Studies On Chitin Hydrogel Functional Materials

As the largest ecosystem on earth,the ocean provides 96.5%of water resources and80%of biomass resources.Chitin,mainly derived from marine crustaceans,is the most abundant natural polysaccharide in marine.Chitin-based functional material has attracted great attention because of its inherent bioactivity,biosafety and biodegradability.This thesis focuses on the fabrication of a series of chitin-based functional hydrogels by simple,green methods and evaluating their potential applications in pressure sensor,solar desalination,and distillation power generation.Meanwhile,scanning electron microscopy（SEM）,polarizing microscope（POM）,solid state ¹³C NMR,wide-angle X-ray diffraction（WAXS）,water contact angle（CA）measurement,mechanical test,finite element analysis,etc.have been used for the characterization of their structure and properties.The major innovations of this thesis include the following aspects:（1）Chitosan wrinkled hydrogel was constructed via gradient crosslinking strategy and mechanical difference,which has the potential as a new type of pressure sensor.（2）Based on the double crosslinking strategy,chitin hydrogel with high porosity and high water contain was fabricated,enabled with continuously water supplement and salt diffusion via osmotic pressure,and applied as high-efficiency salt-resistance solar desalination.（3）The ultra-thin chitin aerogel was prepared by adherent freeze-drying technology,and used as a new type of power generation device by converting the osmotic energy into electric energy.Chitosan solution was obtained by dissolving chitosan powder in alkali/urea water solvent system.By pre-stretching chemically cross-linked chitosan elastic hydrogel in water for a short period of time to introduce gradient physical crosslinking.The outer chitosan chains and bundles form aggregates by physically crosslinking,quickly creating a closely packed nanofiber layer as a shell on the hydrogel surface.After removing the stretching force,the significant modulus gradient between the relatively stiff shell and the inner elastic networks of the chemically cross-linked hydrogel drives the formation of the wrinkling surface topography due to mechanical difference.Moreover,the chitosan wrinkled hydrogel can act as an excellent matrix for fabricating pressure sensor by integrating conductive polymer,greatly expanding the application of chitosan in smart soft materials.Chitin solution was obtained by dissolving chitin powder in alkali/urea water solvent system.Double crosslinking strategy was employed to construct chitin hydrogel.A small amount of chemical crosslinking constructed the large framework of hydrogel,physical crosslinking resulted in the formation of numerous interpenetrating porous structures.Meanwhile,interfacial bonding strategy was adopted to introduce polydopamine（PDA）onto the chitin hydrogel surface by the oxidation polymerization of dopamine,resulting in the formation of Chitin/PDA composite hydrogel.Taking advantage of the high porosity（90.36%）and high water contain（92.56%）of chitin hydrogel,and the solar absorption ability of PDA,Chitin/PDA composite hydrogel could be used as efficient solar seawater evaporators.The abundant hydrophilic groups（hydroxy,amidogen,acetamido）derived from the chitin substrate provided superior water retention ability.Moreover,the numerous interpenetrating porous channels in the chitin hydrogel was beneficial for water supplement and salt diffusion via osmotic pressure,and thus high energy conversion efficiency（80.8%）was achieved.Such chitin hydrogel-based solar evaporator by synchronously capitalizing marine biomass and seawater resource offers a simple,cost-effective way for clean water supply.Also based on the chitin solution obtained by alkali/urea water solvent dissolution.The chemical gel with 1mm thickness was prepared by chemical crosslinking and then the physical crosslinking was introduced through ethanol coagulation bath.Subsequently,ultrathin chitin aerogel was successfully prepared by adherent freeze-drying technique.The numerous nano-pores and charged characteristics on the aerogel surface making it suitable for serving as ion screening channels.Combined with the technology of thermal osmotic energy conversion and membrane distillation,the simultaneous harvesting of fresh water and electric energy was realized by utilizing low-grade waste heat.Driven by the pressure difference,fresh water generated by membrane distillation flows through the charged nano-channels on the surface of chitin aerogel.Based on the"Debye effect",the double electric layer at the solid-liquid interface was formed on the surface of the charged nano-channels of chitin aerogel,which could screen the charge of fluid and convert the permeating energy into electric energy.In this paper,chitin,the most abundant polysaccharide in the marine and its derivative chitosan were used as raw materials to successfully construct chitosan wrinkled hydrogel,chitin composite hydrogel,and chitin aerogel.The structure and properties of these materials were studied,and their potential applications in pressure sensor,water treatment,and energy were evaluated.These fundamental researches concerning utilization of marine renewable resources exhibit both theoretical value and practical application prospects,and accord well with the principles of sustainable development.