| 1. |
- Özeren, Hüsamettin Deniz, et al.
(författare)
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Role of Hydrogen Bonding in Wheat Gluten Protein Systems Plasticized with Glycerol and Water
- 2021
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Ingår i: Polymer. - : Elsevier BV. - 0032-3861 .- 1873-2291. ; 232, s. 124149-
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Tidskriftsartikel (övrigt vetenskapligt/konstnärligt)abstract
- Many biopolymers are stiff and brittle and require plasticizers. To optimize the choice and amount of plasticizer, the mechanisms behind plasticization need to be understood. For polar biopolymers, such as polysaccharides and proteins, plasticization depends to a large extent on the hydrogen bond network. In this study, glycerol-plasticized protein systems based on wheat gluten were investigated, in combination with the effects of water. The methodology was based on a combination of mechanical tests and molecular dynamics simulations (MD). The simulations accurately predicted the glycerol content where the experimental depression in glass transition temperature (Tg) occurred (between 20 and 30 wt.% plasticizer). They also predicted the strong water-induced depression in Tg. Detailed analysis revealed that in the dry system, the main effect of glycerol was to break protein-protein hydrogen bonds. In the moist system, glycerol was partly outcompeted by water in forming hydrogen bonds with the protein, making the glycerol plasticizer less effective than in dry conditions. These results show that MD can successfully predict the plasticizer concentration at which the onset of efficient plasticization occurs. MD can therefore be an important tool for understanding plasticizer mechanisms, even in a complex system, on a level of detail that is impossible with experiments.
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| 2. |
- Olabarrieta, Idoia, et al.
(författare)
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Aging properties of films of plasticized vital wheat gluten cast from acidic and basic solutions
- 2006
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Ingår i: Biomacromolecules. - : American Chemical Society (ACS). - 1525-7797 .- 1526-4602. ; 7:5, s. 1657-1664
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Tidskriftsartikel (refereegranskat)abstract
- 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.
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| 3. |
- Özeren, Hüsamettin Deniz
(författare)
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Prediction of Real Tensile Properties using Extrapolations from Atomistic Simulations: An Assessment on Thermoplastic Starch
- 2021
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Ingår i: Polymer. - : Elsevier BV. - 0032-3861 .- 1873-2291. ; 228:123919
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Tidskriftsartikel (refereegranskat)abstract
- Atomistic molecular dynamics (MD) simulations can be used to predict mechanical properties, such as stiffness and strength, for polymers. A concern is unavoidably high strain rates in simulations compared with those in physical experiments. To quantitatively capture the mechanical properties of the ‘real’ material, i.e., to predict absolute values rather than just qualitative trends, extrapolation to realistic strain rates is required. In this study, different strain-rate extrapolation strategies involving time-temperature shifting with the Williams-Landel-Ferry equation (above Tg) and the Eyring equation (below Tg) were evaluated, using thermoplastic starch as an example. MD simulations were first used to compute the stiffness and strength at three (high) strain rates over a wide range of temperatures. The mechanical MD data were then horizontally time-temperature shifted, resulting in master curves with strain-rate (x-axis) versus mechanical properties (y-axis). The precision in the prediction of experimental data was quite good in several cases, but was dependent on the extrapolation method and the specific thermoplastic starch system. A notable finding was that the simulations could be simplified using fewer simulation strain rates and temperatures. The extrapolation techniques used here are expected to be valid for other polymer systems, but this remains to be validated.
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| 4. |
- Janewithayapun, Ratchawit, 1998, et al.
(författare)
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Nanostructures of etherified arabinoxylans and the effect of arabinose content on material properties
- 2024
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Ingår i: Carbohydrate Polymers. - : Elsevier BV. - 0144-8617 .- 1879-1344. ; 331
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Tidskriftsartikel (refereegranskat)abstract
- To further our understanding of a thermoplastic arabinoxylan (AX) material obtained through an oxidation-reduction-etherification pathway, the role of the initial arabinose:xylose ratio on the material properties was investigated. Compression molded films with one molar substitution of butyl glycidyl ether (BGE) showed markedly different tensile behaviors. Films made from low arabinose AX were less ductile, while those made from high arabinose AX exhibited elastomer-like behaviors. X-ray scattering confirmed the presence of nanostructure formation resulting in nano-domains rich in either AX or BGE, from side chain grafting. The scattering data showed variations in the presence of ordered structures, nano-domain sizes and their temperature response between AX with different arabinose contents. In dynamic mechanical testing, three transitions were observed at approximately −90 °C, −50 °C and 80 °C, with a correlation between samples with more structured nano-domains and those with higher onset transition temperatures and lower storage modulus decrease. The mechanical properties of the final thermoplastic AX material can therefore be tuned by controlling the composition of the starting material.
