| 1. |
- Andersson, Thorbjörn, et al.
(författare)
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Degradation of LDPE LLDPE and HOPE in film extrusion
- 2004
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Ingår i: TAPPI PLACE Conference. - 1595100628 ; , s. 77-92
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Konferensbidrag (refereegranskat)abstract
- The degradation of different polyethylenes, LDPE, LLDPE, and HDPE, with and without antioxidants and at different oxygen concentrations in the polymer granulates have been studied in extrusion coating processing. The degradation was followed by On Line Rheometry, Size Exclusion Chromatography, Surface Oxidation Index measurements, and GC-MS Chromatography. The degradations starts in the extruder where primary radicals are formed which are subject the auto oxidation when oxygen is present. In the extruder, cross-linking and chain scission reactions are dominating at low and high melt temperatures, respectively, for LDPE, and chain scission is over all dominating for the more linear LLDPE and HDPE resins. Additives such as antioxidants react with primary radicals formed in the melt. Degradation taking place in the film between the die orifice and the quenching point is mainly related to the exposure time to air-oxygen. Melt temperatures above 280
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| 2. |
- Andersson, Thorbjörn, et al.
(författare)
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Degradation of low density polyethylene during extrusion. : IV. Off-flavor compounds in extruded films of stabilized LDPE
- 2005
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Ingår i: Journal of Applied Polymer Science. - : Wiley. - 0021-8995 .- 1097-4628. ; 95:3, s. 583-595
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Tidskriftsartikel (refereegranskat)abstract
- This study was aimed at finding a correlation between the experienced off-flavor in packed foods and the presence of specific degradation products in LDPE pack-aging films. The possibility to trap degradation products by chemical reactions with scavengers, i.e., a zeolite additive or antioxidants, was investigated This would prevent degradation products from migrating to the polymer film surface and further into food in contact with the film. It was found that off-flavor noted in water packed in LDPE films depended on extrusion temperature and exposure time for the melt to oxygen, that is, the parameters that influence the contents of oxidation products that are able to migrate from the polymer film. It was also found that adsorption of oxidative degradation products in a zeolite additive or protection of LDPE by using antioxidants could prevent off-flavor in the packed product (water). However, the antioxidant should be selected with regard to extrusion temperature because thermal instability in the additive might jeopardize the intended effect. Multifunctional antioxidants seem to provide improved protection, the most effective one evaluated in this work being Irganox E201, i.e., vitamin E. Concentrations of oxidized degradation products are well correlated to the perceived off-flavor in the packed water. The highest correlation between off-flavor and oxidized components was found for ketones in the range of C 7 to C9 and aldehydes in the range of C6 to C9.
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| 3. |
- Andersson, Thorbjörn, et al.
(författare)
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Degradation of low density polyethylene during extrusion : III. Volatile compounds in extruded films creating off-flavor
- 2005
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Ingår i: Journal of Applied Polymer Science. - : Wiley. - 0021-8995 .- 1097-4628. ; 95:4, s. 847-858
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Tidskriftsartikel (refereegranskat)abstract
- This study was aimed at finding a correlation between the experienced off-flavor in packaged foods and the presence of specific degradation products in PE packaging films. The possibility to trap degradation products by chemical reactions with scavengers, that is, zeolites and maleic anhydride grafted LLDPE, were investigated. This trapping would prevent the degradation products from migrating to the polymer film surface and further into food in contact with the film. This work concludes that off-flavor in water packed in LDPE-films depends on extrusion temperature and the content of oxidation products in the polymer film. At lower extrusion temperatures, reactive additives to the LDPE material could control the release of off-flavor giving compo nents. Adsorbents, such as zeolites, which are able to adsorb degradation products, are effective also at higher extrusion temperatures. The amount of oxidized degradation products in the films correlated well to the perceived off-flavor in the packed water. The presence of aldehydes and ketones have a clear impact on the off-flavor. The best correlation between off-flavor and oxidized components were found for C7-C9 ketones, and aldehydes in the range of C5 to C8.
