Construction, Structure And Properties Of Novel Cellulose, Chitin Hydrogels

Hydrogels, unique "soft" materials with high swelling ratio, mechanical strength, transparency, biodegradability, and biocompatibility, have been applied widely in agriculture, industry, biomedical materials, and physical hygiene. The research on polymer hydrogels have covered large interdisciplinary area crossing polymer physics, condensed matter, material science, life science, and medicine. Cellulose and chitin are the most abundant bioresouce on the earth, and will be the main chemical resource of the future. This work focused on construction of cellulose and chitin hydrogels by using NaOH/urea aqueous solution developed in our group. The structure, properties, and structure-activity relationship of hydrogels were characterized by liquid/solid state 13CNMR,,Fourier transform infrared spectroscopy (FTIR), differential scanning calorimetry (DSC), X-ray diffraction (XRD), scanning electron microscope (SEM), transmission electron microscopy (TEM), rheological measurements, dynamic mechanical analysis (DMA) thermogravimetric analysis (TGA), UV-vis spectroscopy(UV), photoluminescence spectra (PL) and mechanical testing. The correlation of structure to properties was studied, and biobased functional hydrogels were constructed to evaluate their potential applications.The innovation of this work was as follows:cellulose hydrogels and composite hydrogel with excellent properties were fabricated successfully in NaOH/urea aqueous solution. Superabsorbent hydrogels were constructed by introducing high hydrophilic polymers into hydrogel networks, and the effect of cellulose stiff chains were clarified. Cellulose/quantum dots (QDs) hydrogels were prepared by embedding CdSe/ZnS nanoparticles in cellulose matrices. By using IPN technique or cross-linking amphoteric cellulose derivatives, a series of stimuli-responsive hydrogels were fabricated. Chitin was dissolved in NaOH/urea aqueous solution, and chitin hydrogels (hybrid hydrogels) were prepared.The primary content and conclusion of this work can be divided into ten parts.Firstly, transparent hydrogels have been synthesized from cellulose in NaOH/urea aqueous solutions by using ECH as crosslinker. With the increase of the cellulose concentration, the transparency and equilibrium swelling ratio of the hydrogels decreased, while the reswelling water uptake and the storage modulus increased. Cellulose hydrogels prepared by heating displayed better light transmittance, higher equilibrium swelling ratios, higher water uptakes and relatively weaker mechanical strength. However, Cellulose hydrogels prepared by freezing method had faster swelling rate and higher mechanical strength.The cellulose/PVA hydrogels prepared by freezing/throwing method had dense structure and exhibited strong interaction between cellulose and PVA, high strength and storage modulus. However, cellulose/PVA hydrogels prepared by chemical cross-linking with ECH had good swelling ratio and high water uptake, due to cross-linking reaction destroyed the crystallization of polymer chains.Cellulose/poly(ethyl glycol) (PEG) hydrogels were fabricated by introducing low molecular weight PEG into cellulose hydrogel network. These hydrogels showed excellent mechanical properties, which was hundredfold of cellulose hydrogels. DMA and DSC results indicated that the hydrogen bonds of cellulose were destroyed by PEG and new hydrogen bonds formed between cellulose and PEG. SEM and TEM results revealed that cellulose/PEG hydrogels had nanoporous morphology, leading to the high strength of hydrogels.Macroporous hydrogels fabricated from cellulose and sodium alginate (SA) in NaOH/urea aqueous system by chemical crosslinking had high swelling ratio. SEM and DMA results indicated that hydrogels had macroporous structure and high strength. In the hydrogels, SA played an important role on increasing pore size and swelling ratio, whereas cellulose contributed to support the pore wall. This work provided a simple way to construct macroporous hydrogels by combining of natural polymers with semi-stiff chain and high hydrophilic properties.Furthermore, novel superabsorbent hydrogels were fabricated by using cellulose as support and CMC as high hydrophilic polymer, which had superabsorbent capability and high swelling ratio (more than 1000). The hydrogels were sensitive to inorganic aqueous solution, physical saline water and synthetic urine, showing