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| 5. |
- Nilsson, Fritjof, Docent, 1978-, et al.
(författare)
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Nanocomposites and polyethylene blends: two potentially synergistic strategies for HVDC insulation materials with ultra-low electrical conductivity
- 2021
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Ingår i: Composites Part B: Engineering. - : Elsevier BV. - 1359-8368 .- 1879-1069. ; 204
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Tidskriftsartikel (refereegranskat)abstract
- Among the various requirements that high voltage direct current (HVDC) insulation materials need to satisfy, sufficiently low electrical conductivity is one of the most important. The leading commercial HVDC insulation material is currently an exceptionally clean cross-linked low-density polyethylene (XLPE). Previous studies have reported that the DC-conductivity of low-density polyethylene (LDPE) can be markedly reduced either by including a fraction of high-density polyethylene (HDPE) or by adding a small amount of a well dispersed, semiconducting nanofiller such as Al2O3 coated with a silane. This study demonstrates that by combining these two strategies a synergistic effect can be achieved, resulting in an insulation material with an ultra-low electrical conductivity. The addition of both HDPE and C8–Al2O3 nanoparticles to LDPE resulted in ultra-insulating nanocomposites with a conductivity around 500 times lower than of the neat LDPE at an electric field of 32 kV/mm and 60–90 °C. The new nanocomposite is thus a promising material regarding the electrical conductivity and it can be further optimized since the polyethylene blend and the nanoparticles can be improved independently.
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| 6. |
- Olabarrieta, Idoia, et al.
(författare)
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Properties of new and aged montmorillonite-wheat gluten composite films
- 2006
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Ingår i: Journal of Agricultural and Food Chemistry. - : American Chemical Society (ACS). - 0021-8561 .- 1520-5118. ; 54:4, s. 1283-1288
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Tidskriftsartikel (refereegranskat)abstract
- 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.
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| 7. |
- Rehman, Hafeez Ur, et al.
(författare)
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High-cycle-life and high-loading copolymer network with potential application as a soft actuator
- 2019
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Ingår i: Materials & design. - : ELSEVIER SCI LTD. - 0264-1275 .- 1873-4197. ; 182
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Tidskriftsartikel (refereegranskat)abstract
- Thermo-responsive polymer materials ate appealing in emerging fields including soft robotics, artificial muscles, and actuators. However, realising a single smart polymer material that can achieve immense strain, fast actuation, and high loading remains a challenge. We attempted to address these limitations by fabricating a thermo-responsive copolymer network structure of poly(urethane-caprolactone-siloxane). The relative concentrations of these precursors were adjusted to realise a high mechanical strength of >= 17 MPa, 100% shape fixation, and a quick shape recovery time of <= 15 s. Experimental results revealed that the soft segments largely determines the extensibility and crystallinity of the copolymer material. The thermal gradient of the soft part enables the copolymer to self-heal during shape recovery. The copolymer network was applied to a load lifting device as an artificial muscle and was able to lift 200 times its weight with a short response time of <5 s and maximum power density that was half that of mammalian skeletal muscles. With its fast actuation, high loading, and self-healing abilities, the developed therrno-activated smart copolymer material is potentially applicable to a wide range of fields such as soft robotics, biomimetic devices, and prosthetics.
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| 8. |
- Ullsten, Henrik, et al.
(författare)
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Enlarged processing window of plasticized wheat gluten using salicylic acid
- 2006
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Ingår i: Biomacromolecules. - : American Chemical Society (ACS). - 1525-7797 .- 1526-4602. ; 7:3, s. 771-776
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Tidskriftsartikel (refereegranskat)abstract
- The temperature window for the extrusion of glycerol-plasticized wheat gluten was increased by the use of salicylic acid, a known scorch retarder and radical scavenger. It was possible to extrude 30 wt % glycerol-wheat gluten films with a die-head temperature as high as 135 °C, rather than 95 °C, by incorporating only 1 wt % salicylic acid. Small effects of shear-induced heating during extrusion at the higher temperatures suggested that the acid acted as a lubricant and viscosity reducer. The latter was suggested to originate primarily from the salicylic-acid-induced reduction in the degree of protein aggregation/cross-linking, as indicated by size-exclusion high-performance liquid chromatography and chemiluminescence. Electron paramagnetic resonance spectroscopy on extruded films indicated that the beneficial effect of salicylic acid was due to its radical scavenging effect. Tensile tests on extrudates revealed that the materials produced at the substantially higher processing temperature were still ductile. The complex shear modulus increased more slowly with increasing salicylic acid content above 110-120 °C, indicating that the aggregation/cross-linking rate was slower with salicylic acid, th t is, that it did have a scorch-retarding effect, besides yielding a lower final degree/complexity of aggregation.
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