Preparation and characterization of thermo-sensitive gel with phenolated alkali lignin

Pan Jiang,Haisong Wang,Sheng Yu,Haiming Li,Xueru Sheng,Jinghui Zhou,Jie Lu

doi:10.1038/s41598-018-32672-z

Abstract

Thermo-sensitive gel exhibits great potential industrial application. It has been widely used in tissue repair, drug release and water purification for its property of phase transition in response to external stimuli, reusability and biocompatibility. In this study, a novel lignin-based thermo-sensitive gel was synthesized with alkali lignin by two steps. Firstly, phenolated lignin (PPAL) was synthesized with purified alkali lignin (PAL) catalyzed by sulfuric acid. Subsequently, thermo-sensitive gel was achieved by thermal polymerization of phenolated alkali lignin and N-isopropylacrylamide (NIPAAm). Furthermore, the prepared hydrogels were characterized in terms of thermal behavior, interior morphology and their swelling behavior. Compared with PAL-based gel, the obtained PPAL-based gel exhibits a higher crosslinking density and lower critical solution temperature (LCST) due to the increase of reaction site and smaller space volume of the hydrophobic side groups grafted on NIPAAm. TGA data revealed that thermal stability of gel was enhanced (50% weight loss at ~380 °C) by using lignin as precursor. SEM images showed that a more regular interior morphology, better compressive strength was also found (PPAL0.05, 11.15 KPa). Furthermore, the swelling ratio of PPAL-based gel was lower than that of PAL-based gel due to its more complex structure.

Highlights

With the depletion of fossil energy and the development of polymer industry, bio-renewable polymers have attracted a greater attention
Preparation of phenolated lignin (PPAL) was synthesized with purified alkali lignin (PAL) according to the steps shown in methods
Comparing to PAL, the characteristic peak on PPAL varied as below: (i) -OH stretching vibration at 3430 cm−1 was broadened; (ii) C-O stretching vibration at 1224 cm−1 was more visible compared with that in PAL; (iii) a new characteristic peak occurred at 749 cm−1 which was attributed to the C-H out-plane flexural vibration on aromatic rings

Summary

Introduction

With the depletion of fossil energy and the development of polymer industry, bio-renewable polymers have attracted a greater attention. The content of several types hydroxyl groups in PAL and PPAL was investigated by 31P-NMR (as shown in Fig. 5 and Table 1). PPAL exhibited lower temperature at 50% weight loss (382.9 °C) than that of PAL (432.5 °C).

Results

Conclusion