A recent advancement on preparation, characterization and application of nanolignin

The Impact of Lignin Biopolymer Sources, Isolation, and Size Reduction from the Macro- to Nanoscale on the Performances of Next-Generation Sunscreen

In recent years, concerns about the harmful effects of synthetic UV filters on the environment have highlighted the need for natural sun blockers. Lignin, the most abundant aromatic renewable biopolymer on Earth, is a promising candidate for next-generation sunscreen due to its inherent UV absorbance and its green, biodegradable, and biocompatible properties. Lignin's limitations, such as its dark color and poor dispersity, can be overcome by reducing particle size to the nanoscale, enhancing UV protection and formulation. In this study, 100-200 nm lignin nanoparticles (LNPs) were prepared from various biomass by-products (hardwood, softwood, and herbaceous material) using an eco-friendly anti-solvent precipitation method. Pure lignin macroparticles (LMPs) were extracted from beech, spruce, and wheat straw using an ethanol-organosolv treatment and compared with sulfur-rich kraft lignin (KL). Sunscreen lotions made from these LMPs and LNPs at various concentrations demonstrated novel UV-shielding properties based on biomass source and particle size. The results showed that transitioning from the macro- to nanoscale increased the sun protection factor (SPF) by at least 2.5 times, with the best results improving the SPF from 7.5 to 42 for wheat straw LMPs and LNPs at 5 wt%. This study underscores lignin's potential in developing high-quality green sunscreens, aligning with green chemistry principles.

Preparation and Characterization of Lignin Nanoparticles from Different Plant Sources

This article presents new research on producing lignin nanoparticles (LNPs) using the antisolvent nanoprecipitation method. Acetone (90%) served as the lignin solvent and water (100%) as the antisolvent, using five types of lignins from various sources. Comprehensive characterization techniques, including NMR, GPC, FTIR, TEM, and DLS, were employed to assess both lignin and LNP properties. The antioxidant activity of the LNPs was evaluated as well. The results demonstrated the successful formation of spherical nanoparticles below 100 nm with initial lignin concentrations of 1 and 2%w/v. The study highlighted the crucial role of lignin purity in LNP formation and colloidal stability, noting that residual carbohydrates adversely affect efficiency. This method offers a straightforward, environmentally friendly approach using cost-effective solvents, applicable to diverse lignin sources. The innovation of this study lies in its demonstration of a cost-effective and eco-friendly method to produce stable, nanometric-sized spherical LNPs. These LNPs have significant potential as reinforcement materials due to their reinforcing capability, hydrophilicity, and UV absorption. This work underscores the importance of starting material purity for optimizing the process and achieving the desired nanometric dimensions, marking a pioneering advancement in lignin-based nanomaterials.

Optimization of areca leaf sheath nanolignin synthesis by a mechanical method for in situ modification of ultra-low molar ratio urea-formaldehyde adhesives

This study addresses the optimization of the nanolignin preparation method from the areca leaf sheath (ALS) by a mechanical process using a high shear homogenizer at 13,000-16,000 rpm for 1-4 h and its application in enhancing the performance of ultralow molar ratio urea-formaldehyde (UF) adhesive. Response surface methodology (RSM) with a central composite design (CCD) model was used to determine the optimum nanolignin preparation method. The mathematical model obtained was quadratic for the particle size response and linear for the zeta potential response. Under the optimum conditions, a speed of 16,000 rpm for 4 h resulted in a particle size of 227.7 nm and a zeta potential of -18.57 mV with a high desirability value of 0.970. FE-SEM revealed that the characteristic changes of lignin to nanolignin occur from an irregular or nonuniform shape to an oval shape with uniform particles. Nanolignin was introduced during the addition reaction of UF resin synthesis. UF modified with nanolignin (UF-NL) was analyzed for its adhesive characteristics, functional groups, crystallinity, and thermomechanical properties. The UF-NL adhesive had a slightly greater solid content (73.23 %) than the UF adhesive, a gelation time of 4.10 min, and a viscosity of 1066 mPa.s. The UF-NL adhesive had similar functional groups as the UF adhesive, with a lower crystallinity of 59.73 %. Compared with the control plywood which has a tensile shear strength value of 0.79 MPa, the plywood bonded with UF-NL had a greater tensile shear strength of 1.07 MPa, with a lower formaldehyde emission of 0.065 mg/L.

