| 11. |
- Lindman, Björn, et al.
(author)
-
The relevance of structural features of cellulose and its interactions to dissolution, regeneration, gelation and plasticization phenomena
- 2017
-
In: Physical Chemistry Chemical Physics. - : Royal Society of Chemistry (RSC). - 1463-9076 .- 1463-9084. ; 19:35, s. 23704-23718
-
Research review (peer-reviewed)abstract
- Cellulose is the most abundant polymer and a very important renewable resource. Since cellulose cannot be shaped by melting, a major route for its use for novel materials, new chemical compounds and renewable energy must go via the solution state. Investigations during several decades have led to the identification of several solvents of notably different character. The mechanisms of dissolution in terms of intermolecular interactions have been discussed from early work but, even on fundamental aspects, conflicting and opposite views appear. In view of this, strategies for developing new solvent systems for various applications have remained obscure. There is for example a strong need for using forest products for higher value materials and for environmental and cost reasons to use water-based solvents. Several new water-based solvents have been developed recently but there is no consensus regarding the underlying mechanisms. Here we wish to address the most important mechanisms described in the literature and confront them with experimental observations. A broadened view is helpful for improving the current picture and thus cellulose derivatives and phenomena such as fiber dissolution, swelling, regeneration, plasticization and dispersion are considered. In addition to the matter of hydrogen bonding versus hydrophobic interactions, the role of ionization as well as some applications of new knowledge gained are highlighted.
|
|
| 12. |
- Lindman, Björn, et al.
(author)
-
The relevance of structural features of cellulose and its interactions to dissolution, regeneration, gelation and plasticization phenomena
- 2017
-
In: Physical Chemistry, Chemical Physics - PCCP. - 1463-9076 .- 1463-9084. ; 19:35, s. 23704-23718
-
Journal article (peer-reviewed)abstract
- Cellulose is the most abundant polymer and a very important renewable resource. Since cellulose cannot be shaped by melting, a major route for its use for novel materials, new chemical compounds and renewable energy must go via the solution state. Investigations during several decades have led to the identification of several solvents of notably different character. The mechanisms of dissolution in terms of intermolecular interactions have been discussed from early work but, even on fundamental aspects, conflicting and opposite views appear. In view of this, strategies for developing new solvent systems for various applications have remained obscure. There is for example a strong need for using forest products for higher value materials and for environmental and cost reasons to use water-based solvents. Several new water-based solvents have been developed recently but there is no consensus regarding the underlying mechanisms. Here we wish to address the most important mechanisms described in the literature and confront them with experimental observations. A broadened view is helpful for improving the current picture and thus cellulose derivatives and phenomena such as fiber dissolution, swelling, regeneration, plasticization and dispersion are considered. In addition to the matter of hydrogen bonding versus hydrophobic interactions, the role of ionization as well as some applications of new knowledge gained are highlighted.
|
|
| 13. |
- Lindman, Björn, et al.
(author)
-
The Subtleties of Dissolution and Regeneration of Cellulose: Breaking and Making Hydrogen Bonds
- 2015
-
In: BioResources. - : BioResources. - 1930-2126. ; 10:3, s. 3811-3814
-
Journal article (other academic/artistic)abstract
- Cellulose dissolution and regeneration are old topics that have recently gained renewed attention. This is reflected in both applications - earlier and novel - and in scientific controversies. There is a current discussion in the literature on the balance between hydrogen bonding and hydrophobic interactions in controlling the solution behavior of cellulose. Some of the key ideas are recalled.
|
|
| 14. |
- Magalhães, Solange, et al.
(author)
-
Brief overview on bio-based adhesives and sealants
- 2019
-
In: Polymers. - : MDPI AG. - 2073-4360. ; 11:10
-
Journal article (peer-reviewed)abstract
- Adhesives and sealants (AS) are materials with excellent properties, versatility, and simple curing mechanisms, being widely used in different areas ranging from the construction to the medical sectors. Due to the fast-growing demand for petroleum-based products and the consequent negative environmental impact, there is an increasing need to develop novel and more sustainable sources to obtain raw materials (monomers). This reality is particularly relevant for AS industries, which are generally dependent on non-sustainable fossil raw materials. In this respect, biopolymers, such as cellulose, starch, lignin, or proteins, emerge as important alternatives. Nevertheless, substantial improvements and developments are still required in order to simplify the synthetic routes, as well as to improve the biopolymer stability and performance of these new bio-based AS formulations. This environmentally friendly strategy will hopefully lead to the future partial or even total replacement of non-renewable petroleum-based feedstock. In this brief overview, the general features of typical AS are reviewed and critically discussed regarding their drawbacks and advantages. Moreover, the challenges faced by novel and more ecological alternatives, in particular lignocellulose-based solutions, are highlighted.
|
|
| 15. |
|
|
| 16. |
- Medronho, Bruno, et al.
