Lignin self-assembly phenomena and valorization strategies for pulping, biorefining, and materials development: Part 1. The physical chemistry of lignin self-assembly

Physical chemistry aspects are emphasized in this comprehensive review of self-assembly phenomena involving lignin in various forms. Attention to this topic is justified by the very high availability, low cost, and renewable nature of lignin, together with opportunities to manufacture diverse products, for instance, polymers/resins, bioplastics, carbon fibers, bio-asphalt, sunscreen components, hydrophobic layers, and microcapsules. The colloidal lignin material, nanoparticles, and microstructures that can be formed as a result of changes in solvent properties, pH, or other adjustments to a suspending medium have been shown to depend on many factors. Such factors are examined in this work based on the concepts of self-assembly, which can be defined as an organizing principle dependent on specific attributes of the starting entities themselves. As a means to promote such concepts and to facilitate further development of nano-scale lignin products, this article draws upon evidence from a wide range of studies. These include investigations of many different plant sources of lignin, processes of delignification, solvent systems, anti-solvent systems or other means of achieving phase separation, and diverse means of achieving colloidal stability (if desired) of resulting self-assembled lignin structures. Knowledge of the self-organization behavior of lignin can provide significant structural information to optimize the use of lignin in value-added applications. Examples include chemical conditions and preparation procedures in which lignin-related compounds of particles organize themselves as spheres, hollow spheres, surface-bound layers, and a variety of other structures. Published articles show that such processes can be influenced by the selection of lignin type, pulping or extraction processes, functional groups such as phenolic, carboxyl, and sulfonate, chemical derivatization reactions, solvent applications, aqueous conditions, and physical processes, such as agitation. Precipitation from non-aqueous solutions represents a key focus of lignin self-assembly research. The review also considers stabilization mechanisms of self-assembled lignin-related structures.

Simulation and application assessment of the efficacy of fosthiazate-loaded microcapsules against root-knot nematode

BACKGROUND

Although microencapsulation technology is an effective pesticide formulation method, the correlation between the release properties of microcapsules and pesticide concentrations in soil and their efficacy has not been thoroughly investigated. Here, the effects of the release properties of the nematicide Fosthiazate (FTZ) from microcapsules on their efficacy against the nematode Meloidogyne incognita were examined using experimental and mathematical approaches.

RESULTS

Gradual release of FTZ from both polyurea microcapsules (PU-MC) and melamine-formaldehyde microcapsules (MF-MC) was observed over 30 days in the release test, and each release curve was completely distinct. In the biological test, the efficacy of both microcapsules against M. incognita 42 days after the application was 8-15% higher than that of the non-encapsulated FTZ at a concentration of 2.0 mg FTZ kg-1 soil. Soil degradation experiments suggested that the microcapsules worked effectively to protect the FTZ from degradation, which resulted in higher efficacy at a later stage. A simulation study to predict the concentration of FTZ outside the microcapsule found that the timing of supplying FTZ was important and suggested that the mixture of non-encapsulated FTZ (non-MC) and MF-MC showed enhanced efficiency for the entire cultivation period in the biological test; the efficacy against nematodes was also confirmed by the measurement of nematode density using the Bearman funnel method.

CONCLUSION

The release properties of FTZ from microcapsules are critical for their effective application against M. incognita, and the established simulation study is a useful step in designing suitable release properties under complex soil conditions. © 2024 Society of Chemical Industry.