Spray Coating of Wood with Nanoparticles from Lignin and Polylactic Glycolic Acid Loaded with Thyme Essential Oils

Ensuring the longevity of wooden constructions depends heavily on the preservation process. However, several traditional preservation methods involving fossil-based compounds have become outdated because they pose a significant risk to the environment and to human health. Therefore, the use of bio-based and bioactive solutions, such as essential oils, has emerged as a more sustainable alternative in protecting wood from biotic attacks. The entrapment of essential oils in polymeric carrier matrices provides protection against oxidation and subsequent degradation or rapid evaporation, which implies the loss of their biocidal effect. In this work, lignin as well as PLGA nanoparticles containing the essential oils from two different thyme species (Thymus capitatus and T. vulgaris) were applied on beech wood samples using spray coating. The prepared coatings were investigated using FTIR imaging, SEM, as well as LSM analysis. Release experiments were conducted to investigate the release behavior of the essential oils from their respective lignin and PLGA carrier materials. The study found that lignin nanoparticles were more effective at trapping and retaining essential oils than PLGA nanoparticles, despite having larger average particle diameters and a more uneven particle size distribution. An analysis of the lignin coatings showed that they formed a uniform layer that covered most of the surface pores. PLGA nanoparticles formed a film-like layer on the cell walls, and after leaching, larger areas of native wood were evident on the wood samples treated with PLGA NPs compared to the ones coated with lignin NPs. The loading capacity and efficiency varied with the type of essential oil, while the release behaviors were similar between the two essential oil types applied in this study.

Corn straw lignin - A sustainable bioinspired finish for superhydrophobic and UV-protective cellulose fabric

Hydrophobic textiles have been considered extensively for self-cleaning, phase-separating, and biomedical curing applications. We focused on preparing an eco-friendly lignin-based bio-finish to develop superhydrophobic cellulose fabric under mild conditions. The mass spectroscopic analysis expressed that the lignin comprised the major constituents of p-coumaryl alcohol, ferulic acid, coniferyl alcohol, and sinapyl alcohol. The surface morphological analysis indicated the formation of a regular lignin coating on the cellulose fabric. The bio-finished cellulose fabric prepared (at 2 %, w/v, lignin) expressed the maximum water contact angle (WCA) of 157.2° and remained in the hydrophobic range (119°) after ten standard washes. The treated fabric expressed the WCA values of 135.0 and 133.0° after exposure to pH 2 and 12 aqueous media, respectively. The infrared spectroscopic analysis indicated the functional chemistry of the precursors involved and possible alteration in their chemical interactions during processing. The lignin-treated cellulose was observed to be less crystalline as compared to the untreated one. Such fabric expressed acceptable comfort, sensorial properties, and thermal stability up to 333 °C. The treated fabrics could block up to 92.24 % UV-A and 98.62 % UV-B radiations. Consequently, the lignin-based finish sourced from wasted corn straw was found cost-effective and efficient for producing superhydrophobic cellulose fabric.

