| 1. |
- Azhdar, Bruska, et al.
(författare)
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A new method for assessing the efficiency of stabilizers in polyolefins exposed to chlorinated water media
- 2009
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Ingår i: Polymer testing. - : Elsevier BV. - 0142-9418 .- 1873-2348. ; 28:6, s. 661-667
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Tidskriftsartikel (refereegranskat)abstract
- The chlorine used as disinfectant in tap water degrades most materials, including polyethylene. The most adequate (functional) test method, the pressure test, is complicated and expensive because the chlorinated aqueous media (Cl-2 or ClO2 in water) are unstable and they undergo reactions that are dependent on the pH. A new method which assesses the protection efficiency of phenolic antioxidants in polyolefins was developed. The method uses a liquid hydrocarbon analogue, squalane, in which antioxidants are dissolved. The organic phase was dispersed in the aqueous chlorinated phase (containing 10 ppm of either Cl-2 or ClO2; pH=6.8) at 70 degrees C by intense stirring. The depletion of antioxidant (Irganox 1010) was monitored by standard DSC determination of the oxidation induction time. It was shown that 300 min of exposure was sufficient to obtain useful data.
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| 2. |
- Carlsson, Magnus, et al.
(författare)
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A comparative study on the degradation of cotton linters induced by carbonate and hydroxyl radicals generated from peroxynitrite
- 2005
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Ingår i: Holzforschung. - 0018-3830 .- 1437-434X. ; 59:2, s. 132-142
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Tidskriftsartikel (refereegranskat)abstract
- Carbonate (CO3.(-)) and hydroxyl (HO.) radicals were chemically produced in cotton linter suspensions using peroxynitrite as a radical precursor. Both radicals could degrade cotton linters, as shown by viscosity and GPC-SEC measurements. As evidenced by the viscosity measurements, the presence of oxygen during the cotton linter treatments slightly increased cellulose degradation by both radicals. For the carbonate radical, more than 90% of the viscosity losses could be recovered by reductive NaBH4 treatment before measuring the viscosity, whereas only approximately 40% of the viscosity was recovered after hydroxyl radical degradation and subsequent NaBH4 treatment. This indicates that carbonate radicals mainly abstract H-atoms adjacent to hydroxyl groups, i.e., at C-2, C-3 and C-6. This intramolecular selectivity may reflect a polar effect, whereby hydrogen atom abstractions from these positions are favoured. In addition, abstraction at C-6 would be sterically and statistically favoured.
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| 3. |
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| 4. |
- Carlsson, Magnus, et al.
(författare)
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The Carbonate Radical as One-Electron Oxidant of Carbohydrates in Alkaline media
- 2005
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Ingår i: Holzforschung. - 0018-3830 .- 1437-434X. ; 59:2, s. 143-146
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Tidskriftsartikel (refereegranskat)abstract
- The mechanism by which the carbonate radical anion reacts with D-glucose in alkaline aqueous solutions has been studied by means of gamma-radiolysis. From the product analysis it is concluded that the reaction sequence is initiated by a one-electron transfer between the carbonate radical anion and deprotonated D-glucose. In the presence of molecular oxygen, the major, if not only products of this reaction sequence are formic acid, arabinose and gluconic acid and reaction schemes are proposed to account for the observed formation of these products.
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| 5. |
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| 6. |
- Liao, Haidong, et al.
(författare)
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Generation of Free OHaq radicals by Black Light Illumination of Degussa P25 TiO2 Aqueous Suspensions
- 2013
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Ingår i: Catalysts. - : MDPI AG. - 2073-4344. ; 3:2, s. 418-443
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Tidskriftsartikel (refereegranskat)abstract
- This work demonstrates how formation of strongly chemiluminescent 3-hydroxyphthalic hydrazide by hydroxylation of non-chemiluminescent phthalic hydrazide can be applied as a selective reaction probe to obtain information on authentic hydroxyl radical, i.e., (OHaq)-O-center dot, formation, in black light illuminated Degussa P25 TiO2 aerated suspensions in the pH range from 3 to 11. The (OHaq)-O-center dot formation was found to be strongly pH dependent. At alkaline pH, the apparent quantum efficiency of (OHaq)-O-center dot formation was estimated to be at the similar to 10(-2) level whereas at acidic pH it was near zero. Addition of phosphate and fluoride ions substantially enhanced the (OHaq)-O-center dot production in the acidic pH range. It is suggested that (OHaq)-O-center dot-radical formation in TiO2 photocatalysis can occur by oxidation of hydroxyl ions in the water layer adsorbed on TiO2 surfaces.