Sustainable lignin-modified epoxy nanocarriers for enhanced foliar insecticide efficacy and food safety

Reducing pesticide residues while extending their efficacy period is a critical challenge in the development of controlled-release pesticides. This study focuses on loading avermectin onto lignin-modified epoxy resin nanocarriers via the creation of photostable nanocapsules (NCs) for evaluating their efficacy against Plutella xylostella. This study also assesses the NCs' resistance to water scour on plant leaves by comparing them with traditional preparations. These NCs feature a stable core-shell structure, an encapsulation efficiency of 92.90 % and slow-release properties. Compared to emulsifiable concentrate (EC) and microemulsion (ME) under UV irradiation, the loading of nanocarriers significantly prolonged the degradation time of avermectin by fivefold. The Nano-formula demonstrated enhanced insecticidal activity in comparison to traditional preparations. Field tests revealed that the efficacy of the NCs on Day 7 (92.55 %) and Day 14 (78.54 %) significantly surpassed that of traditional preparations. Additionally, NCs are more readily washed off cabbage leaves by water than EC and ME, aiding in the reduction of pesticide residues. This technology is particularly suitable for leafy vegetable crops in arid regions or greenhouses, enhancing effectiveness period while minimizing pesticide residues. This research offers novel insights and directions for the development of controlled-release pesticides.

Lignin-based nano-enabled agriculture: A mini-review

Nowadays sustainable nanotechnological strategies to improve the efficiency of conventional agricultural practices are of utmost importance. As a matter of fact, the increasing use of productive factors in response to the growing food demand plays an important role in determining the environmental impact of agriculture. In this respect, low-efficiency conventional practices are becoming obsolete. On the other hand, the exploitation of nanoscaled systems for the controlled delivery of fertilizers, pesticides and herbicides shows great potential towards the development of sustainable, efficient and resilient agricultural processes, while promoting food security. In this context, lignin - especially in the form of its nanostructures - can play an important role as sustainable biomaterial for nano-enabled agricultural applications. In this review, we present and discuss the current advancements in the preparation of lignin nanoparticles for the controlled release of pesticides, herbicides, and fertilizers, as well as the latest findings in terms of plant response to their application. Special attention has been paid to the state-of-the-art literature concerning the release performance of these lignin-based nanomaterials, whose efficiency is compared with the conventional approaches. Finally, the major challenges and the future scenarios of lignin-based nano-enabled agriculture are considered.

State-of-the-Art: Applications and Industrialization of Lignin Micro/Nano Particles

As a new product of high-value utilization of lignin, lignin micro/nano particles (LMNPs) have attracted the attention of researchers due to their non-toxicity, corrosion-resistance, UV resistance, and other excellent characteristics and potential application value. This article outlined the main preparation methods of LMNPs at the current stage, summarized and compared them from three perspectives of preparation technology, final product state and product composition. Subsequently, based on the different focuses of the properties of LMNPs, their application research progress as fillers, UV blockers, drug delivery carriers, among others, were introduced. Then a concise analysis of the technical and economic assessment and life cycle assessment of LMNPs in the process of industrialization was made. Finally, the main problems at present and the future development directions were analyzed and prospected to provide references for the deep processing of forest resources and the development of bio-based nanomaterials.

Coumarin-Containing Light-Responsive Carboxymethyl Chitosan Micelles as Nanocarriers for Controlled Release of Pesticide

Currently, controlled release formulations (CRFs) of pesticides in response to biotic and/or abiotic stimuli have shown great potential for providing “on-demand” smart release of loaded active ingredients. In this study, amphiphilic biopolymers were prepared by introducing hydrophobic (7-diethylaminocoumarin-4-yl)methyl succinate (DEACMS) onto the main chain of hydrophilic carboxymethylchitosan (CMCS) via the formation of amide bonds which were able to self-assemble into spherical micelles in aqueous media and were utilized as light-responsive nanocarriers for the controlled release of pesticides. FTIR and NMR characterizations confirmed the successful synthesis of the CMCS-DEACMS conjugate. The critical micelle concentration (CMC) decreased with the increase in the substitution of DEACMS on CMCS, which ranged from 0.013 to 0.042 mg/mL. Upon irradiation under simulated sunlight, the hydrodynamic diameter, morphology, photophysical properties and photolysis were researched by means of dynamic light scattering (DLS), transmission electron microscopy (TEM), UV-vis absorption spectroscopy and fluorescence spectroscopy. Moreover, 2,4-dichlorophenoxyacetic acid (2,4-D) was used as a model pesticide and encapsulated into the CMCS-DEACMS micelles. In these micelle formulations, the release of 2,4-D was promoted upon simulated sunlight irradiation, during which the coumarin moieties were cleaved from the CMCS backbone, resulting in a shift of the hydrophilic–hydrophobic balance and destabilization of the micelles. Additionally, bioassay studies suggested that this 2,4-D contained which micelles showed good bioactivity on the target plant without harming the nontarget plant. Thereby, the light-responsive CMCS-DEACMS micelles bearing photocleavable coumarin moieties provide a smart delivery platform for agrochemicals.

