Molecular iodine has been introduced into the alkali lignin (AL) solutions to adjust the π-π aggregation, and the effect of lignin-iodine complexes on the aggregation and assembly characteristics of AL have been investigated by using fluorescence, UV-vis spectroscopy, light scattering, and viscometric techniques. Results show that AL form π-π aggregates (i.e., J-aggregates) in THF driven by the π-π interaction of the aromatic groups in AL, and the π-π aggregates undergo disaggregation in THF-I(2) media because of the formation of lignin-iodine charge-transfer complexes. By using iodine as a probe to investigate the aggregation behaviors and assembly characteristics, it is estimated that about 18 mol % aromatic groups of AL form π-π aggregates in AL molecular aggregates. When molecular iodine is introduced into the AL solutions, lignin-iodine complexes occur with charge-transfer transition from HOMO of the aromatic groups of AL to the LUMO of iodine. The formation of lignin-iodine complexes reduces the affinity of the aromatic groups approaching each other due to the electrostatic repulsion and then eliminates the π-π interaction of the aromatic groups. The disaggregation of the π-π aggregates brings a dissociation behavior of AL chains and a pronounced molecular expansion. This dissociation behavior and molecular expansion of AL in the dipping solutions induce a decrease in the adsorbed amount and an increase in the adsorption rate, when AL is transferred from the dipping solution to the self-assembled adsorbed films. Consequently, the adsorption behavior of AL can be controlled by adjusting the π-π aggregation. Above observations give insight into the occurrence of J-aggregation of the aromatic groups in the AL molecular aggregates and the disaggregation mechanism of AL aggregates induced by the lignin-iodine complexes for the first time. The understanding can provide an academic instruction in the efficient utilization of the alkali lignin from the waste liquor and also leads to further development in expanding functionalities of the aromatic compounds through manipulation of the π-π aggregation.

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Considering the superior ultraviolet (UV) absorptivity and environmental friendliness of lignin, a novel lignin-based microsphere was prepared. Through self-assembly, sodium lignosulfonate (SL) and cetyltrimethylammonium bromide (CTAB) aggregated into uniform colloidal spheres (SL-CTAB). SL-CTAB performed a reversible aggregation behavior and was used as the shell material to prepare microspheres to encapsulate avermectin (AVM), a kind of photosensitive pesticide. Moreover, the microsphere (AVM@SL-CTAB) exhibited an uniform spherical structure. To reveal the excellent embedding capability of AVM@SL-CTAB, the controlled release and antiphotolysis performance for AVM were systematically investigated in this work. As a result, the encapsulation efficiency value of AVM@SL-CTAB reached to 62.58 ± 0.06%. The release of AVM from AVM@SL-CTAB was still going on after 70 h, and its cumulative release amount at that time was 49.96 ± 1.13%. The release process of AVM@SL-CTAB could be controlled by adjusting the doped proportion of SL-CTAB. The half-life (DT50) of AVM in AVM@SL-CTAB under UV irradiation could be prolonged for 7.35 times that of uncoated AVM. The enhanced photoprotection and the controlled release of AVM implied that SL-CTAB possessed a great application prospect for efficient pesticide utilization.

Lignosulfonate is a type of macromolecular surfactant widely used as interfacial additive in various industrial fields and it is produced during chemical pulping process. In this paper, we present a new effective method for measurement of the critical aggregation concentration (CAC) of sodium lignosulfonate (SL) in water solution, with which a value of 0.38 g L(-1) was obtained. Through the determination of CAC and observation by DLS, the state and dynamics of the formation of the SL micelles were disclosed. The results showed that SL was the state of individual molecules when its mass concentration was less than CAC; the individual SL molecules started to aggregate above CAC and thus micelles formed and grew with increasing SL concentration. The SL solution was quickly frozen and the structures of SL molecules or micelles were observed by ESEM, revealing that the spherical micelles were the main form of SL in the solution. Based on the results, the spherical hollow vesicular structure is proposed as a model of the aggregated micelles of SL in the solution.

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Aggregation-induced emission plays a role in the origin of lignin fluorescence owing to the agglomeration of carbonyl groups and restriction of intramolecular rotation.

In this study, a novel and water-soluble ligninbased polyoxyethylene ether (KL-PEG) was synthesized from kraft lignin (KL) and poly(ethylene glycol) (PEG). PEGs with various polyoxyethylene ether lengths were functionalized preferentially with epichlorohydrin using BF 3 -Et 2 O as the Lewis acid catalyst and then grafted onto KL by blocking the phenolic hydroxyl groups. The generated KL-PEG copolymer was purified successively by extraction, dissolution, and precipitation using butanone, alcohol, and diethyl ether, respectively. The effect of reactant ratios on the structure of the KL-PEG copolymer was investigated by Fourier transform infrared spectra (FTIR), ultraviolet spectrophotometer (UV), gel permeation chromatography (GPC), and functional groups content determination. Solubility and FTIR results revealed the successful introduction of PEG into KL. The PEG content in the KL-PEG copolymer could be controlled by varying the mass ratio of PEG to KL, and the molecular weight could be governed by the molar ratio of epichlorohydrin to PEG. The KL-PEG copolymer was further used as a novel dispersant for 50% dimethomorph suspension concentrates and showed better dispersing and rheological properties comparing with lignosulfonate and PEG. This novel amphiphilic KL-PEG copolymer possessing a renewable lignin backbone and branched PEGs could be a promising dispersant for similar applications, including agricultural suspension concentrates.

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