Preparation, Characterization And Application Of Cyclodextrin Grafting Wood Flour Functional Material

As an abundant biomass resource, poplar wood flour has the excellent properties of extensive sources, low price, biodegradability, environmental friendliness, easy processability and so on. Therefore, the research, concerning the improvement of the bioavailability and additional value of wood flour, has become a hot topic in the field of comprehensive development of forest resources.In this paper, new wood flour-based material with extended functionality—cyclodextrin grafting wood flour functional material (β-CD-CA-WF or β-CD-BTCA-WF) are prepared by an esterification crosslinking between β-cyclodextrin (β-CD) and wood flour (WF) in the presence of polycarboxylic acid crosslinker (citric acid, CA or1,2,3,4-Butanetetracarboxylic acid, BTCA). Meanwhile, the preparation conditions and stability of ester bond and Lewis acid-base properties of the functional material, the load and release characteristics of eugenol, the mechanism of adsorption between the prepared material and Pb2+are studied. The main contents and results are listed as follow:(1) The grafting rate and the active β-CD content of β-CD-CA-WF and β-CD-BTCA-WF were evaluated by the method of weight gain and the technique of phenolphthalein probe, respectively. Based on the aforementioned two evaluations, the optimum conditions for preparing the functional material were found as follows:The curing temperature was chosen at180℃and the β-CD concentrations in impregnation solution were80g/L and120g/L for CA and BTCA, respectively. Two optimal compositions of the impregnation solutions were CA/β-CD/NaH2PO2, BTCA/β-CD/NaH2PO4. BTCA demonstrated a higher grafting rate than CA, while, CA gave a higher active β-CD content. Fourier Transform Infrared Spectroscopy (FTIR) also demonstrated that β-CD was successfully grafted onto the surface of wood flour. The stability of ester bond of β-CD-CA-WF was analysed by the technology of quantitative ultraviolet-visible (UV-vis) spectroscopy. The results showed that the stability of ester bond of β-CD-CA-WF was strong, and the functional material could be preserved in hot water (below80℃) for a long time.(2) The surface energy and Lewis acid-base constant of β-CD-CA-WF were determined by the technique of Inverse Gas Chromatography (IGC). The results indicated that the dispersive component of surface free energy of β-CD-CA-WF increased with the increase of temperature, and the surface of the functional material presented a Lewis basic character, inclining to adsorb Lewis-acidic molecules.(3) An antibacterial fragrance material (EG/β-CD-CA-WF) was prepared by loading antibacterial fragrant molecule (eugenol, EG) on β-CD-C A-WF through lyophilization method. UV-vis spectrometer was applied to determine the EG content encapsulated by β-CD-CA-WF. It was found that the encapsulated EG content was reached to1.31%, which could confirm a potential application in antibacterial areas. The release characteristics of EG/β-CD-CA-WF were evaluated at25℃and75%relative humidity (RH). The results revealed that the release amount of EG in EG/β-CD-CA-WF was less than10%after504h, and the release of EG was controlled by a combination mechanism of diffusion and first-order release kinetics. Besides, the results of Thermogravimetric Analysis (TGA) were proved that β-CD-CA-WF had a thermo-protect effect on the loaded EG.(4) Pb2+was chosen as a model adsorbate in this batch adsorption experiment, and the influence of contact time, pH and initial Pb2+mass concentration on the adsorption capacity of β-CD-CA-WF was examined. The adsorption of Pb2+by β-CD-CA-WF was investigated with the emphasis on the adsorption kinetics and thermodynamics, and the adsorption mechanism was preliminarily discussed as well. The results showed that the equilibrium was reached within30min at298K. The adsorption capacity was found to be the maximum in a4.0～8.0pH range and increases with the increase in initial Pb2+mass concentration. The adsorption of Pb2+was observed to be monolayer adsorption and a chemisorption process. Intraparticle diffusion was not the only rate-determining step in the adsorption process, and the value of entropy and enthalpy change were calculated to be54.45J/(mol·K) and13.75KJ/mol for Pb2+adsorption, respectively.