Lignin hydrogel drive, fast response to pH

Fast pH responsive hydrogel having a high practical value in many fields driving, sensing and separating the like. Traditional pH responsive hydrogel having a generally poor physical strength and toughness, and prepared by chemical cross-linking method hydrogel poor performance in terms of pH response speed and reversibility. In recent years, researchers interpenetrating network topology or a multi-functional nano material introduced into the pH of the aqueous gel structure, the plurality of hydrogel with good mechanical properties and pH-responsive prepared. But most require expensive starting materials or the manufacturing process cumbersome. So far, the preparation of low cost, high performance pH responsive hydrogel remains a challenge. In fact, the lignin as nature\’s most abundant renewable aromatic polymer, not only the cost but also protonated and ionization will occur in acid or alkaline conditions. Over the years, the pulp and paper industry is the use of this unique response of the pH realized the extraction of cellulose and lignin removal. 木质素水凝胶驱动器,可快速pH响应 Based on this, Tianjin University of Science and Technology Professor Dai Linfu , who delivered a speech entitled on \”Chemistry of Materials\” \” All-lignin-based hydrogel with fast pH-stimuli-responsiveness formechanical switching and actuation \”research papers reported a novel, rapid pH responsive hydrogel lignin . The lignin hydrogel reflected in the acid / base solution in a rapid, multiple, reversible hard / soft, curved / recovery behavioral changes, bending / recovery rates of up to 8.0 ° / s and 6.5 ° / s . Breaking stress / strain may be 18.0kPa / 17.4% (pH 14.0) raised to 36.0 kPa / 29.4% (pH 1.0) . With these features, the successful design studies prepared hooking means in response to pH, and fluid switching means. This low-cost, rapid pH-responsive hydrogel lignin not only provides a unique material platform for the development of smart materials, but also opens up new fields of application for the lignin-based material.

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1. Preparation of lignin hydrogels

study is very simple, basic open-loop controlled synthesis process, the most common industrial sulfate raw lignin, low molecular weight polyethylene glycol diglycidyl ether as a crosslinking agent to obtain a hydrogel lignin. potassium alkaline reaction system used in the reaction plays the dual role of promoting dissolution of lignin and ring-opening reaction.

木质素水凝胶驱动器,可快速pH响应
1. Synthesis of lignin FIG hydrogels, the structure and components Characterization

2. PH responsive hydrogel performance lignin

Figure 2 shows the bending of lignin hydrogel / recovery behavior in acid / base solution. Prepared a sheet-like strip lignin hydrogel just 27s to bend to 216 ° in 0.1 M HCl solution, then dipped into a solution of 0.1 MKOH recoverable deformation after 30s ( 10). Compared with other studies, the lignin hydrogels pH responsive excellent bending rate (8.0 ° / s) and the strain recovery rate (6.5 ° / s).

木质素水凝胶驱动器,可快速pH响应
Figure 2. The hydrogel lignin in an acid / alkali solution bending / recovery Characterization

3. Lignin hydrogel pH drive means

FIG. 3 shows a driving performance of the lignin hydrogel. Lignin hydrogel is first formed a sheet-like strip in response to the hooking means for pH. Lignin bar hydrogel may spontaneously hooking the bent and 0.1 M HCl solution is equivalent to six times the weight of the weight. Subsequently, the hydrogel is made of lignin and adhered to the rectangular chip Parafilm ® M circular film, with the filter assembly into a fluid valve means, exhibit good pH response switching function.

木质素水凝胶驱动器,可快速pH响应
FIG. 3. The pH of the aqueous gel formed in response lignin hooking means and a fluid switching means

4. PH responsive hydrogel lignin mechanism

Figure 4 shows the water content, microstructure and mechanical properties of the hydrogel lignin in acid environment. With lower pH environment (14.0 to 1.0), The water content of the gel of lignin of 92% to 49%, breaking stress of 18.0 kPa increased to 36.0 kPa, strain at break from 17.4% to 29.4%. Show cross-sectional microstructure of the material, the lignin in an alkaline environment having a hydrogel macroporous structure loose, and water in an acid environment clear gel contraction, and exhibits a dense network of smaller pore structure. This is due to the acidic environment of the lignin molecule occurs protonation of the carboxyl group, to promote hydrophobic interaction between the lignin molecules, thereby forming physical crosslinks. After re-enter the hydrogel in an alkaline environment, carboxy ionization occurs again, the soft lignin recovery network structure.

木质素水凝胶驱动器,可快速pH响应
Figure 4. lignin hydrogel water content at different pH environments, microstructure and mechanical properties

found that the lignin single hydrogel occurs only side bent radially this phenomenon may be caused by the internal stress of the hydrogel. To test this idea, the lignin / polyethylene glycol diglycidyl ether was poured into the suspension study Parafilm®M film is molded, the elastic potential energy of the lignin characterize the entire hydrogel membrane indirectly by detecting the Parafilm® M . Hydrogel visualize the change in potential energy of deformation substantially in line with the actual trend. This suggests that through rational design and molding method, this cheap, green lignin hydrogel is expected to achieve more intelligent applications.

木质素水凝胶驱动器,可快速pH响应
Figure 5. The internal stress of the hydrogel lignin Characterization

[highlight] Summary

In summary, the authors reported a low-cost, simple preparation process and the hydrogel material having lignin quick responsiveness pH. Alternately soaking solution by a simple acid-base, the hydrogel may lignin showed rapid, multiple, reversible hard / soft, curved / recovery behavior change. With these characteristics, studies to achieve the pH response hooking behavior and flow control. This low-cost, rapid pH-responsive hydrogel lignin not only provides a unique material platform for the development of smart materials, but also opens up new fields of application for the lignin-based material. The full text link: https: //pubs.acs.org/doi/10.1021/acs.chemmater.0c01198

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