| 1. |
- Christiernin, Maria, et al.
(författare)
-
Comparison between 10 000 year old and contemporary spruce lignin
- 2009
-
Ingår i: Wood Science and Technology. - : Springer Science and Business Media LLC. - 0043-7719 .- 1432-5225. ; 43:1-2, s. 23-41
-
Tidskriftsartikel (refereegranskat)abstract
- Wood from white spruce Picea glauca that had been preserved by rapid burial in lake sediments 10,000 years ago, was investigated and compared to a contemporary reference white spruce wood. The 10,000-year old sample appeared to have an intact primary cell wall and middle lamella, whereas the carbohydrate monomer distribution, and microscopic images showed that the secondary wall was at least partially removed, indicating that this structure had been selectively attacked by bacteria. The Klason lignin amount in the aged spruce was found to be 60%. The relative lignin monomer content in the aged spruce was 9% lower than that of the reference wood, showing that there were fewer beta-O-4' linkages in the aged sample. This finding was supported by SEC analysis of the thioacidolysed samples as a larger proportion of lignin oligomers were observed in the aged spruce than in the reference material. This indicates a somewhat greater number of condensed bonds in the aged spruce than in the reference spruce sample. Quantitative C-13 NMR analysis and HSQC techniques applied on milled wood lignins (MWL) revealed no significant structural differences between the aged spruce and the reference.
|
|
| 2. |
- Eriksson, Malin, et al.
(författare)
-
Cellulose thin films : Degree of cellulose ordering and its influence on adhesion
- 2007
-
Ingår i: Biomacromolecules. - : American Chemical Society (ACS). - 1525-7797 .- 1526-4602. ; 8:3, s. 912-919
-
Tidskriftsartikel (refereegranskat)abstract
- Adhesion measurements have been performed with thin cellulose films using continuum contact mechanics with application of the JKR theory. Three different cellulose surfaces were prepared, one crystalline and two surfaces with a lower degree of crystalline order. Adhesion between two cross-linked poly(dimethylsiloxane) (PDMS) caps, as well as the adhesion between PDMS and the various cellulose surfaces, was measured. The work of adhesion (from loading) was found to be similar for all three surfaces, and from contact angle measurement with methylene iodide it was concluded that dispersive interactions dominate. However, the adhesion hysteresis differed significantly, being larger for a less ordered cellulose surface and decreasing with increasing degree of crystalline order. This is suggested to be due to the surface groups' ability to orient themselves and participate in specific or nonspecific interactions, where a surface with a lower degree of crystalline order has a higher possibility for reorientation of the surface groups. The mobility of cellulose chains increases with water uptake, resulting in stronger adhesive joints. These films will hence allow for determination of the contributions of hydrogen bonding and inter-diffusion on the adhesion, determined from the unloading data, as the thermodynamic work of adhesion was found to be independent of the cellulose surface used.
|
|
| 3. |
|
|
| 4. |
- Eriksson, Malin, et al.
(författare)
-
Paper strength as an adhesion problem
- 2005
-
Ingår i: Appita Annu. Conf.. ; , s. 51-58
-
Konferensbidrag (refereegranskat)abstract
- The wet and dry adhesion between polymer coated silica surfaces was measured with a view to understanding the influence of polymer additives on the wet and dry strength in paper. The wet adhesion measurements were performed with the AFM colloidal probe technique whereas the dry measurements were made using the new micro adhesion measurement apparatus (MAMA). As expected, cationic dextran (DEX) increased dry adhesion more than the hydrophobically modified cationic dextran (HDEX). Surprisingly HDEX gave strong wet adhesion most probably due to hydrophobic association.
|
|
| 5. |
- Lidenmark, Cecilia, 1976-, et al.
(författare)
-
The adhesive behavior of extracted latex polymers towards silicon oxide and cellulose
- 2013
-
Ingår i: International Journal of Adhesion and Adhesives. - : Elsevier. - 0143-7496 .- 1879-0127. ; 44, s. 250-258
-
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.
|
|
| 6. |
- Norgren, Magnus, et al.
(författare)
-
Smooth model surfaces from lignin derivatives. II. Adsorption of polyelectrolytes and PECs monitored by QCM-D
- 2007
-
Ingår i: Langmuir. - : American Chemical Society (ACS). - 0743-7463 .- 1520-5827. ; 23:7, s. 3737-3743
-
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.
|
|
| 7. |
- Norgren, Magnus, et al.