Effects of microencapsulated abamectin on the mechanical, cross-linking, and release properties of PBS

Herein, nanocomposite microencapsulated abamectin (A-G-G) have been prepared by composite coacervation method with gelatin and gum arabic as the wall materials and abamectin (A-W) as core material. The formation mechanism of A-G-G was determined by fourier-transform infrared spectroscopy, scanning electron microscopy, and other characterization methods. Then, polybutylene succinate (PBS)/A-G-G composite films with different contents of A-G-G microcapsules were prepared. The effects of adding A-G-G microcapsules on the mechanical and sustained-release properties of the composite films were studied. Results show that there is a strong interaction between the CO groups in PBS and free OH of the A-G-G microcapsules. With an increase in the A-G-G microcapsule content, the elongation at the break of composite films increases significantly. When the A-G-G content is 15 %, the elongation at break of the composite films reaches 178.6 ± 6.26 %. The maximum water absorption is 329 ± 5.84 %. Overall, the PBS/A-G-G composite films exhibit good slow-release performance.

Lignin-Graft-Poly(lactic-co-glycolic) Acid Biopolymers for Polymeric Nanoparticle Synthesis

A lignin-graft-poly(lactic-co-glycolic) acid (PLGA) biopolymer was synthesized with two types of lignin (LGN), alkaline lignin (ALGN) and sodium lignosulfonate (SLGN), at different (A/S)LGN/PLGA ratios (1:2, 1:4, and 1:6 w/w). 1H NMR and Fourier-transform infrared spectroscopy (FT-IR) confirmed the conjugation of PLGA to LGN. The (A/S)LGN-graft-PLGA biopolymers were used to form nanodelivery systems suitable for entrapment and delivery of drugs for disease treatment. The LGN-graft-PLGA NPs were generally small (100-200 nm), increased in size with the amount of PLGA added, monodisperse, and negatively charged (-48 to -60 mV). Small-angle scattering data showed that particles feature a relatively smooth surface and a compact spherical structure with a distinct core and a shell. The core size and shell thickness varied with the LGN/PLGA ratio, and at a 1:6 ratio, the particles deviated from the core-shell structure to a complex internal structure. The newly developed (A/S)LGN-graft-PLGA NPs are proposed as a potential delivery system for applications in biopharmaceutical, food, and agricultural sectors.

A Facile Approach to Increasing the Foliage Retention of Pesticides Based on Coating with a Tannic Acid/Fe3+ Complex

The effective utilization of many conventional pesticide formulations is less than 30%, which can increase the environmental impact of these substances. This degree of waste could be reduced by improving the adhesion of pesticides to foliage. In the present work, a complex comprising tannic acid (TA) and Fe3+ ions was used to encapsulate azoxystrobin and avermectin water dispersible granule (WDG) formulations (termed Az-WDG-TA and Av-WDG-TA) to improve adhesion. The treated pesticides exhibited improved photostability as well as sustained continuous release behavior. The retention proportions of the Az-WDG-TA and Av-WDG-TA on cucumber and lettuce foliage were improved by more than 50%. The ability of solutions of these materials to wet foliage was also enhanced after coating, such that the toxicity of Av-WDG-TA to aphids and the antifungal activity of Az-WDG-TA to Fusarium oxysporum were increased by nearly 50%. Given the low cost of TA and Fe3+ compounds and the simple synthesis process, this method represents a promising means of producing foliage-adhesive pesticide formulations with increased retention and bioavailability.

