Quantification of radiation induced crosslinking in a commercial, toughened silicone rubber, TR55 by H MQ-NMR

Radiation induced degradation in a commercial, filled silicone composite has been studied by SPME/GC-MS, DMA, DSC, swelling, and multiple quantum NMR. Analysis of volatile and semi-volatile species indicates degradation via decomposition of the peroxide curing catalyst and radiation induced backbiting reactions. DMA, swelling, and spin-echo NMR analysis indicate an increase in crosslink density of near 100% upon exposure to a cumulative dose of 250 kGray. Analysis of the sol fraction via Charlesby-Pinner analysis indicates a ratio of chain scission to crosslinking yields of 0.38, consistent with the dominance of the crosslinking observed by DMA, swelling and spin-echo NMR and the chain scissioning reactions observed by MS analysis. Multiple quantum NMR has revealed a bimodal distribution of residual dipolar couplings near 1 krad/s and 5 krad/s in an approximately 90:10 ratio, consistent with bulk network chains and chains associated with the filler surface. Upon exposure to radiation, the mean 〈Ω_d〉 for both domains and the width of both domains increased. The MQ-NMR analysis provided increased insight into the effects of ionizing radiation on the network structure of silicone polymers.     

Kinetics of levulinic acid formation from carbohydrates at moderate temperatures

The kinetic curves of levulinic acid accumulation in the process of saccharide dehydration at 80-98^oC are compared. The structural features of the substrates and 5-hydroxymethylfurfural, which is the intermediate of the process, explain the observed difference in the rates of fructose and glucose conversion. Sulfuric acid can be effectively used under moderate conditions to synthesize levulinic acid with yields exceeding 35 mol % for glucose and 50% for sucrose at 98^oC.     

The stabilization effect of radiation crosslinking on positive temperature coefficient performances of carbon black-polymer composites

In this paper, we report the results of systematic study of effect of radiation crosslinking on PTC/NTC phenomena of carbon black(CB) filled vinyl polymers. We conclude that the effect of radiation crosslinking greatly improves the PTC intensity and electrical reproductivity in thermal cycling.     

•OH对聚二甲基硅氧烷乳液辐射效应的影响

通过凝胶和溶胶分析与分子量测定的方法，研究了不同体系下，^•OH对PDMS乳液γ辐射效应的影响. 结果表明，^•OH不仅可引发聚二甲基硅氧烷的分子间交联，也能促进其降解. 对于纯PDMS乳液，在所研究的剂量范围内，^•OH对其辐射交联行为影响较小. 但若体系中加入H2O2、KIO4 和 N2O这些提高^•OH生成产额的添加剂时，^•OH对PDMS的促降解作用会随着吸收剂量增加而表现更明显，导致凝胶含量与纯乳液辐照情况相比下降较多. 即使加入交联剂-三羟甲基丙烷三甲基丙烯酸酯（TMPTMA），在过量的^•OH存在下，当吸收剂量大于40 kGy以上时，TMPTMA不仅没有提高交联度，反而会与^•OH协同，使PDMS的凝胶含量下降更显著，同时产生更多的小分子聚合物，并使PDMS的平均分子量分布变窄. 这可能是由于交联剂首先与^•OH作用，形成的产物会加快PDMS的降解.     

Separation and quantification of beer carbohydrates by high-performance liquid chromatography with evaporative light scattering detection

An HPLC method with an evaporative light scattering detector was optimized and validated for quantification of carbohydrates in beer. The chromatographic separation was achieved using a Spherisorb NH2, 5 microm chromatographic column and gradient elution with acetonitrile/water. The determinations were performed in the linear range of 0.05-5.0 g/L for fructose, 0.05-5.0 g/L for glucose, 0.05-15.0 g/L for maltose, 0.05-10.0 g/L for maltotriose, and 0.05-5.0 g/L for maltotetraose. The detection limits were 0.005 g/L for fructose, 0.008 g/L for glucose, and 0.01 g/L for maltose, maltotriose, and maltotetraose. The reliability of the method in terms of precision and accuracy was evaluated in three beer matrices, low alcohol beer, 6% alcohol beer, and beer made with part of adjuncts (4.5% alcohol). Relative standard deviations (RSDs) ranged between 1.59 and 5.95% (n = 10), and recoveries ranged between 94 and 98.4%.     

·OH对聚二甲基硅氧烷乳液辐射效应的影响

通过凝胶和溶胶分析与分子量测定的方法,研究了不同体系下,"OH对PDMS乳液γ辐射效应的影响.结果表明,"OH不仅可引发聚二甲基硅氧烷的分子间交联,也能促进其降解.对于纯PDMS乳液,在所研究的剂量范围内,"OH对其辐射交联行为影响较小.但若体系中加入H2O2、KIO4和N2O这些提高"OH生成产额的添加剂时,"OH对PDMS的促降解作用会随着吸收剂量增加而表现更明显,导致凝胶含量与纯乳液辐照情况相比下降较多.即使加入交联剂-三羟甲基丙烷三甲基丙烯酸酯(TMPTMA),在过量的"OH存在下,当吸收剂量大于40kGy以上时,TMPTMA不仅没有提高交联度,反而会与"OH协同,使PDMS的凝胶含量下降更显著,同时产生更多的小分子聚合物,并使PDMS的平均分子量分布变窄.这可能是由于交联剂首先与"OH作用,形成的产物会加快PDMS的降解.     

