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

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.

Recent Research Progress on Lignin-Derived Resins for Natural Fiber Composite Applications

“…In recent years, lignin has been used with various polymers to prepare composites and epoxy resins for different applications, i.e., surfactants, coatings, lubricants, plasticizers, carbon fiber, wastewater treatment, stabilizing agents, and fire retardant [ 1 , 8 , 45 , 46 , 47 ]. Several studies have been described the phenolization/demethylation of lignin by using various types of catalysts such as H 2 SO 4 [ 45 ], hydrogen bromide (HBr), hydrogen iodide (HI) [ 48 ], 1-dodecanethiol (DSH) [ 44 ], and Na 2 SO 3 [ 49 ] to improve the reactivity and also to reduce the molecular weight of lignin for thermoset applications ( Figure 2 a) [ 45 , 50 , 51 ]. Since HI has strong nucleophile behavior, it is a more effective catalyst for lignin demethylation than H 2 SO 4 , DSH, HBr, and Na 2 SO 3 .…”

Multi‐C−C/C−N‐Coupled Light‐Emitting Aliphatic Terpolymers: N−H‐Functionalized Fluorophore Monomers and High‐Performance Applications

“…The relatively restrained degradations up to 200 °C have been attributed to the lower content of anhydride linkages in hydrophobic 3 and 4 . The continued slow thermal decomposition above 200 °C has been ascribed to delayed imide formation by the cyclization of in situ generated thermostable tertiary amides and the slow rupture of N‐branched moieties; the formation of such tertiary amides and associated N ‐branched structures was manifested earlier in the FTIR and NMR analyses. Notably, the drastic loss of mass in the temperature range 350–430 °C could be related to the lack of anhydride linkages and the decomposition of the thermolabile esters, leading to negligible residues (see Figure S3 a).…”

Lignin-Based Hydrogels: Synthesis and Applications

“…N-isopropylacrylamide (NIPAAm) was also employed to be polymerized with phenolated alkali lignin. Pre-activation of lignin led to higher crosslinking density and higher effect of the lignin content on the final lower critical solution temperature (LCST) of the resulted hydrogels due to the increase on the amount of reaction sites [59].…”