Endre søk
Begrens søket
123456 151 - 200 of 251
RefereraExporteraLink til resultatlisten
Permanent link
Referera
Referensformat
  • apa
  • harvard1
  • ieee
  • modern-language-association-8th-edition
  • vancouver
  • Annet format
Fler format
Språk
  • de-DE
  • en-GB
  • en-US
  • fi-FI
  • nn-NO
  • nn-NB
  • sv-SE
  • Annet språk
Fler språk
Utmatningsformat
  • html
  • text
  • asciidoc
  • rtf
Treff pr side
  • 5
  • 10
  • 20
  • 50
  • 100
  • 250
Sortering
  • Standard (Relevans)
  • Forfatter A-Ø
  • Forfatter Ø-A
  • Tittel A-Ø
  • Tittel Ø-A
  • Type publikasjon A-Ø
  • Type publikasjon Ø-A
  • Eldste først
  • Nyeste først
  • Skapad (Eldste først)
  • Skapad (Nyeste først)
  • Senast uppdaterad (Eldste først)
  • Senast uppdaterad (Nyeste først)
  • Disputationsdatum (tidligste først)
  • Disputationsdatum (siste først)
  • Standard (Relevans)
  • Forfatter A-Ø
  • Forfatter Ø-A
  • Tittel A-Ø
  • Tittel Ø-A
  • Type publikasjon A-Ø
  • Type publikasjon Ø-A
  • Eldste først
  • Nyeste først
  • Skapad (Eldste først)
  • Skapad (Nyeste først)
  • Senast uppdaterad (Eldste først)
  • Senast uppdaterad (Nyeste først)
  • Disputationsdatum (tidligste først)
  • Disputationsdatum (siste først)
Merk
Maxantalet träffar du kan exportera från sökgränssnittet är 250. Vid större uttag använd dig av utsökningar.
  • 151.
    Nordqvist, David
    et al.
    KTH, Skolan för kemivetenskap (CHE), Fiber- och polymerteknik.
    Hedenqvist, Mikael S.
    KTH, Skolan för kemivetenskap (CHE), Fiber- och polymerteknik.
    Properties of amylopectin/montmorillonite composite films containing a coupling agent2007Inngår i: Journal of Applied Polymer Science, ISSN 0021-8995, E-ISSN 1097-4628, Vol. 104, nr 6, s. 4160-4167Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The addition of clay to polymers has the combined effects of enhancing both the strength / stiffness and the barrier properties. This investigation presents a novel approach to further enhance the strength / stiffness of cast plasticized amylopectin (AP)/Na+-montmorillonite clay films using a water-soluble coupling agent, poly[(isobutylene-alt-maleic acid, ammonium salt)-co-(isobutylene-alt-maleic anhydride)], between the filler and the matrix. The addition of clay increased the strength and stiffness of the film and the addition of 0.4 parts of a coupling agent per 1 part clay further increased these properties. The trends were the same after each treatment, and there were always significant differences in stiffness and strength between the films without clay and with clay with 0.4 parts of the coupling agent. The increase in stiffness / strength in the presence of a small amount of the coupling agent suggested that it had a bridging effect, presumably through strong secondary bonds to the clay and to the matrix. Infrared spectroscopy and moisture swelling experiments indicated that ester bonds were formed between the coupling agent and AP. X-ray spectroscopy and transmission electron microscopy revealed that the clay-particle / polymer structure was qualitatively independent of the presence of the coupling agent showing a mixture of intercalated clay stacks and exfoliated platelets.

  • 152.
    Nordqvist, David
    et al.
    KTH, Skolan för kemivetenskap (CHE), Fiber- och polymerteknik.
    Hedenqvist, Mikael S.
    KTH, Skolan för kemivetenskap (CHE), Fiber- och polymerteknik.
    Transport Properties of Nanocomposites Based on Polymers and Layered Inorganic Fillers2009Inngår i: Packaging Nanotechnology / [ed] Amar K Mohanty; Manjusri Misra; Hari Singh Nalwa, Stevenson Ranch, Calif.: American Scientific Publishers , 2009Kapittel i bok, del av antologi (Annet vitenskapelig)
  • 153.
    Nordqvist, David
    et al.
    KTH, Skolan för kemivetenskap (CHE), Fiber- och polymerteknik.
    Idermark, Johan
    KTH, Skolan för kemivetenskap (CHE), Fiber- och polymerteknik.
    Hedenqvist, Mikael S.
    KTH, Skolan för kemivetenskap (CHE), Fiber- och polymerteknik.
    Gällstedt, M.
    STFI-Packforsk.
    Ankerfors, M.
    STFI-Packforsk.
    Lindström, T.
    STFI-Packforsk.
    Enhancement of the wet properties of transparent chitosan-acetic-acid-salt films using microfibrillated cellulose2007Inngår i: Biomacromolecules, ISSN 1525-7797, E-ISSN 1526-4602, Vol. 8, nr 8, s. 2398-2403Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    This report presents a new route to enhance the wet properties of chitosan-acetic-acid-salt films using microfibrillated cellulose (MFC). The enhancement makes it easier to form chitosan-acetic-acid-salt films into various shapes at room temperature in the wet state. Chitosan with MFC was compared with the well-known buffer treatment. It was observed that films containing 5 wt % MFC were visually identical to the buffered/unbuffered films without MFC. Field-emission scanning electron microscopy indicated that MFC formed a network with uniformly distributed fibrils and fibril bundles in the chitosan matrix. The addition of MFC reduced the risk of creases and deformation in the wet state because of a greater wet stiffness. The wet films containing MFC were also extensible. Although the stiffness, strength and extensibility were highest for the buffered films, the wet strength of the MFC-containing unbuffered films was sufficient for wet forming operations. The effects of MFC on the mechanical properties of the dry chitosan films were small or absent. It was concluded that the addition of MFC is an acceptable alternative to buffering for shaping chitosan films/products in the wet state. The advantages are that the "extra" processing step associated with buffering is unnecessary and that the film matrix remains more water-soluble.

  • 154.
    Nordqvist, David
    et al.
    KTH, Skolan för kemivetenskap (CHE), Fiber- och polymerteknik.
    Sico, G.
    KTH, Skolan för kemivetenskap (CHE), Fiber- och polymerteknik.
    Hedenqvist, Mikael S.
    KTH, Skolan för kemivetenskap (CHE), Fiber- och polymerteknik.
    Nanocomposites based on amylopectin, microfibrillated cellulose and montmorilloniteInngår i: Carbohydrate Polymers, ISSN 0144-8617, E-ISSN 1879-1344Artikkel i tidsskrift (Annet vitenskapelig)
  • 155.
    Olabarrieta, Idoia
    et al.
    KTH, Skolan för kemivetenskap (CHE), Fiber- och polymerteknik.
    Cho, Sung Woo
    KTH, Skolan för kemivetenskap (CHE), Fiber- och polymerteknik, Polymera material.
    Gällstedt, Mikael
    STFI-Packforsk.
    Sarasua, Jose-Ramon
    Engineering Faculty, University of Basque Country.
    Johansson, Eva
    Department of Crop Science, The Swedish University of Agricultural Sciences.
    Hedenqvist, Mikael S
    KTH, Skolan för kemivetenskap (CHE), Fiber- och polymerteknik.
    Aging properties of films of plasticized vital wheat gluten cast from acidic and basic solutions2006Inngår i: Biomacromolecules, ISSN 1525-7797, E-ISSN 1526-4602, Vol. 7, nr 5, s. 1657-1664Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    In order to understand the mechanisms behind the undesired aging of films based on vital wheat gluten plasticized with glycerol, films cast from water/ethanol solutions were investigated. The effect of pH was studied by casting from solutions at pH 4 and pH 11. The films were aged for 120 days at 50% relative humidity and 23 C, and the tensile properties and oxygen and water vapor permeabilities were measured as a function of aging time. The changes in the protein structure were determined by infrared spectroscopy and size-exclusion and reverse-phase high-performance liquid chromatography, and the film structure was revealed by optical and scanning electron microscopy. The pH 11 film was mechanically more stable with time than the pH 4 film, the latter being initially very ductile but turning brittle toward the end of the aging period. The protein solubility and infrared spectroscopy measurements indicated that the protein structure of the pH 4 film was initially significantly less polymerized/ aggregated than that of the pH 11 film. The polymerization of the pH 4 film increased during storage but it did not reach the degree of aggregation of the pH 11 film. Reverse-phase chromatography indicated that the pH 11 films were to some extent deamidated and that this increased with aging. At the same time a large fraction of the aged pH 11 film was unaffected by reducing agents, suggesting that a time-induced isopeptide cross-linking had occurred. This isopeptide formation did not, however, change the overall degree of aggregation and consequently the mechanical properties of the film. During aging, the pH 4 films lost more mass than the pH 11 films mainly due to migration of glycerol but also due to some loss of volatile mass. Scanning electron and optical microscopy showed that the pH 11 film was more uniform in thickness and that the film structure was more homogeneous than that of the pH 4 film. The oxygen permeability was also lower for the pH 11 film. The fact that the pH 4 film experienced a larger and more rapid change in its mechanical properties with time than the pH 11 film, as a consequence of a greater loss of plasticizer, was presumably due to its initial lower degree of protein aggregation/ polymerization. Consequently, the cross-link density achieved at pH 4 was too low to effectively retain volatiles and glycerol within the matrix.

  • 156.
    Olabarrieta, Idoia
    et al.
    KTH, Tidigare Institutioner                               , Polymerteknologi.
    Forsström, Dan
    KTH, Tidigare Institutioner                               , Polymerteknologi.
    Gedde, Ulf
    KTH, Tidigare Institutioner                               , Polymerteknologi.
    Hedenqvist, Mikael
    KTH, Tidigare Institutioner                               , Polymerteknologi.
    Transport properties of chitosan and whey blended with poly(ε-caprolactone) assessed by standard permeability measurements and microcalorimetry2001Inngår i: Polymer, ISSN 0032-3861, E-ISSN 1873-2291, Vol. 42, nr 9, s. 4401-4408Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Blends of poly(p-caprolactone) (PCL) with chitosan and a whey-protein-isolate (WPI) were prepared by solution mixing and film casting. The purpose was to increase the water vapour resistivity of chitosan and whey by blending them with a hydrophobic biodegradable polymer. The water vapour transmission rate was determined by a standard technique and by a new technique based on microcalorimetry. The blends were characterised by scanning electron microscopy (SEM), density measurements and thermogravimetry. Oxygen permeability was measured on the pure components and on some of the blends. The incorporation of PCL yielded a pronounced decrease in water vapour transmission rate of both chitosan and the WPI measured at a relative humidity gradient of 11 to 0%. A volume content of 17-18% of PCL lowered the water vapour transmission rate by 70-90%. It was found that the majority of the PCL particles were ellipsoidal in chitosan and fibrous in the WPI and the data indicated that the particle shape had an important influence on the water vapour transmission rate. The large decrease in water vapour transmission rate was also due to a reduction in water solubility because of limited swelling of the constrained chitosan or WPI matrix in the presence of PCL. SEM revealed that the miscibility/compatibility between PCL and the matrices was good. The water vapour transmission rate of the films decreased with increasing vacuum-drying time of the chitosan and WPI solutions. Microcalorimetry provided accurate estimates of water vapour transmission rate. Furthermore. this technique proved to be very flexible and the water vapour transmission rate could be determined over a broad range of relative humidities in a single experiment.

