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- 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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| 6. |
- Thunwall, Mats, 1973
(författare)
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On processing of thermoplastic starch
- 2005
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Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Starch is a biodegradable material produced in many different crop plants. Since it is biodegradable, inexpensive, generally has good barrier properties and comes from a renewable source it would be an ideal material to use in e.g. packaging applications. A major drawback is that starch is hygroscopic and that the mechanical and barrier properties are strongly affected by the water content. To decrease brittleness of starch materials, plasticisers, such as glycerol, can be used. By using starch from crops giving a desired chain constitution with regard to molecular weight, amount of branches and lengths of branches, problems associated with the hydrophobicity might be reduced. Starch consists of two polymers, amylose and amylopectin, the former is regarded as linear and the latter as branched. In this work, potato starches with two different amylose contents have been melt-processed with glycerol as plasticiser. The processing techniques used included extrusion and compression moulding. Of special interest was here the processability of the starches and the properties of final processed material. The characterisation techniques used were mainly capillary viscometry, mechanical testing and dynamic-mechanical analysis. Changes in the crystallinity were evaluated with x-ray diffraction. Processing of high amylose (HAP) materials was in general more difficult than materials with lower amylose contents. High moisture and glycerol contents combined with high shear rates, were required to melt the HAP-material sufficiently and turn it into thermoplastic sheets. The problems encountered included insufficient melt tenacity, pressure and flow fluctuations and clogging of the extruder die. The melt viscosities of HAP were higher than that of normal potato starch (NPS) at similar glycerol and moisture contents. By increasing the moisture content, the viscosities could however be reduced significantly. On the positive side, HAP-materials exhibited higher mechanical strength and stiffness. This was partly explained by a higher transition (softening) temperature observed for the HAP-material using dynamic mechanical analysis. Extruded and compression moulded samples appeared transparent and x-ray diffraction measurements indicated no crystallinity of the processsed sheets.
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| 10. |
- Thunwall, Mats, 1973
(författare)
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Thermoplastic processing of starch and cellulose-containing polymers
- 2007
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Starch and cellulose are two naturally occurring polymers that have the potential to reduce the dependence on fossil resources if used as replacements or as complements to synthetic polymers. There are however some problems associated with the use of these polymers that have to be addressed and solved. In this thesis, problems related to the processing of thermoplastic starch and cellulose-containing polymers are primarily in focus. Starch and cellulose are very similar in chemical structure but only starch can be processed thermoplastically, i.e. it can be melted and remelted again, provided that plasticizers, usually water and glycerol are present. Cellulose can on the other hand be used as a reinforcement in a synthetic polymer thus giving a composite material. Starch grades with different amylose contents and hydroxypropylated/oxidised starch were melt-processed together with glycerol and water as plasticizers. The processing techniques included extrusion, compression moulding and film blowing. The latter constituted a challenge but could be performed by optimising the processing conditions as well as the composition of the thermoplastic starch. The rheological behaviour of the starch melts were determined both in shear and in extension and the processed material was evaluated with respect to its mechanical and thermal performances. Further the influence of the processing on the morphology and the molecular structure was characterised. Cellulosic fibres with and without a clay coating were melt-blended with polypropylene or poly(lactic acid). The fibres were coated with non-delaminated or delaminated clay (nanoclay) with the aim to reduce the degree of fibre flocculation normally encountered with this type of systems. The morphology and the mechanical properties of injection-moulded or extruded composites were evaluated.In the case of starch processing, high amylose content materials were found to be more difficult to process but their mechanical performance was better. Though the melt tenacity of starch was quite low it was possible to produce films from starch by film-blowing. Moisture and glycerol content as well as temperature were identified as governing parameters for a successful processing of thermoplastic starch. The fibre flocculation in the cellulose-containing materials was reduced as a result of the coating of fibres with the clay.
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