| 1. |
- Altskär, Annika, et al.
(author)
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Some effects of processing on the molecular structure and morphology of thermoplastic starch
- 2008
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In: Carbohydrate Polymers. - : Elsevier BV. - 0144-8617 .- 1879-1344. ; 71:4, s. 591-597
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Journal article (peer-reviewed)abstract
- Hydroxypropylated and oxidised potato starch (HONPS) was used together with glycerol and water to produce thermoplastic starch. The amount of glycerol was kept constant at 22 parts by weight per 100 parts of dry starch. The thermoplastic starch was converted into films/sheets using three different processing techniques; casting, compression moulding and film blowing. The last two methods represent typical thermoplastic conversion techniques requiring elevated processing temperatures. By means of size-exclusion chromatography, it was found that compression moulding and film blowing led to some degradation of high-molecular weight amylopectin as well as of high-molecular weight amylose-like molecules. The degradation was significantly less pronounced for the cast films. The morphology of the specimens was quite complex and phase separations on different levels were identified. In the cast films and, to a lesser extent, in the compression-moulded specimens, a fine network structure could be distinguished. Such a structure could however not be ascertained in the film-blown material and this is discussed in terms of the thermo-mechanical treatment of the starch materials. © 2007 Elsevier Ltd. All rights reserved.
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| 2. |
- Gomez-Martinez, D., et al.
(author)
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Correlation between viscoelasticity, microstructure, and molecular properties of zein and pennisetin melts
- 2012
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In: Journal of Applied Polymer Science. - : Wiley. - 1097-4628 .- 0021-8995. ; 125:3, s. 2245-2251
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Journal article (peer-reviewed)abstract
- Cereals are a large source of biopolymers, where mainly the starch is used for food and feed. A rapidly growing cereal application is the production of biofuel, mainly produced from corn in the US. The starch is fermented to ethanol leaving spent grain rich in cereal proteins as a by-product. The corn protein zein is currently extracted on a large scale and used in, for example, material applications. Similarly, pennisetin can be extracted from pearl millet, a crop critical for food security in sub-Saharan Africa. The formation of viscoelastic melts is crucial for (bio)plastics production and the viscoelasticity, microstructure, and molecular properties of zein and pennisetin melts were determined here. The proteins were mixed with plasticizers (polyethyleneglycol or glycerol/citric acid) to form melts. The melts displayed a phase separated microstructure with protein-rich and plasticizer-rich regions with distinctly separate Tgs. The pennisetin melts formed cross-links at temperatures above 60 degrees C, which could be related to the high content of cysteine and methionine, as compared to zein. As a consequence, pennisetin melts showed a more thermocomplex behavior than zein melts. For zein melts, the mixture of glycerol and citric acid interacted with protein in addition to being a plasticizer causing a high-molecular weight shoulder in the molecular weight distribution. The study showed that, although both zein and pennisetin form viscoelastic melts, the choice of plasticizer strongly affects both melt structure and physical properties.
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| 3. |
- Barreto, C., et al.
(author)
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Multiwall carbon nanotube/PPC composites: Preparation, structural analysis and thermal stability
- 2013
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In: European Polymer Journal. - : Elsevier BV. - 0014-3057 .- 1873-1945. ; 49:8, s. 2149-2161
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Journal article (peer-reviewed)abstract
- The focus of this report concerns the preparation nanocomposites from poly(propylene carbonate) (PPC) and multiwall carbon nanotubes (MWNTs). A solvent route using tetrahydrofuran, ethoxylated non- ionic surfactants combined with sonication was found to be successful in deagglomerating and dispersing the nanotubes. Transmission electron microscopy revealed highly disentangled and dispersed nanotubes and was supported by the qualitative stability evaluations. The morphology and molecular mobility of the prepared nanocomposites (0.5, 3.0 and 5.0 wt% of nanotubes) were characterized by rheology, microscopy, low-field solid-state nuclear magnetic resonance, and electrical conductivity. The networking of nanotubes was highest with a stearyl alcohol ethoxylate surfactant, and was found to improve with the sonication time. Nanotube percolation was established, both rheologically and electrically, from a filler content of approximately 0.5 wt%. A higher tendency toward particle agglomeration was observed at higher MWNT loadings. Only minor changes in the glass transition temperature were measured presumably due to the presence of solvent and surfactant residues. The thermal stability was marginally improved by increasing the loading and dispersion of the nanotubes, and appeared to be modified by solvent and surfactant residues.
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