  • 157.
    Olabarrieta, Idoia
    et al.
    KTH, Skolan för kemivetenskap (CHE), Fiber- och polymerteknik.
    Gällstedt, Mikael
    Ispizua, Iban
    Sarasua, Jose-Ramon
    Hedenqvist, Mikael S.
    KTH, Skolan för kemivetenskap (CHE), Fiber- och polymerteknik.
    Properties of new and aged montmorillonite-wheat gluten composite films2006Inngår i: Journal of Agricultural and Food Chemistry, ISSN 0021-8561, E-ISSN 1520-5118, Vol. 54, nr 4, s. 1283-1288Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The properties of new and aged glycerol-plasticized vital wheat gluten films containing ≤4.5 wt % natural or quaternary ammonium salt modified montmorillonite clay were investigated. The films were cast from pH 4 or pH 11 ethanol/water solutions. The films, aged for ≤120 days, were characterized by tensile testing, X-ray diffraction, and transmission electron microscopy. In addition, water vapor permeability (11% relative humidity) and the content of volatile components were measured. The large reduction in the water vapor permeability with respect to the pristine polymer suggests that the clay platelets were evenly distributed within the films and oriented preferably with the platelet long axis parallel to the film surface. The film prepared from pH 11 solution containing natural clay was, as revealed by transmission electron microscopy and X-ray diffraction, almost completely exfoliated. This film was consequently also the strongest, the stiffest, and the most brittle and, together with the pH 11 film containing modified clay, it also showed the greatest decrease in water vapor permeability. The large blocking effect of the clay had no effect on the aging kinetics of the films. During aging, the pH 4 and pH 11 film strength and the pH 4 film stiffness increased and the pH 4 film ductility decreased at the same rate with or without clay. This suggests that the aging was not diffusion rate limited, that is, that the loss of volatile components or the migration of glycerol or glycerol/wheat gluten phase separation was not limited by diffusion kinetics. The aging rate seemed to be determined by slow structural changes, possibly involving protein denaturation and aggregation processes.

  • 158.
    Olabarrieta, Idoia
    et al.
    KTH, Tidigare Institutioner                               , Fiber- och polymerteknologi.
    Hedenqvist, Mikael
    KTH, Tidigare Institutioner                               , Fiber- och polymerteknologi.
    Gedde, Ulf W.
    KTH, Tidigare Institutioner                               , Fiber- och polymerteknologi.
    Jansson, A.
    KTH, Tidigare Institutioner                               , Fiber- och polymerteknologi.
    Mechanical and physical properties of chitosan and whey blended with poly(ε- caprolactone)2002Inngår i: International Journal of Polymeric Materials, ISSN 0091-4037, E-ISSN 1563-535X, Vol. 51, nr 3, s. 275-289Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Properties important for packaging were studied on blends of 0-15 wt% poly( caprolactone) and chitosan and a whey-protein-isolate. The blends were obtained by solution mixing, and films were produced by solvent casting. Transparency was measured by UV/VIS spectroscopy and the printability was qualitatively estimted by using a red ethanol dye. Mechanical properties of solid films and seals were assessed by tensile tests. Stiffness and folding endurence were also measured. The blend morphology was characterized by scanning electron microscopy. It was found that all the blends were transparent. The whey-protein-isolate had the best printability properties and printability remained in the poly( -caprolactone)-blends. Film stiffness decreased and strain at break increased strongly when the pure chitosan and the pure whey-protein-isolate were wetted. The addition of poly( -caprolactone) to chitosan and whey-protein-isolate had only a moderate effect on the toughness properties but a strong effect on the modulus which could be predicted by the Halpin-Tsai model. The modulus of the whey-protein-isolate increased and the modulus of the chitosan decreased with the addiion of poly( -caprolactone). It was found that it was impossible to seal chitosan with a standard heat-pulse sealing technique. The whey-protein-isolate was sealable but the strength of the seals was lower than the intrinsic strength of the pure whey-protein-isolate. The folding endurance properties of chitosan and its blends were far better than those of the whey-protein-isolate and its blends.

  • 159. Olsson, Erik
    et al.
    Hedenqvist, Mikael S.
    KTH, Skolan för kemivetenskap (CHE), Fiber- och polymerteknik.
    Johansson, Caisa
    Järnström, Lars
    Influence of citric acid and curing on moisture sorption, diffusion and permeability of starch films2013Inngår i: Carbohydrate Polymers, ISSN 0144-8617, E-ISSN 1879-1344, Vol. 94, nr 2, s. 765-772Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Starch films with different amounts of citric acid produced by solution casting were subjected to different curing temperatures and compared with films plasticized with glycerol. The films were tested in a controlled moisture generator, which enabled the moisture sorption to be measured and the diffusion coefficient and water vapor permeability to be calculated. It was shown that increasing the amount of citric acid added led to a reduction in the equilibrium moisture content, diffusion coefficient and water vapor permeability of the films, the values of which were all considerably lower than the values obtained for the films plasticized by glycerol. It was also seen that curing the film with 30 pph citric acid at 150 degrees C led to a significant reduction in the equilibrium moisture content, the diffusion coefficient and the water vapor permeability at high relative humidity which suggests that crosslinking occurred. The calculated water vapor permeability data were comparable with the value obtained with direct measurements.

  • 160.
    Olsson, Richard T.
    et al.
    KTH, Skolan för kemivetenskap (CHE), Fiber- och polymerteknologi.
    Hedenqvist, Mikael
    KTH, Skolan för kemivetenskap (CHE), Fiber- och polymerteknologi.
    Gedde, Ulf
    KTH, Skolan för kemivetenskap (CHE), Fiber- och polymerteknologi.
    Salazar-Alvarez, German
    KTH, Skolan för kemivetenskap (CHE), Fiber- och polymerteknologi.
    Muhammed, M.
    KTH, Skolan för kemivetenskap (CHE), Fiber- och polymerteknologi.
    Synthesis and characterization of cubic cobalt ferrite nanoparticles2005Inngår i: Ninth International Conference on Ferrites (ICF-9) / [ed] Soohoo, RF, 2005, s. 835-840Konferansepaper (Fagfellevurdert)
    Abstract [en]

    The preparation of approximately 20 g cubic cobalt ferrite nanoparticles (edge length 30-60 nm) with composition CoxFe3-xO4 (0.85 center dot x center dot 1.00 +/- 0.02) using the co-precipitation method in a batch type reactor has been investigated. The morphology, composition, size and size distribution of the synthesized particles were characterized by transmission electron microscopy, X-ray diffraction and the BET method. The majority of the particles were cubic although spherical particles were also observed. Aging of the suspensions resulted in a narrowing of the initial size distribution with no effect on the morphology and composition of the particles.

  • 161.
    Olsson, Richard T.
    et al.
    KTH, Skolan för kemivetenskap (CHE), Fiber- och polymerteknik.
    Hedenqvist, Mikael S.
    KTH, Skolan för kemivetenskap (CHE), Fiber- och polymerteknik.
    Deng, Jinglan
    Neway, Bereket
    KTH, Skolan för kemivetenskap (CHE), Fiber- och polymerteknik.
    Savage, Steven J.
    Gedde, Ulf W.
    KTH, Skolan för kemivetenskap (CHE), Fiber- och polymerteknik.
    Characterization of particle dispersion and mechanical properties of nanocomposites based on cobalt ferrite nanoparticles with functional silesquioxane coatings.Manuskript (preprint) (Annet vitenskapelig)
  • 162.
    Olsson, Richard T.
    et al.
    KTH, Skolan för kemivetenskap (CHE), Fiber- och polymerteknik.
    Hedenqvist, Mikael S.
    KTH, Skolan för kemivetenskap (CHE), Fiber- och polymerteknik.
    Ström, Valter
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Teknisk materialfysik.
    Deng, J.
    Savage, S. J.
    Gedde, Ulf W.
    KTH, Skolan för kemivetenskap (CHE), Fiber- och polymerteknik.
    Core-Shell Structured Ferrite-Silsesquioxane-Epoxy Nanocomposites: Composite Homogeneity and Mechanical and Magnetic Properties2011Inngår i: Polymer Engineering and Science, ISSN 0032-3888, E-ISSN 1548-2634, Vol. 51, nr 5, s. 862-874Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Epoxy-based composites of ferrite nanoparticles (50 nm) with 3-glycidoxypropyl- (GPTMS), aminopropyl(APTMS), or methyl-silsesquioxane (MTMS) coatings are reported. The GPTMS coatings (30-nm thick) allowed uniform particle dispersion in the epoxy and prevented sedimentation of the nanoparticles, whereas the APTMS-coated particles formed agglomerates, leading to particle sedimentation. The particles with the thinnest coating (MTMS - 3 nm) agglomerated in the composites without sedimentation. The composites based on GPTMS-coated particles showed higher fracture toughness than the composites based on MTMS-coated particles. The uniformity and thickness of the coatings were related to alcohol composition of the coating media. Coating removal by a novel ultrasonic etching allowed precise determination of the effective ferrite content in the coated nanoparticles. A markedly lower coercivity for nanoparticles without coatings as compared with the nanoparticles with thicker coatings was observed. The saturation magnetization and the coercivity of the composites were independent of coating and casting procedures.

  • 163.
    Olsson, Richard T.
    et al.
    KTH, Skolan för kemivetenskap (CHE), Fiber- och polymerteknik.
    Hedenqvist, Mikael S.
    KTH, Skolan för kemivetenskap (CHE), Fiber- och polymerteknik.
    Ström, Valter
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap.
    Deng, Jinglan
    School of Science, Wuhan University of Technology.
    Savage, Stephen J.
    Swedish Defence Research Agency (FOI), Linköping.
    Gedde, Ulf W.
    KTH, Skolan för kemivetenskap (CHE), Fiber- och polymerteknik.
    Core-shell nanostructured cobalt ferrite-sisesquioxane-epoxy composites: nanofiller surface treatment, particle dispersion, mechanical and magnetic propertiesInngår i: Chemistry of Materials, ISSN 0897-4756, E-ISSN 1520-5002, s. 1-44Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Magnetic core-shell cobalt ferrite-silsesquioxane-epoxy nanocomposites have been prepared with uniform nanoparticle distribution. The nanoparticles were surface-treated with methyl- (MTMS), aminopropyl- (APTMS), glycidoxypropyl- (GPTMS) trimethoxy-silane. The optimum coating process was performed in a water/merthanol solution on the particles directly after their synthesis without prior drying. The GPTMS-coatings were 30 nm thick and the nanoparticles dispersed well in epoxy without sedimentation. The MTMS-coated nanoparticles (3 nm coating) formed weak agglomerates in epoxy but showed no sedimentation. The APTMS-coated particles formed stronger agglomerates, which led to sedimentation of the aorticles during molding. The GPTMS-based composites showed higher fracture toughness than the MTMS-based composites. This was attributed to the presence of large agglomerates in the latter systems and to the stronger interface between coating and epoxy in the former systems. Ultrasonic alkaline etching allowed precis determination of the ferrite content of the core-shell nanoparticles. Magnetometry showe a markedly lower coercivity for nanoparticles with thin coatings (MTMS) than for the nanoparticles with thicker coatings (GPTMS) suggesting the occurrence of magnetic exchange interaction in the former systems. The nanocomposites showed no influence of surface coating on coercivity or saturation magnetization suggesting that the inter-particle distances were greater than 0.5 nm.

