| 1. |
- Agfors, Gunnar, et al.
(författare)
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KEMI : den gränslösa vetenskapen
- 2011
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Bok (populärvet., debatt m.m.)abstract
- Kemi – handlar inte det bara om farliga ämnen och onödiga tillsatser? Det är kanske bildenmånga har av kemi, men faktum är att utan kemi skulle vi inte ha det höga välstånd vi har i dag.Tack vare kemisk kunskap har vi tillgång till läkemedel som botar sjukdomar och lindrar smärta– med hjälp av syntetiska antibiotika kan infektionssjukdomar som tidigare var dödliga botas,magsår kan behandlas utan dyra och plågsamma operationer och många cancerformer kanframgångsrikt behandlas med syntetiska preparat. Konstgödsel och medel som hindrar skadeinsektergör att skördar kan ökas och svälten i världen därigenom begränsas. Tack vare kemin harvi även tillgång till alla de material vi behöver för att tillverka allt från kläder, rengöringsprodukteroch kosmetika till bilar, TV-apparater och reservdelar till kroppen. Det är genom kemisk syntes vikan framställa dessa och alla de övriga produkter vi behöver för vårt dagliga liv och det är keminsom visar vägen till hållbar produktion som utnyttjar förnybara råvaror och ger minimala mängderavfall. Kemisk kunskap är också oumbärlig för utveckling av nanoteknik och medicinskdiagnostik och andra till kemin angränsande områden. Kemin bidrar alltså till att finna lösningartill många av de komplexa globala problem vi står inför: hälsa, klimat, brist på råvaror, utnyttjandetav nya energikällor och tillgång till livsmedel för att föda jordens ökande befolkning. DET ÄR OM ALLT DETTA DEN HÄR BOKEN HANDLAR.
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| 2. |
- Ankerfors, Caroline, et al.
(författare)
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A comparison of polyelectrolyte complexes and multilayers : Their adsorption behaviour and use for enhancing tensile strength of paper
- 2009
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Ingår i: Nordic Pulp & Paper Research Journal. - 0283-2631 .- 2000-0669. ; 24:1, s. 77-86
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Tidskriftsartikel (refereegranskat)abstract
- This paper compares the adsorption behaviour and paper-strength-enhancing properties of polyelectrolyte complexes (PECs) and polyelectrolyte multilayers (PEMs) of polyallylamine hydrochloride and polyacrylic acid. Model adsorption experiments using SPAR (stagnation point adsorption reflectometry) and QCM-D (quartz crystal microbalance with dissipation) showed that the amount of complexes adsorbed was lower than the amount adsorbed when forming a multilayer using the same polymer system. From these experiments, in combination with AFM and ESEM imaging, it was concluded that the PEC adsorption stopped before full surface coverage was reached. Tensile testing of handsheets treated with PECs and PEM showed a significant increase in both tensile index and strain-at-break using both systems. The largest strength improvement was achieved with the fibres treated with the largest number of PEMs, but the largest effect per adsorbed amount of polymer was achieved by PEC treatment.
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| 3. |
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| 4. |
- Ankerfors, Caroline, et al.
