| 1. |
- Altskär, Annika, et al.
(författare)
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Some effects of processing on the molecular structure and morphology of thermoplastic starch
- 2008
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Ingår i: Carbohydrate Polymers. - : Elsevier BV. - 0144-8617 .- 1879-1344. ; 71:4, s. 591-597
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Tidskriftsartikel (refereegranskat)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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| 9. |
- Arino, I., et al.
(författare)
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The Influence of the Measuring/Viewing Angle on the Color of Injection-Molded Plastics
- 2010
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Ingår i: International Journal of Polymeric Materials and Polymeric Biomaterials. - : Informa UK Limited. - 0091-4037 .- 1563-535X. ; 59:4, s. 292-306
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Tidskriftsartikel (refereegranskat)abstract
- A multi-angle spectrophotometer was used to measure the CIELab coordinates L∗, a∗ and b∗ in different angles relative to the incident light. The specimens used were acrylonitrile-butadiene-styrene injection-molded plaques in different colors and with different surface textures. Variations in the coordinates when changing the measuring angle depended on the color and the texture. In general, however, smooth (glossy) surfaces were measured to be darker and of higher chroma than textured surfaces and as the gloss of the surfaces decreased (due to texturing), the lightness of the surfaces increased and the absolute values of a∗ and b∗ decreased over the range of measuring angles (not too close to the specular reflection angle). A psychometric study involving a human test panel was used as a complement to the measurement. The agreement between the measurements and this study cannot be said to be satisfactory, unless the variation in the color coordinates was quite clear. Possible reasons are discussed.
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| 10. |
- Arino Marine, Ruth, 1980, et al.
(författare)
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Enhancing the electrical conductivity of carbon black/graphite nanoplatelets: Poly(ethylene-butyl acrylate) composites by melt extrusion
- 2016
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Ingår i: Journal of Applied Polymer Science. - : Wiley. - 1097-4628 .- 0021-8995. ; 133:3
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Tidskriftsartikel (refereegranskat)abstract
- The influence of processing parameters such as screw geometry, temperature profile, and screw speed on the electrical properties of hybrid composites consisting of graphite nanoplatelets and carbon black in ethyl butyl acrylate was studied. Two different screws were used to compound the hybrid composites at two different temperatures and two different screw speeds. A beneficial effect was noted with regard to the electrical properties when adding nanoplatelets to the filler system. The cause could be a synergistic effect due to the difference in particle shape of the two fillers. Lower percolation thresholds were obtained with the conventional screw due to less breakage of the graphite nanoplatelets compared to the barrier screw. No significant changes of the electrical properties were observed when changing the temperature profiles or the screw speeds. Furthermore, the melt viscosity of the compounds was not appreciably affected at the rather low filler contents used here.
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| 13. |
- Filli, Kalep, et al.
(författare)
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Development and characterization of extruded biodegradable foams based on zein and pearl millet flour
- 2011
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Ingår i: Annual Transactions the Nordic Rheology Society. ; 19, s. 139-145
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Konferensbidrag (refereegranskat)abstract
- The aim was to establish a preliminary processing window for extrusion foaming of blends of zein and pearl millet flour and to estimate the properties of the extrudates. The weight ratios of zein:pearl millet flour were 75:25, 72:28 or 70:30 and foamed extrudates with a circular geometry were produced with bulk densities between about 350 and slightly higher than 500 kg/m3. Compounds with a higher zein content tended to give a more foamed structure. The stiffness (modulus) in compression of the foams was in the range 25-50 MPa with higher values at a higher bulk density. At a given density, the specimens with a higher zein content appeared to give a stiffer structure.
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| 16. |
- Forsgren, Lilian, 1990, et al.
(författare)
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Composites with surface-grafted cellulose nanocrystals (CNC)
- 2019
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Ingår i: Journal of Materials Science. - : Springer Science and Business Media LLC. - 0022-2461 .- 1573-4803. ; 54:4, s. 3009-3022
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Tidskriftsartikel (refereegranskat)abstract
- Hydroxyazetidinium salts were used to surface-modify cellulose nanocrystals (CNC) by grafting the salts onto the sulphate ester groups on the CNC surfaces. The grafting was confirmed by ζ-potential measurements and by the thermal degradation behaviour of the modified CNC. The thermal stability (onset of degradation) of the CNC was improved by the surface modification (almost 100 °C). Composites containing surface-modified or unmodified CNC (0.1, 1.0 and 10 wt%) with an ethylene-based copolymer as matrix were produced by compression moulding. The thermal stability of the composites was not, however, markedly improved by the surface grafting onto the CNC. It is suggested that this is due to a degrafting mechanism, associated with the alkaline character of the system, taking place at high temperatures. Model experiments indicated, however, that this did not occur at the conditions under which the composites were produced. Furthermore, in the case of a reference based on pH-neutralised polymeric system and modified CNC, an upward shift in the onset of thermal degradation of the composite was observed. The addition of the CNC to the polymer matrix had a strong influence of the mechanical performance. For example, the tensile modulus increased approximately three times for some systems when adding 10 wt% CNC. The surface grafting of the hydroxyazetidinium salts appeared mainly to affect, in a positive sense, the yield behaviour and ductility of the composites. The results of the mechanical testing are discussed in terms of interactions between the grafted units and the matrix material and between the grafted groups.