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| 7. |
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| 8. |
- Lokander, Mattias, et al.
(författare)
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Oxidation of Natural Rubber based Magnetorheological Elastomers
- 2004
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Ingår i: Polymer degradation and stability. - : Elsevier BV. - 0141-3910 .- 1873-2321. ; 86:3, s. 467-471
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Tidskriftsartikel (refereegranskat)abstract
- The Theological properties of magnetorheological (MR) materials can be changed continuously, rapidly and reversibly by an applied magnetic field. Solid MR materials consist of magnetically polarisable particles, generally iron, in an elastomer matrix. The high iron concentrations required (about 30% by volume) in order to get a substantial magnetorheological effect should influence the long-term stability of the materials. In this paper, the oxidative stability of natural rubber-based magnetorheological elastomers has been studied by chemiluminescence and oven ageing. The results show that the oxidative stability of natural rubber decreases dramatically when large amounts of iron particles are incorporated in the matrix. This is probably due to the large amounts of oxygen on the surface of the particles. Conventional antioxidants can be used to prolong the lifetime of magnetorheological elastomers, but in order to get acceptable lifetime of the materials a careful selection of the antioxidant system has to be made.
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| 9. |
- Pourmand, Payam, et al.
(författare)
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Effect of gamma radiation on carbon-black-filled EPDM seals in water and air
- 2017
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Ingår i: Polymer degradation and stability. - : Elsevier. - 0141-3910 .- 1873-2321. ; 146, s. 184-191
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Tidskriftsartikel (refereegranskat)abstract
- The effects of gamma radiation in air and water on a highly filled carbon-black-containing EPDM seal, used in transportation valves for old-fuel rods, were investigated. Samples were irradiated at a dose rate of 7 kGy h(-1) until total doses of 0.35, 1.4, 2.1 and 3.5 MGy were reached. The doses were chosen to correspond to 1, 4, 6 and 10 years of service. Infrared spectroscopy, mechanical indenter and NMR relaxation time (T-2) measurements indicated an oxidative crosslinking of the seal, which increased monotonically with the dose. The effects were larger in air than in water, and in air, diffusion-limited oxidation was observed. The compression set increased with increasing dose of radiation and was the highest for seals irradiated in air. The water uptake into the rubber, which was always lower than 1 wt.%, increased with the dose, showing the effect of increased polarity by the oxidation of the rubber.
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| 10. |
- Shanks, David, et al.
(författare)
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Improved Antioxidant Formulations for Polymeric Materials : Synergistic Protective Effects in Combinations of Organotellurium Compounds with Conventional Phenolic Antioxidants or Thiols
- 2003
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Ingår i: Polymer degradation and stability. - 0141-3910 .- 1873-2321. ; 81:2, s. 261-271
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Tidskriftsartikel (refereegranskat)abstract
- As judged by differential scanning calorimetry experiments at 190 °C and chemiluminescence measurements at 150 °C, addition of 0.10–0.30 wt.% of certain organotellurium compounds to polypropylene caused a notable protection against oxidation of the material. The best stabilizers (diaryl telluride 3 and alkyl aryl telluride 4), offered a similar degree of protection as commercial stabilizer formulations comprising a mixture of Irganox® 1010 and Irgafos® 168 (0.1 wt.% of each). The protective effect of the organotelluriums was substantially improved in combinations with sterically hindered phenols or thiols. The protection was often much better than the added effects of the individual components and, thus, can be considered as synergistic. Evaluation of a series of stabilizers where tellurium had been exchanged for selenium and sulfur (compounds 2) showed that the synergistic protective effect was unique for tellurium.
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