Aqueous Dispersions of Esterified Lignin Particles for Hydrophobic Coatings

Investigation of synergistic effects incorporating esterified lignin and guar gum composite aerogel for sustained oil spill cleanup

The recently developed aerogel demonstrates a high capacity for pollutant absorption, making it an environmentally friendly option for oily water treatment. In an effort to reduce the adverse effects of the black liquor accumulation in the pulp industry, this study focused on utilizing the mentioned abundant bio-resource lignin, which can be applied to various high-value applications such as 3D porous materials for oil spill cleanup. Lignin, precipitated from the black liquor, was esterified using maleic anhydride as the esterifying reagent to enhance the hydrophobicity. Then, the composite aerogel fabricated from esterified lignin and guar gum (GG) was successfully prepared through the facile freeze-drying, using glutaraldehyde (GA) as the cross-linker. The resulting aerogel exhibited high porosity values exceeding 95%, low density (27.4 mg/cm3), and an impressive absorption capacity of 32.5 g/g for sunflower oil. These results demonstrate the potential of black liquor utilization as a bio-waste source of lignin and highlight the cost-effective guar gum-esterified lignin composite aerogel, which exhibits remarkable oil absorption capabilities and environmental sustainability promotion.

Preparation and Characterization of Low CTE Poly(ethersulfone) Using Lignin Nano Composites as Flexible Substrates

Polyethersulfone (PES) has outstanding thermal and dimensional stability. It is considered an engineering thermoplastic. However, its high coefficient of thermal expansion (CTE) hinders its use in automobiles, microelectronics, and flexible display areas. To overcome its high coefficient of thermal expansion (CTE), recent studies have focused on reducing its high CTE and improving its mechanical properties by adding nano-sized fillers or materials. The addition of nanofiller or nanofibrils to the PES matrix often has a positive effect on its mechanical and thermal properties, making it a flexible display substrate. To obtain ideal flexible substrates, we prepared polyethersulfone with lignin nanocomposite films to reduce CTE and improve the mechanical and thermal properties of PES by varying the relative ratio of PES in the lignin nanocomposite. In this study, lignin as a biodegradable nanofiller was found to show high thermal, oxidative, and hydrolytic stability with favorable mechanical properties. PES/lignin nanocomposite films were prepared by solution casting according to the content of lignin (0 to 5 wt.%). PES/lignin composite films were subjected to mechanical, thermo-mechanical, optical, and surface analyses. The results showed enhanced thermomechanical and optical properties of PES, with the potential benefits of lignin filler materials realized for the development of thermoplastic polymer blends.

Wood-derived bio-coating materials incorporating hydrophobic lignin and hierarchically porous biochar for high-efficiency coating slow-release fertilizers

Coating slow-release fertilizers (CSRFs) have gained significant attention for their potential to improve nutrient utilization efficiency and prevent environmental pollution through mitigating soil and water contamination. This study developed a novel wood waste-derived composition as a bio-coating material for urea slow-release by integrating modified lignin (PCL) and activated biochar (ABC). PCL was prepared by grafting palmitoyl chloride (PC) with hydrophobic groups to the lignin via an esterification reaction. ABC with a high surface area and hierarchically porous structure created rich channels for ion transportation. These results increased the water-retention ability with a reduced absorbing/expelling rate and confer an excellent Cr(VI) adsorption capacity to the PCL and ABC hybrid coating material (PCL/ABC). The as-prepared PCL/ABC-based CSRF (PCL/ABC-CSRF) showed improving fertilizer slow-release properties for real application (nitrogen release persistence for 40 days at soil). The rice (Oryza sativa L.) hydroponics study suggested that such novel PCL/ABC was conducive to the rice growth in micro metallic contaminated hydroponics by eliminating the accumulation of chromium metal in rice roots. Overall, this study provides an attractive platform for developing biodegradable, heavy-metal adsorbable, and high-efficient CSRFs and a feasible and effective way for functionalized utilization of wood waste.

Functional surfaces, films, and coatings with lignin - a critical review

Lignin is the most abundant polyaromatic biopolymer. Due to its rich and versatile chemistry, many applications have been proposed, which include the formulation of functional coatings and films. In addition to replacing fossil-based polymers, the lignin biopolymer can be part of new material solutions. Functionalities may be added, such as UV-blocking, oxygen scavenging, antimicrobial, and barrier properties, which draw on lignin's intrinsic and unique features. As a result, various applications have been proposed, including polymer coatings, adsorbents, paper-sizing additives, wood veneers, food packaging, biomaterials, fertilizers, corrosion inhibitors, and antifouling membranes. Today, technical lignin is produced in large volumes in the pulp and paper industry, whereas even more diverse products are prospected to be available from future biorefineries. Developing new applications for lignin is hence paramount - both from a technological and economic point of view. This review article is therefore summarizing and discussing the current research-state of functional surfaces, films, and coatings with lignin, where emphasis is put on the formulation and application of such solutions.

