Acetylated Kraft Lignin Research Articles

Achieving carbonized minitablet-shaped structures from lignin – The importance of heating rate on shape

Shape-anisotropic building blocks are vital in the creation of hierarchical materials in nature, as it enables directional alignment, property anisotropy and overall functionality improvement in biological materials. Likewise, the performance of carbonized superstructures could potentially be more precisely designed by using anisotropic building blocks. Lignin represents an important and sustainable alternative in the production of carbonized materials, which is due to its abundance and high carbon content (∼60%). However, to expand its utility, for producing carbonized shape-anisotropic materials, adequate synthesis and pyrolysis-protocols are essential. Here, a fractionated and acetylated Kraft lignin was used to successfully self-assemble shape-anisotropic microcapsules. Then a carbonization procedure (slow heating at 0.6 °C min−1), that retained the original shape-anisotropy after carbonization, was developed. The formation mechanism was discussed as a function of the heating rate. The overall strategy was template-free and the attained shape-anisotropies were well-defined and narrow in size distribution. This is a scalable route for achieving shape-anisotropic carbonized building blocks from lignin.

Simultaneous Improvement of Surface Wettability and UV Resistance of Wood with Lignin-Based Treatments.

Recent advancements in wood modification aim to enhance the inherent qualities of this versatile biological material, which includes renewability, ease of processing, and thermal insulation. This study focuses on evaluating the effectiveness of lignin as a protective agent for less durable wood species, namely, Pinus nigra and Fagus sylvatica L. The impregnation of wood with three various forms of lignin, such as kraft lignin, acetylated kraft lignin, and lignin nanoparticles, was carried out using the vacuum technique at room conditions. The results showed that the treatments significantly improve the hydrophobicity of wood surfaces, particularly in pine wood, and provide protection against UV ageing. Additionally, the treatments contributed to the stabilisation of moisture content at different humidity levels. Although slight colour variations were observed, their impact on the visual appearance was minimal, and the thermal analysis confirmed enhanced thermal properties. Additionally, plasma treatment further enhanced hydrophobicity after treatments, offering potential benefits in terms of moisture resistance and durability. The findings of this study highlight the promising effects of lignin-based treatments on wood properties, providing sustainable solutions for wood protection in various sectors. However, further optimisation is needed to fully explore the potential of lignin and lignin nanoparticles.

Kraft lignin and its derivates – A study on the adsorption of mono and multielement metals, potential use for noble metal recycling and an alternative material for solid base catalyst

Lignin is a natural polymer containing diverse functional groups and displaying an affinity for metals. Kraft lignin can be used as a carbon source, as a cleaving lignin structure for aromatic macromers or in the addition and modification of functional groups by the development of new active chemical sites. In this context, the aim of the present study is to investigate the adsorption of mono and multi-element metals solutions on lignin derivatives (unmodified Kraft lignin, acetylated Kraft lignin, charcoal Kraft lignin and activated carbon Kraft lignin). Parameters that affect adsorption processes, such as pH, contact time and adsorbent dose, were optimized in each case. The best adsorption condition was obtained at pH 7.00, a contact time of 120 min and with adsorbent dose of 30 mg. Also, unmodified Kraft lignin shows high adsorption selectivity (99%) for gold and palladium in acidic solutions. Acetylated and charcoal Kraft lignin resulted in lower adsorption levels in comparison with unmodified Kraft lignin. Activated carbon, however, reached adsorptions of over 86% for all metals. Finally, unmodified Kraft lignin impregnated with palladium presents a promising heterogeneous support in the Suzuki-Miyaura reaction.

Selective Modification of Aliphatic Hydroxy Groups in Lignin Using Ionic Liquid

A facile, sustainable method for the selective modification of aliphatic hydroxy (R–OH) groups in Kraft lignin was developed using an ionic liquid, 1-ethyl-3-methylimidazolium acetate (EmimOAc), as a solvent and catalyst. Selective R–OH modification was achieved by a one-pot, two-step homogeneous reaction: (i) acetylation of R–OH and aromatic OH (Ar–OH) groups with isopropenyl acetate (IPAc) as an acyl donor and (ii) subsequent selective deacetylation of the generated aromatic acetyl (Ar–OAc) groups. In step (i), IPAc reacts rapidly with Ar–OH but slowly with R–OH. The generated Ar–OAc is gradually deacetylated by heating in EmimOAc, whereas the aliphatic acetyl (R–OAc) groups are chemically stable. In step (ii), all R–OH is acetylated by IPAc and Ar–OAc which is a better acyl donor than IPAc, contributing to the rapid acetylation of the remaining R–OH, and selective deacetylation of the residual Ar–OAc is completed by adding a tiny amount of water as a proton source. This two-step reaction resulted in selective R–OH modification (>99%) in Kraft lignin with the remaining being almost all Ar–OH groups (93%). Selectively modified Kraft lignin was obtained with an acceptably high isolated yield (85%) and repeatability (N = 3). Furthermore, despite the lower substitution degree, it exhibited solubility in common solvents, heat-meltability, and thermal stability comparable to completely acetylated Kraft lignin.