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| 4. |
- Andersson, Thorbjörn
(författare)
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Oxidative Degradation of Polyethylene - A Cause of Off-flavour
- 2004
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Polyethylene is the most frequently used polymer material in food packaging today. The polymer is often processed by film extrusion and extrusion coating between 250°C and 325°C. Although polyethylene has high thermal stability some degradation takes place and the degradation products formed will migrate to the packed food, which will give food off-flavour tastes when consumed. With an increase in extrusion temperature the risk of detecting off-flavour in the packed product would increase. Additives in the polyethylene might reduce degradation but the effects are unclear and probably depend on the additive’s stability to the high processing temperatures used in extrusion coating. The aim of this research was to understand the behaviour of polyethylene and polyethylene degradation products, from the inlet of the extruder to the final packaging film and the packed product. The degradation is initiated in the extruder during the melting and metering of the polymer. The polymer degradation starts with chain scission reactions forming radicals, and via auto-oxidative process the oxygen dissolved in the polymer forms peroxides and other products. Some of the radicals are combined resulting in higher molar mass and an increase in the viscosity of the melt. At an extrusion temperature of below 300°C cross-link reactions predominate while at higher process temperatures chain scission reactions predominate. When the melt exits the die orifice the radicals react with the oxygen present in the atmosphere nearest to the melt surface leading to an auto-oxidative degradation. The low molar mass degradation products will evaporate from the melt forming “extruder smoke”. Higher molar mass degradation products will remain at the film surface as alcohols, aldehydes, ketones, carboxylic acids and esters depending on the temperature of the melt, the exposure time to the atmosphere and the oxygen concentration in air-gap gas. This makes the passage through the air-gap the most critical processing step from degradation point of view. The oxidative degradation products are shown to give the highest off-flavour, the aldehydes and ketones being the most prominent ones. The presence of carboxylic acids seems to be necessary to carry the hydrophobic carbonyl compounds into the product and to generate off-flavour when reaching the mouth. There are clear synergistic effects between aldehydes and ketones and between aldehydes and carboxylic acids. The most off-flavour giving products present in the extruded film are C7-C9 ketones and C5-C8 aldehydes together with the carboxylic acids. Different types of additives can be used as scavengers to adsorb degradation products or radicals as well as antioxidants to stabilise the radicals, which slows down the degradation reaction rates. It is important to select the additive from extrusion process temperature because different additives have different thermal stability. It is possible to control the off-flavour of the polyethylene films when controlling the extrusion temperatures and exposure time and oxygen content in the air-gap or by using selected additives.
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| 5. |
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| 6. |
- Andersson, Thorbjörn, et al.
(författare)
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The effects of selected aldehydes, ketones and carboxylic acids on off-flavours in water
- 2005
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Ingår i: International journal of food science & technology. - : Wiley InterScience. - 0950-5423 .- 1365-2621. ; 40:9, s. 993-1004
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Tidskriftsartikel (refereegranskat)abstract
- The effects of selected aldehydes, ketones and carboxylic acids on the development of off-flavours in water were studied. Combinations of hexanal, octanal, 2-octanone, 5-nonanone, hexanoic acid and nonanoic acid were rated by the off-flavour intensities they created in water at concentrations just at or below the threshold value of each analyte. Two different sensory panels evaluated the off-flavours induced by different combinations of the analytes. The observations of the two panels agreed well. From these studies, it could be concluded that aldehydes play an important role in the development of off-flavours intensities in water. There were synergistic effects between aldehydes and ketones, as well as between aldehydes and carboxylic acids. Small amounts of aldehydes and carboxylic acids – well below their respective threshold values – caused an increase in the off-flavour intensity. No synergism between ketones and carboxylic acids could be observed
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| 7. |
- Brinkfeldt, Klas, et al.
(författare)
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High temperature packaging for SiC power transistors
- 2012
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Ingår i: Proceedings - 2012 45th International Symposium on Microelectronics, IMAPS 2012. ; , s. 1124-1130
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Konferensbidrag (refereegranskat)abstract
- Power transistors based on silicon carbide (SiC) are now commercially available. They have a higher efficiency and higher voltage blocking capabilities than conventional silicon devices. The wide-band gap and chemical inertness of SiC makes it suitable to high temperature operation. However, there is a need for new packaging for power transistors that can operate in higher temperatures. We have developed a package based on ceramics and silver for high temperature operation of SiC power transistors. Three types of SiC devices from different manufacturers are packaged and tested in room temperature. Though the devices were still functional after the packaging process, their performance seem to have degraded. This could be a result of the high temperature packaging process and the measurement setup. FEM simulations are also performed to investigate the thermo-mechanical behavior of the package. The target operating temperature of the package is 400°C. Modeling show stress concentrations at the corners of the device chip and suggests that this stress is decreased if the substrate metallization is changed from copper to silver.
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| 8. |
- Brinkfeldt, Klas, et al.