The Biomodified Lignin Platform: A Review

A reliance on fossil fuel has led to the increased emission of greenhouse gases (GHGs). The excessive consumption of raw materials today makes the search for sustainable resources more pressing than ever. Technical lignins are mainly used in low-value applications such as heat and electricity generation. Green enzyme-based modifications of technical lignin have generated a number of functional lignin-based polymers, fillers, coatings, and many other applications and materials. These bio-modified technical lignins often display similar properties in terms of their durability and elasticity as fossil-based materials while also being biodegradable. Therefore, it is possible to replace a wide range of environmentally damaging materials with lignin-based ones. By researching publications from the last 20 years focusing on the latest findings utilizing databases, a comprehensive collection on this topic was crafted. This review summarizes the recent progress made in enzymatically modifying technical lignins utilizing laccases, peroxidases, and lipases. The underlying enzymatic reaction mechanisms and processes are being elucidated and the application possibilities discussed. In addition, the environmental assessment of novel technical lignin-based products as well as the developments, opportunities, and challenges are highlighted.

Functional Lignin Building Blocks: Reactive Vinyl Esters with Acrylic Acid

Introducing vinyl groups onto the backbone of technical lignin provides an opportunity to create highly reactive renewable polymers suitable for radical polymerization. In this work, the chemical modification of softwood kraft lignin was pursued with etherification, followed by direct esterification with acrylic acid (AA). In the first step, phenolic hydroxyl and carboxylic acid groups were derivatized into aliphatic hydroxyl groups using ethylene carbonate and an alkaline catalyst. The lignin was subsequently fractionated using a downward precipitation method to recover lignin of defined molar mass and solubility. After recovery, the resulting material was then esterified with AA, resulting in lignin with vinyl functional groups. The first step resulted in approximately 90% of phenolic hydroxyl groups being converted into aliphatic hydroxyls, while the downward fractionation resulted in three samples of lignin with defined molar masses. For the esterification reaction, the weight ratio of reagents, reaction temperature, and reaction time were evaluated as factors that would influence the modification efficacy. ¹³C NMR spectroscopy analysis of lignin samples before and after esterification showed that the optimized reaction conditions could reach approximately 40% substitution of aliphatic hydroxyl groups. Both steps only used lignin and the modifying reagent (no solvent), with the possibility of recovery and reuse of the reagent by dilution and distillation. An additional second esterification step of the resulting lignin sample with acetic acid or propionic acid converted 90% of remaining hydroxyl groups into short-chain carbon aliphatic esters, making a hydrophobic material suitable for further copolymerization with synthetic hydrophobic monomers.

Enhanced hydrophobic paper-sheet derived from Miscanthus × giganteus cellulose fibers coated with esterified lignin and cellulose acetate blend

Biobased packaging materials derived from carbon-neutral feedstocks are sustainable alternatives to conventional fossil-based polymers. In this study, a method was developed to prepare paper-sheets derived from Miscanthus × giganteus cellulose fibers for potential food contact applications. The papers were hydrophobized with modified lignin from Miscanthus × giganteus biomass and commercial Kraft alkali lignin through hydroxyethylation with ethylene carbonate, followed by esterification with propionic acid. The esterified lignin (10 % w/w) and cellulose acetate (5 % w/w, based on lignin content) were dissolved in acetone and applied as a coating on the miscanthus paper sheets. The esterified lignins were characterized using FTIR, NMR, DSC, TGA, and elemental analyses. The uncoated and coated paper-sheets had contact angle values 52.4° and >130°, respectively, indicating an increased surface hydrophobicity of the coated paper samples. The water vapor transmission rate decreased significantly from 213.7 (uncoated paper-sheet) to 63.3 g/m².d (coated paper-sheet). The tensile strength of the coated paper (64.6 MPa) was higher than the uncoated counterpart (57.1 MPa). Results from this study suggest that the esterified lignin coated miscanthus paper is a promising hydrophobic food packaging material alternative to conventional fossil-based thermoplastics.

Barrier Dispersion-Based Coatings Containing Natural and Paraffin Waxes

Petroleum, synthetic, and natural waxes have been used as hydrophobic bases for dispersions intended for use as barrier coatings for packaging paper. Oil-in-water dispersions with alkaline pH were prepared by a two-step homogenization procedure containing paraffin wax, with various characteristics, the Fischer–Tropsch synthesis product or beeswax. The size of the dispersed particles determined by dynamic light scattering depended on the type of hydrophobic base used and was in the range of 350–440 nm. The ability of dispersion particles in aggregation driven by electrostatic attraction, evaluated by Zeta potential analysis by electrophoretic light scattering, was from −26 to −50 mV. Static multiply light scattering was used for 30 days of stability assessment and helped to select the dispersion with a Sarawax SX70 wax base as the most stable. Dispersions were further used for coating the backing of kraft paper by the Meyer rod method. Coated paper with an applied coating of 6 g/m² had very good hydrophobic properties (Cobb60 < 4 g/m²), sufficient strength properties, and air permeation, which enabled its application as a packaging material. The dispersions based on Sarawax SX70 wax were evaluated as the best coating for Mondi ProVantage Kraftliner 125 g/m² backing paper. Good hydrophobic properties and strength properties indicate the possibility of using the SX70-based wax dispersion coating as a replacement for PFAS coatings in some applications.