  • 164.
    Olsson, Richard T.
    et al.
    KTH, Skolan för kemivetenskap (CHE), Fiber- och polymerteknik.
    Salazar-Alvarez, German
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap.
    Hedenqvist, Mikael S.
    KTH, Skolan för kemivetenskap (CHE), Fiber- och polymerteknik.
    Gedde, Ulf W.
    KTH, Skolan för kemivetenskap (CHE), Fiber- och polymerteknik.
    Lindberg, F.
    Structural Chemistry, Arrhenius Laboratory, Stockholm University.
    Savage, Steven J.
    Swedish Defense Research Agency (FOI), Linköping.
    Controlled synthesis of near-stoichiometric cobalt ferrite nanoparticles2005Inngår i: Chemistry of Materials, ISSN 0897-4756, E-ISSN 1520-5002, Vol. 17, nr 20, s. 5109-5118Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Large batches of more than 18 g of cobalt ferrite nanoparticles (CoxFe3-xO4, x being close to 1) have been prepared by the chemie douce approach using aqueous solutions of metal salts at 90 degrees C mixed with solutions of hydroxide ions under air atmosphere. By suitable choice of the metal ion to hydroxide ion ratio, it was possible to prepare nanoparticles with the stoichiometric composition (CoFe2O4). The composition and the density of the nanoparticles could be controlled by varying the metal ion to hydroxide ion molar ratio in the reactor. Adjusting the initial concentration ratios of the reactants prior to the mixing allowed the variation of the average size of the nanoparticles. The repeatability of the average particle diameter of the synthesis was typically 5 nm and average particle sizes could be controlled between 50 and 80 nm determined by nitrogen adsorption measurements (consistent with the number size average 35-60 mn obtained by transmission electron microscopy studies). Aging of the suspensions resulted in a narrowing of the initial broad unimodal distribution. The narrowing of the size distribution was associated with the phase transformation of delta-FeOOH platelets to spinel phase. The spinel nanoparticles had different morphologies: cubic, spherical, and occasionally irregular. Nanoparticles with the stoichiometric composition were a mixture of cubical and spherical shapes. Nanoparticles with less than the stoichiometric cobalt content had an irregular morphology, whereas nanoparticles with greater than the stoichiometric concentration of cobalt were predominantly spherical.

  • 165.
    Ozeren, Husamettin Deniz
    et al.
    KTH, Skolan för kemi, bioteknologi och hälsa (CBH), Fiber- och polymerteknologi.
    Nilsson, Fritjof
    KTH, Skolan för kemi, bioteknologi och hälsa (CBH), Fiber- och polymerteknologi.
    Olsson, Richard
    KTH, Skolan för kemi, bioteknologi och hälsa (CBH), Fiber- och polymerteknologi.
    Hedenqvist, Mikael S.
    KTH, Skolan för kemi, bioteknologi och hälsa (CBH), Fiber- och polymerteknologi.
    Prediction of plasticization mechanisms for biobased plastics through a combined experimental and molecular dynamics simulations approach2018Inngår i: Abstract of Papers of the American Chemical Society, ISSN 0065-7727, Vol. 256Artikkel i tidsskrift (Annet vitenskapelig)
  • 166.
    Pallon, L. K. H.
    et al.
    KTH, Skolan för kemivetenskap (CHE), Fiber- och polymerteknologi.
    Hoang, A. T.
    Pourrahimi, A. M.
    KTH, Skolan för kemivetenskap (CHE), Fiber- och polymerteknologi.
    Hedenqvist, Mikael S.
    KTH, Skolan för kemivetenskap (CHE), Fiber- och polymerteknologi.
    Nilsson, Fritjof
    KTH, Skolan för kemivetenskap (CHE), Fiber- och polymerteknologi.
    Gubanski, S.
    Gedde, U. W.
    KTH, Skolan för kemivetenskap (CHE), Fiber- och polymerteknologi.
    Olsson, Richard T.
    KTH, Skolan för kemivetenskap (CHE), Fiber- och polymerteknologi.
    The impact of MgO nanoparticle interface in ultra-insulating polyethylene nanocomposites for high voltage DC cables2016Inngår i: Journal of Materials Chemistry A, ISSN 2050-7488, Vol. 4, nr 22, s. 8590-8601Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Low density polyethylene (LDPE) nanocomposites with a reduced conductivity of two orders of magnitude are reported as a novel insulation material for high voltage distribution of renewable energy. The key to the high insulation capacity was to provide 70 nm hexagonal MgO nanoparticles with relatively tong, preferably 18 units long, hydrocarbon functional silsesquioxane coatings. This rendered the surface of the particles completely hydrophobic and also served as a protective layer against adsorption of polar low molecular weight atmospheric substances (H2O and CO2). The elimination of trace amounts of water, in combination with the provided carbon functionality, dramatically improved the dispersion of MgO nanoparticles. The lowest volume conductivity was ca. 7 x 10(-16) s m(-1) for 3 wt% surface coated nanoparticles. Extensive electron microscopy characterization was further used to relate the measured volume conductivity, acquired under conditions that resemble 800 kV high voltage direct current (HVDC) cables, to the distribution of the nanoparticles in the polymer matrix. The results show that an appropriate surface-modification approach yielded uniformly dispersed MgO nanoparticles up to contents as high as 9 wt%, with maintained 10-100 times reduced volume conductivity. Simulations of the MgO nanoparticles distribution revealed that the required interaction radius of the MgO-phase was 775 nm, setting a lower limit of particle amount to effectively work as electrical insulation promoters. The reduced volume conductivity values and scalable processing chemistry reported allow for the production of the next generation insulation material for HVDC cables.

  • 167.
    Pallon, Love K. H.
    et al.
    KTH, Skolan för kemivetenskap (CHE), Fiber- och polymerteknologi.
    Nilsson, Fritjof
    KTH, Skolan för kemivetenskap (CHE), Fiber- och polymerteknologi.
    Yu, Shun
    KTH, Skolan för kemivetenskap (CHE), Fiber- och polymerteknologi.
    Liu, Dongming
    KTH, Skolan för kemivetenskap (CHE), Fiber- och polymerteknologi.
    Diaz, Ana
    Holler, Mirko
    Chen, Xiangrong R.
    Gubanski, Stanislaw
    Hedenqvist, Mikael S.
    KTH, Skolan för kemivetenskap (CHE), Fiber- och polymerteknologi.
    Olsson, Richard T.
    KTH, Skolan för kemivetenskap (CHE), Fiber- och polymerteknologi.
    Gedde, Ulf W.
    KTH, Skolan för kemivetenskap (CHE), Fiber- och polymerteknologi.
    Three-Dimensional Nanometer Features of Direct Current Electrical Trees in Low-Density Polyethylene2017Inngår i: Nano letters (Print), ISSN 1530-6984, E-ISSN 1530-6992, Vol. 17, nr 3, s. 1402-1408Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Electrical trees are one reason for the breakdown of insulating materials in electrical power systems. An understanding of the growth of electrical trees plays a crucial role in the development of reliable high voltage direct current (HVDC) power grid systems with transmission voltages up to 1 MV. A section that contained an electrical tree in low-density polyethylene (LDPE) has been visualized in three dimensions (3D) with a resolution of 92 nm by X-ray ptychographic tomography. The 3D imaging revealed prechannel-formations with a lower density with the width of a couple of hundred nanometers formed around the main branch of the electrical tree. The prechannel structures were partially connected with the main tree via paths through material with a lower density, proving that the tree had grown in a step-by-step manner via the prestep structures formed in front of the main channels. All the prechannel structures had a size well below the limit of the Paschen law and were thus not formed by partial discharges. Instead, it is suggested that the prechannel structures were formed by electro-mechanical stress and impact ionization, where the former was confirmed by simulations to be a potential explanation with electro-mechanical stress tensors being almost of the same order of magnitude as the short-term modulus of low-density polyethylene.

  • 168.
    Pallon, Love K. H.
    et al.
    KTH, Skolan för kemivetenskap (CHE), Fiber- och polymerteknologi.
    Olsson, Richard T.
    KTH, Skolan för kemivetenskap (CHE), Fiber- och polymerteknologi.
    Liu, D.
    KTH, Skolan för kemivetenskap (CHE), Fiber- och polymerteknologi.
    Pourrahimi, Amir Masoud
    KTH, Skolan för kemivetenskap (CHE), Fiber- och polymerteknologi.
    Hedenqvist, Mikael S.
    KTH, Skolan för kemivetenskap (CHE), Fiber- och polymerteknologi.
    Hoang, A. T.
    Gubanski, S.
    Gedde, Ulf W.
    KTH, Skolan för kemivetenskap (CHE), Fiber- och polymerteknologi.
    Formation and the structure of freeze-dried MgO nanoparticle foams and their electrical behaviour in polyethylene2015Inngår i: Journal of Materials Chemistry A, ISSN 2050-7488, Vol. 3, nr 14, s. 7523-7534Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Electrically insulating low-density polyethylene (LDPE) nanocomposites based on dispersed MgO nanoparticle foams are reported. The foams were obtained via freeze-drying aqueous suspensions of precipitated ca. 40 nm wide and 10 nm thick Mg(OH)(2) nanoparticles and dewatering (calcining) at 400 degrees C, resulting in a 25 times more voluminous powder compared to conventionally dried nanoparticles. This powder handling prior to extrusion melt-processing greatly facilitated the nanocomposite preparation since no particle grinding was necessary. Large quantities of particles were prepared (>5 g), and the nanoparticle foams showed improved dispersion in the LDPE matrix with 70% smaller aggregate sizes compared to the conventionally dried and ground nanopowders. The nature of the nanoparticle foams was evaluated in terms of their dispersion on Si-wafers using ultrasonication as a dispersing aid, which showed to be detrimental for the nanoparticle separation into solitary particles and induced severe aggregation of the calcined nanoparticles. The grind-free MgO nanoparticles/LDPE-composite was evaluated by electrical measurement. The prepared composite showed an initial ca. 1.5 orders of magnitude lower charging current at 10(2) s, and a 4.2 times lower charging current after 16 hours compared to unfilled LDPE. The results open a way for improved insulation to be implemented in the future high-voltage cable system and present a new promising nanoparticle powder handling technique that can be used on a large scale.