Characterization and Biological Action of Avermectin Granules on the Moroccan Locust, Dociostaurus maroccanus (Orthoptera: Acrididae)

Granules composed of alfalfa and sunflower meal that were impregnated with avermectins (AVMs) were developed for use against the Moroccan locust, Dociostaurus maroccanus (Thunberg). Laboratory experiments with granules containing 0.15% of AVMs fed to locust nymphs resulted in 100% death within 5 d. The quantification of AVM loss after exposure of AVM-containing preparative forms to UV light for various time periods was performed using high-performance liquid chromatography (HPLC). The results showed no loss of AVMs from the granules after 3 h of their exposure to UV light. The effect of UV radiation on a thin layer of the AVM solution led to the rapid degradation of AVMs. Only 0.2% of the initial AVM amount was detected after 3 h of exposure. In the granulated form, the AVM content remained stable for 10 mo when stored at room temperature in the dark. A method combining solid-phase extraction with HPLC was developed for the quantification of AVMs in locust nymphs. The granulated AVMs are characterized by their high resistance to UVB radiation. The use of plant-based granules impregnated with AVMs can be considered a very promising tool for locust control.

Synthesis of a Hindered Amine-Grafted Lignin-Based Emulsifier and Its Application in a Green Emulsifiable Concentrate

4-Amion-2,2,6,6-tetramethylpiperidine (Temp) was grafted into sodium lignosulfonate (SL) to obtain hindered amine-modified lignosulfonate (SL-Temp). Then, the polymer surfactant (SL-Temp-CTAB) was prepared using cetyltrimethylammonium bromide (CTAB) and SL-Temp. Obtained SL-Temp-CTAB was used as an emulsifier to prepare a green emulsifiable concentrate (EC) of avermectin (AVM), which shows good emulsifying property and storage stability. The prepared AVM green EC can form AVM-loaded microspheres with nanometer particle size distribution after emulsification in water. After ultraviolet irradiation for 70 h, the AVM retention rate of the green EC prepared using SL-Temp-CTAB was 75.8%, which is much higher than that of commercial EC (0.4%) and the green EC prepared using unmodified SL (31.4%). Moreover, the AVM green EC prepared using SL-Temp-CTAB has slow-release performance, and the release equilibrium time is 5.3 times the commercial EC. Therefore, the newly prepared AVM green EC using a lignin-based functional emulsifier shows good antiphotolysis and slow-release performance compared to the traditional EC.

Enzyme and pH dual-responsive avermectin nano-microcapsules for improving its efficacy

The overdosage use of pesticide was harmful to the environment and human health, which was mainly caused by the low utilization rate of the pesticide. However, the pesticide microcapsule with sustained-release and stimulating response properties could effectively solve this problem. Preparation of carboxymethyl cellulose grafting dimethyldiallylammonium chloride (CMC-g-PDMDAAC) through grafting polymerization and trapping as well as encapsulation of avermectin (AVM) via electrostatic interactions resulted in the formation of AVM/CMC-g-PDMDAAC microcapsules. The results showed that the particle size was 200~300 nm. The encapsulation efficiency was as high as 72.06%. Furthermore, the remaining rate of encapsulated AVM increased from 50.0 to 81.60% after UV irradiation for 359 min. The microcapsules exhibited significant enzyme and pH stimuli responsiveness. Finally, CMC-g-PDMDAAC had no significant difference effect on the toxicity of AVM, AVM could be found, and DMDAAC featured a synergistic effect on the toxicological effects of AVM. Graphical abstract.