Lignin Nanoparticles with Entrapped Thymus spp. Essential Oils for the Control of Wood-Rot Fungi

After decades of utilization of fossil-based and environmentally hazardous compounds for wood preservation against fungal attack, there is a strong need to substitute those compounds with bio-based bioactive solutions, such as essential oils. In this work, lignin nanoparticles containing four essential oils from thyme species (Thymus capitatus, Coridothymus capitatus, T. vulgaris, and T. vulgaris Demeter) were applied as biocides in in vitro experiments to test their anti-fungal effect against two white-rot fungi (Trametes versicolor and Pleurotus ostreatus) and two brown-rot fungi (Poria monticola and Gloeophyllum trabeum). Entrapment of essential oils provided a delayed release over a time frame of 7 days from the lignin carrier matrix and resulted in lower minimum inhibitory concentrations of the essential oils against the brown-rot fungi (0.30-0.60 mg/mL), while for the white-rot fungi, identical concentrations were determined compared with free essential oils (0.05-0.30 mg/mL). Fourier Transform infrared (FTIR) spectroscopy was used to assess the fungal cell wall changes in the presence of essential oils in the growth medium. The results regarding brown-rot fungi present a promising approach for a more effective and sustainable utilization of essential oils against this class of wood-rot fungi. In the case of white-rot fungi, lignin nanoparticles, as essential oils delivery vehicles, still need optimization in their efficacy.

Poly(Lactic Acid) Composites with Lignin and Nanolignin Synthesized by In Situ Reactive Processing

Poly(lactic acid) (PLA) composites with 0.5 wt% lignin or nanolignin were prepared with two different techniques: (a) conventional melt-mixing and (b) in situ Ring Opening Polymerization (ROP) by reactive processing. The ROP process was monitored by measuring the torque. The composites were synthesized rapidly using reactive processing that took under 20 min. When the catalyst amount was doubled, the reaction time was reduced to under 15 min. The dispersion, thermal transitions, mechanical properties, antioxidant activity, and optical properties of the resulting PLA-based composites were evaluated with SEM, DSC, nanoindentation, DPPH assay, and DRS spectroscopy. All reactive processing-prepared composites were characterized by means of SEM, GPC, and NMR to assess their morphology, molecular weight, and free lactide content. The benefits of the size reduction of lignin and the use of in situ ROP by reactive processing were demonstrated, as the reactive processing-produced nanolignin-containing composites had superior crystallization, mechanical, and antioxidant properties. These improvements were attributed to the participation of nanolignin in the ROP of lactide as a macroinitiator, resulting in PLA-grafted nanolignin particles that improved its dispersion.

Current roles of lignin for the agroindustry: Applications, challenges, and opportunities

Lignin has the potential to be used as an additive, coating agent, fertilizer, plant growth stimulator, and packaging material in the agroindustry due to its functional aromatic structure. The quantitative measurement of functional groups is a significant element of the research for lignin structure since they directly impact their optical, dispersion, and chemical properties. These physical and chemical properties of lignin strongly depend on its type and source and its isolation procedure. Thus, lignin provides numerous opportunities for the circular economy in the agroindustry; however, studying and resolving the challenges associated with its separation, purification, and modification is required. This review discusses the most recent findings on lignin use in agroindustry and historical facts about lignin. The properties of lignin and its roles as coating agents, pesticide carriers, plant growth stimulators, and soil-improving agents have been summarized. The emerging challenges in the field of lignin-based agroindustry are considered, and potential future steps to overcome these challenges are discussed.

Lignin nanoparticle reinforced multifunctional polyvinyl alcohol/polyurethane composite hydrogel with excellent mechanical, UV-blocking, rheological and thermal properties