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| 17. |
- Forsgren, Lilian, 1990, et al.
(författare)
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Injection Molding and Appearance of Cellulose-Reinforced Composites
- 2019
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Ingår i: Polymer Engineering and Science. - : John Wiley and Sons Inc.. - 0032-3888 .- 1548-2634. ; 60:1, s. 5-12
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Tidskriftsartikel (refereegranskat)abstract
- Composite materials based on an ethylene-acrylic acid (EAA) copolymer and 20 wt% cellulose fibers were compounded by two runs in a twin-screw extruder. The composite material with cellulose fibers (CF) and a reference of unfilled EAA were injection molded into plaques using three different temperature profiles with end zone temperatures of 170°C, 200°C, and 230°C. The injection molded samples were then characterized in terms of their mechanical properties, thermal properties, appearance (color and gloss), and surface topography. The higher processing temperatures resulted in a clear discoloration of the composites, but there was no deterioration in the mechanical performance. The addition of cellulose typically gave a tensile modulus three times higher than that of the unfilled EAA, but the strength and strain at rupture were reduced when fibers were added. The processing temperature had no significant influence on the mechanical properties of the composites. Gloss measurements revealed negligible differences between the samples molded at the different melt temperatures but the surface smoothness was somewhat higher when the melt temperature was increased. In general, addition of the cellulose to the EAA reduced the gloss level and the surface smoothness.
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| 18. |
- Forsgren, Lilian, 1990, et al.
(författare)
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Water-assisted extrusion and injection moulding of composites with surface-grafted cellulose nanocrystals – An upscaling study
- 2021
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Ingår i: Composites Part B: Engineering. - : Elsevier BV. - 1359-8368. ; 208
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Tidskriftsartikel (refereegranskat)abstract
- The large-scale surface modification of cellulose nanocrystals (CNC) was carried out to produce CNC-containing composites, in a scale of 3 kg, using industrial-scale melt processing techniques such as twin-screw extrusion and injection moulding. Two different polymer matrices, ethylene-acrylic acid copolymer (EAA) and low-density polyethylene (LDPE), were reinforced with 10 wt% unmodified cellulose nanocrystals (CNC) or surface-treated CNC, where a 2-hydroxyproyl-N-diallyl group had been grafted onto the sulphate half-ester groups on the CNC surfaces. This was achieved by mixing an aqueous CNC dispersion and the polymer pellets directly in the twin-screw extruder followed by a second dry compounding step prior to shaping by injection moulding. The injection-moulded materials were characterized with respect to their mechanical properties and thermal stability. The addition of 10 wt % CNC resulted in all cases in an increase in the yield strength and stiffness by 50–100%, most significantly for the EAA based composites. There were indications of the presence of a stable interphase and a percolating network in the EAA-based materials, according to dynamic-mechanical measurements. A reduction in thermal stability was observed for the melt-processed samples containing diallyl-modified CNC and discoloration in the EAA based samples.
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| 19. |
- Härdelin, Linda, 1977, et al.
(författare)
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Hemicellulose foam
- 2014
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Ingår i: Proc Materials for Tomorrow. ; , s. Nr 24-
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Konferensbidrag (övrigt vetenskapligt/konstnärligt)
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| 24. |
- Iannuzzi, Giovanna, 1977, et al.
(författare)
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Color changes due to thermal ageing and artificial weathering of pigmented and textured ABS
- 2013
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Ingår i: Polymer Engineering and Science. - : Wiley. - 0032-3888 .- 1548-2634. ; 53:8, s. 1687-1695
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Tidskriftsartikel (refereegranskat)abstract
- Acrylonitrile-butadiene-styrene copolymers (ABS) are known to be sensitive towards ageing which can lead to color changes, primary interest in this study. The color changes were expressed in terms of the CIELAB color system. ABS plaques were subjected to heat ageing and artificial weathering. Uncolored ABS and dark gray colored specimens were employed. The pigmented ABS plaques were also imposed with different surface textures. In general, the uncolored material suffered from the most severe discoloration and the artificial weathering produced the strongest effect. For both types of specimens, a clear yellowing took place. Both the pigment system and the surface texture affected the color development during the ageing test. The latter can be of significant importance in certain applications when components with different surface textures are placed adjacent to each other. The surface micro-hardness increased with increasing ageing time and its change followed that of the discoloration. Chemical changes of the surface layers were characterized by FTIR and were in accordance with results reported in the literature; i.e., an increase of the bands associated with carbonyl groups with increasing ageing time and a decrease of the bands associated with the polybutadiene phase clearly indicated chemical degradation due to ageing treatments.
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