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- Iselau, Frida, 1979, et al.
(författare)
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Competitive adsorption of amylopectin and amylose on cationic nanoparticles: a study on the aggregation mechanism
- 2016
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Ingår i: Soft Matter. - : Royal Society of Chemistry (RSC). - 1744-6848 .- 1744-683X. ; 12:14, s. 3388-3397
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Tidskriftsartikel (refereegranskat)abstract
- In this study we investigate the interactions between cationic nanoparticles and anionic starch, where the starch was composed of 20 wt% of amylose, a linear polymer, and 80 wt% of amylopectin, a branched polymer. The mechanism of aggregation was investigated by scattering techniques. It was found that the cationic particles formed large aggregates with the starch as a result of selective adsorption of the amylopectin. Amylose did not participate significantly in the aggregate formation even when the charge ratio of starch to particles was <1. For starch to particle ratio 41 stabilization was recovered mostly due to the large hindrance brought about by the highly branched amylopectin. This results in a shift of the stabilization mechanism from electrostatic to electrosteric. The internal structure of the aggregates was composed of primary particles with starch coils adsorbed on the surface. This information supports the proposed aggregation mechanism, which is based on adsorption of the negatively charged starch in patches on the positively charged nanoparticles causing attractive interaction between the particles.
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| 2. |
- Iselau, Frida, 1979, et al.
(författare)
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Formation and relaxation kinetics of starch-particle complexes
- 2016
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Ingår i: Soft Matter. - 1744-6848 .- 1744-683X. ; 12:47, s. 9509-9519
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Tidskriftsartikel (refereegranskat)abstract
- The formation and relaxation kinetics of starch-particle complexes were investigated in this study. The combination of cationic nanoparticles in suspension and anionic starch in solution gave rise to aggregate formation which was studied by dynamic light scattering, revealing the initial adsorption of the starch molecules on the particle surface. By examining the stability ratio, W, it was found that even in the most destabilized state, i.e. at charge neutralization, the starch chains had induced steric stabilization to the system. At higher particle and starch concentrations relaxation of the aggregates could be seen, as monitored by a decrease in turbidity with time. This relaxation was evaluated by fitting the data to the Kohlrausch-Williams-Watts function. It was found that irrespective of the starch to particle charge ratio the relaxation time was similar. Moreover, a molecular weight dependence on the relaxation time was found, as well as a more pronounced initial aggregated state for the higher molecular weight starch. This initial aggregate state could be due to bridging flocculation. With time, as the starch chains have relaxed into a final conformation on the particle surface, bridging will be less important and is gradually replaced by patches that will cause patchwise flocculation. After an equilibration time no molecular weight dependence on aggregation could be seen, which confirms the patchwise flocculation mechanism.
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| 3. |
- Iselau, Frida, 1979
(författare)
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Towards a mechanism for surface hydrophobization of paper - Effect of combinations of polyelectrolytes and polymer particles
- 2016
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Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Paper materials are cost effective and light weighted, they can easily be recycled and their use as an alternative to plastics is advantageous from an environmental andsustainability perspective. However, competing with plastics for packaging applications is a challenge for cellulosic products. The material needs to be strong and stiff also when exposed to liquids or moisture during transportation and storage. To achieve this for paper materials, which are intrinsically hydrophilic due to thenature of the cellulose, they need to be hydrophobized.Packaging paper materials are often made from recycled fibers. The constitution of the paper matrix can therefore vary a lot and the addition of hydrophobic compoundsto the pulp in the paper production process is difficult to optimize. Therefore the recent development in paper hydrophobization has been towards Surface modification, so-called surface sizing. There is a plethora of surface sizing Products and these products are very efficient in making the paper surface more water resistant, but there is a lack of fundamental knowledge on how they work. The aim of this licentiate project, which can be regarded as the first part of a doctoral thesis work, is to explore and identify which physicochemical properties of the formulation used for surface sizing are governing the efficiency.In surface sizing the particle suspension is first mixed with starch in solution. Starchparticles and starch is the subject of one study described in this thesis. In this studythe interactions between starch and three types of particles, differing in the type of stabilizer used, are explored. The different stabilizers rendered the particles cationic, anionic or amphoteric. It was found that the cationic particles formed aggregates with the starch and that it is mainly the high molecular weight, highly branchedamylopectin fraction of the starch that participates in the aggregation. The aggregate formation, as well as the relaxation kinetics, are also investigated and it wasconcluded that the amylopectin chains give rise to steric stabilization even at the mostdestabilized state, i.e. at maximum aggregation. The relaxation kinetics is found tobe molecular weight dependent while the equilibrated state is not, leading to a proposed aggregation mechanism based on patchwise flocculation. Finally the efficiency in reducing the water uptake of test paper sheets is assessed.The cationic particles are the most efficient in decreasing the water uptake and the efficiency is enhanced by aggregation.
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