  • 169.
    Pallon, Love
    et al.
    KTH, Skolan för kemivetenskap (CHE), Fiber- och polymerteknologi.
    Yu, Shun
    KTH, Skolan för kemivetenskap (CHE), Fiber- och polymerteknologi.
    Liu, Dongming
    KTH, Skolan för kemivetenskap (CHE), Fiber- och polymerteknologi.
    Diaz, Ana
    Paul Scherrer Institute.
    Holler, Mirko
    Paul Scherrer Institute.
    Nilsson, Fritjof
    KTH, Skolan för kemivetenskap (CHE), Fiber- och polymerteknologi.
    Chen, Xiangrong
    Chalmers University of Technology .
    Gubanski, Stanislaw
    Chalmers University of Technology.
    Hedenqvist, Mikael S.
    KTH, Skolan för kemivetenskap (CHE), Fiber- och polymerteknologi.
    Olsson, Richard
    KTH, Skolan för kemivetenskap (CHE), Fiber- och polymerteknologi.
    Gedde, Ulf W.
    KTH, Skolan för kemivetenskap (CHE), Fiber- och polymerteknologi.
    Three-dimensional nanometre features of direct current electrical trees in low-density polyethyleneManuskript (preprint) (Annet vitenskapelig)
  • 170. Piri, Imelda Saran
    et al.
    Das, Oisik
    KTH, Skolan för kemi, bioteknologi och hälsa (CBH), Fiber- och polymerteknologi.
    Hedenqvist, Mikael S.
    KTH, Skolan för kemi, bioteknologi och hälsa (CBH), Fiber- och polymerteknologi.
    Vaisanen, Taneli
    Ikram, Shafaq
    Bhattacharyya, Debes
    Imparting resiliency in biocomposite production systems: A system dynamics approach2018Inngår i: Journal of Cleaner Production, ISSN 0959-6526, E-ISSN 1879-1786, Vol. 179, s. 450-459Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    A biocomposite production system (BPS) contains a wide range of elements that are vulnerable to internal as well as external factors that may stimulate a system to be disrupted. Hence, there is a need to manifest resiliency in order to withstand the inevitable change without affecting its robustness and stability. The three aspects of a resilient BPS are interconnectivity, adaptability and transformability. The interconnectivity concept deals with the reliability and effectiveness of the supply chain network and production systems' resourcefulness. The adaptability aspect reinforces the agility and adjusting capacity of a system towards versatility and flexibility across the range of elements involved in the production system. Transformability deals with the capacity of a system to alter into a new system based on research, innovation and creativity. Therefore, the core aspects of resiliency in a BPS would result in increased stability and effectiveness. System dynamics models have been developed depicting the cause and effect of each of the three aspects. Finally, a model has been presented which could enable researchers and organizations to take guided decision towards a more robust and resilient BPS.

  • 171. Plackett, David
    et al.
    Anturi, Harvey
    KTH, Skolan för kemivetenskap (CHE), Fiber- och polymerteknik, Biokompositer.
    Hedenqvist, Mikael S.
    KTH, Skolan för kemivetenskap (CHE), Fiber- och polymerteknik, Polymera material.
    Ankerfors, Mikael
    Gällstedt, Mikael
    Lindström, Tom
    Siró, Istvan
    Physical Properties and Morphology of Films Prepared from Microfibrillated Cellulose and Microfibrillated Cellulose in Combination with Amylopectin2010Inngår i: Journal of Applied Polymer Science, ISSN 0021-8995, E-ISSN 1097-4628, Vol. 117, nr 6, s. 3601-3609Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Two types of microfibrillated cellulose (MFC) were prepared using either a sulfite pulp containing a high amount of hemicellulose (MFC 1) or a carboxymethylated dissolving pulp (MFC 2). MFC gels were then combined with amylopectin solutions to produce solvent-cast MFC-reinforced amylopectin films. Tensile testing revealed that MFC 2-reinforced films exhibited a more ductile behavior and that MFC 1-reinforced films had higher modulus of elasticity (E-modulus) at MFC loadings of 50 wt % or higher. Pure MFC films had relatively low oxygen permeability values when data were compared with those for a variety of other polymer films. MFC 1 and MFC 2 films had similar opacity but differences in appearance which were attributed to the presence of some larger fibers and nanofiber agglomerates in MFC 2. Field emission scanning electron microscopy (FE-SEM) and atomic force microscopy (AFM) were used to illustrate the morphology of MFC nanofibers in pure films and in an amylopectin matrix.

  • 172.
    Pourmand, Payam
    et al.
    KTH, Skolan för kemivetenskap (CHE), Fiber- och polymerteknologi.
    Hedenqvist, Lisa
    KTH, Skolan för kemivetenskap (CHE), Fiber- och polymerteknologi.
    Pourrahimi, Amir Masoud
    KTH, Skolan för kemivetenskap (CHE), Fiber- och polymerteknologi.
    Furo, Istvan
    KTH, Skolan för kemivetenskap (CHE), Kemi, Tillämpad fysikalisk kemi.
    Reitberger, Torbjörn
    KTH, Skolan för kemivetenskap (CHE), Fiber- och polymerteknologi.
    Gedde, Ulf
    KTH, Skolan för kemivetenskap (CHE), Fiber- och polymerteknologi, Polymera material.
    Hedenqvist, Mikael S.
    KTH, Skolan för kemivetenskap (CHE), Fiber- och polymerteknologi, Polymera material.
    Effect of gamma radiation on carbon-black-filled EPDM seals in water and air2017Inngår i: Polymer degradation and stability, ISSN 0141-3910, E-ISSN 1873-2321, Vol. 146, s. 184-191Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    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.

  • 173.
    Pourmand, Payam
    et al.
    KTH, Skolan för kemivetenskap (CHE), Fiber- och polymerteknologi, Polymera material.
    Hedenqvist, Lisa
    KTH, Skolan för kemivetenskap (CHE), Fiber- och polymerteknologi, Polymera material.
    Pourrahimi, Amir Massoud
    KTH, Skolan för kemivetenskap (CHE), Fiber- och polymerteknologi, Polymera material.
    Furó, Istvan
    KTH, Skolan för kemivetenskap (CHE), Kemi, Tillämpad fysikalisk kemi.
    Reitberger, Torbjörn
    KTH, Skolan för kemivetenskap (CHE), Kemi.
    Gedde, Ulf W.
    KTH, Skolan för kemivetenskap (CHE), Fiber- och polymerteknologi, Polymera material.
    Hedenqvist, Mikael S.
    KTH, Skolan för kemivetenskap (CHE), Fiber- och polymerteknologi, Polymera material.
    Effect of radiation on carbon-black-filled EPDM seals in water and air2017Manuskript (preprint) (Annet vitenskapelig)
    Abstract [en]

    The effects of γ-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 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 in service. Infrared spectroscopy, mechanical indenter and NMR relaxation time (T2) 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 doses 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 effects of increased polarity/oxidation of the rubber.

  • 174.
    Pourmand, Payam
    et al.
    KTH, Skolan för kemi, bioteknologi och hälsa (CBH), Kemi, Kemi.
    Hedenqvist, Mikael S.
    KTH, Skolan för kemi, bioteknologi och hälsa (CBH), Fiber- och polymerteknologi.
    Furo, Istvan
    KTH, Skolan för kemi, bioteknologi och hälsa (CBH), Kemi, Kemi.
    Gedde, Ulf W
    KTH, Skolan för kemi, bioteknologi och hälsa (CBH), Fiber- och polymerteknologi.
    Deterioration of highly filled EPDM rubber by thermal ageing in air: Kinetics and non-destructive monitoring2017Inngår i: Polymer testing, ISSN 0142-9418, E-ISSN 1873-2348, Vol. 64, s. 267-276Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The effects of air ageing at different temperatures between 110 and 170 degrees C on cable transit seals based on highly filled EPDM rubber used in nuclear power plants were studied. The changes of the macroscopic mechanical properties (Young's modulus, indentation modulus and strain-at-break) were in accordance with the Arrhenius equation with an activation energy of 110 kJ mol(-1). Profiling to assess the structure and property gradients within aged blocks was performed via IR spectroscopy, micro-indentation, gravimetric analysis of n-heptane-extracted samples and non-invasive portable NMR spectroscopy. A previously developed methodology was used to separate the deterioration into three different processes: polymer oxidation that was diffusion-limited at all temperatures, migration of low-molar-mass species to the surrounding media and anaerobic changes to the polymer network. The methodology allowed the assessment of the kinetics (rate as a function of time and temperature) of the different processes. It was noticed that polymer oxidation yielded more crosslinking at higher temperatures than at lower temperatures. The data obtained by both the portable NMR (a non-invasive method) and the indentation modulus profiling showed correlations with strain-at-break data, indicating their usefulness as condition monitoring methods.

  • 175.
    Pourmand, Payam
    et al.
    KTH, Skolan för kemivetenskap (CHE), Fiber- och polymerteknologi.
    Hedenqvist, Mikael S.
    KTH, Skolan för kemivetenskap (CHE), Fiber- och polymerteknologi, Polymera material.
    Furo, Istvan
    KTH, Skolan för kemivetenskap (CHE), Kemi, Tillämpad fysikalisk kemi.
    Gedde, Ulf W.
    KTH, Skolan för kemivetenskap (CHE), Fiber- och polymerteknologi, Polymera material.
    Radiochemical ageing of highly filled EPDM seals as revealed by accelerated ageing and ageing in-service for 21 years2017Inngår i: Polymer degradation and stability, ISSN 0141-3910, E-ISSN 1873-2321, Vol. 144, s. 473-484Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Highly filled EPDM rubber used in cable transit seals in nuclear power plants were exposed to gamma radiation at a high dose rate at 23 degrees C in media with different oxygen partial pressures (1-21.2 kPa). The motivation of this study was threefold: highly filled polymers are replacing halogen-containing polymers and these materials have rendered less attention in the literature; there is a need to find efficient tools to make possible condition monitoring and extrapolation. Several profiling methods were used: IR microscopy, micro-indentation, micro-sample extraction/gravimetry and non-invasive NMR spectroscopy, and three different deterioration processes were identified: polymer oxidation, migration of low molar mass species, and anaerobic changes in the polymer network. IR microscopy, micro-indentation profiling and the portable NMR method confirmed diffusion-limited oxidation in samples irradiated in air. The inner non-oxidized part of the blocks showed a pronounced change in the indenter modulus by migration of primarily glyceryl tristearate migration was accelerated by the presence of oxygen in the surface layer and anaerobic changes in the polymer network. For extrapolation or for condition monitoring, it is best to use the data obtained by indenter modulus profiling and to use the correlation between indenter modulus and strain-at-break to quantify the sample status. Non-invasive NMR profiling provided useful data but was less precise than the indenter modulus data to predict the strain-at-break.

