Mechanical properties after irradiation

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... 

In PP with a narrow distribution molecular weight, more load-bearing chains or tie molecules are present in the amorphous domains, i.e. between crystallites, than in the pol)m er with a higher molecular weight distribution. The result is a better maintenance of mechanical properties after irradiation, for such a kind of PP. 

Table 10.6 shows the changes in mechanical properties after UV exposure and weathering. Samples have been irradiated with an ultraviolet lamp of 300 W and 700 Lux. 

The mechanical properties exhibited by a polymer after irradiation are a complex function of molecular weight and molecular weight distribution and the number and type of new structures formed. Thus, it is difficult to draw structure/radiation resistance conclusions from the change in the mechanical properties alone. However, the changes in mechanical properties are direct indications of the ultimate usefulness of the polymer in a radiation environment. 

Since the polymerization of TEGDA can easily be studied with DSC as well as with dynamic mechanical thermal analysis (DMTA) we have repeated our study with this monomer in order to see whether or not mechanical properties depend on the intensity rather than on the dose of UV irradiation. DMTA also reveals whether or not postcuring occurs during thermal after-treatment, similar to what has been observed with other thermosetting materials (8). 

In the case of Mylar, the electrical breakdown and the dielectric constant showed little change after the irradiation of 7 x 106 Gy at 5 K, although all mechanical properties fell down to unusable levels [87]. 

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