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RADIATION CHEMISTRY AND PHYSICS, RADIATION TECHNOLOGIES 39

Simultaneously, with radiation yield of H2, the prepared from isophorene cyanate. consumption of from the space above the To some extent the protection effect spreads over sample inserted in the was estimated (Fig.4(b)). the whole polymeric material. Proportion between Considerable scattering of results makes detailed urethane and urea groups do not influence hy- analysis impossible. However, all G(O2) values for drogen abstraction processes that proceed only in aliphatic PSURURs are in a similar range as G(H2) regions or in methyl groups of siloxane data found for aromatic analogues. Thus, unex- units. It seems that aliphatic PSURURs have a ten- pectedly, O2 consumption in aliphatic PSURURs dency to efficient crosslinking. is much lower than the hydrogen yield. Such a dis- proportion between results might be tentatively References interpreted as a result of very efficient recombi- [1]. Kozakiewicz J.: Advances in moisture-curable siloxane- nation between carbon centered radicals leading -urethane . In: Advances in urethane science to crosslinking. It seems that in aliphatic PSURURs and technology. Eds. K.C. Frisch, D. Klempner. Lan- the yield of oxidation processes is very limited, caster-Basel: Technomic Publ. Co. Inc., 2000, vol. 14, however this suggestion needs further investiga- pp. 97-149. tions. [2]. Kornacka E.M., Kozakiewicz J., Legocka I., Przybylski In aromatic PSURURs, the concentration of J., Przybytniak G., Sadło J.: Polym. Degrad. Stabil., 91, 82 (2006). radicals situated at hard segments is lower than in [3]. Kwiatkowski R., Włochowicz A., Kozakiewicz J., Przy- aliphatic ones due to efficient dissipation of ioniz- bylski J.: Fibres Text. East. Eur., 11, 5, 107 (2003). ing radiation energy. Therefore, the relative con- [4]. Yilgör E., Yilgör I.: , 42, 7953 (2001). centration of methylene radicals is higher and the [5]. Yilgör E., Burgaz E., Yurtsever E., Yilgör I.: Polymer, yield of dehydrogenation is much smaller than in 41, 849 (2000).

RADIATION EFFECTS IN POLYPROPYLENE/ BLENDS Wojciech Głuszewski, Zbigniew P. Zagórski