Microwave-assisted selective acetylation of Kraft lignin: Acetic acid as a sustainable reactant for lignin valorization

Lignin acetylation, one of the most widespread chemical modifications used for improve the solubility of this biopolymer in organic solvents and increase polymer-lignin compatibility, has been performed for decades using time-consuming methodologies and acetylating agents with serious drawbacks. Moreover, traditional acetylation reactions generally conduce to non-selective acetylation of both aliphatic and phenolic groups. In this work, we demonstrated that partial and selective acetylation of kraft lignin can be carried out through a greener, simple and fast microwave-assisted process using acetic acid as solvent and acetylating agent. Structural characterization via FTIR, 1H-13C HSQC and 31P NMR demonstrated that acetylation reaction occurs selectively only in aliphatic hydroxyls, preserving the phenolic hydroxyls. Optimal reaction conditions were obtained using 1% (v/v) of H2SO4 as catalyst and only 5 min as reaction time. The acetylated Kraft lignin (AKL) obtained, have enhanced solubility in organic solvents (ethyl acetate, chloroform and dichloromethane) compared to unmodified Kraft lignin (KL) and antioxidant capacity almost 8 times higher than a commercial antioxidant BHT. These characteristics make the partially and selectively acetylated Kraft lignin a potential green antioxidant additive to be used in polymers blends.

Effect of soft segment molecular weight and NCO:OH ratio on thermomechanical properties of lignin-based thermoplastic polyurethane adhesive

During the last decades lignin has been largely applied on development of reactive polyurethanes. More recently, significant efforts were dedicated to synthesizing lignin-based thermoplastic polyurethanes (LTPUs). However, the relationship between molecular structure, properties and feasible LTPU applications still lacks in the literature. Aiming to overcome this absence, kraft lignin was chemically modified by partial acetylation in order to reduce the reactive sites and avoid the formation of a highly cross-linked structure. The extent of the functionalization reaction was properly investigated by Fourier transformed infra-red spectroscopy (FTIR-ATR) and quantitative 31P nuclear magnetic resonance analysis and the results revealed that the hydroxyl content from the parental lignin could be reduced by half in a controlled manner. In the second stage of this research, lignin-based thermoplastic polyurethanes (LTPUs) were successfully synthesized using the partially acetylated Kraft lignin macromonomer as the polyol to form a stable and thermo-formable polymer. The effect of lignin content, soft segment molecular weight, and the NCO:OH ratio on chemical, thermal, and mechanical properties were investigated. At last, LTPUs were applied as hot-melt adhesive for wood and their mechanical behavior evaluated by single lap shear tests. The results elucidated how those parameters influence LTPU properties and might be used as a design tool to tune LTPUs properties, supporting the development of industrial LTPU application.

Preparation and characterization of cellulose triacetate polymer inclusion membrane blended with acetylated kraft lignin: effect of AKL and application to the copper (II) extraction from acidic media

Preparation and characterization of cellulose triacetate polymer inclusion membrane blended with acetylated kraft lignin: effect of AKL and application to the copper (II) extraction from acidic media

Fractionation and DOSY NMR as Analytical Tools: From Model Polymers to a Technical Lignin

One key challenge hindering the valorization of lignin is its structural complexity. Artificial lignin-like materials provide a stepping stone between the simplicity of model compounds and the complexity of lignin. Here, we report an optimized synthesis of an all-G β-O-4 polymer 1 designed to model softwood lignin. After acetylation, the polymer Ac-1(V) was fractionated using a protocol that involved only volatile organic solvents, which left no insoluble residue. Using diffusion ordered spectroscopy NMR in combination with gel permeation chromatography, it was revealed that this fractionated material behaved like a flexible linear polymer in solution (average α > 0.5). Acetylated kraft lignin was subsequently processed using the same fractionation protocol. By comparison with the model polymer, we propose that the acetylated kraft lignin is composed of two classes of materials that exhibit contrasting physical properties. One is comparable to the acetylated all-G β-O-4 polymer Ac-1, and the second has a significantly different macromolecular structure.

