Construction Of κ-carrageenan Based Functional Hydrogel

Environmental problems are becoming increasingly serious and have become the focus of global attention since the 21st century.In order to effectively solve the problem of carbon emissions,biomass resources have become an ideal substitute for petroleum-based products due to their good renewable,degradable and biocompatibility.Moreover,it have gradually become a research hotspot in the fields of biology,chemistry,chemical engineering,materials and environment.κ-Carrageenan（κCG）,as a natural sulfate polysaccharide extracted from seaweed,not only has good thickening,stability and emulsifying properties,used in the fields of food and medicine,but also shows good biological activities such as anti-tumor and immune regulation in the fields of biological tissue engineering,wound dressing and flexible electronic devices.However,traditionalκ-carrageenan based functional materials are mainly derived from their hot water solvent system.The three-dimensional network structure of hydrogels can be constructed through the reversible transformation of"sol-gel"during the heating and cooling process.These hydrogels are usually hard and brittle,which greatly limits their application as load-bearing materials in the field of biological tissue engineering.Meanwhile,κ-carrageenan contains a large number of hydrophilic sulfate groups,and the swelling of gel obtained from the hot water system is low,which can’t be used as an effective component of superabsorbent polymer materials.Therefore,this paper aims to find and build a new typeκ-carrageenan based hydrogel and to explore its application prospects in various fields.The main innovation of this paper is（1）Using Na OH/urea aqueous solution to dissolveκ-carrageenan at low temperature,without building a second network structure,constructing a high strength through the combination of molecular chain conformation regulation and stepwise mechanics training.The fracture strain and toughness ofκ-carrageenan based hydrogel increased 8.5 and 11.5 times,respectively;（2）In the same dissolution system,starch is added by using one-pot synthesis to prepareκ-carrageenan/starch superabsorbent hydrogel（CG/S SAH）.The highest swelling degree of the prepared SAH reached 1882.64g/g,which is far higher than that of most superabsorbent polymer systems at present.The main research contents and conclusions of this paper include the following two parts:To make a kind of All-κCG hydrogel by dissolving in Na OH/urea aqueous solution through freezing/thawing cycles.The experimental results show that theκCG molecular chain presents a more rigid molecular chain conformation in Na OH/urea system.The chemical cross-linking of epichlorohydrin（ECH）and the physical cross-linking of K⁺jointly promoted the improvement of the mechanical properties of the hydrogel.Then,the stepwise tensile training can promote the alignment of polymer chains,and induce more ordered double helices into the dynamic association domain.The tensile properties and toughness of the hydrogel were further improved.When the molar ratio of ECH andκCG disaccharide unit is fixed at 2.57:1,the fracture strain,stress and toughness of the hydrogel can reach～396%,～0.55 MPa and～151.6MJ m^-3.Compared with the traditional hot water system,the fracture strain and toughness of the hydrogel material increase 8.5 and 11.5 times,respectively.In addition,the hydrogel also shows good stability and excellent mechanical properties under physiological conditions,so the hydrogel has greater potential application prospects in tissue engineering.A series of CG/S SAH was successfully prepared which was dissolved in Na OH/urea system at low temperature by using one-pot synthesis.The covalent binding between starch andκ-carrageenan were confirmed by FTIR and XPS;TGA showed that the addition of starch effectively improved the thermal stability of CG/S SAH.The swelling behavior study showed that when the mass ratio ofκ-carrageenan to starch was 2:1 and the content of ECG was 1.5%,the swelling degree of CG/S SAH could reach 1882.64g/g,which was far higher than most of the current superabsorbent polymer network systems;The fitting of swelling kinetics revealed that the swelling behavior of CG/S superabsorbent hydrogel followed the pseudo-second-order kinetic model,and the diffusion mechanism was non-Fick diffusion.Therefore,this work provides a new idea for the development of natural polysaccharide based superabsorbent hydrogels.To sum up,this paper successfully prepared a new type ofκ-carrageenan functional materials by using the Na OH/urea solvent system and illustrated the relationship between the structure and properties of different typesκ-carrageenan gel materials.The basic researches provided scientific evidence and academic value for the construction materials with highly added value from the least exploited resourceκ-carrageenan,so it has important academic value and application prospects.