Irradiation high density polyethylene

Lawton, E. J., J. S. Balwit, and R. S. Powell Paramagnetic-resonance studies of irradiated high-density polyethylene. 1. Radical species and the effect of environment on their behaviour. J. Chem. Phys. 33, 295 (1960). 

The importance of the presence of hydrogen gas was first demonstrated by Dole and Cracco in 1961 (49-51) by measuring the rate of hydrogen exchange from irradiated high density polyethylene to gaseous D2, and explored more completely... 

Several years after this, Randall and co-workers (62-64) studied irradiated high density polyethylenes using NMR, and identified a number of new struc-... 

Lawton E, Balwit J, Powell R. Paramagnetic-resonance stedies of irradiated high-density polyethylene. H. Effect of irradiation dose on the radical species trapped at room temperature. J Chem Phys 1960 33(2) 405-12. 

Szadkowska-Nicze, M., Mayer, J., and Kroh, J., Excimer formation in irradiated high density polyethylene doped with aromatics,/. Photochem. Photobiol. A Chem., 54, 389,1990. 

Allyl Free Radicals. Ayscough and Evans (3) have recently studied, by ESR measurements, the types of allylic free radicals produced by gamma-irradiation of several monomeric olefins. In irradiated polyethylene the allyl free radical is quite stable, persisting for several months at room temperature (31). The presence of these allyl free radicals is most noticeable in the case of high density polyethylene, and this type of free radical is undoubtedly the cause of the slow oxidation of polyethylene at room temperature, which lasts for 40 or more days after irradiation (10). Williams and Dole (40) could observe little if any oxidation of low density polyethylene when it was exposed to air after irradiation. By oxidation we mean formation of carbonyl groups as detected by infrared absorption studies at 1725 cm"1. Parenthetically, it should be noted that adding an oxygen. molecule to a free radical produces initially another type of free radical, a peroxy free radical, but in this paper we shall not discuss free radicals of this or any other types except those of hydrocarbons. 

Recently, Ramamurthy and Weiss and their coworkers reported the photo-Fries rearrangement of three 1-naphthyl phenylacelates (Fig. 36) in cation-ex-changed zeolite Y and high-density polyethylene films [193], When the substrates were irradiated in hexane to <30% conversion, the eight photoproducts in Fig. 36 were detected. The photoproduct distributions from polyethylene or a Y-zeolite are drastically different from those in solution. Cage-escape products (54 and 55) are absent in both constrained media, and in zeolite Y, only 49 was detected. The... 

For example, irradiation of either 2-naphthyl acetate (2-NA) or 2-naphthyl myristate (2-NM) in the rubbery state of a low density polyethylene (LDPE) or a high density polyethylene (HDPE) yields a variety of in-cage rearrangement products and 2-naphthol (2-NOL), a cage-escape product (Table 13.2). Both LDPE and HDPE consist of amorphous and crystalline regions LDPE has a larger volume... 

Figure 17. Core-level spectra of a high-density polyethylene sample after exposure to a stream of oxygen rich in singlet molecular oxygen vs. time of x-ray irradiation...

Long-term oxidative degradation of an ion-beam irradiated polymer was studied. Silicon oxide thin layers were deposited on the surfaces of high density polyethylene (HDPE) to suppress the oxygen permeation. HDPE samples irradiated with a C6+ ion-beam were stored up to 12 months after the irradiation and the evolution of the chemical structure was followed by micro-Fourier transform infrared (micro-FT-IR) spectroscopy. Silicon oxide layers were found effective to suppress the long-term oxidative degradation of the ion-irradiated polymer. 

The concentrations of structures produced in irradiated polyethylene are on the order of 1 per 10,000 carbon atoms for absorbed doses of approximately 2.0 Mrad. Although the approach of examining polyethylenes irradiated with absorbed doses less than the gel dose placed a premium on sensitivity, we were able to detect the first direct radiation induced long chain branches in high density polyethylene (4). 

Phillips Marlex 6003, a high density polyethylene (Mw = 53,000 Mp = 18,000) possessing predominantly saturated end groups was irradiated to 4.0 Mrad in vacuum in pellet form as supplied. NBS 1475 is a commercial polyethylene containing 111 ppm of Irganox 1010. Other experiments involved heating in vacuum to 500 K for 24 h prior to irradiation to 3.0 Mrad at 500 K. The NBS 1475 sample required a greater amount of irradiation to reach the gel dose than did Marlex 6003. 

Irradiation of Marlex 6003 Polyethylene. Results of 13c NMR measurements on Phillips Marlex 6003 polyethylene both prior to and just following a 2.0 Mrad irradiation in vacuum and 298 K are presented in Table IV. The spectra from which these data were obtained are shown in Figures 4 and 5. These results indicate that irradiation of high density polyethylene in vacuum in the solid state reduces the concentration of terminal vinyl unsaturations and increases the concentrations of long chain Y branches, saturated end groups and trans double bonds. The H-link could not be detected following an irradiation of Marlex 6003 in the solid state. 

Long chain Y branches are one of the principal products formed during irradiation of high density polyethylenes in vacuum both in the solid and molten states at absorbed doses below the gel dose. 

Kang, P.H., Nho, Y.C., April 2001. Characteristics of heat shrinkable high density polyethylene crosslinked by y-irradiation. Journal of the Korean Nuclear Society 33 (2). 

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