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- Lôpez-Rubio, A., et al.
(author)
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Enhanced film forming and film properties of amylopectin using micro-fibrillated cellulose
- 2007
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In: Carbohydrate Polymers. - : Elsevier BV. - 0144-8617 .- 1879-1344. ; 68:4, s. 718-727
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Journal article (peer-reviewed)abstract
- This work describes a novel approach to produce amylopectin films with enhanced properties by the addition of micro fibrillated cellulose (MFC). Aqueous dispersions of gelatinized amylopectin, glycerol (0-38 wt%) and MFC (0-10 wt%) were cast at ambient temperature and 50% relative humidity and, after 10 days of storage, the tensile properties were investigated. The structure of the composite films was revealed by optical, atomic force and transmission electron microscopy. The moisture content was determined by thermogravimetry and the temperature-dependent film rigidity was measured by thermal mechanical analysis. Synchrotron simultaneous small- and wide-angle X-ray measurements revealed that the solutions had to be heated to above 85 degrees C in order to achieve complete gelatinization. Optical microscopy and atomic force microscopy revealed uniformly distributed MFC aggregates in the films, with a length of 10-90 mu m and a width spanning from a few hundred nanometers to several microns. Transmission electron microscopy showed that, in addition to aggregates, single MFC microfibrils were also embedded in the amylopectin matrix. It was impossible to cast antylopectin films of sufficient quality with less than 38 wt% glycerol. However, when MFC was added it was possible to produce high quality films even without glycerol. The film without glycerol was stiff and strong but not brittle. It was suggested that this remarkable effect was due to its comparatively high moisture content. Consequently MFC acted both as a "conventional" reinforcement because of its fibrous structure and also indirectly as a plasticiser because its presence led to an increase in film moisture content.
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- Ritums, J. E., et al.
(author)
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Mechanical properties of high-density polyethylene and crosslinked high-density polyethylene in crude oil and its components
- 2006
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In: Journal of Polymer Science Part B. - : Wiley. - 0887-6266 .- 1099-0488. ; 44:4, s. 641-648
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Journal article (peer-reviewed)abstract
- 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.
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