In this study, we innovatively synthesized a multifunctional PVA/PU-LNP composite hydrogel with integrated distinguished UV-blocking, mechanical strength, dynamic viscoelasticity and thermal properties by introducing lignin nanoparticle (LNP) into polyvinyl alcohol (PVA) and polyurethane (PU) mixed matrix through freeze-thaw cycle. The rigid porous network structure was established by hydrogen bond interactions among the well-distributed LNP and PVA/PU molecular chains, which endowed excellent mechanical strength, viscoelasticity, thermal stability and flexibility with PVA/PU-LNP composite hydrogel. The elongation at break and tensile strength of PVA/PU-LNP composite hydrogel were markedly improved from 227.3 % and 247.1 KPa to 460.1 % and 950.4 KPa with the LNP loading of 2 % based on PVA weight, respectively. Meanwhile, PVA/PU-2%LNP hydrogel exhibited prominent compressive resistance and pleasing shape recovery capability. Moreover, the blending of LNP at a low dosage (0.5 %) based on PVA weight effectively shielded 99.34 % of UV light and penetrated 42.27 % of visible light, indicating that PVA/PU-LNP composite hydrogel demonstrated outstanding anti-UV performance. In addition, the incorporation of LNP caused a remarkable decline in the pore size of PVA/PU-LNP composite hydrogel (4.39 ± 0.46 μm to 1.54 ± 0.22 μm), which slightly reduced water uptake capacity of composite hydrogel. Therefore, this work provided a new approach to constructing a multifunctional composite hydrogel.

Surface Treatment of Mongolian Scots Pine Using Phosphate Precipitation for Better Performance of Compressive Strength and Fire Resistance

Wood, as a naturally green and environmentally friendly material, has been widely used in the construction and decoration industries. However, the flammability of wood poses serious safety problems. To improve the fire resistance of wood, In this study, it is proposed to use calcium chloride (CaCl₂) and disodium hydrogen phosphate (Na₂HPO₄, DSP) to impregnate wood for multiple cycles. The experimental results show that phosphate mineral precipitation can be deposited on the surface of the wood. Scanning electron microscopy (SEM) and X-ray diffraction (XRD) are used to analyze the micromorphology of mineral precipitation and use the MIP test to analyze the treated wood pore structure. The results show that with the increase in the number of cycles, the phosphate deposited on the surface of the wood increases, and the cumulative pore volume and water absorption rate of the wood after 10 cycles are 54.3% and 13.75% lower than that of untreated wood respectively. In addition, the cone calorimeter (CONE) confirmed that the total heat release (THR) and total smoke production (TSP) of wood treated in 10 cycles have decreased by 48.7% and 54.2% respectively compared with the untreated wood. Hence, this treatment method not only improves the mechanical properties of wood. It also improves fire resistance.

Bio-based films with high antioxidant and improved water-resistant properties from cellulose nanofibres and lignin nanoparticles

In this study, we propose a simple route for the fabrication of bio-based composite films from cellulose nanofibres (CNF) and lignin. First, CNFs were periodate oxidised to obtain dialdehyde cellulose nanofibres (DACNF). Subsequently, lignin nanoparticles (LNPs) with diameters between 50 and 150 nm were prepared using kraft lignin and mixed with DACNF to fabricate DACNF-LNP nanocomposite films via a condensation reaction. The addition of LNPs rendered the films with high ultraviolet-shielding and antioxidant properties. The water contact angle increased for the composite films compared with that of pure CNF film, while the water vapor transmission rate (WVTR) decreased. The mechanical properties of the nanocomposite films were significantly improved by the addition of LNPs. The dry tensile stress of DACNF-LNPs5 with 5 % LNPs significantly increased from 47 to 164 MPa. It was also higher than that of CNF-LNPs5 (105 MPa), in which CNFs were not periodate oxidised. After immersion in water for 1 h, the wet tensile strength of DACNF-LNPs5 was 31 MPa, 3 times higher than that of CNF-LNPs5 (7 MPa). These results indicate that the water-resistant properties of the composite films were significantly enhanced. The films prepared from green and renewable bioresources exhibited potential applications in food packaging and biomedical materials.

