Preparation Of Cyclodextrin Grafting Cellulose Beads And Encapsulation, Release Characteristic Of The Cyclodextrin Inclusion Complexes

As the second generation supermolecular compound, cyclodextrin (CD) has a wide variety of guest molecules and shows a promising application in the fields of medical care, food, environment and molecule self-assemble. The combination of cyclodextrin and natural polymers for preparing cyclodextrin polymers, not only has the property of a cyclodextrin-specific, but also has the properties of easy modification, stability, environmental friendly and renewable which belongs to the natural polymers. Meanwhile, this investigation enlarges the application of cyclodextrin. Besides, as one of the most important forest biomass resources in the Northeast of China, cellulose is rich in storage but suffers from inadequate comprehensive utilization. Thereafter, the research, development and application of cellulose and its relevant areas have attracted great attention of many agricultural and forestry scientists and have become the hotspot and the emphasis of highly efficient utilization of biomass resources.In this paper, cellulose beads are prepared by our self-made circumrotation centrifugal machine. Host molecules of cyclodextrins are grafted onto the surface of the cellulose beads in the presence of polycarboxylic acids. Besides, nanoscale silver particles are also introduced onto the surface of the cellulose beads by the technique of in suit chemical reduction method. In the end, a multi-functional material of cellulose beads loading with inorganic nanoparticles is obtained. Meanwhile, the detection of cyclodextrin by phenolphthalein probe molecule, the preparation and characteristic of cellulose beads, the graft of cyclodextrin host molecule on cellulose beads surface, the encapsulation, release and application of iodine encapsulated byβ-cyclodextrin, the encapsultation, release and application of eugenol encapsulated byβ-cyclodextrin, the preparation, characteristic and application of cellulose beads loading with nanoscale silver particles are discussed in details. The contents and results of this article are included as follows:1. The binding constants (Ka) of phenolphthalein/β-cyclodextrin, phenolphthalein/(2-hydroxypropyl)-β-cyclodextrin, and phenolphthalein/(2,6-dimethyl)-β-cyclodextrin complexes were measured by ultraviolet-visible spectrophotometer. By regression of van't Hoff plot, thermodynamic parameters (△H°and△S°) of these complexes'formation were obtained. Based on these parameters, steric hindrance influence, spontaneous, and enthalpically driven process for the interaction of phenolphthalein with cyclodextrins were further proved, and phenolphthalein, as a probe molecule, was used to determinate the cyclodextrins' content due to less than 0.6% relative standard deviation and recoveries with the range of 90-103%.2. Cellulose beads were prepared by the natural cellulose fibers and controlled by three key steps during the preparation process, including the dissolving of the cellulose fiber, the preparation of the liquid cellulose beads and the solidification of the liquid cellulose beads. The viscosity of the xanthate solution was the main factor that influenced the preparation of the cellulose beads, for this reason, the influencing factors of the xanthate solution's viscosity were also discussed in details. In the end, the results were demonstrated that the shape of products were kept in spherical, the packing density, tap density, true density, compression ratio and void ratio were 0.2780 g mL-1,0.2869 g mL-1,2.92%,0.4080 g mL-1,29.9%, respectively. The products of the cellulose beads showed a distinct physical property compared with the cellulose fiber and would have a potential investigation value on the application of the carrier materials.3. Functional host molecules ofβ-cyclodextrin were grafted onto the cellulose beads in presence of polycarboxylic acids, such as 1,2,3,4-Butanetetracarboxylic acid, citric acid, tartaric acid. The novelty of this study was the using of phenolphthalein probe molecule technique to determine the surface activity cyclodextrin contents. Based on the determination results of the method phenolphthalein molecule probe and weight gain, key factors of the grafting ofβ-cyclodextrin, including crosslinking agent, catalyst, curing temperature and cyclodextrin concentration in the impregnating bath, were investigated. Besides, the grafting of (2,6-dimethyl)-β-cyclodextrin and (2-hydroxypropyl)-β-cyclodextrin on the cellulose beads were also discussed. By discussing of the results of the phenolphthalein probe detection, a microscopic observation of the grafting process was given and