Preparation And Application Of Alkyl Chain Cross-Linked Water-Soluble Lignin-based Polymer

Lignin is the most abundant biopolymer among all renewable natural resources, and it is also a kind of polyphenolic material which contains rich aromatic rings. The modified water soluble lignin-based polymers have been widely applied in industry due to its hydrophobic aromatic ring and hydrophilic functional groups. Modification methods are desirable to increase weight-average molecular weight(Mw) of lignin, which is of high importance for the improvement of its application performance. However, these methods do not lead to lignin with ultra-high Mw over 50000 Da which is needed in many industrial applications. To address this problem, the paper carried out a series of studies based on the alkyl chain-coupled modification and application of lignin.The present work describes a one pot modification of alkali lignin(AL) via sulfomethylation leading to AL-S and alkylation with different proportions of 1,6-dibromohexane in NaOH aqueous solution leading to alkAL-S samples. Gel permeation chromatography(GPC) showed a significant increase of Mw from 5200 Da of AL-S to 201000 Da of alkAL-S with high degree of alkylation. Phenolic hydroxyl group analysis, FTIR and 1H-NMR spectroscopy confirmed the efficient polymerization by a nucleophilic substitution reaction mechanism. Moreover, alkAL-S with high Mw showed unexpected viscosity-reducing effect, stability and good rheological properties on low rank coal-water slurry(CWS), which are even better than those in case of naphthalene sulfonate formaldehyde(NSF). In addition, hollow nanospheres were obtained via self-assembly of water soluble alkAL-S and investigated by DLS, SEM and TEM, but solid colloidal spheres with AL-S. Moreover, the element analysis and XPS results revealed the hollow sphere structure with a hydrophilic core and a hydrophobic shell. It facilitated the efficient encapsulation of pesticide carbendazim into the hollow sphere via electrostatic interaction, which was investigated by SEM, TEM, elemental analysis and XPS.Adsorption behavior is the main research measure to investigate the dispersion mechanism of lignin-based polymer in suspension system, and the Mw is the key factor because it can affect the three-dimensional network structure and the ratio of hydrophilicity and hydrophobicity of lignin-based polymer. In order to further study the adsorption behavior of narrow distribution alkAL-S polymer on Au surface, Fraction-1, Fraction-2 and Fraction-3 with different Mw were obtained via ultrafiltration of alkAL-S. GPC results showed that the Mws of three fractions are 5800, 43600 and 152000 Da, respectively, and the polydisperse index(PDI) of three fractions ranged from 1.49 to 1.81. The adsorption properties via Quartz Crystal Microbalance(QCM-D) showed that the adsorption amounts of all three fractions were far higher than that of AL-S, and Fraction-1 with low Mw exhibited the maximum adsorption amount on Au surface under the condition of salt free. It is mainly contributed by its hydrophobic chain and compact adsorbed layer on Au surface. The effect of ionic strength on the adsorption behavior was also investigated. When the NaCl concentration of the solution is 0.5 M, the adsorption amounts of three fractions were improved remarkablely, Fraction-3 is particularly pronounced, and achieves the maximum adsorption amount. NaCl could shield electrostatic repulsion and promote the aggregation of alkAL-S fractions, which improves the adsorption behavior of three fractions on Au surface. Fraction-3 with the highest Mw exhibits the highest aggregation, which makes it exhibit the biggest adsorption amount.In order to prove the wide applicability of alkyl chain bridged modification method, Lignosulfonate(LS) was used as raw material to prepare ultrahigh Mw lignosulfonate-based polymers(ALS) via alky chain coupling polymerization. GPC showed a significant increase in Mws from 42800 Da of ALS1 to 251000 Da of ALS5 as one of the highest Mws among reported lignosulfonates(LSs), to date. The self-assembly behavior of ALS was studied in mixed solution of water and ethanol. When the ratio of H2O/EtOH is 1/9, hollow nanospheres were obtained via self-assembly of ALS and investigated by DLS, SEM, TEM and AFM. The hollow sphere structure with a hydrophilic core and a hydrophobic shell was confirmed by XPS and elemental analysis. Stable solid nanospheres were obtained from ALS by the addition of cetyl trimethyl ammonium bromide(CTAB). The results indicate that the ALS will be potentially useful in many applications due to the presence of electrostatic attraction between sulfonic group and other cationic groups to achieve efficient encapsulation of guest molecules including pesticide, food and drug. When the ratio of H2O/EtOH is 1/3, block-like self-assembly was readily performed with supramolecular lignosulfonate-based polymer ALS for the first time. SEM, TEM, AFM, XPS and XRD were applied to explore the regular intrinsic characteristics of the unique aggregates. The formation process of block-like self-assembly was driven by the hierarchical growth of sheet subunits, which were formed from ALS nanoaggregates.The approaches for high-value-added utilization of lignin, as the biomass containing rich aromatic rings in nature, are still of urgent importance to be developed. Inspired by the electron transfer process during oxidation of electron-rich phenol derivative structure and serious aggregation properties of lignin, we studied the hole transporting properties by hole-only devices using lignosulfonate-based polymer as active layer for the first time. LS with more phenolic group content, has higher hole mobility than ALS with less phenolic group content, which further suggested that phenolic group is conducive to the hole transporting property. In experiment, LS and ALS were applied to be dopants in conductive polymer PEDOT, which acted as the hole transport material(HTM) of solar cells with a device structure of ITO/HTM/PTB7:PC71BM/Al. The results showed that the photovoltaic performance of PEDOT:LS was better than that of PEDOT:ALS, and the highest PCE was 5.19%. Then, phloroglucinol was introduced into LS molecule via alkyl chain coupling polymerization to prepare alkyl chain briged phenolated-lignosulfonate(PLS). The-OH content was increased from 0.81 to 1.19 mmol/g. CV and 1HNMR results further indicated that phloroglucinol was successfully introduced in LS molecule via alkyl chain coupling polymerization method. PEDOT:PLS and PEDOT:LS were prepared and applied as HTLs in polymer solar cells with a device structure of ITO/HTL/PTB7-Th:PC71BM/PFN/Al. It was found that the PCE of PEDOT:PLS-1:2 reached to 8.37%, which was comparable to that of PEDOT:PSS-4083(8.34%), and both of them were far higher than that of PEDOT:LS(7.1%).