Selective aminolysis of acetylated lignin: Toward simultaneously improving thermal-oxidative stability and maintaining mechanical properties of polypropylene

Even with outstanding radical capturing ability, the utilization of lignin as a natural antioxidant in polypropylene (PP) still has been pended. Usually, the compatibility of its blends is improved based on the reaction of hydroxyl content, thus leading to the decreasing content of phenolic hydroxyl (Ph-OH) group and inferior thermal-oxidative stability of lignin blends. Here, the selective aminolysis of acetylated Kraft lignin (pyr-KL) was investigated, which structures were characterized using FTIR, 31P-NMR and GPC. The Ph-OH group of acetylated KL could be released by the addition of pyrrolidine; however the aliphatic hydroxyl group is still blocked. With the control of reaction conditions, the highest oxidation induction time of pyr-KL/PP (0.5wt% loading) reaches up to 22.6min, almost 2.6 times than that of pure PP. More importantly, the mechanical properties of PP were also maintained under the loading of pyr-KL, which is much better than that of curde KL/PP.

Size‐Exclusion Chromatography and Aggregation Studies of Acetylated Lignins in N,N‐Dimethylacetamide in the Presence of Salts

The molar masses of acetylated kraft lignin and organosolv lignin are determined using both dynamic light scattering and size‐exclusion chromatography (SEC). Preparative gel fractionation of both lignins is allowed for the further analysis of low‐polydispersity lignin fractions. Fundamental information about the aggregation behavior of different molecular weight lignins in different solvent systems is provided. Two different solvent systems are used for SEC. Universal calibration is used for analysis. Applying the Flory–Fox theory, the obtained molecular weights are allowed for determining the maximum glass transition temperature at theoretical infinite molecular weight, Tg∞, of both acetylated lignins. image

Kraft lignin as filler in PLA to improve ductility and thermal properties

Kraft lignin (KL) and acetylated Kraft lignin (AKL) were used as filler for the elaboration of composites with poly(lactic acid) (PLA) in different concentrations (0.5, 1, 5, 10 and 20%) by extrusion method at 200°C. Characterization of both lignins has been performed using HPLC, FT-IR, GPC, DSC and TGA. KL presented only 0.3% of ash content and molecular weight around 2000g/mol. The esterification increased the molecular weight and decreases the polydispersity of the lignin (AKL). Also, AKL had lower Tg and higher thermal stability than unmodified Kraft lignin. Lignin content increased the thermal stability of PLA, with the addition of both types of lignins. Contact angle was measured to assess the change in the hydrophobicity of PLA with the addition of lignins. Mechanical properties of different materials were also investigated in order to know the effect of lignin addition in PLA. Maximum strength was not severely affected at low concentrations of both lignins, but it decreased dramatically, especially in composites with 10 and 20% of KL. Elongation at break increased with the addition of low contents of AKL, at high content of both lignins the material becomes quite brittle.

Hydrogenolysis of a γ-Acetylated Lignin Model Compound with a Ruthenium–Xantphos Catalyst

Catalytic hydrogenolysis of a γ-acetylated dimer lignin model compound is effected using a Ru–xantphos catalyst. Mechanistic investigations show mono-aryl degradation products are generated from the β-O-4 substrate as well as a terminal alkene ketone dimer (bis-aryl) that further dimerizes to a tetra-aryl product. Preliminary results using an acetylated kraft lignin as a substrate are also discussed.

Preparation and characterization of thermoplastic polyurethanes using partially acetylated kraft lignin

Thermoplastic polyurethanes were prepared using 90 % acetylated softwood kraft lignin, polyethylene glycol and 4,4-methylene diphenyl diisocyanate. Due to the glass transitions of the compatible soft and hard segment mixtures, the polyurethanes exhibited the first glass transitions at −40 to 10 °C, and the transition temperatures increased with increasing hard segment content. Due to the glass transitions of the microphase separated hard domains, the second glass transitions occurred at 150 °C. The viscous responses during the second transitions decreased as the separated hard domains-induced chemical and physical crosslinks increased. The Young’s modulus and tensile strength increased with increasing hard segment content, whereas the breaking strain decreased. The phase morphology changed from an isolated hard domain structure to an interconnected one as the physical crosslinks increased, which caused drastic changes in the increasing or decreasing tendency of the tensile strength or breaking strain. Because of the phase morphology, the polyurethanes exhibited viscoplasticity or viscoelasticity.