Lignin reinforced hydrogels with fast self-recovery, multi-functionalities via calcium ion bridging for flexible smart sensing applications.

Hydrogels have found applications in many different fields. However, poor mechanical properties, such as low elasticity and lack of rapid recovery under large deformation, can severely limit their applications. In this study, we developed lignin reinforced hydrogels made of calcium ion containing ternary polymers (lignosulfonate (LS), alginate (Alg), and polyacrylic acid (PAA)). The resultant hydrogel has excellent elasticity, rapid self-recovery, and multi-functionalities. The covalent PAA network acts as the elastic scaffold of hydrogel, while calcium bridging networks of LS, Alg, and PAA, as well as the strong hydrogen bonding network in the system, function as sacrifice bonds to dissipate energy and transfer stress. The PAA/LS/Alg/Ca hydrogels exhibit rapid and durable elastic recovery ability under large deformation with the highest compressive stress of 835 kPa (95% strain), highest tensile fracture stress of 357 kPa, and highest tensile strain of 1144%. In addition, these tough hydrogels show UV resistance, self-healing, antifreeze, and excellent electro-conductivity. When assembled into a strain sensor, stable and reliable electrical responses with 375 ms response time are demonstrated. The PAA/LS/Alg/Ca hydrogel strain sensors can monitor human movements with responsive and accurate physiological signals. These results support the conclusion that the PAA/LS/Alg/Ca hydrogel strain sensors have great application potential in flexible wearable electronics and smart devices.

Effect of lignin-based monomer on controlling the molecular weight and physical properties of the polyacrylonitrile/lignin copolymer.

In this work, lignin was grafted with acrylonitrile to control the molecular weights and molecular architecture of polyacrylonitrile (PAN)/lignin copolymer. Lignin-acrylonitrile monomer (LA-AN) and its copolymers with AN were synthesized successfully. First, lignin was aminated (LA) and then grafted with 2-chloroacrylonitrile to prepare LA-AN. The copolymerization of LA-AN and AN was carried out using 2,2-azobis(2-methylpropionitrile) as initiator. The modification, grafting, and copolymerization were confirmed with Fourier transform infrared spectroscopy, proton nuclear magnetic resonance spectroscopy, and X-ray photoelectron spectroscopy. Contrary to the previous studies, gel permeation chromatography showed that the molecular weight of the copolymers was increased significantly due to the presence of lignin (up to 203,944). Viscosity analysis revealed that the addition of lignin reduces the viscosity of the copolymer solution. While thermogravimetric analysis showed improvement in the degradation temperature, and lowering of the melt temperature, as revealed by differential scanning calorimetry. These findings indicated that the attaching acrylonitrile on lignin molecules result in control of the molecular weight and molecular structure of PAN/Lignin copolymers which results in enhanced solubility, spinnability, and other properties associated with molecular weight.

Photocatalytic degradation of dyes over a xylan/PVA/TiO2 composite under visible light irradiation.

In this study, a xylan/PVA/TiO2 composite was prepared and used for the photocatalytic degradation of dyes in solution. Fourier-transform infrared, X-ray diffraction, and X-ray photoelectron spectroscopic analyses confirmed that the xylan/PVA/TiO2 composite was successfully prepared. Furthermore, the composite was evaluated as a photocatalyst for the photodegradation of ethyl violet and Astrazon Brilliant Red 4G dyes under visible light irradiation. The effects of various experimental parameters on the decolorization rate were investigated. Dye decolorization rates of more than 94% were achieved. The major active radical species for EV and ABR photodegradation was found to be positive holes (h+).