Polypropylene irradiation

Table II. Chemiluminescence (counts/2 min.) at ambient temperature from polypropylene irradiated at day 0 with a dose of 5MR.

Figure 7. Top and Middle Loss of impact strength of polypropylene, irradiated to 5MR, vs. storage time at 25 and 60°C. Bottom Ambient chemiluminescence from irradiated (5MR) polypropylene samples vs. storage time at 25°C.

Fig. 7. ESR spectra of polypropylene irradiated with ultraviolet light at 77 °K Measurements at 77 °K. a immediately after the irradiation b the sample as (a) after being kept at 77 °K for 2 days, the broad component of the spectrum (a) c the spectral component which decayed during the first 2 hr at 77 °K. the sharp component of spectrum (a). [J. Polymer Sri. Part C 12, 263 (1966), Fig. 4]...

Tsuji et al. (77) observed that the component other than methyl radicals observed in the spectrum immediately after irradiation is mainly a four-line one. This spectrum changed into an apparent eightline spectrum after standing in the dark for several days at —196° C, and reverted to the original four-line spectrum on UV irradiation. These changes of spectra are identical to those reported by Iwasaki et al. (80) for polypropylene irradiated with ionizing radiation, and are attributed to radical conversions as follows. 

Fig. 8. Wavelength dependence of radical formation in polypropylene. Irradiations were carried out at —196° C in nitrogen atmosphere by applying a series of color glass filters a UV-35 filter (>325mg), for 29min b UV-33 filter (>300mg), for 21min cUV-31 filter (> 275 mg), for 20 min d UV-29 filter (>255 mg), for 18 min e UV-27 filter (>227 mg), for 18 min f UV-25 filter (>205 mg), for 22 min and g no filter, for 18 min. The separation between two Mn++ peaks is 86.7 gauss. The arrow mark shows a signal due to color centers induced in the quartz sample tube by irradiation. [J. Polymer Sci B 10, 139 (1972), Fig. 1]...

The ESR spectrum of polypropylene irradiated with a medium pressure mercury source in vacuo exhibits four narrow bands equally spaced. This is due to the methyl radical superimposed on the spectrum, believed to be a sextet, assigned to --CH2— CH—CH2—, and a quartet which overlap [31, 32]. The quartet has been attributed to... 

Polypropylene irradiated in the presence of oxygen can result in the following autoxidative reactions (2,3) ... 

This autoxidative scheme can be verified by ESR studies. The 17-line spectrum reported in the literature to be the alkyl (4) radical R formed during polypropylene irradiation at room temperature is shown in Figure 1(a) (3, 5). When the polypropylene irradiated in vacuum is exposed to oxygen, ESR spectra change progressively, as illustrated in Figure 1. After several days the peroxy radical (6) [Figure 1(d)] is the dominant species. If the sample is irradiated and then allowed to decay in vacuum, the peroxy radical does not form, as illustrated in... 

Figure 3. Electron spin resonance spectra of polypropylene irradiated in air at room temperature (5.0 Mrads). (a) Intermediate spectrum to oxygen diffusion during irradiation, (b) peroxy radical.

Table 18 Change in elongation at break for polypropylene irradiated in various conditions (concentration 1 % w/w). The data were taken from [95S1]. (yy ( °Co) exposure dose rate 7 kGy.h ).

In the spectrum of amorphous polypropylene irradiated with a dosage of 4000 Mrad at -196 °C and measured at -130 °C, in addition to the band at 6.08 pm, a weaker band appears with a maximum near 6.00 pm, possibly due to internal bonds ... 

In the latter case, D6.08 is the sum of the optical densities of the vinylidene and vinyl absorption bands in this region. An optical density ratio for these bands of approximately this value was found (1.75 to 3.3) for the products of thermal degradation of polypropylene. It is seen that only in the case of amorphous polypropylene irradiated with gamma-radiation from Co is the ratio (D11.23 + D10.99)/D6.08 close to the value calculated from the extinction coefficients of these bands. In the spectra of irradiated isotactic polypropylene, the intensity of the 6.08 pm band is greater than would be expected if only vibration of terminal double bonds contributes to absorption in this region. This increase in absorption in the 6.08-pm region can be related to absorption by the internal double bond in the allyl radical, the vibrational frequency of which is lowered by conjugation of the Jt-electrons of the double bond... 

Figure 3. Melting endotherms of recrystallized polypropylenes irradiated for 0, 48, 60, 96, 192 and 240 hrs.

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