a conception of surface activity cyclodextrin was put forward which describes the cyclodextrin's ability of encapsulation on the modified cellulose beads.4. By regression of the Hildebrand-Benesi equation, the iodine/β-cyclodextrin (iodine/β-CD) binding constant of 1286 L mol-1 and the stoichiometric ratio of 1:1 (iodine:β-cyclodextrin) were obtained. Two major factors of encapsulation temperature and stirring time during the preparation process of the solid state iodine/β-CD inclusion complex were investigated. In order to determine the iodine content in the complex powder, a quantitative method by iodimetry was investigated, and its accuracy and expeditiousness were verified by high performance liquid chromatography (HPLC). Release behaviors of iodine/β-CD powder were investigated by iodimetry and thermo gravimetric (TG) analyzer respectively. The loss percentage of iodine was 5.8 wt.% for 7 days exposing under room temperature and a time versus release curve was established. The TG diagram not only proved the thermo stability of the iodine in iodine/β-CD complex, but also clarified the thermal decomposition behaviors of the iodine/β-CD. For verifying the germicidal activity of iodine encapsulated byβ-cyclodextrin, the aspergillus niger, which is a kind of common fungus in the food, was taken as evaluation media. By the method of disc diffusion, iodine/β-CD showed a bacteriostasis effect of aspergillus niger. In order to have functional properties, material ofβ-cyclodextrin grafting cellulose beads loaded with iodine guest molecule was prepared. The iodine content of this novel product was 3.1%, and the results demonstrated its application potential in bacteriostasis material.5. Solid state eugenol/β-cyclodextrin inclusion complex (EG/β-CD) was prepared by lyophilization method and characterized by Powder X-ray Diffraction (XRD) and Fourier Fransform Infrared Spectroscopy (FTIR). UV-vis spectrometer was used to determine the EG content encapsulated in the complex. In order to estimate the release characteristics of the EG/β-CD powder, Avrami's equation and Thermogravimetric (TG) analyzer were respectively used. The loss percentage of EG was no more than 10 wt.% for 4 weeks when exposing at 25℃and 75% humidity, and the release of EG was controlled by a combination mechanism of diffusion and first-order mode. TG results not only proved the thermo stability of the EG in EG/β-CD complex, but also clarified the thermal decomposition behaviors of the EG/β-CD. The antibacterial activity of the EG/β-CD complex was investigated using agar cup-plate diffusion method and bacterial strains of Escherichia coli,Salmonella paratyphi B, and Staphyloccocus aureus were used. The results indicated that EG/β-CD had a selective antimicrobial active against Escherichia coli. Similarly, the material ofβ-cyclodextrin grafting cellulose beads loaded with eugenol guest molecule was also prepared by the lyophilization method, and the eugenol content was 2.6%. The results demonstrated that the novel material not only had the flavor of eugenol, but also had a potential application on bacteriostasis material field.6. In order to prepare a novel material with properties of encapsulation of functional guest moluecules and strong bacteriostasis effect, nano-sacle silver particles were deposited on the carrier material of cyclodextrin grafting cellulose beads. The surface of novel material was studied by Scanning Electron Microscope (SEM), X-ray Photoelectron Spectroscopy (XPS) and Electron Bachscattered Diffraction (EBSD). The results indicated that the size of nano-silver on the surface of the novel carrier material was in the range of 500-800 nm,and the valence state of the silver particles was kept at zero. The morphology and particle size of the novel materal were kept unchanged compared with the beads which were not deposited with nano-silver. Phenolphthalein probe molecule technique was used to detect the surface activity cyclodextrin content, and the results demonstrated that the deposition of nano-silver had no influence on the encapsulation ability of the cyclodextrins which were grafted on the surface of the cellulose beads. The acid and base resistance of the nano-silver on the bead materials was carried out by Atomic Absorption Spectrometer (AAS). The stability of the nano-silver was enhanced due to the coordination between surface cyclodextrin and nano-silver particles. Tube dilution method was used to study the bacteriostasis effect. The minimal inhibitory doses of the novel material against Escherichia coli and Staphyloccocus aureus were 0.0125 g and 0.025 g, respectively. The minimal bactericidal doses for the two bacteria were 0.025 g and 0.025 g, respectively.