(författare)
-
Study of thin films of kraft lignin and two DHPs by means of single-molecule force spectroscopy (SMFS)
- 2012
-
Ingår i: Holzforschung. - Berlin : Walter de Gruyter. - 0018-3830 .- 1437-434X. ; 66:5, s. 615-622
-
Tidskriftsartikel (refereegranskat)abstract
- The adhesion of single and associated lignin chains to a substrate has been studied by means of single-molecule force spectroscopy (SMFS). Softwood kraft lignin (KL) and two lignin polymer models (dehydrogenation polymers, DHPs) based on coniferyl alcohol (DHPc.alc.)and coniferaldehyde (DHPc.ald.) were in focus. The desorption force from the "silicon nitride SMFS tip" for the KL was significantly greater than that of the DHPs. The higher desorption force was interpreted as being due to the interaction of carboxyl groups through hydrogen bonding with the tip as well as to the less compact polymeric layer at the interface. The distribution of the extended chain lengths was determined, and self-association of lignin chains was observed. For both KL and the DHPc.ald., chains were extended significantly beyond the limit that would be expected for polymers with the corresponding degree of polymerization. The alpha-carbon on the DHPc.alc. has a strong intramolecular hydrogen bonding interaction with the adjacent aryl ether, which inhibits the possibility of the ether to participate in intermolecular hydrogen bonding with nearby lignin chains. Thus, the self-association for KL and DHPc.ald. was found to be dominated by intermolecular hydrogen bonding with carboxylic groups and aryl ether functionalities.
|
|
| 8. |
- Notley, Shannon M., et al.
(författare)
-
Adsorbed layer structure of a weak polyelectrolyte studied by colloidal probe microscopy and QCM-D as a function of pH and ionic strength
- 2004
-
Ingår i: Physical Chemistry, Chemical Physics - PCCP. - : Royal Society of Chemistry (RSC). - 1463-9076 .- 1463-9084. ; 6:9, s. 2379-2386
-
Tidskriftsartikel (refereegranskat)abstract
- The adsorbed layer structure of a weak polyelectrolyte poly(2-vinylpyridine), on silica and mica, has been studied using colloidal probe microscopy (CPM) and the quartz crystal microbalance (QCM-D). The adsorbed layer structure was found to be highly dependent on both the solution conditions from which it was adsorbed and the molecular weight. Conditions were altered to favour both flat adsorbed layers and the development of significant steric layers. The structural reconformation of the large steric layer was furthermore studied as a function of pH. The equilibrium interaction force, measured using CPM as a function of surface separation, was used to determine the relative extension of the polyelectrolyte away from the interface. At low pH (3.2) and high ionic strength, the adsorbed polyelectrolyte molecules adopt a highly extended conformation; as the pH is increased (to 4.6 then to 5.5) the polymer chains collapse progressively towards the interface. Reversal of this pH cycle causes a re-protonation of the adsorbed polymers and highlights the finite timescale for this process to occur. The kinetics of this process was measured from the amount of trapped solvent within the polyelectrolyte layer as determined from the QCM-D. Upon decrease in pH, the adsorbed chains swell before partially collapsing. We propose that this is due to cross-linking of the polymer in the protonated state. Furthermore, the combination of techniques used in this study, namely optical reflectometry, CPM and QCM-D, allows the determination of the solvent content of the adsorbed film of polyelectrolyte as well as the extension of the polymer from the interface as a function of pH.
|
|
| 9. |
- Notley, Shannon M., et al.
(författare)
-
Adsorption of a strong polyelectrolyte to model lignin surfaces
- 2008
-
Ingår i: Biomacromolecules. - : American Chemical Society (ACS). - 1525-7797 .- 1526-4602. ; 9:7, s. 2081-2086
-
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.
|
|
| 10. |
- Notley, Shannon M., et al.
(författare)
-
Surface Energy and Wettability of Spin-Coated Thin Films of Lignin Isolated from Wood
- 2010
-
Ingår i: Langmuir. - : American Chemical Society (ACS). - 0743-7463 .- 1520-5827. ; 26:8, s. 5484-5490
-
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.
|
|