Valorization of nano-based lignocellulosic derivatives to procure commercially significant value-added products for biomedical applications

Biowaste, produced from nature, is preferred to be a good source of carbon and ligninolytic machinery for many microorganisms. They are complex biopolymers composed of lignin, cellulose, and hemicellulose traces. This biomass can be depolymerized to its nano-dimensions to gain exceptional properties useful in the field of cosmetics, pharmaceuticals, high-strength materials, etc. Nano-sized biomass derivatives overcome the inherent drawbacks of the parent material and offer promises as a potential material for a wide range of applications with their unique traits such as low-toxicity, biocompatibility, biodegradability and environmentally friendly nature with versatility. This review focuses on the production of value-added products feasible from nanocellulose, nano lignin, and xylan nanoparticles which is quite a novel study of its kind. Dawn of nanotechnology has converted bio waste by-products (hemicellulose and lignin) into useful precursors for many commercial products. Nano-cellulose has been employed in the fields of electronics, cosmetics, drug delivery, scaffolds, fillers, packaging, and engineering structures. Xylan nanoparticles and nano lignin have numerous applications as stabilizers, additives, textiles, adhesives, emulsifiers, and prodrugs for many polyphenols with an encapsulation efficiency of 50%. This study will support the potential development of composites for emerging applications in all aspects of interest and open up novel paths for multifunctional biomaterials in nano-dimensions for cosmetic, drug carrier, and clinical applications.

Antibacterial lignin-based nanoparticles and their use in composite materials

Lignin, one of the most abundant biopolymers on earth, has been traditionally considered a low-value by-product of the pulp and paper industries. This renewable raw material, besides being a source of valuable molecules for the chemical industry, also has antioxidant, UV-absorbing, and antibacterial properties in its macromolecular form. Moreover, lignin in the form of nanoparticles (LigNPs) presents advantages over bulk lignin, such as higher reactivity due to its larger surface-to-volume ratio. In view of the rapid surge of antimicrobial resistance (AMR), caused by the overuse of antibiotics, continuous development of novel antibacterial agents is needed. The use of LigNPs as antibacterial agents is a suitable alternative to conventional antibiotics for topical application or chemical disinfectants for surfaces and packaging. Besides, their multiple and unspecific targets in the bacterial cell may prevent the emergence of AMR. This review summarizes the latest developments in antibacterial nano-formulated lignin, both in dispersion and embedded in materials. The following roles of lignin in the formulation of antibacterial NPs have been analyzed: (i) an antibacterial active in nanoformulations, (ii) a reducing and capping agent for antimicrobial metals, and (iii) a carrier of other antibacterial agents. Finally, the review covers the inclusion of LigNPs in films, fibers, hydrogels, and foams, for obtaining antibacterial lignin-based nanocomposites for a variety of applications, including food packaging, wound healing, and medical coatings.

Recent Advances in the Development of Fire-Resistant Biocomposites—A Review

Biocomposites reinforced with natural fibers represent an eco-friendly and inexpensive alternative to conventional petroleum-based materials and have been increasingly utilized in a wide variety of industrial applications due to their numerous advantages, such as their good mechanical properties, low production costs, renewability, and biodegradability. However, these engineered composite materials have inherent downsides, such as their increased flammability when subjected to heat flux or flame initiators, which can limit their range of applications. As a result, certain attempts are still being made to reduce the flammability of biocomposites. The combustion of biobased composites can potentially create life-threatening conditions in buildings, resulting in substantial human and material losses. Additives known as flame-retardants (FRs) have been commonly used to improve the fire protection of wood and biocomposite materials, textiles, and other fields for the purpose of widening their application areas. At present, this practice is very common in the construction sector due to stringent fire safety regulations on residential and public buildings. The aim of this study was to present and discuss recent advances in the development of fire-resistant biocomposites. The flammability of wood and natural fibers as material resources to produce biocomposites was researched to build a holistic picture. Furthermore, the potential of lignin as an eco-friendly and low-cost FR additive to produce high-performance biocomposites with improved technological and fire properties was also discussed in detail. The development of sustainable FR systems, based on renewable raw materials, represents a viable and promising approach to manufacturing biocomposites with improved fire resistance, lower environmental footprint, and enhanced health and safety performance.