Elongation, polymers radiation, effects

Additional work was performed by Gardner (Refs 92 99) on proplnts for future missions in space. A PBAA AP/Al proplnt, an aluminized double-base proplnt, and a polyurethane—AP/Al proplnt were studied as a function of Co radiation, with a dose rate of 2.54 x 10 R/hr and total doses ranging up to 1.5 x 10 R. The effects were noted on tests with the burning rate, tensile stress, elongation modules and hardness of the three materials. The PBAA proplnt withstood 1.5 X lO R. On the tensile strength, the double base and polyurethane decrease significantly at a dose of 4 x 10 R. On elongation, the double base decreased on stress at max strain after 10 R, while the polyurethane pro-pint decreased on modulus and hardness after a dose of 10 R. Estimates of the radiation effects on polymers are listed in Table 19... 

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). 

Figure 3.118 shows the effect of y radiation on the break elongation of PVF, PVDF, ETFE, FEP, and PFA. It can be seen that the impact on PVF, PVDF, and ETFE is smaller than the radiation impact on FEP and PFA FEP fares better than PFA. Figure 3.119 provides a comparison of the radiation resistance of several fluoroplastics as a function of radiation dose, as expressed by the retained elongation as percent of initial break elongation of the pol5mier. FEP is the most radiation resistant of the perfluoro-polymers while PTFE is the most susceptible. ETFE has far superior radiation resistance to all the perfluoroplastics shown in Fig. 3.119. 

Fig.1. The effect of radiation dose on the mechanical properties of a polychloroprene polymer. E denotes elongation at break, H represents Shore D hardness, and R represents the tensile strength [18]...

The absorption of UV light by plastics results in discolouration, embrittlement and a marked fall-off in such physical properties as tensile strength, elongation at break and impact resistance. It is therefore obviously necessary to protect polymers from the degradative effects of UV radiation, particularly in the case of those plastics designed for outdoor service or certain severe indoor applications, such as wall coverings or guards for fluorescent tubes. As it is not usually practical to shield the plastics material from the source of radiation, protection is usually afforded by the inclusion of suitable additives in the polymer. 

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