Several applications of polymers demand resistance cation of radiolysis extent, but in the chosen sys- towards ionizing radiation, e.g. for disposable tem of polypropylene/polystyrene, also formations medical devices sterilized by radiation, for appli- of methane and carbon monoxide (after oxidative cations in nuclear industry and in nuclear reactors, experiments) in the function of dose and compo- also for outer space localizations etc. Depending sition were studied, as well as kinetics of oxygen on the nature and extent of radiation damage, sol- consumption in the presence of air. Further stages ution of the problem consists in application of ad- of oxidative degradation of polypropylene were ditives, produced for general application of poly- studied by diffuse reflection spectrophotometry mers. They work often very well also as a protection (DRS) [4,5]. from radiation damage, especially when they con- Introduction of small molecule additives into tain aromatic groups which act as energy sink via polymer composition is simple, but preparation of energy transfer mechanism. Some additives are not aliphatic/aromatic polymer blends is more com- acceptable, especially in medical applications and plicated and demanded new procedures. The one of the aims of this investigation was to answer of polypropylene/polystyrene, i.e. of a semicrystal- a question if an aromatic polymer as an additive line, nonpolar polymer with a polar, can limit the extent of radiation damage. However, amorphous polymer is known to be immiscible. the main topic of the project is basic research on Mechanical mixing proved formation of unsatis- classic aliphatic/aromatic energy transfer, this time factory blend from the point of view of energy extended from small molecules to polymers. transfer, but other approaches resulted in a proper Freeman [1] first has found that in irradiated mixture. simple system of cyclohexane/benzene, radiolytic Sample “A” was prepared by mixing commercial hydrogen was not formed in proportion to the com- polymers: polypropylene Malen P J-400Z*1632/01 position, i.e. benzene was reducing the hydrogen from Basell-Orlen and polystyrene from Owispol- yield to a higher degree than was expected. The -Dwory. The proportions were: 0, 10, 25, 50, 75, effect was investigated later in several laboratories 100% of polystyrene. In spite of the most thorough and was called “deviation from the mixture law”. blending injection and pressing in a mechanical It was investigated also in frozen systems, gaining way, the surface area of contact between both poly- interesting facts connected with the - mers was assumed not to be as most favourable line state. Deviation from the mixture law was never for energy transfer and, therefore, two other pro- investigated systematically in the field of radiation cedures of sample preparation have been developed. chemistry of polymers. Albano et al. investigated Sample “B” was prepared from virgin polypropy- the polypropylene/polystyrene (PP/PS) 20/80% lene (F 401) in the shape of powder, collected from blends, at low doses [2] and high doses [3] (70-400 the Orlen-Olefins production line, without addi- kGy) with resulting full protection of polypropylene, tives, next impregnated with polystyrene dissolved to be expected. in a styrene (fresh distilled, free from As in the case of cyclohexane/benzene system, stabilizers) in proportion of polypropylene/poly- the hydrogen production was used as a basic indi- styrene as above. Afterward, the styrene was removed 40 RADIATION CHEMISTRY AND PHYSICS, RADIATION TECHNOLOGIES by evaporation during gentle heating. Sample “C” was prepared by soaking polypropylene powder with stabilizer – free styrene and /graft- ing in the gamma field from cobalt-60 at a dose rate of 1.5 kGy/h. All added styrene has polymerized totally, but the adjusted percentage was checked gravimetrically as in sample ”B”. Polymerization grafting of styrene proceeds in a chain mechanism in the presence of polypropylene, with high radia- tion yield (12 000 effects/100 eV), due to the gen- erous supply of free radicals by irradiated polypro- pylene. Styrene alone (the same batch), gamma- or electron beam irradiated, polymerizes very slowly and the progress of reaction can be followed by the increase of viscosity only. All proportions of both polymers were checked by weighing the final prepa- Fig.2. Radiation yield of methane in the function of polypro- pylene/polystyrene composition. A curve does not rations. All irradiations, except gamma exposure start at the same point as curves B and C, because a mentioned above, were done with electron linacs, commercial polypropylene containing already addi- “Elektronika” 10/10 (10 MeV, 9 kW) or “LAE 13/9” tives was in this case used. Curves B and C start from (up to 13 MeV, 9 kW straight beam, or 6 kW bent virgin polypropylene. Dose – 25-100 kGy. beam of improved monoenergetic spectrum) [6]. Determination of hydrogen, methane, and second- tion against radiolysis of polypropylene by poly- ary product carbon monoxide as well as of oxygen styrene (Figs.1 and 2). Mechanical methods can- consumption were done by gas chromatography not secure sufficiently large interphase for energy using a Shimadzu GC 2040 and GC 2010, molecu- transfer. Classical case of previously investigated, lar sieves 5A, in carrier gas argon. protection phenomena, i.e. benzene/cyclohexane The applied methods of analysis and investiga- was effective only in liquid state or frozen from the tion, i.e. gas chromatography together with diffuse gas phase. Application of grafting of styrene on reflection spectrophotometry have shown to be polypropylene, by two slightly different procedures effective in recognition of protection effects in ali- resulted in a proper response to expected protec- phatic/aromatic blends of polymers. Key interme- tion effect. It extended, according to a vague esti- diates and final products of radiolysis have been mate to be a distance of 9-12 mers of polypropy- determined, i.e. hydrogen, methane and carbon lene. Thus, the classical case of monoxide. effect in the benzene/cyclohexane system has been extended into the field of polymers. The solid state system benzene/cyclohexane shows energy transfer only if it is crystallized from the gas phase to secure close contact of constituents. In the case of polymeric system of polypropylene/polystyrene, the mechani- cal mixing is not sufficient and the effect of energy transfer occurs only in the case of impregnated and grafted samples. Chains of both polymers, aliphatic and aromatic must have sufficient area of contact- ing, or exhibit low distance sites for energy transfer to the aromatic structure, which is the sink of en- ergy. This investigation was supported by a grant No. 0989/T08/2005/28 from the Polish Ministry of Edu- cation and Science.

Fig.1. Radiation yield of hydrogen in the function of References polypropylene/polystyrene composition. A curve does not start at the same point as curves B and C, [1]. Freeman G.R.: J. Chem. Phys., 33, 71 (1960). because a commercial polypropylene containing al- [2]. Albano C., Reyes J., Ichazo M., Gonzáles J., Hernán- ready additives was in this case used. Curves B and dez M., Rodrígues M.: Polym. Degrad. Stabil., 80, 251 C start from virgin polypropylene. Dose – 25-100 (2003). kGy. [3]. Albano C., Reyes J., Ichazo M.N., González J., Rodrí- guez M.: Nucl. Instrum. Meth. Phys. Res. B, 208, 485 For the preparation of blends and mixtures of (2003). aliphatic/aromatic polymers three methods have [4]. Zagórski Z.P.: Int. J. Polimer. Mater., 52, 323 (2003). been proposed. Conventional blending of polypro- [5]. Zagórski Z.P.: Rafalski A.: Radiat. Phys. Chem., 48, pylene and polystyrene in Brabender and/or by 595 (1996). injection does not give desired results of protec- [6]. Zagórski Z.P.: Radiat. Phys. Chem., 22, 409 (1983).