| 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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| 2. |
- Elfstrand, Lidia, et al.
(författare)
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Changera in starch structure during manufacturing of starch microspheres for use in parenteral drug formulations: Effects of temperature treatment
- 2009
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Ingår i: Carbohydrate Polymers. - : Elsevier BV. - 0144-8617. ; 75:1, s. 157-165
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Tidskriftsartikel (refereegranskat)abstract
- Starch microspheres were produced by emulsification of a starch dispersion in an aqueous polyethylene glycol (PEG) solution. Crystalline/ordered structure was formed within these starch droplets during incubation at 6 °C for 25 h followed by incubation at 37 °C for 28 h. After incubation at 37 °C the crystalline structure in the samples was of type B. The crystallization process of microspheres was compared with crystallization in a model system. The crystalline structure of the microspheres melted at temperatures almost 20 °C lower than in the model system incubated under the same conditions, as determined by differential scanning calorimetry. It was thus concluded that the crystallization process within microspheres was different than that of bulk starch and the ability of the starch molecules to reorganize themselves within the dispersed starch phase of an aqueous two-phase system at the higher incubation temperature was limited. It was also observed that the presence of PEG or carbonate buffer protected the molecular order formed by the starch molecules during incubation from breakdown during freeze-drying.
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| 3. |
- Elfstrand, Lidia, et al.
(författare)
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Recrystallization of waxy maize starch during manufacturing of starch microspheres for drug delivery: Influence of excipients
- 2007
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Ingår i: Carbohydrate Polymers. - : Elsevier BV. - 0144-8617. ; 69:4, s. 732-741
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Tidskriftsartikel (refereegranskat)abstract
- The formation of ordered structure, such as crystallites, in starch was studied by means of differential scanning calorimetry (DSC). The influence of time/temperature treatment and additives such as polyethylene glycol (PEG), bovine serum albumin (BSA) and a carbonate buffer on the formation was investigated. The experiments were planned with a CCC (Central Composite Circumscribed) design. For all three investigated systems it could be concluded that the incubation time at 6 °C was the decisive factor for the amount of ordered structure obtained during the incubation, while the incubation time at 37 °C was the decisive factor for the thermal stability of the crystallites as expressed by Ton, Tm and Tc. The additives seemed to mainly affect the nucleation phase of crystallization process. The additives decreased the time required in order to obtain a certain level of ordering in the incubated starch samples. The carbonate buffer decreased the amount of ordered structure in starch as judged by DSC enthalpy values, while increasing the melting temperature of these structures. The additives PEG and BSA lowered the melting temperatures of the starch in the systems but increased the enthalpy values. By optimization procedure a specific amount of ordered structure with desired thermal characteristics could be predicted.
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| 4. |
- Elfstrand, Lidia, et al.
(författare)
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Recrystallization of waxy maize starch during manufacturing of starch microspheres for drug delivery: Optimization by experimental design
- 2007
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Ingår i: Carbohydrate Polymers. - : Elsevier BV. - 0144-8617. ; 68:3, s. 568-576
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Tidskriftsartikel (refereegranskat)abstract
- Gelatinized starch/water dispersions with a water content of 70% w/w were studied in order to evaluate the influence of the incubation time at two fixed temperatures (6 and 37 degrees C) on the recrystallization behavior. The starch material was produced from waxy maize starch by acid hydrolysis followed by a mechanical treatment, i.e. a high pressure homogenization. Empirical models for the recrystallization of the model starch dispersions were investigated by using a central composite circumscribed (CCC) design in two factors involving I I trials. The rebuilt crystalline structure was estimated by measuring the melting transition parameters with differential scanning calorimetry (DSC). The designed models for the melting enthalpy, the melting transition temperatures, and the melting interval as the responses were reproducible and predictable and the results were analyzed by using a response surface modeling. Operative conditions for the formation of the most thermally stable crystalline structure with the highest possible crystallinity were determined. It was also concluded that the decisive factor for the crystallinity of the given starch material was a prolonged storage at 6 'C, while thermal characteristics of the crystallites could be controlled by storage at 37 degrees C. An interaction effect was observed between the incubation time at these two experimental temperatures regarding enthalpy values and the melting interval of the samples. (c) 2006 Elsevier Ltd. All rights reserved.
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| 5. |
- Erkselius, Stefan, et al.
(författare)
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Free radical degradation of hydroxyethyl cellulose
- 2005
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Ingår i: Carbohydrate Polymers. - : Elsevier BV. - 0144-8617. ; 62:4, s. 344-356
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Tidskriftsartikel (refereegranskat)abstract
- The degradation of hydroxyethyl cellulose (HEC) using sodium persulfate (NaPS) as free radical generator was studied at 60, 70 and 80 degrees C with different NaPS/HEC ratios. During the degradation reaction samples were withdrawn at regular intervals. The amount of persulfate remaining was analyzed by titration and the evolution of the HEC molecular weight distribution and viscosity was followed using size exclusion chromatography (SEC) and rheology, respectively. The results show how the molecular weight of HEC is decreased by varying the NaPS/HEC ratio, reaction time and temperature. It was found that the NaPS/HEC ratio must be kept low in order to maintain the control of the degradation process, since when the NaPS/HEC ratio was too high the degradation rate of HEC was too fast, and the molecular weight distribution became bimodal. Additionally, the decomposition rate of NaPS was found to be independent of pH in the range between pH 2 and 7. (c) 2005 Elsevier Ltd. All rights reserved.
