Preparation And Evaluation Of Lignin-based Temperature-sensitive Nanocapsules

Lignin,as the second most abundant natural renewable biomass resource,is the main component of biomass such as wood and annual plants,and its content is 1530%.The basic structural unit of lignin is phenylpropane,which may be the most promising substitute for petroleum-based materials in the production of aromatic compounds.However,lignin has always been treated as waste or prepared as a lowvalue-added product.In this paper,sodium lignosulfonate and poly-Nisopropylacrylamide are used as raw materials.Lignin-based temperature-sensitive capsules with controllable size were successfully prepared by free radical reaction.In order to broaden the application of lignin temperature-sensitive materials in rapid detection and antibacterial aspects.The capsule was loaded with the fluorescent dye Rhodamine B and the broad-spectrum antibiotic tetracycline hydrochloride.In addition,the release of model compounds at different temperatures was also explored respectively,and the kinetic model of sustained release was analyzed.The main results are as follows:(1)Sodium lignosulfonate was grafted with an excess of bromopropene.The results of FTIR and 1H-NMR showed that sodium lignosulfonate was successfully functionalized by allyl groups.The results of UV spectra at different temperatures showed that the critical solution temperature(LCST)of the prepared PNIPAM was 32℃.(2)Through simple free radical reaction and ’Self-removing’ process,ligninbased temperature-sensitive nanocapsules were synthesized.Single factor experiments found that the dosage of anionic surfactant sodium lauryl sulfate and the concentration of NaCl have the most prominent effect on the particle size of the capsules.The minimum particle size can be controlled at 263.8±0.4 nm..Interestingly,when the temperature is higher than the LCST,the particle size of the capsule will increase and the absorbance of the suspension will increase.This change is reversible.(3)Rhodamine B was loaded with lignin-based temperature-sensitive capsules of different particle sizes,and it was found that the encapsulation efficiency was closely related to the particle size of the lignin-based temperature-sensitive capsules.Roughly showing a trend that the smaller the particle size,the greater the encapsulation efficiency.The highest encapsulation rate can reach 94.7%.Temperature will affect the release of rhodamine B from lignin-based temperature-sensitive capsules.After 24 hours of release,the release amount of rhodamine B can reach up to 65.67%at 37℃.At 25℃,the sustained release amount is only 5%.The kinetic model of its sustainedrelease rhodamine B is mainly based on first-order kinetics and Korsmeyer-Peppas model.(4)The prepared lignin-based temperature-sensitive capsules were loaded with tetracycline hydrochloride,and the maximum drug load could reach 886 mg/g.The sustained release of tetracycline hydrochloride and the kinetic analysis of the sustained release results were carried out at different temperatures.The results of the study show that tetracycline hydrochloride is hardly released when it is below the LCTS,and the release amount is significantly increased above the LCST.At 37 ℃,the normalized results show that the kinetic model of lignin-based temperaturesensitive nanocapsules is mainly based on the Korsmeyer-Peppas model.It is Higuchi type at 25℃.The effect of lignin-based temperature-sensitive nanocapsules loaded with tetracycline hydrochloride on the growth of E.coli under different temperature conditions was measured by the size of the inhibition zone.The results showed that the size of the inhibition zone was 20.15 ± 0.81 mm at 37℃,and 15.01 ± 0.38 mm at 30℃.