  • 176.
    Pourmand, Payam
    et al.
    KTH, Skolan för kemivetenskap (CHE), Fiber- och polymerteknologi.
    Hedenqvist, Mikael S.
    KTH, Skolan för kemivetenskap (CHE), Fiber- och polymerteknologi, Polymera material.
    Furó, Istvan
    KTH, Skolan för kemivetenskap (CHE), Kemi, Tillämpad fysikalisk kemi.
    Gedde, Ulf W
    KTH, Skolan för kemivetenskap (CHE), Fiber- och polymerteknologi, Polymera material.
    Deterioration of highly filled EPDM rubber exposed to thermal ageing in air: kinetics and non-destructive monitoringManuskript (preprint) (Annet vitenskapelig)
    Abstract [en]

    The effects of thermal ageing on EPDM cable transit seals were investigated. Samples were aged in air at 110, 120, 150 and 170 °C, and evaluated with tensile testing, indenter modulus profiling, oxidation profiling (using IR spectroscopy), nuclear magnetic resonance (NMR) spectroscopy profiling. The ageing resulted in an increase in the indenter modulus, the degree of oxidation and in a decrease in the NMR transverse relaxation time, T2. Diffusion-limited oxidation (DLO) occurred with a large oxidation gradient close to the sample surface. The portable NMR MOUSE (non-invasive method) was used to obtain detailed degradation profiles, up to a depth of 5 mm of the aged samples. The results indicated a deterioration process that was attributed to several mechanisms, i.e. oxidation, anaerobic crosslinking and migration of oil extender. By combining the data acquired from the profiling, separation and quantification of these three contributing mechanisms was determined. Additionally, it was shown that the portable NMR data correlated well with the strain at break data, highlighting the potential use of the portable NMR for condition monitoring.

  • 177.
    Pourmand, Payam
    et al.
    KTH, Skolan för kemivetenskap (CHE), Fiber- och polymerteknologi. Royal Inst Technol KTH, Fibre & Polymer Technol, Stockholm, Sweden..
    Hedenqvist, Mikael S.
    KTH, Skolan för kemivetenskap (CHE), Fiber- och polymerteknologi. Royal Inst Technol KTH, Fibre & Polymer Technol, Stockholm, Sweden..
    Gedde, Ulf W
    KTH, Skolan för kemivetenskap (CHE), Fiber- och polymerteknologi. Royal Inst Technol KTH, Fibre & Polymer Technol, Stockholm, Sweden..
    Condition monitoring and characterization of deformations in EPDM seals used in nuclear power plants2016Inngår i: Abstract of Papers of the American Chemical Society, ISSN 0065-7727, Vol. 251Artikkel i tidsskrift (Annet vitenskapelig)
  • 178.
    Pourmand, Payam
    et al.
    KTH, Skolan för kemivetenskap (CHE), Fiber- och polymerteknologi.
    Linde, Erik
    KTH, Skolan för kemivetenskap (CHE), Fiber- och polymerteknologi.
    Hedenqvist, Mikael
    KTH, Skolan för kemivetenskap (CHE), Fiber- och polymerteknologi.
    Furo, Istvan
    KTH, Skolan för kemivetenskap (CHE), Kemi, Tillämpad fysikalisk kemi.
    Dvinskikh, Sergey
    KTH, Skolan för kemivetenskap (CHE), Kemi, Tillämpad fysikalisk kemi.
    Gedde, U. W.
    KTH, Skolan för kemivetenskap (CHE), Fiber- och polymerteknologi.
    Profiling of thermally aged EPDM seals using portable NMR, indenter measurements and IR spectroscopy facilitating separation of different deterioration mechanisms2016Inngår i: Polymer testing, ISSN 0142-9418, E-ISSN 1873-2348, Vol. 53, s. 77-84Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The changes occurring in EPDM cable transit seals during thermal ageing and the causes of these changes were investigated. Samples were aged at a temperature of 170 °C, and subsequently evaluated with respect to the distance from the surface with modulus profiling, infrared (IR) spectroscopy and nuclear magnetic resonance (NMR) spectroscopy, based on the extractable mass fraction profiles for initial and aged materials. The ageing resulted in an increase in the modulus and in the degree of oxidation and in a decrease in the NMR transverse relaxation time, T2. The NMR data were obtained in a non-invasive manner by ex situ experiments performed with a portable low-field spectrometer (NMR MOUSE). The results showed deterioration processes that can be attributed to different mechanisms i.e. oxidation, anaerobic crosslinking and migration of oil extender. The unique combination of parameter profiles made it possible to resolve and quantify these three contributing mechanisms. The NMR results highlight the potential of this method for on-site testing.

  • 179.
    Pourrahimi, A. M.
    et al.
    KTH, Skolan för kemivetenskap (CHE), Fiber- och polymerteknologi.
    Liu, D.
    KTH, Skolan för kemivetenskap (CHE), Fiber- och polymerteknologi.
    Ström, Valter
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap.
    Hedenqvist, Mikael S.
    KTH, Skolan för kemivetenskap (CHE), Fiber- och polymerteknologi.
    Olsson, Richard T.
    KTH, Skolan för kemivetenskap (CHE), Fiber- och polymerteknologi.
    Gedde, Ulf W.
    KTH, Skolan för kemivetenskap (CHE), Fiber- och polymerteknologi.
    Heat treatment of ZnO nanoparticles: new methods to achieve high-purity nanoparticles for high-voltage applications2015Inngår i: Journal of Materials Chemistry A, ISSN 2050-7488, Vol. 3, nr 33, s. 17190-17200Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Novel methods based on orienting and coating of ZnO nanoparticles were studied in order to obtain uniform, nano-sized and ultra-pure ZnO grains/particles after heat treatment. A 1 nm zinc-hydroxy-salt complex layer on the nanoparticle surfaces was revealed by thermogravimetry and infrared spectroscopy. This 'phase' gradually decomposed into ZnO during the heat treatment while sintering occurred above 600 degrees C, as revealed by scanning-and transmission-electron microscopy. The c-axis alignment of the nanoparticles provided smaller pores than those associated with non-oriented nanoparticles, presenting the means to obtain high-density ceramics. The orientation resulted in a smaller grain size after heat treatment than that of the nonaligned nanoparticles. Another method that involved three steps - silane coating, heat treatment and silica layer etching - was used to remove the ionic species from the nanoparticle surface while preserving its hydroxylated surface. These ultra-pure nanoparticles are expected to be key components in the development of HVDC insulation polyethylene nanocomposites.

  • 180.
    Pourrahimi, Amir Masoud
    et al.
    KTH, Skolan för kemivetenskap (CHE), Fiber- och polymerteknologi.
    Hoang, Tuan A
    Chalmers.
    Liu, Dongming
    KTH, Skolan för kemivetenskap (CHE), Fiber- och polymerteknologi.
    Pallon, Love K H
    KTH, Skolan för kemivetenskap (CHE), Fiber- och polymerteknologi.
    Gubanski, Stanislaw
    Chalmers.
    Olsson, Richard T
    KTH, Skolan för kemivetenskap (CHE), Fiber- och polymerteknologi.
    Gedde, Ulf W.
    KTH, Skolan för kemivetenskap (CHE), Fiber- och polymerteknologi.
    Hedenqvist, Mikael S.
    KTH, Skolan för kemivetenskap (CHE), Fiber- och polymerteknologi.
    Highly Efficient Interfaces in Nanocomposites Based on Polyethylene and ZnO Nano/Hierarchical Particles: A Novel Approach toward Ultralow Electrical Conductivity Insulations.2016Inngår i: Advanced Materials, ISSN 0935-9648, E-ISSN 1521-4095, Vol. 28, nr 39, s. 8651-8657Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Polyethylene nanocomposites based on functionalized ZnO nano/hierarchical particles with highly effective interfacial surface area are presented, for the next generation of ultralow transmission-loss high-voltage DC insulating materials.

  • 181.
    Pourrahimi, Amir Masoud
    et al.
    KTH, Skolan för kemivetenskap (CHE), Fiber- och polymerteknik, Polymera material.
    Liu, Dongming
    KTH, Skolan för kemivetenskap (CHE), Fiber- och polymerteknik, Polymera material.
    Pallon, Love K. H.
    KTH, Skolan för kemivetenskap (CHE), Fiber- och polymerteknik, Polymera material.
    Andersson, Richard L.
    KTH, Skolan för kemivetenskap (CHE), Fiber- och polymerteknik, Polymera material.
    Martinez Abad, A.
    Lagaron, J. -M
    Hedenqvist, Mikael S.
    KTH, Skolan för kemivetenskap (CHE), Fiber- och polymerteknik, Polymera material.
    Ström, Valter
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Teknisk materialfysik.
    Gedde, Ulf W.
    KTH, Skolan för kemivetenskap (CHE), Fiber- och polymerteknik, Polymera material.
    Olsson, Richard T.
    KTH, Skolan för kemivetenskap (CHE), Fiber- och polymerteknik, Polymera material.
    Water-based synthesis and cleaning methods for high purity ZnO nanoparticles - comparing acetate, chloride, sulphate and nitrate zinc salt precursors2014Inngår i: RSC Advances, ISSN 2046-2069, E-ISSN 2046-2069, Vol. 4, nr 67, s. 35568-35577Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    A low temperature (60 degrees C) aqueous synthesis method of high purity ZnO nanoparticles intended as fillers for ultra-low electrical conductivity insulations is described. Particles were prepared under identical conditions from different zinc salts based on nitrate, chloride, sulphate or acetate to compare their abilities to form high yields of sub-50 nm particles with narrow size distribution. The acetate salt gave uniform 25 nm ZnO particles with a conical prism shape. The chloride and sulphate derived particles showed mixed morphologies of nanoprisms and submicron petals, whereas the nitrate salt yielded prisms assembled into well-defined flower shapes with spiky edges. The micron-sized flower shapes were confirmed by Xray diffraction to consist of the smaller prism units. Photoluminescence spectroscopy showed emission in the blue-violet region with little variation depending on precursor salt, suggesting that the spectra were dependent on the primary nanoprism formation and rather independent of the final particle morphology. Microscopy revealed that the salt residuals after the reaction showed different affinity to the particle surfaces depending on the type of salt used, with the acetate creating ca. 20 nm thick hydrated shells; and in falling order of affinity: chloride, sulphate and nitrate. An acetate ion shielding effect during the synthesis was therefore assumed, preventing nanoparticle fusion during growth. Varying the concentrations of the counter-ions confirmed the shielding and only the acetate anions showed an ability to stabilize solitary nanoprisms formation in reaction yields from 2 to 10 g L-1. Ultrasonic particle surface cleaning was significantly more efficient than water replacement, resulting in a stable aqueous dispersion with a high zeta potential of 38.9 mV at pH 8.

  • 182.
    Pourrahimi, Amir Masoud
    et al.
    KTH, Skolan för kemi, bioteknologi och hälsa (CBH), Fiber- och polymerteknologi.
    Olsson, Richard
    KTH, Skolan för kemi, bioteknologi och hälsa (CBH), Fiber- och polymerteknologi, Polymera material.
    Hedenqvist, Mikael S.
    KTH, Skolan för kemi, bioteknologi och hälsa (CBH), Fiber- och polymerteknologi.
    The Role of Interfaces in Polyethylene/Metal-Oxide Nanocomposites for Ultrahigh-Voltage Insulating Materials2018Inngår i: Advanced Materials, ISSN 0935-9648, E-ISSN 1521-4095, Vol. 30, nr 4, artikkel-id 1703624Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Recent progress in the development of polyethylene/metal-oxide nanocomposites for extruded high-voltage direct-current (HVDC) cables with ultrahigh electric insulation properties is presented. This is a promising technology with the potential of raising the upper voltage limit in today's underground/submarine cables, based on pristine polyethylene, to levels where the loss of energy during electric power transmission becomes low enough to ensure intercontinental electric power transmission. The development of HVDC insulating materials together with the impact of the interface between the particles and the polymer on the nanocomposites electric properties are shown. Important parameters from the atomic to the microlevel, such as interfacial chemistry, interfacial area, and degree of particle dispersion/aggregation, are discussed. This work is placed in perspective with important work by others, and suggested mechanisms for improved insulation using nanoparticles, such as increased charge trap density, adsorption of impurities/ions, and induced particle dipole moments are considered. The effects of the nanoparticles and of their interfacial structures on the mechanical properties and the implications of cavitation on the electric properties are also discussed. Although the main interest in improving the properties of insulating polymers has been on the use of nanoparticles, leading to nanodielectrics, it is pointed out here that larger microscopic hierarchical metal-oxide particles with high surface porosity also impart good insulation properties. The impact of the type of particle and its inherent properties (purity and conductivity) on the nanocomposite dielectric and insulating properties are also discussed based on data obtained by a newly developed technique to directly observe the charge distribution on a nanometer scale in the nanocomposite.