Co-encapsulation of imidacloprid and lambda-cyhalothrin using biocompatible nanocarriers: Characterization and application

A well-known strategy for managing pest resistance is application of mixture of pesticides. Conventionally formulated pesticides have several environmental incompatibilities. The use of biocompatible and biodegradable nanocarriers in formulating pesticides could improve environmental protection. In this study, a mixture of imidacloprid and lambda-cyhalothrin was co-encapsulated for the first time using liposomes as nanocarrier to simultaneously deliver these insecticides. Ethanol injection was used to produce self-assembled liposomes. The formed nanoliposomes were coated with different concentrations of chitosan. Nanoparticles were characterized by dynamic light scattering (DLS), scanning electron microscope (SEM) and FT-IR spectroscopy. The encapsulation efficiencies of lambda-cyhalothrin and imidacloprid were about 93% and 51%, respectively. The insecticide carrying liposomes had a size and surface charge of 57 nm and +0.6 mV, respectively. The size and surface charge of the particles produced were increased to 69 nm and +31 mV after being coated with chitosan (0.1%, W/V). In this study, residual activity of technical grade imidacloprid, lambda-cyhalothrin and their mixture and the effect of adjuvants used in commercial and nano formulations of these insecticides on Myzus persicae Sulzer was investigated. The insecticidal effects and duration of residual activity of nano-formulations was correlated with concentration of chitosan in final formulation. In accordance with the life cycle of M. persicae, using the mixture of imidacloprid and lambda-cyhalothrin improves the residual effect over their use alone. The use of lipid nanocarriers makes the improvement even further and can be a better alternative to conventional combination of these insecticides due to their more environmental friendliness.

Effects of Lignin-Based Hollow Nanoparticle Structure on the Loading and Release Behavior of Doxorubicin

Because of their exceptional absorption capacity, biodegradability, and nontoxicity, nanomaterials fabricated from renewable natural resources have recently become an increasingly important research area. However, the mechanism of drug encapsulation by lignin nanoparticles and the role of nanoparticle structure on the stability and loading performance still remain unknown. Herein, lignin hollow nanoparticles (LHNPs) were prepared and applied as promising vehicles for the antineoplastic antibiotic drug doxorubicin hydrochloride (DOX). The hydrogen bonding and π-π interactions contributed to the encapsulation of hydrophilic DOX by LHNPs with hydrophobic cavities. The encapsulation of DOX was enhanced by the pore volume and surface area. In addition, the nanoparticles contributed to the cellular uptake and the accumulation of the drug within HeLa cells. This work provides a scientific basis for future studies on the selective entrapment properties of hollow polymer nanoparticles derived from biomass material as vehicles for overcoming pharmacokinetic limitations.

Lignin for Nano- and Microscaled Carrier Systems: Applications, Trends, and Challenges

To liberate society from its dependence on fossil-based fuels and materials it is pivotal to explore components of renewable plant biomass in applications that benefit from their intrinsic biodegradability, safety, and sustainability. Lignin, a byproduct of the pulp and paper industry, is a plausible material for carrying various types of cargo in small- and large-scale applications. Herein, possibilities and constraints regarding the physical-chemical properties of the lignin source as well as modifications and processing required to render lignins suitable for the loading and release of pesticides, pharmaceuticals, and biological macromolecules is reviewed. In addition, the technical challenges, regulatory and toxicological aspects, and future research needed to realize some of the promises that nano- and microscaled lignin materials hold for a sustainable future are critically discussed.