smart swelling and shrinking behaviors, as well as controlled release of BSA.Cellulose/quantum dots (QDs) hydrogels were created by cross-linking cellulose chains with epichlorohydrin containing water-soluble QDs (CdSe/ZnS) when the hydrophilic-hydrophobic transition of QDs occurred by hydrolyzing ligand. The relatively hydrophobic CdSe/ZnS core-shell nanoparticles were dispersed well and embedded firmly in the cellulose matrices through electrostatic attraction and hydrophobic interactions. The cellulose-QDs hydrogels emitted strong fluorescence with different colors of green, greenish-yellow, yellow and red, depending on the size of the CdSe/ZnS nanoparticles, and exhibited relatively high fluorescence (PL) quantum yields as well as good transparence and mechanical strength, leading to great promises in applications in the fields of fluoroimmunoassay and biological labeling.Novel hydrogels composed of cellulose and poly(N-isopropylacrylamide) (PNIPAAm) were created with IPN strategy. Cellulose hydrogel was employed as the first network, and PNIPAAm was polymerized/cross-kinked in presence of cellulose hydrogel as the second network, leading to the double networks structure. The two different networks exhibited good compatibility and homogeneous morphology in the IPN hydrogels. Analyses of FT-IR and solid 13CNMR supported that the first network and the second network were formed independently, and there was no chemical reaction between them. These IPN hydrogels displayed uniform porous network, good mechanical strength and temperature-sensitive properties.A series of ampholytic hydrogels through chemical cross-linking were constructed successfully from two cellulose-based polyelectrolytes (QC and CMC). The swelling ratios of these QC/CMC hydrogels changed dramatically from 8.6 to 498 g/g, depending on the chemical composition of QC and CMC. Therefore, ampholytic hydrogels with required swelling ratio could be obtained by fine-tuning the mass ratio of QC and CMC. These hydrogels exhibited multiple responsive behaviors, including pH and salt. CMC in the hydrogels with high CMC content contributed to the expansion of the hydrogel network, and the swelling ratio changed slightly in different pH solutions.Chitin power was dissolved successfully in 8 wt% NaOH/4 wt% urea aqueous solution via a freezing/thawing method to produce a transparent solution. For the first time, it has been demonstrated that the chitin dissolution was. a physical process without showing an occurrence of any derivatives and a new class of hydrogels from chitin solution was created successfully. The gelation of the chitin solution occurred rapidly in the presence of ECH, leading to the perfect formation of hydrogels. The chitin hydrogels exhibited a uniform microporous structure, smart swelling ratio, and excellent mechanical strength. In particular, the results from 293 T cell culture indicated that chitin hydrogels had non-toxicity and good biocompatibility, due to the fact of chitin is one of the active ingredients in the exoskeleton of arthropods or in the cell walls of fungi and yeasts, and its native properties benefited the growing of cells.Chitin/nano-hydroxyapatite (nano-HA) hydrogels were prepared by introducing hydroxyapatite nanoparticles in chitin hydrogels. Nano-HA with particle size of 10-30 nm was well dispersed in the chitin hydrogel matrix. Hybrid hydrogels exhibited uniform structure and good compressive strength. Moreover, COS-7 cells were well adhered, proliferated, and grown on the hydrogel surface, showing good biocompatibility. Due to the excellent osteoinduction effect and osteoconductivity of hydroxyapatite, these hybrid hydrogels may be promising for bone tissue engineering applications.This work developed a series of cellulose and chitin based hydrogels by using our "green" solvent system, and clarified the relationships between their structure and properties of hydrogel. Moreover, a series of functional materials including high strength hydrogels, superabsorbent hydrogels, stimuli-responsive hydrogels, photoluminescent hydrogel, chitin hydrogels, and inorganic/organic hybrid hydrogels were constructed and evaluated. These basic researches provided valuable information for construction, and development of biobased hydrogels with different properties from renewable resource, and are accordance with national sustainable strategy. Therefore, this thesis is highly valuable for academic study and great potential.