  • 183.
    Pourrahimi, Amir Masoud
    et al.
    KTH, Skolan för kemivetenskap (CHE), Fiber- och polymerteknologi.
    Pallon, Love K. H.
    KTH, Skolan för kemivetenskap (CHE), Fiber- och polymerteknologi.
    Liu, Dongming
    KTH, Skolan för kemivetenskap (CHE), Fiber- och polymerteknologi.
    Hoang, Tuan Anh
    Gubanski, Stanislaw
    Hedenqvist, Mikael S.
    KTH, Skolan för kemivetenskap (CHE), Fiber- och polymerteknologi.
    Olsson, Richard T.
    KTH, Skolan för kemivetenskap (CHE), Fiber- och polymerteknologi.
    Gedde, Ulf W.
    KTH, Skolan för kemivetenskap (CHE), Fiber- och polymerteknologi.
    Polyethylene Nanocomposites for the Next Generation of Ultralow-Transmission-Loss HVDC Cables: Insulation Containing Moisture Resistant MgO Nanoparticles2016Inngår i: ACS Applied Materials and Interfaces, ISSN 1944-8244, E-ISSN 1944-8252, Vol. 8, nr 23, s. 14824-14835Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The use of MgO nanoparticles in polyethylene for cable insulation has attracted considerable interest, although in humid media the surface regions of the nanoparticles undergo a conversion to a hydroxide phase. A facile method to obtain MgO nanoparticles with a large surface area and remarkable inertness to humidity is presented. The method involves (a) low temperature (400 degrees C) thermal decomposition of Mg(OH)(2), (b) a silicone oxide coating to conceal the nanoparticles and prevent interparticle sintering upon exposure to high temperatures, and (c) heat treatment at 1000 degrees C. The formation of the hydroxide phase on these silicone oxide-coated MgO nanoparticles after extended exposure to humid air was assessed by thermogravimetry, infrared spectroscopy, and X-ray diffraction. The nanoparticles showed essentially no sign of any hydroxide phase compared to particles prepared by the conventional single-step thermal decomposition of Mg(OH)(2). The moisture-resistant MgO nanoparticles showed improved dispersion and interfacial adhesion in the LDPE matrix with smaller nanosized particle clusters compared with conventionally prepared MgO. The addition of 1 wt % moisture-resistant MgO nanoparticles was sufficient to decrease the conductivity of polyethylene 30 times. The reduction in conductivity is discussed in terms of defect concentration on the surface of the moisture-resistant MgO nanoparticles at the polymer/nanoparticle interface.

  • 184.
    Qadeer, Muhammad I.
    et al.
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap.
    Azhdar, Bruska
    KTH, Skolan för kemivetenskap (CHE), Fiber- och polymerteknik.
    Hedenqvist, Mikael S.
    KTH, Skolan för kemivetenskap (CHE), Fiber- och polymerteknik.
    Savage, S. J.
    Anomalous high temperature oxidation of Sm 2(Fe,Co,Cu,Zr) 17 particles2012Inngår i: Corrosion Science, ISSN 0010-938X, E-ISSN 1879-0496, Vol. 65, s. 453-460Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Sm 2Co 17 alloys are attractive as high temperature permanent magnets; however their magnetic properties are prone to degrade by oxidation. The oxidation mechanism is not clearly understood, and inconsistent results are reported in the literature.This work correlates the oxidation of Sm 2(Co,Fe,Cu,Zr) 17 with microstructural and microchemical changes as a consequence of chemical reaction of alloy particles with their environment at high temperature. Thermogravimetric analysis suggests a change in oxidation mechanism occurs at 550°C. Energy dispersive X-ray spectroscopy suggests this is related to the loss of Sm by sublimation.

  • 185.
    Qadeer, Muhammad I.
    et al.
    KTH, Skolan för kemivetenskap (CHE), Fiber- och polymerteknik. KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap.
    Savage, Steven J.
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap. Swedish Defence Research Agency (FOI), Linköping, Sweden .
    Gedde, Ulf W.
    KTH, Skolan för kemivetenskap (CHE), Fiber- och polymerteknik, Polymera material.
    Hedenqvist, Mikael S.
    KTH, Skolan för kemivetenskap (CHE), Fiber- och polymerteknik, Polymera material.
    Rheological and dynamic mechanical properties of polymer-bonded magnets based on Sm2Co17 and polyamide-122014Inngår i: Journal of Materials Science, ISSN 0022-2461, E-ISSN 1573-4803, Vol. 49, nr 21, s. 7529-7538Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The rheological and dynamic mechanical properties of polymer-based composites of Sm2Co17 and polyamide-12 with different particle loadings, sizes, and surface treatments are reported. Sm2Co17 particles were surface-treated with three different silanes: 3-glycidoxy(propyl)trimethoxysilane, 3-amino(propyl)trimethoxysilane (APTMS), and methyltrimethoxysilane (MTMS). It was shown, for the composites with untreated particles, that the viscosity and storage modulus increased with increasing filler content (0-60 vol%) and decreasing filler particle size. In addition, the glass transition temperature increased significantly and the damping decreased with increasing filler content. Of the silanes, the MTMS, which yielded only a thin surface layer, had in general the least effect on the rheological properties of the composite. The composite containing the APTMS-coated filler showed the highest storage modulus. The results give new insights on how to prepare polymer-bonded magnets with optimal process conditions (rheology) and dynamic mechanical properties, by varying the amount of particles, their size, and surface treatment.

  • 186.
    Qadeer, Muhammad Ifran
    et al.
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Keramteknologi.
    Azhdar, Bruska
    KTH, Skolan för kemivetenskap (CHE), Fiber- och polymerteknik, Polymera material.
    Hedenqvist, Mikael
    KTH, Skolan för kemivetenskap (CHE), Fiber- och polymerteknik, Polymera material.
    Savage, Steven J.
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Keramteknologi.
    Improved oxidation resistance of SmCo magnetic alloy powders by silanization2013Inngår i: Progress in organic coatings, ISSN 0300-9440, E-ISSN 1873-331X, Vol. 76, nr 1, s. 94-100Artikkel, forskningsoversikt (Fagfellevurdert)
    Abstract [en]

    The thermal stability of Sm2Co17 powders coated with four different silanes was studied between 25 degrees C and 500 degrees C and isothermally at 400 degrees C. Thermogravimetry data indicated that the silane-based coatings provided improved oxidation resistance. The microstructural analysis of uncoated powders oxidized for 10 h at 400 degrees C revealed the formation of a featureless ca. 10 mu m thick shell, surrounding the unreacted core. The development of this shell was attributed to the inward diffusion of oxygen, decomposition of intermetallic phases and redistribution of alloying elements. The EDS elemental maps revealed that the shell was rich in O, Fe and Co, and depleted in Sm, Zr and Cu. In the presence of the silane-based coatings the thickness of the shell was reduced by more than 80% (to less than 2 mu m) and the redistribution of alloying elements was insignificant. Based on the thermogravimetric analysis at or above ca. 400 degrees C and the nnicrostructural analysis it was possible to assess the relative effectivity of the different silanes in preventing the oxidation of the SmCo powder. Methyltrimethoxysilane (MTMS), which also formed the thinnest coating, was the best silane. (3-Glycidyloxypropyl)trimethoxysilane, forming a thicker coating, was less effective than MTMS, but superior to the two amine-functionalized silanes ((3-aminopropyl)triethoxysilane and (3-aminopropyl)trimethoxysilane).

  • 187.
    Qadeer, Muhammad Ifran
    et al.
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Keramteknologi.
    Savage, Steven J.
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Keramteknologi.
    Hedenqvist, Mikael
    KTH, Skolan för kemivetenskap (CHE), Fiber- och polymerteknik, Polymera material.
    High temperature magnetic properties of Sm-Co and Sm-Co/polyamide-12 materials: effects of temperature, particle size, and silanization2013Inngår i: Journal of Materials Science, ISSN 0022-2461, E-ISSN 1573-4803, Vol. 48, nr 23, s. 8163-8170Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    There is an increasing demand for polymer-bonded magnets (PBM) in high temperature applications. While most research deals with high temperature properties of NdFeB-PBM, only a few studies consider Sm-Co PBM. Therefore, this study, on the thermal and magnetic properties of Sm-Co alloy powders and blends of these with polyamide-12 (PA12), was undertaken. Since the Sm-Co powders were the product of ball milling, they contained a variety of shapes and sizes. Studies on size fractions of these showed that the thermal stability and magnetic properties were improved as the particle size increased. It was suggested that higher residual strains and smaller crystallite sizes in the small particles were responsible for a decrease in the thermal stability and magnetic properties. In addition, energy dispersive X-ray spectroscopy revealed that the oxygen content increased with decreasing particle size (larger specific surface area) and higher oxygen content was possibly also responsible for a decrease in the magnetic properties. It was shown that, in general, the surface modification by silanization, using (3-aminopropyl)trimethoxsilane, increased the saturation magnetization and remanence of both the particles and the Sm-Co/PA12 composite. The silanization also improved the thermal stability of the particles.

  • 188. Rasel, H.
    et al.
    Hedenqvist, Mikael S.
    KTH, Skolan för kemivetenskap (CHE), Fiber- och polymerteknologi.
    Johansson, T.
    Newson, W. R.
    Johansson, E.
    Gällstedt, M.
    New bio-based plastics, from a non-edible plant oil side-stream, for film extrusion2014Inngår i: 19th IAPRI World Conference on Packaging 2014: Responsible Packaging for a Global Market, Victoria University , 2014, s. 586-590Konferansepaper (Fagfellevurdert)
    Abstract [en]

    Renewable sourced PET, PA, PE, starch blends, etc, are fastly growing due to the processability and final performance, that is similar to their petroleum derived options. A bit in the shadow of the development of these plastics, development is ongoing on another group of plastics, made directly of the side-streams of agricultural products: oil plant residues and proteins. They can be used in edible applications but not all of them are suitable for food or forage. Industrial oilseed meal from crambe abyssinica contains relatively high levels of protein that is not suitable for human or animal consumption due to the presence of anti-nutritional compounds. This paper presents research on crambe meal as a base for new plastics, developed to extrude continuous, flexible plastic films based on crambe meal, blended with vital wheat gluten as an elastic component and urea as a protein denaturant. The effect of process parameters, such as screw speed, die temperature and pressure, and the effect of components were studied with regards to the final performance of the film extrudates. E.g. mechanical properties, oxygen permeability and moisture content were determined and surface and cross-section morphologies were examined with electron microscopy. The results showed that crambe-based blends can be extruded as continuous, flexible plastic films, which exhibit barrier properties towards oxygen. Recipes and methods for pelletizing of master batches for post-converting (e.g. extrusion or compression molding) were successfully developed. Addition of a renewable plasticizer improved the extrusion performance and resulted in less hygroscopic films, which further showed the overall highest tensile strength while the extensibility was nearly unaffected. The results provide a first basis to further develop the process and the blend towards potential industrial applications, for example as packaging materials to trays, pots and similar type of packages.