(författare)
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Using jet mixing to prepare polyelectrolyte complexes : Complex properties and their interaction with silicon oxide surfaces
- 2010
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Ingår i: Journal of Colloid and Interface Science. - : Elsevier BV. - 0021-9797 .- 1095-7103. ; 351:1, s. 88-95
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Tidskriftsartikel (refereegranskat)abstract
- The influence of mixing procedure on the properties of polyelectrolyte complexes (PECs) was investigated using two complexation techniques, polyelectrolyte titration and jet mixing, the latter being a new method for PEC preparation. For the low-molecular-weight polyelectrolytes polyacrylic acid (PAA) and polyallyl amine hydrochloride (PAH), shorter mixing times produced smaller PECs, whereas for higher molecular weights of the same polyelectrolytes, PEC size first decreased with decreasing mixing time to a certain level, after which it started increasing again. This pattern was likely due to the diffusion-controlled formation of "pre-complexes", which, in the case of low-molecular-weight polymers, occurs sufficiently quickly to form stable complexes; when polyelectrolytes are larger, however, non-equilibrium pre-complexes, more prone to aggregation, are formed. Comparing the techniques revealed that jet mixing produced smaller complexes, allowing PEC size to be controlled by mixing time, which was not the case with polyelectrolyte titration. Higher polyelectrolyte concentration during jet mixing led to the formation of larger PECs. It was also demonstrated that PEC size could be changed after preparation: increasing the pH of the PEC dispersion led to an irreversible increase in PEC size, whereas lowering the pH did not influence PEC size. The adsorption behavior of PECs formed from weak polyelectrolytes on model substrates was studied using QCM-D, SPAR, and AFM imaging; the results indicated that increasing the pH increased the amount of PECs adsorbed to model surfaces. However, the amount of PECs adsorbed to the model surfaces was low compared with other systems in all studied cases.
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| 5. |
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| 6. |
- Fall, Andreas, et al.
(författare)
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Colloidal Stability of Aqueous Nanofibrillated Cellulose Dispersions
- 2011
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Ingår i: Langmuir. - : American Chemical Society (ACS). - 0743-7463 .- 1520-5827. ; 27:18, s. 11332-11338
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Tidskriftsartikel (refereegranskat)abstract
- Cellulose nanofibrils constitute an attractive raw material for carbon-neutral, biodegradable, nanostructured materials. Aqueous suspensions of these nanofibrils are stabilized by electrostatic repulsion arising from deprotonated carboxyl groups at the fibril surface. In the present work, a new model is developed for predicting colloidal stability by considering deprotonation and electrostatic screening. This model predicts the fibril-fibril interaction potential at a given pH in a given ionic strength environment. Experiments support the model predictions that aggregation is induced by decreasing the pH, thus reducing the surface charge, or by increasing the salt concentration. It is shown that the primary mechanism for aggregation upon the addition of salt is the surface charge reduction through specific interactions of counterions with the deprotonated carboxyl groups, and the screening effect of the salt is of secondary importance.
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| 7. |
- Nordenström, Malin
(författare)
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Colloidal interactions and arrested dynamics of cellulose nanofibrils
- 2020
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Over the past decades, concerns for the environment have increased and efforts to achieve a sustainable society have intensified. One particular challenge is to replace fossil-based plastics with biodegradable materials produced from renewable resources. Cellulose nanofibril (CNF)-based materials are strong candidates due to their excellent mechanical properties, nano-dimensions and molecular structure, which is suitable for modification. CNFs can be obtained from wood and are elongated, often charged, particles which are usually handled in aqueous dispersions. The colloidal stability is sensitive, and instability results in aggregation or transition to an arrested state. Since the properties of CNF-based materials rely on dispersion of the CNFs, an understanding of the colloidal behaviour is crucial.This work has focused on the interactions and dynamics of CNFs in different colloidal states. Arrested states of CNFs were studied in detail and it was found that two types of arrested state exist, with different colloidal interactions and mechanisms governing their formation. The dynamics in arrested and dispersed states were studied by tracer diffusion measurements, and it was found that small amounts of CNFs can constitute an excellent stabiliser for other particle dispersions according to a so far unexplored mechanism.The effects of altering the colloidal interactions using different strategies were also evaluated. The counterions of CNFs were exchanged and the impact on the swelling behaviour was measured. Based on the results, different contributions to the counterion-dependent interactions are discussed. Two strategies for using polymers to alter the interactions were furthermore studied. Polyethylene glycol (PEG) was grafted to CNFs in order to increase the arrested state threshold concentration. PEG, carboxymethyl cellulose and lignin, were also used as additives which improved the redispersion of dried CNF, especially in the case of samples containing lignin.
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| 8. |
- Nordenström, Malin, et al.
