| 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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| 11. |
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| 12. |
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| 13. |
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| 14. |
- Stenman, David, et al.
(författare)
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Reactivity of the carbonate radical anion towards carbohydrate and lignin model compounds
- 2003
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Ingår i: Journal of wood chemistry and technology. - 0277-3813 .- 1532-2319. ; 23:1, s. 47-69
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Tidskriftsartikel (refereegranskat)abstract
- The kinetic selectivity for the reaction of the carbonate radical anion towards lignin and carbohydrate model compounds was determined by pulse radiolysis in the pH-span 8-13. For the cellulose model compound methyl-β-D-glucopyranoside a pKA-value of 14.4 was estimated.
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| 15. |
- Yu, Wenbin, et al.
(författare)
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Antioxidant consumption in squalane and polyethylene exposed to chlorinated aqueous media
- 2012
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Ingår i: Polymer degradation and stability. - : Elsevier BV. - 0141-3910 .- 1873-2321. ; 97:11, s. 2370-2377
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Tidskriftsartikel (refereegranskat)abstract
- Squalane stabilized with 0.2 wt.% of Irganox 1010 and a medium-density polyethylene containing 0.1 wt.% of the same antioxidant were exposed to two different aqueous media (water solutions containing either 10 ppm Cl-2 or 10 ppm ClO2, both buffered to pH = 6.8) at different temperatures between 30 and 70 degrees C. The squalane phase was characterized by differential scanning calorimetry (oxidation induction time, OIT) and infrared spectroscopy, and the aqueous media were analysed after concentrating the analytes using liquid-liquid extraction by liquid chromatography, mass spectrometry and infrared spectroscopy. OIT measurements were carried out on the polyethylene samples after exposure to the chlorinated aqueous media. Exposure of the squalane systems to water containing ClO2 resulted in discolouration by the formation of quinoid structures and a faster depletion of the antioxidant than exposure to water containing Cl-2. The activation energy for the loss of antioxidant activity on exposure to ClO2-water was very low (<10 kJ mol(-1)) in the squalane test (no diffusion control) and 21 +/- 2 kJ mol(-1) at a depth of 1-2 mm from the surface of polyethylene plaques (diffusion control). Calculation from earlier published OIT data from a HDPE exposed to Cl-2-water yielded an activation energy for the loss antioxidant activity of 68 kJ mol(-1). The antioxidant degradation products obtained from the exposure to the ClO2 aqueous medium were found at a higher concentration, were more polar and exhibited a higher proportion of low molar mass species than those obtained after exposure to the Cl-2 aqueous medium. The important chemical difference between ClO2 and Cl-2 is that the former is a one-electron oxidant whereas the latter preferentially reacts by hydrogen substitution. Possible further reactions, in agreement with the observations made, are proposed.
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| 16. |
- Yu, Wenbin, et al.
(författare)
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Chlorine dioxide resistance of different phenolic antioxidants in polyethylene
- 2015
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Ingår i: Polymer degradation and stability. - : Elsevier BV. - 0141-3910 .- 1873-2321. ; 111, s. 1-6
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Tidskriftsartikel (refereegranskat)abstract
- A series of polyethylene tape samples containing 8 different phenolic antioxidants (concentration = 0.1 +/- 0.01 wt.%) were exposed to water containing 10 ppm chlorine dioxide buffered to pH = 6.8 at 70 degrees C for different periods of time. The degradation rate and depletion time of the antioxidants in the polyethylene were obtained by oxidation induction time measurements using DSC. The majority of the tape samples (6 out of 8) showed a simple behaviour: the rate of antioxidant loss decreased and the antioxidant depletion time increased in linear fashion with increasing initial molar concentration of phenolic groups in the polymer. The tape that contained Hostanox O3 had a high initial phenolic concentration but it exhibited a short antioxidant depletion time due to the limited solubility of this antioxidant in polyethylene. Tapes containing Irganox 1330 and Cyanox 1790 showed antioxidant depletion times that were almost twice that of the other antioxidants with the same initial molar concentration of phenolic groups.
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| 17. |
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| 18. |
- Yu, Wenbin, et al.
(författare)
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Deterioration of polyethylene pipes exposed to water containing chlorine dioxide
- 2011
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Ingår i: Polymer degradation and stability. - : Elsevier BV. - 0141-3910 .- 1873-2321. ; 96:5, s. 790-797
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Tidskriftsartikel (refereegranskat)abstract
- Chlorine species used as disinfectants in tap water have a deteriorating effect on many materials including polyethylene. There are only very few scientific reports on the effect on polyethylene pipes of water containing chlorine dioxide. Medium-density polyethylene pipes stabilized with hindered phenol and phosphite antioxidants were pressure tested with water containing 4 ppm chlorine dioxide at 90 degrees C and pH = 6.8 as internal medium. The stabilizers were rapidly consumed towards the inner pipe wall; the rate of consumption was four times greater than in chlorinated water (4 ppm, pH = 6.8) at the same temperature. The depletion of stabilizer occurred far into the pipe wall. A supplementary study on a polymer analogue (squalane) containing the same stabilizer package showed that the consumption of the phenolic antioxidant was 2.5 times faster when exposed water containing chlorine dioxide than on exposure to chlorinated water. The subsequent polymer degradation was an immediate surface reaction. It was confirmed by differential scanning calorimetry, infrared spectroscopy and size exclusion chromatography that in the surface layer which came into contact with the oxidising medium, the amorphous component of the polymer was heavily oxidized leaving a highly crystalline powder with many carboxylic acid chain ends in extended and once-folded chains. Scanning electron microscopy showed that propagation of cracks through the pipe wall was assisted by polymer degradation.
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