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In pulp production processes, lignin is generated in large quantities as a by‐product. It is often burned to generate heat and electricity. Despite the large‐scale production of lignin, its utilization in high‐value applications has remained a challenge. Recently, the production of lignin nanoparticles (LNP) and lignin polymers has gathered attention. The potential to use LNPs as reinforcement filler, UV absorbent, antioxidant, and drug carrier has been reported, while lignin polymers might be suitable for the production of composites, hydrogels, flocculants, and coagulants. This review paper provides insights into the production and application of LNP and lignin polymers. In addition, the challenges associated with the characterization and use of these products are comprehensively reviewed. [ABSTRACT FROM AUTHOR]

Lignin has been produced in large quantities in the pulp manufacturing process; however, its valorization has been challenging. The production of lignin polymers has shown pathways to produce water soluble products to be used as flocculants and dispersants. However, these lignin-based polymers may interact with each other and form large flocs that could reduce their efficiency in interacting with other colloidal particles. This study aims at evaluating the self-assembly of kraft lignin-acrylamide polymers in aqueous environments under different salt concentrations. The sedimentation studies using a vertical scan analyzer showed that a higher molecular weight lignin polymer had a higher tendency for sedimentation than a lower molecular weight one. Quartz crystal microbalance with dissipation (QCM-D) was used for studying the self-assembly behavior of lignin polymers with different molecular weights. The results suggested that lignin polymer with the higher molecular weight of 96,992 g/mol had a higher tendency to self-assemble by forming a loose floc as compared to that with a lower molecular weight. Also, salt disrupted the self-assembly of lignin polymers greatly. [ABSTRACT FROM AUTHOR]

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Currently, lignin is mainly produced in pulping processes, but it is considered as an under-utilized chemical since it is being mainly used as a fuel source. Lignin contains many hydroxyl groups that can participate in chemical reactions to produce value-added products. Flocculants, adsorbents, and dispersants have a wide range of applications in industry, but they are mainly oil-based chemicals and expensive. This paper reviews the pathways to produce water soluble lignin-based flocculants, adsorbents, and dispersants. It provides information on the recent progress in the possible use of these lignin-based flocculants, adsorbents, and dispersants. It also critically discusses the advantages and disadvantages of various approaches to produce such products. The challenges present in the production of lignin-based flocculants, adsorbents, and dispersants and possible scenarios to overcome these challenges for commercial use of these products in industry are discussed. [ABSTRACT FROM AUTHOR]

Abstract In this work, fly ash (FA) and polydiallyldimethylammonium chloride (PDADMAC) were utilized to treat the spent liquor (SL) of thermomechanical pulping (TMP) process in an effort to remove its lignocelluloses. The incorporation of PDADMAC into the system reduced the dosage of FA required for achieving acceptable lignocellulose removals. The maximum lignocellulose removals of 81%, 78%, 56%, 53% and 97% were achieved for lignin, hemicellulose, COD, BOD, and turbidity via treating SL with 100 g/L of FA at 25 °C for 60 min and subsequently treating with 100 mg/L of PDADMAC at 25 °C for 30 min, respectively. Comparing the two-step processes, FA pretreatment with PDADMAC post treatment was more effective than the two step process of PDADMAC pretreatment and FA post treatment. In this case, the FA pretreatment generated metal-organic complexes, and the addition of PDADMAC facilitated the formation of large flocs that could be separated from the system readily. A one stage process of combined PDADMAC and FA was less effective than the two-stage process of FA and PDADMAC treatments in removing lignocelluloses from SL. Graphical abstract Image 1 Highlights • Spent liquor of mechanical pulping process contains lignocelluloses. • Fly ash and cationic polymer were used for treating spent liquor. • A two-step treatment of fly ash and cationic polymer was very effective. • A one step treatment of fly ash or cationic polymer was not as effective. [ABSTRACT FROM AUTHOR]