(författare)
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Model verification of heat exchangers in a flow test rig
- 2015
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Ingår i: 2015 16th International Conference on Thermal, Mechanical and Multi-Physics Simulation and Experiments in Microelectronics and Microsystems, EuroSimE 2015. - : Institute of Electrical and Electronics Engineers Inc.. - 9781479999507 ; , s. 7103135-
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Konferensbidrag (refereegranskat)abstract
- In power electronics, more efficient removal of heat from the junction of power devices leads to a higher power rating per die, which in turn leads to fewer die and reduced system volume. Since temperature is a main driver in expected failure modes an increase in cooling capability can also enhance margins of the device reliability. Previously, CFD simulations of two novel heat exchanger designs that will be used in a power module with double sided cooling have been reported on. The heat exchangers are fabricated by direct 3D manufacturing of copper structures, which allows almost complete freedom in geometric design. Two novel geometries of heat exchanger cooling structures have previously been modeled in terms of thermal performance and expected pressure drop. A flow rig has been designed and calibrated to measure thermal performance and pressure drops of these heat sinks. For calibration purposes, measurements of the thermal response of wave structured and unstructured heat sinks are reported here. The results show that, as expected, the heat sink temperatures are lower for all flow rates in the wavestructured geometry. A thermal CFO model accurately predicts the behavior of the temperature difference between inlet and outlet versus flow rate, but predicts higher absolute temperature values. It was also found that the model underestimates the pressure drop over the tested heat sillies. The pressure drop across a novel pine cone geometry heat sink fabricated by additive manufacturing methods was also measured. Comparisons to a reduced model, which neglects everything before the inlet and after the outlet of the tested device, showed that the behavior of this pine structured heat sink was not predicted correctly. The pressure drop increased more rapidly with flow rates in the model than in the measurements. The main source of error in the measurements and simulations comes from a lack of thermal loading. Future work to improve the flow rig includes possibilities to increase the temperature loading at the bottom of the heat sink under test.
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| 9. |
- Börjesson, Anders, et al.
(författare)
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Molecular modelling of oxygen and water permeation in polyethylene
- 2013
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Ingår i: Polymer. - : Elsevier. - 0032-3861 .- 1873-2291. ; 54:12, s. 2988-
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Tidskriftsartikel (refereegranskat)abstract
- Monte Carlo and molecular dynamics simulations were performed to calculate solubility, S, and diffusion, D, coefficients of oxygen and water in polyethylene, and to obtain a molecular-level understanding of the diffusion mechanism. The permeation coefficient, P, was calculated from the product of S and D. The AMBER force field, which yields the correct polymer densities under the conditions studied, was used for the simulations, and it was observed that the results were not sensitive to the inclusion of atomic charges in the force field. The simulated S for oxygen and water are higher and lower than experimental data, respectively. The calculated diffusion coefficients are in good agreement with experimental data. Possible reasons for the discrepancy in the simulated and experimental solubilities, which results in discrepancies in the permeation coefficients, are discussed. The diffusion of both penetrants occurs mainly by large amplitude, infrequent jumps of the molecules through the polymer matrix.
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| 10. |
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| 11. |
- Erdtman, Edvin, et al.
(författare)
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A molecular-level computational study of the diffusion and solubility of water and oxygen in carbonaceous polyethylene nanocomposites
- 2016
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Ingår i: Journal of Polymer Science Part B. - : Wiley. - 0887-6266 .- 1099-0488. ; 54:5, s. 589-602
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Tidskriftsartikel (refereegranskat)abstract
- Monte Carlo and molecular dynamics simulations were performed to investigate the effect on the solubility, diffusion, and permeability of water and oxygen when adding graphene or single-walled carbon nanotubes (SWCNTs) to polyethylene (PE). When compared with pure PE, addition of graphene lowered the solubility of water, whereas at lower temperatures, the oxygen solubility increased because of the oxygen–graphene interaction. Addition of SWCNTs lowered the solubility of both water and oxygen when compared with pure PE. A detailed analysis showed that an ordered structure of PE is induced near the additive surface, which leads to a decrease in the diffusion coefficient of both penetrants in this region. The addition of graphene does not change the permeation coefficient of oxygen (in the direction parallel to the filler) and, in fact, may even increase this coefficient when compared with pure PE. In contrast, the water permeability is decreased when graphene is added to PE. The addition of SWCNTs decreases the permeability of both penetrants. Graphene can consequently be added to selectively increase the solubility and permeation of oxygen over water, at least at lower temperatures. © 2015 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2016, 54, 589–602
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| 12. |
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| 13. |
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| 14. |
- Forsgren, Gunnar, 1963-, et al.
(författare)
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Flavour interactions in aqueous solutions of an aldehyde, a ketone and a carboxylic acid
- 2009
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Tidskriftsartikel (övrigt vetenskapligt/konstnärligt)abstract
- Flavour impressions of aqueous solutions of nonanoic acid, octan-2-one and octanal were investigated. In a pre-study, the psychophysical functions of single component solutions were estimated and good agreements to Fechner’s law were obtained. The findings guided the choice of concentrations used in the main flavour interaction study. In this study, binary mixture interactions of nonanoic acid – octanal and octan-2-one – octanal were investigated in terms of perceived intensity and quality. Ten assessors judged the mixture solutions for flavour intensity by applying a free magnitude estimation procedure and describing their perceived quality impressions. The five assessors who were able to describe the perceived qualities in a consistent and logic way considered both mixtures being heterogeneous. Only three assessors scored intensities of the included single component solutions well in agreement with Fechner’s law. These three assessors’ intensity scorings of the mixtures did not deviate from those of a hypothetic additive model in a clear way. The intensity scorings of most of the other assessors were strongly dominated by one of the two components whereas some assessor did not score systematic at all.
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