Network characteristics of hydrogenated nitrile butadiene rubber networks obtained by radiation crosslinking by electron beam

The effects of high-energy radiation on hydrogenated nitrile butadiene rubber (HNBR) copolymer structure and properties were studied. Characterization by FTIR spectroscopy, swelling and mechanical measurements of irradiated and un-irradiated sample permit us to correlate the change in structure with properties. The modifications obtained are dependent on the radiation dose of the incident electron beam. FTIR spectroscopy in absorption mode shows that irradiation of HNBR first induces trans-vinylene bond formation and secondly small amounts of carbonyl (CO) groups. Moreover, more significant changes were observed with swelling method and mechanical behaviour showing the effect of crosslinking on the elastomer.     

Studies on calcium alginate stanch fibre by radiation sterilization and its biology

This paper explored the technical feasibility of surgical calcium alginate stanch fibre steriliged by radiation. By detecting the biological load before and after irridiation the optimum sterilized dose is 10–12KGY. By determing the Ca⁺⁺ content, a linear regression equation relative to adsorbed dose and Ca⁺⁺ content percentage is given out. lgD=0.13449+7.966x10^-3N(r=0.9935) The result of biological studies of radio sterilized stanch fibre to be applied on adult rabbits and NIH mice by biologic test was performed that the γ-ray sterilized stanchfibre had no irritant effect on both the health and the wound skin, crust formation rate was better than of the check. The total and partial irritation intensity and the allergization rate became zero.     

Complexation behaviour of radiation synthesized poly(vinylbenzyltrimethylammonium chloride) and its gel with potassium hexacyanoferrates (II, III) and potassium persulfate in aqueous medium

High energy gamma radiation has been used to synthesize linear poly(vinylbenzyltrimethylammonium chloride) (PVBT) as well as crosslinked PVBT gels. Complexation behaviour of linear and crosslinked PVBT with K₂S₂O₈, K₃[Fe(CN)₆] and K₄[Fe(CN)₆] have been studied by viscometry, turbidity and equilibrium swelling measurements. The stoichiometry of the complex formed was found to be a function of charge on the anions of complexing species. Crosslinked poly(vinylbenzyltrimethylammonium chloride) gels were found to desorb some of the embedded water when swollen gels were placed in these salt solutions. Existence of strong ionic interactions between polymer chains and complexing salts was confirmed by changes in equilibrium swelling of complexed crosslinked matrices as well as in the stoichiometry of linear PVBT complexes in presence of strong electrolytes like NaCl.     

Radiation effect studies on anticancer drugs, cyclophosphamide and doxorubicin for radiation sterilization

Two anticancer drugs, cyclophosphamide (CPH) and doxorubicin hydrochloride (DOXO), in powder form were exposed to a range of doses of ⁶⁰Co gamma and electron beam radiation to study the effects of ionizing radiation. Pharmacopoeia tests, discolouration, degradation products, effect of irradiation temperature and dose rate were investigated. CPH undergoes less than 2% degradation at 30 kGy. Chromatographic studies revealed formation of several trace level degradation products, discolouration and free radicals in the irradiated CPH. N,N-bis (2-chloroethyl) group in the molecule is particularly sensitive to radiation degradation. Irradiation to 5 kGy at low temperature (77 K) did not result in significant changes. DOXO was observed to be quite radiation resistant and did not undergo significant changes in its physico-chemical properties and degradation product profile. It can be radiation sterilized at normal sterilization dose of 25 kGy.     

Standards and regulations for radiation processing industry in China

To understand the current status and development tendency of radiation processing industry in China, and to know the relationship between the perfecting of standard systems and the increasing of throughput of this industry, a brief introduction on Chinese standards and regulations is given in this paper. Typical documents for setting up and operating an irradiation facility for radiation processing, either a gamma-ray or an electron-beam facility, are introduced in detail. A comparison is made between some of the international standards and those corresponding Chinese national standards. The consideration of development of Chinese standards and regulations indicates a positive tendency for this industry.     

Indirect UV detection of carbohydrates in capillary zone electrophoresis

Summary A new system for the rapid and sensitive analysis of underivatized carbohydrates has been established using capillary zone electrophoresis with indirect UV detection. At an applied potential of 28 kV, sugars and sugar acids could be separated by the combined effects of electroendosmosis and electrophoresis within 20 minutes in a fused silica capillary of 50 m internal diameter and an effective length of 100 cm using 6mM sorbic acid, pH 12.1, as both carrier electrolytie and chromophore. The alkaline pH ensured ionization of the sugars and, hence, their detection by means of charge displacement. Furthermore, the chosen concentration of sorbic acid allowed the smallest fractional change in the background signal to be measured. While the electrophoretic mobilities of the sugars were found to increase within a pH range of 11.9 to 12.3, those of the sugar acids were not affected. Due to the increasing competition of hydroxide ions in the displacement of the chromophore with rising pH, a significant loss of sensitivity is observed at pH values higher than 12.1 and this pH was found to provide sufficient resolution, optimum sensitivity, and a acceptably short analysis time. Under these conditions, a lower detection limit of 2 pmol was obtained for glucose.     