(författare)
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Colloidal interactions in nanocellulose systems
- 2016
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Ingår i: Abstracts of Papers of the American Chemical Society. - : AMER CHEMICAL SOC. - 0065-7727. ; 251
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Tidskriftsartikel (övrigt vetenskapligt/konstnärligt)
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| 9. |
- Ondaral, Sedat, et al.
(författare)
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Surface-Induced Rearrangement of Polyelectrolyte Complexes : Influence of Complex Composition on Adsorbed Layer Properties
- 2010
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Ingår i: Langmuir. - : American Chemical Society (ACS). - 0743-7463 .- 1520-5827. ; 26:18, s. 14606-14614
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Tidskriftsartikel (refereegranskat)abstract
- The adsorption characteristics of two different types of polyelectrolyte complexes (PECs). prepared by mixing poly(allylamine hydrochloride) and poly(acrylic acid) in a confined impinging jet (CIJ) mixer, have been investigated with the aid of stagnation point adsorption reflectometry (SPAR), a quartz crystal microbalance with dissipation (QCM-D), and atomic force microscopy (A FM) using SiO2 surfaces The two sets of PEC were prepared by combining high molecular mass PAH/FAA (PEC-A) and low molt:cubit mass PAH/PAA (PEC-B) The PEC-A showed a higher adsorption to the SiO2 surfaces than the PEC-B The adsorption of the PEC-A also showed a larger change in the dissipation (AD), according to the QCM-D measurements, suggesting that the adsorbed layer of these complexes had a relatively lower viscosity and a lower shear modulus Complementary investigations of the adsorbed layer using A FM imaging showed that the adsorbed layer of PEC-A was significantly different from that of PEC-B and that the changes in properties with adsorption time were very different for the two types of PECs The PEC-A complexes showed a coalescence into larger block of complexes on the SiO2 surface, but this was not detected with the PEC-B The size determinations of the complexes in solution showed that they were very stable over time, and it was therefore concluded that the coalescence of the complexes was induced I the interaction between the complexes and the surface The results also indicated that polyelectrolytes can migrate between the different complexes adsorbed to the surface The results also give indications that the preparation of PEC-B leads to the formation of two different types of polyelectrolyte complexes differing in the amount of polymer in the complexes: i.e., two populations of complexes were formed with similar sizes but with totally different adsorption structures at the solid-liquid interface.
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| 10. |
- Åvitsland, G.A., et al.
(författare)
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AKD sizing of TCP and ECF bleached birch pulp characterized by peroxide edge wicking index
- 2006
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Ingår i: Nordic Pulp and Paper Research Journal. - : Walter de Gruyter GmbH. - 0283-2631 .- 2000-0669. ; 21:2, s. 237-244
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Tidskriftsartikel (refereegranskat)abstract
- To study the impact of extractable materials and xylan on the sizing efficiency of totally chlorine-free (TCF) bleached birch pulp and elemental-chlorine-free (ECF) bleached birch pulp, several pulps with different amounts of extractable material were studied. The content of extractable material in the pulp was shown to be detrimental for sizing efficiency, measured both as Cobb60 values and edge penetration in a model liquid packaging board, and a higher content of extractable material causes a reduced sizing efficiency for a given pulp. No significant difference was observed between extracted TCF and ECF bleached birch pulps, while unextracted pulps containing the same amount of extractable material yielded different sizing efficiencies. The TCF bleached birch pulp had a lower sizing efficiency than did the ECF bleached birch, probably because of differences in the fatty acid composition. A greater amount of extractable material also resulted in a smaller fraction of non-extractable alkyl ketene dimers (AKD) relative to the total amount of AKD in the sheet. Enzymatic removal of xylan and thus the reduction of the surface charge had no measurable effect on sizing efficiency. Extracted TCF and ECF bleached pulps only need a content of 0.05 kg/ton non-extractable AKD or 0.08 kg/ton total AKD in the sheets produced to achieve a good sizing effect.
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