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| 6. |
- Gallstedt, M., et al.
(författare)
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Packaging-related mechanical and barrier properties of pulp-fiber-chitosan sheets
- 2006
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Ingår i: Carbohydrate Polymers. - : Elsevier BV. - 0144-8617 .- 1879-1344. ; 63:1, s. 46-53
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Tidskriftsartikel (refereegranskat)abstract
- In order to investigate ways of incorporating an oxygen- or air-barrier component, in this case chitosan or chitosan-acetic acid salt (chitosan salt), at an early stage in the paper-making process, sheets of chitosan and pulp fiber were produced in a hand sheet mould or solution cast in petri dishes. Some sheets were buffered in an alkaline solution, in order to reduce the moisture sensitivity. The sheets were characterized with respect to air permeance, oxygen permeability, fracture stress and strain, young's modulus and moisture content. The addition of the chitosan solution to the pulp slurry led to a substantial loss of fiber and chitosan through the wire screen and consequently a low grammage and high sheet porosity and air permeance. Forming a wet pulp fiber sheet before introducing the chitosan solution increased the grammage and the amount of remaining chitosan, the latter revealed by infrared spectroscopy. In addition, pressing the sheets before drying reduced the porosity and the air permeance. Air mixing, included in conventional laboratory sheet making, yielded a more heterogeneous sheet and inferior mechanical and barrier properties. In general, the paper sheets prepared in the hand sheet mould became weaker, softer and less ductile with increasing content of chitosan. Only solution casting in petri dishes resulted in good barrier properties. Scanning electron microscopy showed that holes were absent in this case. In addition, optical microscopy and infrared spectroscopy revealed that the chitosan-salt formed a continuous phase and that it was uniformly distributed in the sheet. Interestingly, the problem of shrinkage when chitosan salt sheets are buffered for improved high-moisture gas-barrier proper-ties, was reduced significantly by the restraining action of the pulp fibers.
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| 7. |
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| 8. |
- Goetz, Lee, et al.
(författare)
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A novel nanocomposite film prepared from crosslinked cellulosic whiskers
- 2009
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Ingår i: Carbohydrate Polymers. - : Elsevier BV. - 0144-8617 .- 1879-1344. ; 75:1, s. 85-89
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Tidskriftsartikel (refereegranskat)abstract
- Cellulose whiskers are increasingly being used as a reinforcing phase in polymer systems and their use is a growing area of importance in bionanocomposite research. Although the reinforcing effect of cellulose whiskers has been studied in various polymers, the impact of crosslinking cellulose whiskers has not been explored so far. This work deals with the development of novel cellulose nanocomposites, wherein the cellulose nanowhiskers are crosslinked with poly(methyl vinyl ether-co-maleic acid) and poly(ethylene glycol). The morphology of the nanocomposite was studied using atomic force microscopy (AFM), which revealed a network structure embedded in a continuous phase. The water sorption studies demonstrated that the crosslinked nanocomposites are capable of absorbing up to ~ 900% water and have potential to be used as hydrogels.
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| 9. |
- Hedin, Jesper, 1980, et al.
(författare)
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UV Induced Cross-linking of Starch Modified with Glycidyl Methacrylate
- 2009
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Ingår i: Carbohydrate Polymers. - : Elsevier BV. - 0144-8617. ; 79:3, s. 606-613
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Tidskriftsartikel (refereegranskat)abstract
- A new way to substitute cornstarch with glycidyl methacrylate (GMA) monomers is presented. This synthetic modification, carried out in DMSO, resulted in a DOS of 0.08. By exposing a water solution with modified starch and potassium persulfate (KPS), a radical initiator, to UV-light a free radical vinyl polymerization reaction is initiated making the starch solution chemically cross-link into a gel. The GMA modification increased the hydrophobicity of the polymer making it less water-soluble, increasing the adsorption tendency to a hydrophobic surface as seen in quartz crystal microbalance with dissipation monitoring (QCM-D) studies. The surface cross-linking process of the modified starch showed that after cross-linking the solubility of the polymer decreased resulting in a stronger adsorbed polymer to the surface compared to the non-modified starch. This proves that even though it is generally believed to be more difficult to cross-link polymers at surfaces this particular modification allowed for near complete cross-linking as suggested by the QCM-D data.
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| 10. |
- Karlberg, Maria, et al.
(författare)
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Solubility of amylose/ionic surfactant complexes in dilute aqueous solutions: Dependence on surfactant concentration
- 2007
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Ingår i: Carbohydrate Polymers. - : Elsevier BV. - 0144-8617. ; 70:3, s. 350-354
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Tidskriftsartikel (refereegranskat)abstract
- The solubility in dilute aqueous solutions of amylose complexed with ionic surfactants has been investigated by turbidity measurements. The turbidity depended on both the amylose and the surfactant concentrations. Low and high surfactant concentrations resulted in macroscopic phase separation, while mixtures at intermediate surfactant concentrations remained monophasic for at least one month. The solubility of the complexes was sensitive to the addition of salt as well as to the surfactant charge and hydrophobic chain length. These results are interpreted in terms of an electrostatic stabilisation of soluble complexes. Complexes with a non-ionic surfactant were not soluble at any mixing ratio. (c) 2007 Elsevier Ltd. All rights reserved.
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