Analysis of carbohydrates in plants by high-performance anion-exchange chromatography coupled with electrospray mass spectrometry

A mass spectrometer was coupled to high-performance anion-exchange chromatography (HPAEC) with the help of electrochemical neutralization of the eluent and post-column addition of lithium chloride for carbohydrate analysis. Parallel selective channels (single ion monitoring) were used to decrease the detection limits and separate unresolved peaks. The mass specific detection allowed the simultaneous analysis of a wide range of sugar alcohols, mono-, di- and oligosaccharides. Carbohydrates extracted from leaves of poplar submitted to drought stress were analyzed using pulsed amperometric detection (PAD), then mass spectrometry. It allowed the confirmation of peak attribution and the identification of salicin as a major compound in the extracts. Different responses to water deficit and re-hydration were obtained for several carbohydrates, suggesting different roles in osmoprotection processes.     

Capillary zone electrophoretic analysis of carbohydrates by direct and indirect UV detection

Summary The analysis of carbohydrates has been always hampered by their lack of UV absorbance above 200 nm, which is an especially challenging problem in capillary electrophoresis due to the very small (nl) sample volumes injected. The introduction of 2-aminopyridine as derivatizing agent allows sensitive direct UV detection of saccharides in the fmol range. However, due to the requirement of the presence of a free aldehyde group only aldoses and uronic acids can be determined. This limitation was recently overcome by means of precolumn derivatization withp-aminobenzoic acid or ethylp-aminobenzoate, which permits the analysis of fructose with a lower mass detection limit of 0.3 and 0.14 pmol, respectively. The detection limits for aldoses were even as low as 15 and 7 fmol. A more universal approach is the use of indirect UV detection, which permits the analysis of carbohydrates, including (1–2)-linked disaccharides and aldonic acids, at the lower pmol level without the need for derivatization.Dedicated to Professor Leslie S. Ettre on the occasion of his 70th birthday.     

Review on the production process and uses of controlled rheology polypropylene—Gamma radiation versus electron beam processing

Controlled rheology polypropylene grades are established commodities in the polymer processing market. However, new types, mainly the so-called high melt strength polypropylene (HMSPP) grades, are being introduced in the last two decades and radiation processing has played an important role. The melt strength properties of a polymer increases with molecular weight and with long-chain branching due to the increase in the entanglement level. As polypropylene (PP) is a linear polymer, the way to improve its elongational viscosity is by the production of a bi-modal polymer. Basell's patents claim the production of long-chain branching on PP by irradiating with electrons under oxygen free atmosphere, followed by two heating steps to allow radical recombination and annihilation reaction. Some other companies have issued patents using electron beam processing, but so far there is no actual production other than the Basell one. As a result of a research joint effort, IPEN, BRASKEM (the biggest Brazilian polymer producer) and EMBRARAD (the major Brazilian radiation processing center) developed a new process to produce HMSPP based on gamma processing. This paper will address some characteristics of each technology and the main industrial opportunities.     

Modification of radiation resistance of Bacillus spores by water

Spores of Bacillus subtilis, containing plasmid (B. subtilis BD 366(pUB110, Trp C2 thr 5)), were prepared free of additives and the effect of water on their radiation sensitivity under aerobic condition was investigated. The moisture content of spores was controlled by (i) drying over CaCl₂ (Aw = 0.0), (ii) equilibrating with the vapor of saturated aqueous NaCl solution (Aw = 0.7), or (iii) suspending in water (Aw = 1.0). The resistance of spores to radiation increased with increasing moisture content. The analysis of spore DNA by agarose gel electrophoresis showed that DNA damage (strand breaks) decreased with increasing water activity of the spores, a finding concomitant with the observed survival rates.     

Chemically modified electrode for the detection of carbohydrates

A nickel-catalysed chemically modified electrode is described which seems to represent a convenient compromise between ease of preparation, reproducibility, precision and detection limits for the determination of carbohydrates in biological matrices.     

The sensitizing effect of acrylates on radiation vulcanization of natural rubber latex

The sensitizing effect of acrylates on radiation vulcanization of natural rubber latex was studied. The results indicate that Gc value of crosslinking (Gc) will be higher at the same radiation dose when a sensitizer exists, and Gc value decreases with the increase of radiation dose (D) conforming to the formula Gc=KD^-α, where K and α are constants depending on sensitizers. The more sensitizers added, the greater the Gc value. However, the viscosity of the natural rubber latex also increases rapidly along with the increase of sensitizers added.Some sensitizers, such as TMPTA, can decrease the optimum dose from about 200 kGy to approximately 20 kGy according to our experiment. The tensile strength of the film can reach round 20 MPa. Other physical properties are comparable to those of unsensitized.