMA (about 1700 MPa) despite the significant improvement in the toughness. The highest values are for PMMA-VTBNX blends and an increase of modulus for PMMA-ABN occurs with an increase in the absorbed dose, while no significant changes with dose are observed for the other systems. 

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