| It has become a hot topic in the fields of chemical engineering and chemistry to use renewable natural resources and produce environmentally friendly green products. Lignin is the second most abundant renewable resource on earth and it is a natural biopolymer. Sodium lignosulfonate(SL) comes from the byproducts of the pulp and paper industry. As a kind of anionic surfactant, SL is abundant, low cost and nontoxic, and it can be widely used in many fields. However, the application performance of SL is poor and it was used as a class of low-end products. It is necessary to have it modified to improve its performance by chemical modification.As a special surfactant emerged in recent years, the cationic/anionic surfactant has good surface activity and is low-cost. But it is difficult to control the preparation process of this surfactant. Flocculation phenomenon always occurs in preparation process which results in failure. In order to solve the poor water-solubility problem of the cationic/anionic surfactant, the ethoxy chain is often introduced into the surfactants.In the present study, SL, which comes from the byproducts of the pulp and paper industry, was chosen as raw materials. The lignin-based polyoxyethylene(SL-PEG) was synthesized by grafting SL with polyethylene glycol(PEG) long chains. The structural characteristics and solution behaviors of SL-PEG were investigated by means of infrared spectrometer, hydrogen nuclear magnetic resonance spectrometer, gel permeation chromatography, ultraviolet spectrograph and surface tension. Results showed that PEG has been grafted in SL; The PEG content of synthesized SL-PEG was ranged from 20% to 50%. The phenolic hydroxyl group of SL decreased after grafting PEG. In addition, the surface tension of SL-PEG increased and surface activity increased compared with SL. The Mw and Mn of SL-PEG were higher than SL. The Mw of SL was 12028 and the Mw of synthesized SL-PEG was on a scale of 16447 to 34473. The synthesis crafts of SL-PEG was studied. Results showed that the reaction time had little effect on the molecular weight of SL-PEG; The molecular weight of SL-PEG was highest when the reaction temperature was 75 ℃ and p H of solution was 11.The structure and charge properties of SL have been investigated by means of gel permeation chromatography, acid-base titration and particulate charge analyzer. Results showed that the contents of sulfonic group, carboxyl, phenolic hydroxyl and the surface charge of SL-PEG reduced. The cationic/anionic surfactant(CA-SL) was prepared by the electrostatic assembly of SL-PEG and cetyl trimethyl ammonium bromide(CTAB). With the use of zeta potential and dynamic light scattering, this research revealed charge properties and particle size distribution of CA-SL. Different mass ratio of CTAB/SL-PEG of CA-SL was prepared based on the results measured by zeta potential. There were molecules and aggregates in CA-SL solution. With the increase of the mass ratio of CTAB/SL-PEG, the particle size of the CA-SL aggregates reached the biggest when the zeta potential was zero and then turned small when the zeta potential was positive.The critical aggregate concentration(CAC) and surface tension of CA-SLwere studied. It was concluded that the CA-SL had stronger ability to lower the surface tension at air/water interface comparing to SL-PEG, but weaker than CTAB. However, the CACs of CA-SLs inside the solution were lower than those of both SL-PEG and CTAB. The CA-SL exhibited more obvious physical and chemical properties of polymeric surfactants than SL-PEG whether on the solution surface or inside the solution. Results showed that with increasing the concentration of Na Cl, the cloud point of CA-SL decreased; And the cloud point of CA-SL decreased below 30℃ when the mass ratio of CA-SL was 0.3 and 0.4. Ethanol can enhance the cloud point of CA-SL and the cloud point of CA-SL increased above 90℃ with adding ethanol. Besides, the ability to reduce interfacial tension of CA-SL was stronger than the SL and SL-PEG.SL-PEG and CA-SL were used as dispersing agent in dimethomorph and imidacloprid pesticide aqueous suspensions(SC). The SC of hydrophobic dimethomorph was prepared. Results indicated that CA-SL and SL-PEG600 had good dispersion effect and can effectively prevent particles growth and coalescence phenomenon of dimethomorph in the process of thermal storage. For the SC using SL-PEG as dispersing agent, xanthan gum had effect on keeping stability of SC but it will cause the particles grow up and the suspension rate decrease after thermal storage. However, for the SC using CA-SL as dispersing agent, xanthan gum had effect on keeping stability of SC and it had little effect on the particles and the suspension rate after thermal storage. The SC of hydrophilic imidacloprid was prepared. When the dispersant content was 4%, the SC using CA-SL as dispersing agent had better thermal storage properties.The characteristics of SL, SL-PEG600, CA-SLP600, SL-PEG1000 and CA-SLP1000 adsorption on dimethomorph were investigated by means of quartz crystal microbalance. The results showed that the order of the five kinds of adsorption frequency(|Δf|) was: SL<SL-PEG1000=SL-PEG600<CA-SLP1000<CA-SLP600 and the order of the dissipation factor(ΔD) was: SL<SL-PEG600<CA-SLP600<SL-PEG1000<CA-SLP1000. The adsorption configuration of SL-PEG on dimethomorph was loose while the adsorption configuration of CA-SL was rigid. The ΔD increased as the |Δf| increased during the adsorption process of these five kinds of dispersant adsorption on dimethomorph. It can be conclude that the thickness of adsorbtion layer of the dispersant increased as adsorption capacity slightly increased. The results of atomic force microscopy showed that the adsorption film of SL-PEG adsorption on dimethomorph was loose while the adsorption film of CA-SL was rigid.In this study, the long hydrophilic chain of the ethoxy was introduced into the SL molecules. Flocculation phenomenon emerged in electrostatic assembly of cationic surfactant and anionic surfactant was solved successfully. The obtained polymeric anionic/cationic surfactant was a new type of anionic/cationic polymer surfactant and It contained many long hydrophobic chains and long hydrophilic polyoxyethylene ether chains simultaneously. The polymeric anionic/cationic surfactant had good surface activity and interfacial adsorption properties and It can be used in SC as lignin-based efficient dispersant. |
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