Preparation And Application Of LCST Regulable Lignin-based Thermo-responsive Materials By ARGET-ATRP

Lignin,as a abundant and renewable resource,has excellent properties such as high carbon content,thermal stability,and biodegradability,which lays the foundation for its combination with functional materials.Due to its complex structure and wide molecular weight distribution,most of the lignin is discharged or burned directly,with low utilization rate and environmental pollution.Lignin-based thermosensitive materials have potential applications in functional materials.The traditional lowest critical dissolving temperature(LCST)polymer poly(N-isopropylacrylamide)(PNIPAM)has the disadvantage of LCST unregulated,while polymer thermosensitive materials such as poly(N-vinylcaprolactam)(PNVCL)have attracted extensive attention due to their good properties of temperature-responsive and regulable LCST.Therefore,it is of great significance to broaden the application field of lignin and improve the utilization value of lignin by analyzing and modifying its structure and grafting LCST regulable thermosensitive monomer.In this paper,lignin was firstly extracted with deep eutectic solvent,and oxidative degraded with 30%hydrogen peroxide.The degraded products were esterified with 2-bromoisobutyryl bromide(BiBB)to prepare lignin macroinitiator(DES-lignin-Br).ARGET-ATRP method was used to prepare lignin-based thermosensitive materials(DES-lignin-g-PNVCL)by graft and copolymerize NVCL.Finally,aspirin was coated with self-assembly and controlled release.The structure and performance of graft copolymerized products and self-assembled coatings were studied.The specific research contents and results are as follows:(1)DES-lignin was extracted from poplar wood powder by deep eutectic solvent composed of choline chloride and lactic acid,and Degraded DES-lignin was prepared by oxidative degradation of 30%hydrogen peroxide.The changes of lignin structure and properties during the process were investigated.The extraction rate of DES-lignin was 92.52%,the yield of Degraded DES-lignin was 72.99%,and the purity of DES-lignin and Degraded DES-lignin were 92.43%and 94.78%,respectively.The phenolic hydroxyl groups contents were 1.484 mmol/g and 2.072 mmol/g,respectively,and the total hydroxyl contents were 3.640 mmol/g and 4.157 mmol/g,respectively.The reactivity and reaction sites increased.The results of gel permeation chromatography(GPC),elemental analysis(EA),fourier transform infrared spectroscopy(FT-IR),dimensional nuclear magnetic resonance spectroscopy(2D-HSQC NMR),and thermogravimetry(TG)demonstrated that Degraded DES-lignin had low molecular weight,few aryl ether bonds and condensation structures,and strong thermal stability.(2)DES-lignin-Br was prepared by esterification of phenolic hydroxyl of Degraded DES-lignin with 2-bromoisobutyryl bromide(BiBB).DES-lignin-g-PNVCL was prepared by graft copolymerization with NVCL by ARGET-ATRP.The reaction mechanism of ARGET-ATRP was described.The analysis of FT-IR,nuclear magnetic resonance spectroscopy(1H-NMR),X-ray electron spectroscopy(XPS),and differential scanning calorimetry(DSC)demonstrated that DES-lignin-g-PNVCL was successfully prepared by ARGET-ATRP,and it had a good temperature response.The LCST of DES-lignin-g-PNVCL can be regulated by changing the molar ratio of phenolic hydroxyl contained in Degraded DES-lignin to BiBB,the amount of DES-lignin-Br added,the ratio of DMF/water,and the concentration of DES-lignin-g-PNVCL,and its fitting equation was within the allowable error range,which can be used to design and prepare the desired LCST thermosensitive materials.(3)DES-lignin-g-PNVCL coated aspirin nanoparticles(Aspirin@LTNP)were prepared with DES-lignin-g-PNVCL and aspirin by ethanol/water self-assembly coated,the safety was evaluated by cytotoxicity test and its controlled release at different temperatures and pH were performed.The coating rate was 88.87%when the dropping speed was 2.0 mL/min,the stirring rate was 500 rpm,the ethanol content was 80%,the mass of DES-lignin-g-PNVCL was 30 mg,and the mass of Aspirin was 10 mg.The analysis of XPS,elemental analysis,SEM,TEM,FT-IR,DLS and UV showed that the Aspirin@LTNP was mainly deposited by π-π force under optimal condition,and its morphology was ellipsoid shape stacked by layer.Hydrophilic chains of Aspirin@LTNP were increased,which lead to externally hydrophilic and internally hydrophobic structures of Aspirin@LTNP.The particle size decreased slightly during the self-assembly process.The red shift occurred at the π-π interaction wavelength of the lignin aromatic ring,which indicated the coating was a physical process.The 96 h cumulative release rate of the micelle was 73.75±1.16%when the temperature under the LCST of DES-lignin-g-PNVCL,while the 96 h cumulative release rate was 28.10±0.92%when the temperature above the LCST of DES-lignin-g-PNVCL,which showed an obvious temperature response.The 96 h cumulative release rate was 63.21 ±0.57%at pH=1.5 and 49.56±0.48%at pH=7.4.The cytotoxicity test results showed that the dosage of Aspirin@LTNP was used in the experiment was safe.