Organosolv Lignin Barrier Paper Coatings from Waste Biomass Resources

The aim of the study was to isolate lignin from organosolv, beech tree (Fagus sylvatica), and Japanese knotweed (Reynoutria japonica), to use it for paper surface and to replace part of the non-renewable product resources with bio-based ones. A total of nine coated samples with different lignin formulations and starch were compounded, prepared, and evaluated. The basic (grammage, thickness, specific density), mechanical (elongation at break, tensile, burst and tear indices), and barrier properties (contact angle, water penetration, water vapour permeability, kit test) of the coated papers were investigated. The analysis showed no significant difference in tensile properties between uncoated and coated samples. Furthermore, the decrease in water vapour transmission rate and the lower contact angle for coated samples were nevertheless confirmed. The novel coating materials show promising products with very good barrier properties. Finally, the correlation between structural, morphological, and (other) natural lignin-based factors was revealed, highlighting the importance of parameters such as the equivalence ratio of aliphatic and phenolic hydroxyl groups or the average molecular weight. Tuning functionality by design could optimise performance in the future.

Unravelling the Hydration Barrier of Lignin Oleate Nanoparticles for Acid- and Base-Catalyzed Functionalization in Dispersion State

Lignin nanoparticles (LNPs) are promising renewable nanomaterials with applications ranging from biomedicine to water purification. However, the instability of LNPs under acidic and basic conditions severely limits their functionalization for improved performance. Here, we show that controlling the degree of esterification can significantly improve the stability of lignin oleate nanoparticles (OLNPs) in acidic and basic aqueous dispersions. The high stability of OLNPs is attributed to the alkyl chains accumulated in the shell of the particle, which delays protonation/deprotonation of carboxylic acid and phenolic hydroxyl groups. Owing to the enhanced stability, acid‐ and base‐catalyzed functionalization of OLNPs at pH 2.0 and pH 12.0 via oxirane ring‐opening reactions were successfully performed. We also demonstrated these new functionalized particles as efficient pH‐switchable dye adsorbents and anticorrosive particulate coatings.

Tailoring renewable materials via plant biotechnology

Plants inherently display a rich diversity in cell wall chemistry, as they synthesize an array of polysaccharides along with lignin, a polyphenolic that can vary dramatically in subunit composition and interunit linkage complexity. These same cell wall chemical constituents play essential roles in our society, having been isolated by a variety of evolving industrial processes and employed in the production of an array of commodity products to which humans are reliant. However, these polymers are inherently synthesized and intricately packaged into complex structures that facilitate plant survival and adaptation to local biogeoclimatic regions and stresses, not for ease of deconstruction and commercial product development. Herein, we describe evolving techniques and strategies for altering the metabolic pathways related to plant cell wall biosynthesis, and highlight the resulting impact on chemistry, architecture, and polymer interactions. Furthermore, this review illustrates how these unique targeted cell wall modifications could significantly extend the number, diversity, and value of products generated in existing and emerging biorefineries. These modifications can further target the ability for processing of engineered wood into advanced high performance materials. In doing so, we attempt to illuminate the complex connection on how polymer chemistry and structure can be tailored to advance renewable material applications, using all the chemical constituents of plant-derived biopolymers, including pectins, hemicelluloses, cellulose, and lignins.

Active Barrier Coating for Packaging Paper with Controlled Release of Sunflower Oils

The use of paper as a sustainable packaging material is favored, but it lacks sufficient barrier properties in terms of water repellence and oil resistance. Novel approaches consider active packaging materials or coatings with controlled release providing additional functionality for delivery of specific components to the surface. In this study, the development of a waterborne coating with organic nanoparticles and encapsulated sunflower oils is presented as a system for thermal release of the oil and on-demand tuning of the final barrier properties of the paper substrate. After synthesis of the nanoparticles, it seems that the encapsulation of various grades of sunflower oil (i.e., either poly-unsaturated or mono-unsaturated) strongly affects the encapsulation efficiency and thermal release profiles. The water contact angles are controlled by the oil release and chemical surface composition of the coating upon thermal heating. The oil resistance of the paper improves as a more continuous oil film is formed during thermal release. In particular, the chemical surface composition of the paper coatings is detailed by means of micro-Raman spectroscopy and surface imaging, which provide an analytical quantification tool to evaluate surface coverage, oil delivery, and variations in organic coating moieties.