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Influence of radiation sterilization on poly(ester urethanes) designed for medical applications

Przybytniak G., Kornacka E., Ryszkowska J., Bil M., Rafalski A., Woźniak P., Lewandowska-Szumieł M.

Nukleonika

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2006

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Vol. 51,suppl.1

121-128

EN

Preparation of scaffolds for tissue regeneration requires elucidation of chemical and physical processes induced by ionizing radiation during radiation sterilization of polymeric materials used for these purposes. Such treatment induces many unintended and desired reactions that lead either to degradation or cross-linking of macromolecules. It was found that in poly(ester urethane) the ester segments are responsible predominantly for radiation induced phenomena. Some radicals generated following irradiation were identified under cryogenic conditions. Upon exposure to sterilizing dose cross-linking was confirmed on the basis of rheological changes in melted polymers. The results obtained by EPR spectroscopy and DRS revealed a relatively high susceptibility of poly(ester urethanes) on oxidation.

2

Effect of hindered amine light stabilizers on the resistance of polypropylene towards ionizing radiation

Przybytniak G., Mirkowski K., Rafalski A., Nowicki A., Legocka I., Zimek Z.

Nukleonika

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2005

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Vol. 50, nr 4

153-159

EN

The influence of hindered amine light stabilizers (HALSs) on physical and mechanical properties of irradiated and non-irradiated isotactic polypropylene (PP) was studied. The stabilizers under investigation were: Tinuvin 765 (T765) and Tinuvin 622 (T622) - derivatives of 1,2,2,6,6-pentamethyl piperidine and Chimassorb 944 (C944) - a derivative of 2,2,6,6-tetramethyl piperidine. It was found that the stabilizers reduce the amount of peroxyl radicals in the amorphous phase of PP. The irradiation with electron beam causes a drop of apparent viscosity both in the original and in the modified PP however the effect is smaller in the presence of HALSs. Admixture of T622 and T765 stabilizers increases the crystallization temperature of non-irradiated PP by about 8 10°C (measured by DSC) what results from the facilitated formation of a large number small microcrystals. It was concluded that HALSs initiate two opposite tendencies - chemical protection against damage initiated by free radicals and, simultaneously, physical enhancement of sensitivity towards irradiation by the increase of nucleation density. In the studied systems, the presence of maleic anhydride does not improve compatibility between the polymeric matrix and HALSs.

3

Radiation chemistry of solid thiosulfate: optical absorption spectra

Zagórski Z., Rafalski A.

Nukleonika

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2000

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Vol. 45, nr 1

109-113

EN

Solid sodium thiosulfate, anhydrous and hydrated (5 H2O), was irradiated with 10 MeV electrons in a pulsed, high-dose (30 kGy) rate regime. The resulting optical absorption was measured by diffuse reflection spectophotometry (DRS) (absorption band in anhydrous salt at 360 nm, in hydrated salt at 418 nm). Absorption decays occurred at t1/2 = 80 h (anhydrous) and t1/2 = 9 h (hydrated) at room temperature. The yellowish radical ion formed in irradiated anhydrous thiosulfate was identified as [źS2O3]-, and not [źS2O3]3-, as proposed in previous nonoptical (EPR) investigations. The absorption spectrum of [źS2O3]- in a solid matrix was similar to the transient spectrum ascribed to the same radical, obtained by pulse radiolysis in aqueous solution, and had a lifetime many orders of magnitude shorter. A similar radical anion, but in the complex with adjacent water molecules from the hydration moiety, was observed in hydrated thiosulfate (Na2S2O3ź5 H2O).