| 1. |
- Ayoub, Ali, et al.
(author)
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Effect of plasticizers and polymer blends for processing softwood kraft lignin as carbon fiber precursors
- 2021
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In: Cellulose. - : Springer Science and Business Media LLC. - 0969-0239 .- 1572-882X. ; 28:2, s. 1039-1053
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Journal article (peer-reviewed)abstract
- Plasticizers depress the glass transition temperature (T-g) of polymers and produce a flowable material at lower temperatures. The use of plasticizers to depress T-g of lignin is important, since at high processing temperatures lignin crosslinks, making it intractable. The goal of this study was to assess plasticizers and polymer blends for the ability to retard a commercial softwood kraft lignin from crosslinking and also serve as thermal and rheological property modifiers during thermal processing in the attempt to produced moldable and spinnable lignin for lignin and carbon fiber products. The T-g of the lignin and the lignin mixed with various amounts of plasticizers and with different thermo-mechanical mixing were determined using differential scanning calorimetry. The T-g and the change in heat capacity at the glass transition (Delta C-p) decreased and increased, respectively, about linearly within this plasticizers range with increased plasticizer weight percentage. Gel permeation chromatography results for extruded lignin as well as extruded lignin-plasticizer blends with glycerol, N-allyurea, citric acid with and without sodium hypophosphite, and oleic acid indicate that the presence of these materials reduced the rate of molecular weight increase at temperatures between 100 and 200 degrees C. Continuous, homogenous films and fibers could be produced by thermal processing with plasticized lignin samples and plasticized lignin-polymer blends, but not with lignin alone. These fibers could be carbonized, yielding up to about 50% of carbon. The present findings have shown the advantages of plasticizers in thermally processing a commercial softwood kraft lignin.
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| 2. |
- Hubbe, Martin A., et al.
(author)
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Recovery of Inorganic Compounds from Spent Alkaline Pulping Liquor by Eutectic Freeze Crystallization and Supporting Unit Operations : A Review
- 2018
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In: BioResources. - : NC State University. - 1930-2126. ; 13:4, s. 9180-9219
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Research review (peer-reviewed)abstract
- After the kraft or soda pulping of lignocellulosic materials to produce pulp suitable for papermaking, the spent pulping liquor typically has been recovered by multi-effect evaporation, followed by incineration in a recovery boiler. This review article considers one unit operation, eutectic freeze crystallization (EFC), that may have potential to save some of the energy that is presently consumed in the evaporation step during recovery of inorganic chemicals from spent pulping liquor. Based on a review of the literature it appears that EFC can be employed to obtain relatively pure sodium sulfate and sodium carbonate, along with relatively pure water (in the form of ice) from the spent liquor, under the assumption that lignin previously has been removed by acidification and precipitation. Issues of inorganic scale formation, during the operation of an EFC process applied to lignin-free black liquor, will require research attention. The chemical reactions to regenerate the active pulping chemicals sodium hydroxide and sodium sulfide from sodium carbonate, sodium sulfate, and other compounds isolated by EFC can be carried out either in a separate operation or by returning the materials to the feed of an existing recovery boiler.
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| 3. |
- Hubbe, Martin A., et al.
(author)
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Lignin Recovery from Spent Alkaline Pulping Liquors Using Acidification, Membrane Separation, and Related Processing Steps : A Review
- 2019
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In: BioResources. - : NORTH CAROLINA STATE UNIV. - 1930-2126. ; 14:1, s. 2300-2351
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Journal article (peer-reviewed)abstract
- The separation of lignin from the black liquor generated during alkaline pulping is reviewed in this article with an emphasis on chemistry. Based on published accounts, the precipitation of lignin from spent pulping liquor by addition of acids can be understood based on dissociation equilibria of weak acid groups, which affects the solubility behavior of lignin-related chemical species. Solubility issues also govern lignin separation technologies based on ultrafiltration membranes; reduction in membrane permeability is often affected by conditions leading to decreased solubility of lignin decomposition products and the presence of colloidal matter. Advances in understanding of such phenomena have potential to enable higher-value uses of black liquor components, including biorefinery options, alternative ways to recover the chemicals used to cook pulp, and debottlenecking of kraft recovery processes.
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| 4. |
- Hubbe, Martin A., et al.
(author)
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Rate-limiting mechanisms of water removal during the formation, vacuum dewatering, and wet-pressing of paper webs : A Review
- 2020
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In: BioResources. - : North Carolina State University. - 1930-2126. ; 15:4, s. 9672-9755
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Journal article (peer-reviewed)abstract
- Because some of the critical events during the removal of water before the dryer section on a paper machine happen very rapidly within enclosed spaces – such as wet-press nips – there have been persistent challenges in understanding the governing mechanisms.In principle, a fullerunderstanding of the controlling mechanisms, based on evidence, should permit progress in achieving both higher rates of production of paper and more reliable control of paper attributes. In addition, energy can be saved, reducing environmental impacts. The goal of this article is to review published work dealing both with the concepts involved in water removal and evidence upon which existing and new theories can be based. The scope of this review includes all of the papermaking unit operations between the jet coming from the headbox and the final wet-press nip of an industrial-scale paper machine. Published findings support a hypothesis that dewatering rates can be decreased by densification of surface layers, plugging of drainage channels by fines, sealing effects, flocculation, and rewetting. Ways to overcome such effects are also reviewed.
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