  • 189. Rasel, H.
    et al.
    Johansson, T.
    Gällstedt, M.
    Newson, W.
    Johansson, E.
    Hedenqvist, Mikael
    KTH, Skolan för kemivetenskap (CHE), Fiber- och polymerteknologi.
    Development of bioplastics based on agricultural side-stream products: Film extrusion of Crambe abyssinica/wheat gluten blends for packaging purposes2015Inngår i: Journal of Applied Polymer Science, ISSN 0021-8995, E-ISSN 1097-4628, Vol. 133, nr 2, artikkel-id 42442Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The purpose of this work was to add economic value to crambe meal, the protein-rich byproduct from the industrial extraction of Crambe abyssinica seed oil, by using it as a potential feedstock for oilseed meal-based plastics. The feasibility to produce continuous, flexible plastic films of glycerol-plasticized crambe meal blended with wheat gluten (WG) to improve extrudate properties and urea as a protein denaturant using extrusion was investigated. The effect of process parameters and blend composition were studied with regard to the extrusion performance and the film properties. Tensile properties and oxygen permeability were determined, and the film morphology was analyzed with scanning electron microscopy. A die temperature between 125 and 130°C resulted in films with the most homogeneous surfaces and highest tensile strength and extensibility. The use of compression molding after extrusion improved the surface quality and film strength and lowered the oxygen permeability. A decrease in the plasticizer content (from 30 to 20 wt %) improved the extrudability and showed the highest tensile strength, whereas the extensibility was essentially unaffected. The importance of the presence of WG was shown by the fact that strength and extensibility decreased when the crambe content was increased from 60 to 80 wt %. It was shown that crambe-based biopolymer blends could be extruded as continuous flexible plastic films that exhibited promising mechanical and oxygen barrier properties. The operational window was, however, found to be narrow. The results provide a first basis to further develop the process and the blend toward industrial applications, for example, as packaging materials. © 2015 Wiley Periodicals, Inc.

  • 190. Rasheed, Faiza
    et al.
    Hedenqvist, Mikael S.
    KTH, Skolan för kemivetenskap (CHE), Fiber- och polymerteknologi, Polymera material.
    Kuktaite, Ramune
    Plivelic, Tomas S.
    Gallstedt, Mikael
    Johansson, Eva
    Mild gluten separation - A non-destructive approach to fine tune structure and mechanical behavior of wheat gluten films2015Inngår i: Industrial crops and products (Print), ISSN 0926-6690, E-ISSN 1872-633X, Vol. 73, s. 90-98Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Despite the increasing production of wheat gluten (WG) for industrial use, minor attention has been given to the impact of the separation procedure on the gluten quality. The purpose of the present study was to probe the effect of the separation treatments (harsh vs mild) on gluten structure, morphology, and performance in bio-based films. The harshly separated industrial WG showed aggregated and pre-cross linked structure in the starting material most likely due to shear forces during gluten separation from flour and heat effect during the drying procedures. Further, when the harshly separated WG was processed into films the pre-crosslinked starting material restricted new crosslinks formation and structural rearrangements at nano-scale. The mechanical integrity of the film was also affected resulting in films with low Young's modulus and strength. WG (from cultivars Diskette, Puntari, and Sleipner) recovered from mild separation showed relatively "native" non-destructed crosslinking pattern and not previously observed structural morphology at nano-scale. When processed into films the mildly separated WG showed well polymerized intimately crosslinked proteins both with disulfide and other covalent crosslinks. The nano-scale morphology showed lamellar and hexagonal arrangements, not reported so far in any study. The structural rearrangements among films from mildly separated WG resulted in materials with improved mechanical integrity as compared to films from harshly separated WG. The present study showed that the quality of WG is significantly affected by the separation procedure which also affects protein polymerization, nano-scale morphology, and tensile properties of films.

  • 191. Rasheed, Faiza
    et al.
    Kuktaite, Ramune
    Hedenqvist, Mikael S.
    KTH, Skolan för kemivetenskap (CHE), Fiber- och polymerteknologi.
    Gallstedt, Mikael
    Plivelic, Tomas S.
    Johansson, Eva
    The use of plants as a "green factory" to produce high strength gluten-based materials2016Inngår i: Green Chemistry, ISSN 1463-9262, E-ISSN 1463-9270, Vol. 18, nr 9, s. 2782-2792Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The aim of the present study was to develop an understanding of how wheat plants can be used as a "green factory" by the modulation of genotype (G) and environmental (E) interactions to fine-tune the structure and increase the strength of gluten based materials. Two wheat genotypes (5 + 10 and 2 + 12) were grown under four nitrogen and two temperature regimes to obtain gluten of various characteristics. Protein microstructure morphology revealed by confocal laser scanning microscopy suggested a higher polymerisation of proteins in glycerol plasticized films from the 5 + 10 compared to the 2 + 12 genotype. Also, films with the highest Young's modulus and maximum stress were obtained from the 5 + 10 genotype, which might be explained by the higher number of cysteine residues and consequently more disulphide crosslinks in this genotype compared to the 2 + 12 one. The presence of two nano-scaled morphologies, hexagonal and lamellar structures and their internal relations were found to be of relevance for formation of beta-sheets and also to be related to performance (strength) of the material. Thus, plants could be used as a "green factory", avoiding the use of chemicals, to tune the tensile properties of the materials. Structural properties such as relatively low protein aggregation, high beta-sheet content and a high hexagonal to lamellar structural ratio at the nano-scale were found to yield films with high stiffness and strength.

  • 192. Rasheed, Faiza
    et al.
    Newson, William R.
    Plivelic, Tomas S.
    Kuktaite, Ramune
    Hedenqvist, Mikael S.
    KTH, Skolan för kemivetenskap (CHE), Fiber- och polymerteknologi.
    Gallstedt, Mikael
    Johansson, Eva
    Macromolecular changes and nano-structural arrangements in gliadin and glutenin films upon chemical modification Relation to functionality2015Inngår i: International Journal of Biological Macromolecules, ISSN 0141-8130, E-ISSN 1879-0003, Vol. 79, s. 151-159Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Protein macromolecules adopted for biological and bio-based material functions are known to develop a structured protein network upon chemical modification. In this study, we aimed to evaluate the impact of chemical additives such as, NaOH, NH4OH and salicylic acid (SA), on the secondary and nano-structural transitions of wheat proteins. Further, the effect of chemically induced modifications in protein macromolecular structure was anticipated in relation to functional properties. The gliadin-NH4OH-SA film showed a supramolecular protein organization into hexagonal structures with 65 angstrom lattice parameter, and other not previously observed structural entities having a characteristic distance of 50 angstrom. Proteins in gliadin-NH4OH-SA films were highly polymerized, with increased amount of disulfide crosslinks and beta-sheets, causing improved strength and stiffness. Glutenin and WG proteins with NH4OH-SA showed extensive aggregation and an increase in beta-sheet content together with irreversible crosslinks. Irreversible crosslinks hindered a high order structure formation in glutenins, and this resulted in films with only moderately improved stiffness. Thus, formation of nano-hierarchical structures based on beta-sheets and disulfide crosslinks are the major reasons of high strength and stiffness in wheat protein based films.

  • 193. Rasheed, Faiza
    et al.
    Newson, William R.
    Plivelic, Tomas S.
    Kuktaite, Ramune
    Hedenqvist, Mikael S.
    KTH, Skolan för kemivetenskap (CHE), Fiber- och polymerteknologi, Polymera material.
    Gällstedt, Mikael
    Johansson, Eva
    Structural architecture and solubility of native and modified gliadin and glutenin proteins: non-crystalline molecular and atomic organization2014Inngår i: RSC Advances, ISSN 2046-2069, E-ISSN 2046-2069, Vol. 4, nr 4, s. 2051-2060Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Wheat gluten (WG) and its components, gliadin and glutenin proteins, form the largest polymers in nature, which complicates the structural architecture of these proteins. Wheat gluten, gliadin and glutenin proteins in unmodified form showed few secondary structural features. Structural modification of these proteins using heat, pressure and the chemical chaperone glycerol resulted in a shift to organized structure. In modified gliadin, nano-structural molecular arrangements in the form of hexagonal closed packed (HCP) assemblies with lattice parameter of (58 angstrom) were obvious together with development of intermolecular disulphide bonds. Modification of glutenin resulted in highly polymerized structure with proteins linked not only by disulphide bonds, but also with other covalent and irreversible bonds, as well as the highest proportion of beta-sheets. From a combination of experimental evidence and protein algorithms, we have proposed tertiary structure models of unmodified and modified gliadin and glutenin proteins. An increased understanding of gliadin and glutenin proteins structure and behavior are of utmost importance to understand the applicability of these proteins for various applications including plastic materials, foams, adhesives, films and coatings.

  • 194.
    Rasheed, Faiza
    et al.
    KTH, Skolan för kemi, bioteknologi och hälsa (CBH), Fiber- och polymerteknologi, Polymera material. Swedish Univ Agr Sci, Dept Plant Breeding, Växtskyddsvägen 1, SE-23053 Alnarp, Sweden.
    Plivelic, Tomas S.
    Lund Univ, MAX IV Lab, Box 118, SE-22100 Lund, Sweden..
    Kuktaite, Ramune
    Swedish Univ Agr Sci, Dept Plant Breeding, Vaxtskyddsvagen 1, SE-23053 Alnarp, Sweden..
    Hedenqvist, Mikael S.
    KTH, Skolan för kemi, bioteknologi och hälsa (CBH), Fiber- och polymerteknologi, Polymera material.
    Johansson, Eva
    Swedish Univ Agr Sci, Dept Plant Breeding, Vaxtskyddsvagen 1, SE-23053 Alnarp, Sweden..
    Unraveling the Structural Puzzle of the Giant Glutenin Polymer-An Interplay between Protein Polymerization, Nanomorphology, and Functional Properties in Bioplastic Films2018Inngår i: ACS OMEGA, ISSN 2470-1343, Vol. 3, nr 5, s. 5584-5592Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    A combination of genotype, cultivation environment, and protein separation procedure was used to modify the nanoscale morphology, polymerization, and chemical structure of glutenin proteins from wheat. A low-polymerized glutenin starting material was the key to protein-protein interactions mainly via SS cross-links during film formation, resulting in extended beta-sheet structures and propensity toward the formation of nanoscale morphologies at molecular level. The properties of glutenin bioplastic films were enhanced by the selection of a genotype with a high number of cysteine residues in its chemical structure and cultivation environment with a short grain maturation period, both contributing positively to gluten strength. Thus, a combination of factors affected the structure of glutenins in bioplastic films by forming crystalline beta-sheets and propensity toward the ordered nanostructures, thereby resulting in functional properties with high strength, stiffness, and extensibility.

