Electron irradiation polypropylene

Chemiluminescence at ambient temperature and at 150°C of several irradiated (electron-beam) polypropylene formulations can be qualitatively correlated with loss of impact strength. The correlation with chemiluminescence is preserved at high vs. low temperatures, even though the ranking changes. 

Irradiated Polypropylene. Part II. Electron Spin Resonance Studies, Adv. Chem. Ser. (1978) 169,151. 

Table 11.43. Electron irradiation of polypropylene (PP) and conjugated diene butyl polymer (CDB) [Berejka and Bradley, 1981]...

Misheva, M., Djourelov, N., Zamfirova, G., Gaydarov, V., Cerrada, M.L., Rodriguez-Amor, V., P6rez, E. Effect of compatibilizer and electron irradiation on free-volume and microhardness of syndiotactic polypropylene/clay nanocomposites. Radiat. Phys. Chem. 77, 138-145 (2008)... 

T. Buch, Electron Spin Resonance Spectroscopy in Irradiated Polypropylenes, Northwestern University, Ann Arbor, MI, USA, 1960. [PhD Thesis]... 

A study of the electron spin resonance (ESR) spectra of irradiated polypropylene has shown that the alkyl radicals formed during irradiation at -196 "C ... 

Electron beam irradiation is one of the methods of cross-linking in fhis process. The other methods use peroxide, multifunctional azide, or an organofunctional silane. Polyethylene resins respond to electron beam irradiation well since the rate of cross-linking exceeds significanfly fhe chain scission. Polypropylene (PP) is prone to P-cleavage, which makes if difficult to cross-link by a free radical process. For fhaf reason, PP resins... 

Alkyl Free Radicals. The primary alkyl free radical, RCH./, has been postulated to exist in gamma-irradiated polyethylene (23), but its presence has never been unambiguously demonstrated. If all the a and p protons interacted equally with the unpaired electron, the primary alkyl free radical ESR spectrum should consist of five lines, in contrast to those of the secondary and tertiary alkyl radicals whose ESR spectra should consist of six and eight lines, respectively (the latter calculated for the tertiary free radical in polypropylene). The existence of the secondary... 

The loss of Impact strength of polypropylene was followed from sheets stored In air at 25°C and 60°C after irradiation with electron beams. A marked difference in efficacy of phenolic and thioether-based stabilizers at the two temperatures was found, with the thioether active alone at 60°C but only synergistically at 25°C. This difference was also reflected qualitatively in differences in chemiluminescence emission from the samples. 

Irradiation of polymers with y- or electron beams is an attractive alternative to chemical sterilization because of its speed, ease of control, and the absence of residue. Radiation treatment of polypropylene, however, also initiates chemical changes which lead ultimately to embrittlement. These changes in physical properties may not become apparent until some time after the treatment. The ability of antioxidants to prevent radiation damage does not always follow the trends observed in thermal oxidation, which has stimulated efforts to develop new stabilizers or optimized combinations of existing ones. 

The thioether alone at room temperature does not protect polypropylene from loss of physical properties after electron-beam treatment, although irradiated samples that are subsequently heated to 150°C are apparently protected from thermal oxidation. 

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.

Radicals, generated in polypropylene fibers during irradiation as well as the transition frcan these reidicals (R ) to peroxy radicals (ROa ) are monitored by electron spin resonance spectroscopy. Experimental data exhibit an anomaly in the temperature dependence of RO, concentration, around the glassy transition temperature (Tq). The dependence of RO, concentration on temperature, around T, is described by a Hil-liam-Landel-Perry equation rather than by an Arrhenius one. Consequently, the transition consists of two steps the first is associated with diffusion processes and the second with the proper chemical reaction. 

A general scheme for the production of such functionalized polymers can be presented as follows The polymer support (polyethylene (PE), polypropylene (PP), polystyrene (PS), polytetrafluoroethylene (FIFE), ethylene-propylene copolymers (CEP), etc.) are subjected to mechanical, chemical, radiation-chemical ( -irradiation or with accelerated electrons) or high-frequency (HF), UV-irradiation treatment with a subsequent grafting of the appropriate monomers ... 

Mihailova, M., Kresteva, M., Aivazova, N., Krestev, V, Nedkov, E., X-ray investigation of polypropylene and poly(ethylene-co-vinyl acetate) blends irradiated with fast electrons WAXS investigation of irradiated i-PP/EVA blends. Radiation Physics and Chemistry 1999, 56(5-6), 581-589. 

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