Lignin-containing fibers extraction and hydrogel preparation for fiber-optic relative humidity sensor fabrication

Herein, a physicochemical pretreatment method, namely, a combination of recyclable acid hydrotrope (p-toluenesulfonic acid, p-TsOH) treatment and ultrasonic treatment (10 s), was employed to extract lignin-containing fibers (LFs) from wood material (poplar). The LFs were used to produce reinforced polyvinyl alcohol (PVA) hydrogels via a dissolution-regeneration process in LiBr.3H(2)O solution. After coating the produced hydrogel on the end face of a single-mode fiber (SMF), a fiber-optic relative humidity sensor (FORHS) was fabricated to monitor environmental humidity. A high sensitivity (4.7 dB) and good repeatability (R-2 = 0.98, the confidence factor) were found within a humidity range from 45 % to 80 %. Therefore, this study provides a sustainable approach for valorization of lignocellulosic biomass.

Automated summary

A physicochemical pretreatment method combining recyclable acid hydrotrope treatment and ultrasonic treatment was employed to extract lignin-containing fibers from wood material, which were then used to produce reinforced polyvinyl alcohol hydrogels for a fiber-optic relative humidity sensor. The sensor demonstrated high sensitivity (4.7 dB) and good repeatability (R-2 = 0.98) within a humidity range of 45% to 80%, providing a sustainable approach for valorization of lignocellulosic biomass.