  • 195. Rehman, Hafeez Ur
    et al.
    Chen, Yujie
    Hedenqvist, Mikael S.
    KTH, Skolan för kemi, bioteknologi och hälsa (CBH), Fiber- och polymerteknologi.
    Li, Hua
    Xue, Wenchao
    Guo, Yunlong
    Guo, Yiping
    Duan, Huanan
    Liu, Hezhou
    Self-Healing Shape Memory PUPCL Copolymer with High Cycle Life2018Inngår i: Advanced Functional Materials, ISSN 1616-301X, E-ISSN 1616-3028, Vol. 28, nr 7, artikkel-id 1704109Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    New polyurethane-based polycaprolactone copolymer networks, with shape recovery properties, are presented here. Once deformed at ambient temperature, they show 100% shape fixation until heated above the melting point, where they recover the initial shape within 22 s. In contrast to current shape memory materials, the new materials do not require deformation at elevated temperature. The stable polymer structure of polyurethane yields a copolymer network that has strength of 10 MPa with an elongation at break of 35%. The copolymer networks are self-healing at a slightly elevated temperature (70 degrees C) without any external force, which is required for existing self-healing materials. This allows for the new materials to have a long life of repeated healing cycles. The presented copolymers show features that are promising for applications as temperature sensors and activating elements.

  • 196. Ritums, J. E.
    et al.
    Hedenqvist, Mikael S.
    KTH, Skolan för kemivetenskap (CHE), Fiber- och polymerteknik.
    Bergman, G.
    Prodan, T.
    Emri, I.
    Sorption behavior in polymers above T-g: Relations between mechanical properties and swelling in limonene2005Inngår i: Polymer Engineering and Science, ISSN 0032-3888, E-ISSN 1548-2634, Vol. 45, nr 9, s. 1194-1202Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The sorption behavior of two highly swelling rubbery polymers, natural rubber and polyethylene, has been studied. The polymers are in many aspects very different. Yet, when the solute mass uptake, in this case limonene, is plotted as a function of the square root of time, both polymers show similar sigmoidal-types of curves. This triggered the research to determine what mechanisms were responsible for the observed similarities and if the degree in sigmoidal behavior and swelling anisotropy could be easily assessed explicitly by any mechanical parameter. It was found that their degrees of swelling anisotropy, described by a solute-surface-concentration relaxation time, could be explained by their relative bulk moduli. It was assumed that the ratio in bulk modulus at zero pressure, determined from compression measurements, could represent the ratio in expansion bulk modulus during swelling. However, the prediction in swelling anisotropy during sorption using the ratio in bulk modulus was slightly less successful when the swelling anisotropy was quantified as the relative ratio of sheet thickness to cross-sectional area side length. It should be noted that the ratio in uniaxial tensile modulus between polyethylene and natural rubber was several orders of magnitude higher than their ratio in swelling anisotropy. The natural rubber sheet became saddle-shaped during limonene sorption and collapsed into a flat shape when the saturation concentration was approached. During desorption, the sheet went from flat to cup-shaped and then flat again at the end of desorption. The saddle and cup shapes occurred in both square and round sheets. These shapes are believed to be a consequence of buckling and deformation due to instabilities in the stress state of the sheet This was, in turn, explained by the normally existing local variation in cross-link density.

  • 197. Ritums, J. E.
    et al.
    Mattozzi, A.
    Gedde, Ulf W.
    KTH, Skolan för kemivetenskap (CHE), Fiber- och polymerteknik.
    Hedenqvist, Mikael S.
    KTH, Skolan för kemivetenskap (CHE), Fiber- och polymerteknik.
    Bergman, G.
    Palmlof, M.
    Mechanical properties of high-density polyethylene and crosslinked high-density polyethylene in crude oil and its components2006Inngår i: Journal of Polymer Science Part B: Polymer Physics, ISSN 0887-6266, E-ISSN 1099-0488, Vol. 44, nr 4, s. 641-648Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The tensile and stress-relaxation properties of an uncrosslinked and a loosely silane-crosslinked high-density polyethylene exposed to organic '' crude-oil '' penetrants were assessed. The measurements were performed on penetrant-saturated samples, surrounded by the organic liquid throughout the experiment. The penetrant solubilities in the two polymers were similar and in accordance with predicted values based on the solubility parameter method. The stiffness and strength of the swollen samples were significantly less than those of the dry samples, indicating a plasticization of the amorphous component. Raman spectroscopy on polyethylene exposed to deuterated n-hexane revealed a penetrant-induced partial melting/dissolution of the crystal surface and an intact crystal core component. The stress-relaxation rates, within the time frame of the experiment (similar to 1 s to 18 h), were approximately the same, independent of silane-crosslinks and the presence of penetrants. This indicated that the mechanical alpha-relaxation, which is the main relaxation process occurring in the measured time interval, was not affected by the penetrants. Consequently, its rate seemed to be independent of the crystal surface dissolution (decrease in the content of crystal-core interface). The shape of the '' log stress-log time '' curves of the swollen samples was, however, different from that of the dry samples. This was most likely attributed to a time-dependent saturation of penetrant to a higher level associated with the stretched state of the polymer sample. The silane crosslinks affected only the elongation at break, which was less than that of the uncrosslinked material.

  • 198. Rombouts, I.
    et al.
    Lagrain, B.
    Delcour, Jan A.
    Leuven Food Science and Nutrition Research Centre (LFoRCe), KULeuven, Belgium.
    Türe, Hasan
    KTH, Skolan för kemivetenskap (CHE), Fiber- och polymerteknik.
    Hedenqvist, Mikael S.
    KTH, Skolan för kemivetenskap (CHE), Fiber- och polymerteknik, Polymera material.
    Johansson, E.
    Kuktaite, Ramune
    Crosslinks in wheat gluten films with hexagonal close-packed protein structures2013Inngår i: Industrial crops and products (Print), ISSN 0926-6690, E-ISSN 1872-633X, Vol. 51, s. 229-235Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Wheat gluten/glycerol (WGG) films were extruded with aqueous ammonia/salicylic acid or urea to investigate the reactions contributing to their hexagonal close-packed protein structures and material properties. The addition of aqueous ammonia and salicylic acid increased the pH, which, in turn, increased the level of intermolecular disulfide and lanthionine cross-links in the WGG films. Increased protein cross-linking reactions resulted in higher material strength and tensile modulus. These cross-linking reactions and the resulting material properties were similar for WGG films with 7.5% and 10% aqueous ammonia. Added urea into WGG film partially degraded into cyanate and ammonium. Cyanate subsequently reacted with lysine and cysteine to ε-carbamyllysine and S-carbamylcysteine, respectively. Even though these reactions resulted in a more alkaline reaction environment, hereby favoring disulfide bond formation and decreasing protein extractability, they also prevented the involvement of cysteine and lysine in protein cross-linking. The alkylation of these reactive amino acids, together with the plasticizing effect of urea, led to lower material strength and elastic modulus with increasing levels of urea.

  • 199.
    Römhild, Stefanie
    et al.
    KTH, Skolan för kemivetenskap (CHE), Fiber- och polymerteknik, Polymera material.
    Bergman, G.
    Hedenqvist, Mikael
    KTH, Skolan för kemivetenskap (CHE), Fiber- och polymerteknik, Polymera material.
    Short-Term and Long-Term Performance of Thermosets Exposed to Water at Elevated Temperatures2009Inngår i: Journal of Applied Polymer Science, ISSN 0021-8995, E-ISSN 1097-4628, Vol. 116, nr 2, s. 1057-Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The water-transport, mechanical, and chemical-structure changes in various vinyl ester, novolac, and urethane-modified vinyl ester thermosets exposed to water at 50 to 95oC for times up to 1000 days have been studied within the framework of a larger study of osmotic blistering in fiber reinforced plastics (FRP) process components. The water sorption saturation concentration did not reach a steady-state value but gradually increased in many cases upon long-term exposure. The diffusion coefficient was not significantly affected. Infrared spectroscopy and gas chromatography-mass spectrometry indicated that the net mass loss from the thermosets on immersion in water was due to the leaching of non-reacted styrene, monomer, and additives. It is suggested that this, together with polymer relaxation processes (as measured on specimens under tension in water at 80oC), is the primary reason for the time-dependent increase in the water saturation concentration. Infrared spectroscopy indicated that, even at the highest temperatures, hydrolysis of the polymer ester groups was small. Correlations were found between the styrene content in the uncured thermosets, the estimated solubility parameters, and the sorption and diffusion coefficients.

  • 200.
    Römhild, Stefanie
    et al.
    KTH, Skolan för kemivetenskap (CHE), Fiber- och polymerteknik, Polymera material.
    Bergman, G.
    Hedenqvist, Mikael
    KTH, Skolan för kemivetenskap (CHE), Fiber- och polymerteknik, Polymera material.
    Transport and adhesion properties of an unlined and a liquid-crystalline polymer-lined vinyl ester thermoset exposed to severe environments2005Inngår i: Journal of Applied Polymer Science, ISSN 0021-8995, E-ISSN 1097-4628, Vol. 95, nr 4, s. 797-806Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The application of liquid-crystalline polymers (LCP) as lining materials for fiber-reinforced plastics was investigated. The lining consisted of one uniaxially and one biaxially oriented LCP and, for comparison, a fluorinated ethylene propylene copolymer. The lining was attached to a glass-fiber-reinforced vinyl ester thermoset. The laminates were examined with respect to their chemical resistance, transport/barrier properties, and lining/matrix adhesion behavior. The transport properties were determined by gravimetric desorption measurements and cup tests. It was shown that the LCP was suitable as a lining in organic solvent and nonoxidizing acid environments. Diffusivities, equilibrium concentrations, and transmission rates of water, methanol, toluene, and trichloroethylene were obtained in the LCP, the fluorinated ethylene propylene copolymer, and also, in the case of the vinyl ester, of hydrochloric acid. In general, the diffusivity and transmission rate in the LCP were one to several orders of magnitude lower than those of the fluorinated ethylene propylene copolymer and the vinyl ester. The reinforcement in the glass-fiber-reinforced plastic led to an increase in the water and methanol diffusivities and transmission rates, which was probably attributable to liquid capillary diffusion. The lap-shear bonding strength between the LCP and the vinyl ester was poor, but it was improved almost sixfold by a combined abrasive and oxygen plasma treatment.

123456 151 - 200 of 251
RefereraExporteraLink til resultatlisten
Permanent link
Referera
Referensformat
  • apa
  • harvard1
  • ieee
  • modern-language-association-8th-edition
  • vancouver
  • Annet format
Fler format
Språk
  • de-DE
  • en-GB
  • en-US
  • fi-FI
  • nn-NO
  • nn-NB
  • sv-SE
  • Annet språk
Fler språk
Utmatningsformat
  • html
  • text
  • asciidoc
  • rtf