| 1. |
- Lidenmark, Cecilia, 1976-, et al.
(författare)
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The adhesive behavior of extracted latex polymers towards silicon oxide and cellulose
- 2013
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Ingår i: International Journal of Adhesion and Adhesives. - : Elsevier. - 0143-7496 .- 1879-0127. ; 44, s. 250-258
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Tidskriftsartikel (refereegranskat)abstract
- The objective with this work is to compare the adhesive behavior for latex polymers of different glass transition temperatures (T-g) at different length scales and with different contact times. This is accomplished by two techniques: AFM colloidal probe force measurements and JKR-measurements. The aim is to compare the results from these two techniques and relate them to the interaction of the latex polymers towards oxidized silicon wafers and silica/cellulose probes. Theory suggests that altering the short timeframes used in the colloidal probe technique does not affect the ranking of the adhesion for the different polymers, but for the macroscopic JKR-technique it influences the measured work of adhesion. It is therefore important to let the system reach a steady state before assuming complete spreading and adhesion. AFM and JKR measurements showed the same trends where the polymer with lowest content of styrene has the lowest T-g and the highest adhesion, due to the larger polymer chain mobility.
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| 2. |
- Norgren, Magnus, et al.
(författare)
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Smooth model surfaces from lignin derivatives. II. Adsorption of polyelectrolytes and PECs monitored by QCM-D
- 2007
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Ingår i: Langmuir. - : American Chemical Society (ACS). - 0743-7463 .- 1520-5827. ; 23:7, s. 3737-3743
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Tidskriftsartikel (refereegranskat)abstract
- For the first time to the knowledge of the authors, well-defined and stable lignin model surfaces have been utilized as substrates in polyelectrolyte adsorption studies. The adsorption of polyallylamine (PAH), poly(acrylic acid) (PAA), and polyelectrolyte complexes (PECs) was monitored using quartz crystal microgravimetry with dissipation (QCM-D). The PECs were prepared by mixing PAH and PAA at different ratios and sequences, creating both cationic and anionic PECs with different charge levels. The adsorption experiments were performed in 1 and 10 mM sodium chloride solutions at pH 5 and 7.5. The highest adsorption of PAH and cationic PECs was found at pH 7.5, where the slightly negatively charged nature of the lignin substrate is more pronounced, governing electrostatic attraction of oppositely charged polymeric substances. An increase in the adsorption was further found when the electrolyte concentration was increased. In comparison, both PAA and the anionic PEC showed remarkably high adsorption to the lignin model film. The adsorption of PAA was further studied on silica and was found to be relatively low even at high electrolyte concentrations. This indicated that the high PAA adsorption on the lignin films was not induced by a decreased solubility of the anionic polyelectrolyte. The high levels of adsorption on lignin model surfaces found both for PAA and the anionic PAA-PAH polyelectrolyte complex points to the presence of strong nonionic interactions in these systems.
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| 3. |
- Notley, Shannon M., et al.
(författare)
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Adsorption of a strong polyelectrolyte to model lignin surfaces
- 2008
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Ingår i: Biomacromolecules. - : American Chemical Society (ACS). - 1525-7797 .- 1526-4602. ; 9:7, s. 2081-2086
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Tidskriftsartikel (refereegranskat)abstract
- The adsorption of a strong, highly charged cationic polyelectrolyte to a kraft lignin thin film was investigated as a function of the adsorbing solution conditions using the quartz crystal microbalance. The polyelectrolyte, PDADMAC, with a molecular weight of 100 kDa and one cationic charge group per monomer, was adsorbed to the anionically charged lignin film in the pH range 3.5-9.5 in electrolyte solution of 0.1 to 100 mM NaCl. At low pH, the adsorbed amount of PDADMAC was minimal, however, this increased as a function of increasing pH. Indeed, the surface excess increased significantly at about pH 8.5, where ionization of the phenolic groups on the lignin macromolecule may be expected. Furthermore, at this elevated pH, the adsorbed amount of PDADMAC decreased as the ionic strength of the solution increased above I mM. This is due to the competitive adsorption of counterions to the lignin surface and indicates that the adsorption of PDADMAC to lignin is of a pure electrosorption nature.
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| 4. |
- Notley, Shannon M., et al.
(författare)
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Surface Energy and Wettability of Spin-Coated Thin Films of Lignin Isolated from Wood
- 2010
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Ingår i: Langmuir. - : American Chemical Society (ACS). - 0743-7463 .- 1520-5827. ; 26:8, s. 5484-5490
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Tidskriftsartikel (refereegranskat)abstract
- The surface energy of lignin films spin-coated onto oxidized silicon water has been determined from contact angle measurements of different test liquids with varying polar and dispersive components. Three different lignin raw materials were used, a kraft lignin from softwood, along with milled wood lignin from softwood and hardwood. Infrared and P-31 NMR spectroscopy was used to identify any major functional group differences between the lignin samples. No significant difference in the total solid vapor surface energy or the different lignin films was observed: however, the polar component for the kraft lignin was much greater than for either of the milled wood lignin samples consistent with the presence of carboxyl groups and higher proportion of phenolic hydroxyl groups as shown by quantitative P-31 NMR on the phosphitylated samples. Furthermore, the total surface energy of lignin of 53-56 mJ m(-2) is of a similar magnitude to cellulose, also found in the wood cell wall; however, cellulose has a higher polar component leading to a lower contact angle with water and greater wettability than the milled wood lignin. Although lignin is not hydrophobic according to the strictest definition or a water contact angle greater than 90 degrees, water may only be considered a partially wetting liquid on a lignin surface. This supports the long-held belief that one of the functions of lignin in the wood cell wall is to provide water-proofing to aid in water transport. Furthermore, these results on the solid vapor surface energy of lignin will provide invaluable insight for many natural and industrial applications including in die design and manufacture of many sustainable products such as paper. fiberboard, and polymer composite blends.
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