| 1. |
- Akhlaghi, Shahin, et al.
(författare)
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Deterioration of acrylonitrile butadiene rubber in rapeseed biodiesel
- 2015
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Ingår i: Polymer degradation and stability. - : Elsevier BV. - 0141-3910 .- 1873-2321. ; 111, s. 211-222
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Tidskriftsartikel (refereegranskat)abstract
- The deterioration of acrylonitrile butadiene rubber (NBR) exposed to rapeseed biodiesel at 90 degrees C was studied. The oxidation of biodiesel and NBR during ageing was monitored by H-1 NMR and infrared spectroscopy, HPLC and titration methods. The oxidation of biodiesel was impeded in the presence of NBR, but promoted in biodiesel-exposed rubber. This was explained as being due to the migration of stabilizer from the rubber to biodiesel, the diffusion of dissolved oxygen from biodiesel into NBR and the absorption of oxidation precursors of biodiesel by the rubber. The resemblance between the anomalous sorption kinetics of biodiesel in NBR and the equilibrium benzene uptake by the aged rubbers revealed that biodiesel caused a network defect in NBR, resulting in a gradual increase in the equilibrium swelling. The cleavage of crosslinks was implausible since the Young's modulus of the rubber at low strains, disregarding an initial decrease, increased with increasing exposure time. The appearance of 'naked' carbon black particles in the scanning electron micrographs of the aged rubbers and a drastic decrease in the strain-at-break of NBR after exposure to biodiesel suggests that internal cavitation was caused by the attack of biodiesel on the acrylonitrile units of NBR.
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| 2. |
- Akhlaghi, Shahin, et al.
(författare)
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Degradation of carbon-black-filled acrylonitrile butadiene rubber in alternative fuels : Transesterified and hydrotreated vegetable oils
- 2016
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Ingår i: Polymer degradation and stability. - : Elsevier. - 0141-3910 .- 1873-2321. ; 123, s. 69-79
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Tidskriftsartikel (refereegranskat)abstract
- The deterioration of acrylonitrile butadiene rubber (NBR), a common sealing material in automobile fuel systems, when exposed to rapeseed biodiesel and hydrotreated vegetable oil (HVO) was studied. The fuel sorption was hindered in HVO-exposed rubber by the steric constraints of bulky HVO molecules, but it was promoted in biodiesel-exposed rubber by fuel-driven cavitation in the NBR and by the increase in diffusivity of biodiesel after oxidation. The absence of a tan δ peak of the bound rubber and the appearance of carbon black particles devoid of rubber suggested that the cavitation was made possible in biodiesel-aged rubber by the detachment of bound rubber from particle surfaces. The HVO-exposed NBR showed a small decrease in strain-at-break due to the migration of plasticizer from the rubber, and a small increase in the Young’s modulus due to oxidative crosslinking. A drastic decrease in extensibility and Payne-effect amplitude of NBR on exposure to biodiesel was explained as being due to the damage caused by biodiesel to the continuous network of bound rubber-carbon black. A decrease in the ZnO crystal size with increasing exposure time suggested that the particles are gradually dissolved in the acidic components of oxidized biodiesel. The Zn2+ cations released from the dissolution of ZnO particles in biodiesel promoted the hydrolysis of the nitrile groups of NBR.
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| 3. |
- Wei, Xinfeng, et al.
(författare)
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Long-term performance of polyamide-based multilayer (bio)diesel fuel lines aged under “in-vehicle” conditions
- 2017
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Ingår i: Polymer degradation and stability. - : Elsevier. - 0141-3910 .- 1873-2321. ; 144, s. 100-109
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Tidskriftsartikel (refereegranskat)abstract
- The behaviour of a polyamide (PA)-based multilayer fuel pipe was investigated in “close to real” conditions using specially-designed ageing equipment with a program designed according to known customer driving modes and conditions (a key life test). The pipe was exposed to petroleum diesel and a combination of petroleum diesel and biodiesel. The fuel exposure pattern, as well as the temperature profile, followed a specified scheme in the key life test. It allowed for the investigation and understanding of complex ageing mechanisms, often observed in multi-layer systems with a variation in the running conditions. The mechanisms involved included migration of plasticizer from the innermost PA6 layer of the pipe to the fuel, and from the PA12 outer layer to the ambient air. At the same time, fuel was absorbed in the inner layer of the pipe. The oxidation of the innermost PA6 layer was promoted by the oxidation products of biodiesel. The diffusion-limited oxidation of the PA6 layer led to the formation of a 30 μm highly oxidized zone at the inner surface of the pipe, resulting in discoloration and oxidative crosslinking of the polymer. The toughness and extensibility of the pipe decreased significantly after prolonged ageing, and the extensibility was only 7% of that of the unaged pipe after 2230 h.
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