Preparation and Characterization of Controlled-Release Avermectin/Castor Oil-Based Polyurethane Nanoemulsions

Avermectin (AVM) is a low-toxic and high-active biopesticide, but it can be easily degraded by UV light. In this paper, biodegradable castor oil-based polyurethanes (CO-PU) are synthesized and used as carriers to fabricate a new kind of AVM/CO-PU nanoemulsion through an emulsion solvent evaporation method, and the chemical structure, colloidal property, AVM loading capacity, controlled-release behavior, foliar adhesion, and photostability of the AVM/CO-PU drug delivery systems are investigated. Results show that AVM is physically encapsulated in the CO-PU carrier nanospheres, the diameter of the AVM/CO-PU nanoparticles is <50 nm, and the AVM/CO-PU films are flat and smooth without any AVM aggregate. The drug loading capacity is up to 42.3 wt % with a high encapsulation efficiency of >85%. The release profiles indicate that the release rate is relatively high at the early stage and then slows, which can be adjusted by loaded AVM content, temperature, and pH of the release medium. The foliar pesticide retention of the AVM/CO-PU nanoemulsions is improved, and the photolysis rate of AVM in the AVM/CO-PU nanoparticles is significantly slower than that of the free AVM. A release mechanism of the AVM/CO-PU nanoemulsions is proposed, which is controlled by both diffusion and matrix erosion.

Spherical and Spindle-Like Abamectin-Loaded Nanoparticles by Flash Nanoprecipitation for Southern Root-Knot Nematode Control: Preparation and Characterization

Southern root-knot nematode (Meloidogyne incognita) is a biotrophic parasite, causing enormous loss in global crop production annually. Abamectin (Abm) is a biological and high-efficiency pesticide against Meloidogyne incognita. In this study, a powerful method, flash nanoprecipitation (FNP), was adopted to successfully produce Abm-loaded nanoparticle suspensions with high drug loading capacity (>40%) and encapsulation efficiency (>95%), where amphiphilic block copolymers (BCPs) poly(lactic-co-glycolic acid)-b-poly(ethylene glycol) (PLGA-b-PEG), poly(d,l-lactide)-b-poly(ethylene glycol) (PLA-b-PEG), or poly(caprolactone)-b-poly(ethylene glycol) (PCL-b-PEG) were used as the stabilizer to prevent the nanoparticles from aggregation. The effect of the drug-to-stabilizer feed ratio on the particle stability were investigated. Moreover, the effect of the BCP composition on the morphology of Abm-loaded nanoparticles for controlling Meloidogyne incognita were discussed. Notably, spindle-like nanoparticles were obtained with PCL-b-PEG as the stabilizer and found significantly more efficient (98.4% mortality at 1 ppm particle concentration) than spherical nanoparticles using PLGA-b-PEG or PLA-b-PEG as the stabilizer. This work provides a more rapid and powerful method to prepare stable Abm-loaded nanoparticles with tunable morphologies and improved effectiveness for controlling Meloidogyne incognita.

Different residue behaviors of four pesticides in mushroom using two different application methods

Pesticide residue in mushrooms is less known. In this study, the risks of beta-cypermethrin, pyriproxyfen, avermectin, and diflubenzuron in oyster and shiitake mushrooms were evaluated using two different treatments: substrate mixture and surface spraying. Almost all the concentrations of these pesticides at day 90 were higher than 80% of the initial concentrations, while it was less than 45% for all cases within 35 days by spraying. For surface spraying, the residues of beta-cypermethrin were 0.0843-1.22 mg kg^-1 in shiitake mushrooms and below 0.005 mg kg^-1 in oyster mushrooms; the residues of pyriproxyfen, avermectin, and diflubenzuron were 0.122-4.84, 0.00501-0.111, and 0.0681-1.91 mg kg^-1, respectively. The residues of beta-cypermethrin, pyriproxyfen, and diflubenzuron in oyster mushrooms (in shiitake mushrooms) at interval of 0, 3, 5 days (1, 5, 7 days) were below their MRLs in China or Japan. The residue of avermectin in both mushrooms was lower than its limit of detection. These results provide information to safe and proper use of the pesticides in oyster and shiitake mushrooms.

Preparation and properties of lambda-cyhalothrin/polyurethane drug-loaded nanoemulsions

A new lambda-cyhalothrin/castor oil-based polyurethane formulation with controlled-release behavior and good foliage adhesion properties is prepared.