Currently, the dissolved lignocelluloses in the spent liquor (SL) of a thermomechanical pulping process are treated in wastewater treatment systems and thus they are wasted. In this work, polydiallyldimethylammonium chloride (PDADMAC), with different molecular weights, was used for flocculating lignocelluloses of SL and thus isolating them from SL. Results showed that the maximum removals were 38% via treating SL with 100 mg/L of PDADMAC (with 1045 kg/mol molecular weight) at 25 °C for 30 min. The focused beam reflectance measurement of the flocculation process revealed that the chord length of the flocs with the maximum square weighted counts was increased from 70 to 100 μm and also their maximum square weighted counts was increased from 5 to 25 μm 2 /s. The flocs contained 60.71–74.41 wt% PDADMAC, the balance of lignocelluloses and the heating value of 24–25 MJ/kg. The high molecular PDADMAC generated flocs with more organics and a higher heating value. [ABSTRACT FROM AUTHOR]

Kraft lignin is currently combusted in the pulping process to produce heat. It can be extracted from the process and converted to value-added products, but its limited water solubility hampers its end use applications. The main objective of this study was to investigate the carboxymethylation of hardwood kraft lignin to produce an anionic water soluble product. The results showed that the optimal conditions for carboxymethylation were 1.5 M NaOH concentration, 3 mol/mol sodium chloroacetate (SCA)/lignin ratio, 40 °C, 4 h and 16.7 g/L lignin concentration. The produced lignin had a charge density and carboxylate group of 1.8 meq/g and 1.68 mmol/g, respectively. The carboxymethylated lignin was further characterized using thermogravimetric analyzer (TGA), Fourier Transform Infrared (FTIR) spectrophotometer, Nuclear magnetic resonance spectroscopy (H NMR) and elemental analyses. Moreover, the application of carboxymethylated lignin as a dispersant for a clay suspension was successfully analyzed by means of a photometric dispersion analyzer. [ABSTRACT FROM AUTHOR]

Hemicelluloses and lignin present in the spent liquor (SL) of neutral sulfite semichemical (NSSC) pulping process can potentially be converted into value-added products such as furfural, hydroxymethylfurfural, levulinic acid, phenols and adhesives. However, the direct conversion of hemicelluloses and lignin of SL into value-added products is uneconomical due to the dilute nature of the SL. To have a feasible downstream process for utilizing lignocelluloses of SL, the lignocelluloses should initially be separated from the SL. In this study, an adsorption process (via applying activated carbon) was considered for isolating the dissolved lignin and hemicelluloses from the SL of an NSSC pulping process. Under the optimal conditions of pH, SL/AC weight ratio, time and temperature of 5.7, 30, 360 min and 30 °C, the maximum lignin and hemicellulose adsorptions were 0.33 and 0.25 g/g on AC. The chemical oxygen demand (COD) and turbidity of the SL were decreased by 11% and 39%, respectively, as a result of lignocellulose adsorption on AC. Also, the incineration behavior of the SL-treated AC was studied with a thermo-gravimetric analysis (TGA). [Copyright &y& Elsevier]

Abstract: Hemicelluloses are the main organics dissolved in the pre-hydrolysis liquor (PHL) of the kraft-based dissolving pulp production process. In this study, two methods were employed to isolate the hemicelluloses from industrial PHL samples. The results showed that the hemicelluloses, precipitated in ethanol after an acidification step (Method 2), had a very high brightness (83% ISO) and low lignin content (0.44%) compared with the hemicelluloses obtained by the direct precipitation in ethanol without the acidification (Method 1), which had a brightness of 17.2% ISO and a lignin content of 5.67%. Furthermore, the hemicelluloses isolated via Method 2 were rendered cationic by using glycidyltrimethylammonium chloride (GTMAC), and the process parameters for the cationization reaction were studied, including the water content, reaction temperature and time, molar ratio of GTMAC/hemicelluloses, and the sodium hydroxide dosage. The optimized conditions for the cationic modification were 35% water content, 5% sodium hydroxide (both based on the mass of hemicelluloses), 1 (mol) GTMAC/hemicelluloses ratio, 65 °C, and 4 h reaction time. Finally, the cationic hemicelluloses were characterized and compared with unmodified hemicelluloses using the FT-IR and NMR analyses. [Copyright &y& Elsevier]