(author)
-
Brief overview on cellulose dissolution/regeneration interactions and mechanisms.
- 2015
-
In: Advances in Colloid and Interface Science. - : Elsevier BV. - 1873-3727 .- 0001-8686. ; 222:Online 28 May 2014, s. 502-508
-
Journal article (peer-reviewed)abstract
- The development of cellulose dissolution/regeneration strategies constitutes an increasingly active research field. These are fundamental aspects of many production processes and applications. A wide variety of suitable solvents for cellulose is already available. Nevertheless, most solvent systems have important limitations, and there is an intense activity in both industrial and academic research aiming to optimize existing solvents and develop new ones. Cellulose solvents are of highly different nature giving great challenges in the understanding of the subtle balance between the different interactions. Here, we briefly review the cellulose dissolution and regeneration mechanisms for some selected solvents. Insolubility is often attributed to strong intermolecular hydrogen bonding between cellulose molecules. However, recent work rather emphasizes the role of cellulose charge and the concomitant ion entropy effects, as well as hydrophobic interactions.
|
|
| 17. |
- Medronho, Bruno, et al.
(author)
-
Probing cellulose amphiphilicity
- 2015
-
In: Nordic Pulp & Paper Research Journal. - 0283-2631 .- 2000-0669. ; 30:1, s. 58-66
-
Journal article (peer-reviewed)abstract
- Cellulose dissolution and regeneration is an increasingly active research field due to the direct relevance for numerous production processes and applications. The problem is not trivial since cellulose solvents are of remarkably different nature and thus the understanding of the subtle balance between the different interactions involved becomes difficult but crucial. There is a current discussion in literature on the balance between hydrogen bonding and hydrophobic interactions in controlling the solution behavior of cellulose. This treatise attempts to review recent work highlighting the marked amphiphilic characteristics of cellulose and role of hydrophobic interactions in dissolution and regeneration. Additionally, a few examples of our own research are discussed focusing on the role of different additives in cellulose solubility. The data does support the amphiphilic behavior of cellulose, which clearly should not be neglected when developing new solvents and strategies for cellulose dissolution and regeneration.
|
|
| 18. |
- Medronho, Bruno, et al.
(author)
-
Silk Fibroin Dissolution in Tetrabutylammonium Hydroxide Aqueous Solution
- 2019
-
In: Biomacromolecules. - : American Chemical Society (ACS). - 1525-7797 .- 1526-4602. ; 20, s. 4107-4116
-
Journal article (peer-reviewed)abstract
- Bombyx mori L. silk fibroin (SF) is widely used in different areas due to its ability to form durable and resilient materials with notable mechanical properties. However, in some of these applications the dissolution of SF is required, and this is not often straightforward due to its inability to be dissolved in the majority of common solvents. This work reports a novel approach to dissolve SF using 40 wt % aqueous tetrabutylammonium hydroxide, TBAOH(aq), at mild temperature. A thorough rheological study combined with small-angle X-ray scattering is presented to correlate the SF state in solution with changes in the rheological parameters. The scattering data suggest that the SF conformation in TBAOH(aq) is close to a random coil, possibly having some compact domains linked with flexible random chains. The radius of gyration (Rg) and the molecular weight (Mw) were estimated to be ca. 17.5 nm and 450 kDa, respectively, which are in good agreement with previous works. Nevertheless, a lower Mw value was deduced from rheometry (i.e., 321 kDa) demonstrating a low degree of depolymerization during dissolution in comparison to other harsh processes. The transition from a dilute to a semidilute regime coincides with the estimated critical concentration and is marked by the presence of a shear-thinning behavior in the flow curves, violation of the empirical Cox-Merz rule, and an upward increase in the activation energy. This work paves the way toward the development of advanced high-tech SF-based materials. © 2019 American Chemical Society.
|
|
| 19. |
|
|
| 20. |
- Pereira, Ana, et al.
(author)
-
Cellulose gelation in NaOH solutions is due to cellulose crystallization
- 2018
-
In: Cellulose. - : Springer Science and Business Media LLC. - 0969-0239 .- 1572-882X. ; 25:6, s. 3205-3210
-
Journal article (peer-reviewed)abstract
- Abstract: Cellulose gelation in 2 M NaOH aqueous solution was followed by time resolved turbidity and rheology measurements. The kinetics of gelation is observed to change from several hours down to few seconds when the temperature is increased from 25 to 30 °C. The increase of turbidity upon gelation demonstrates the formation of larger cellulose aggregates, while wide angle X-ray scattering data confirms the gradual formation of crystalline domains. This suggests that the gelation can be understood as cellulose precipitation/crystallization where an effectively cross linked network and gelation results from that cellulose chains may participate in more than one crystallite. Graphical Abstract: The gelation of cellulose solutions is due to crystallization and precipitation of cellulose.[Figure not available: see fulltext.]
|
|
