Design And Application Of Controllable Structures Of Seaweed Polysaccharide

Seaweed polysaccharide is an important part of marine resources,with wide sources and low prices.The development and application of seaweed polysaccharide is one of the current research hotspots.Agar and Carrageenan are the most common seaweed polysaccharides,and their excellent gel properties and bioactivity make them have a wide applications prospect in bio-based materials,cosmetics,food,biomedicine and other fields.Based on practical applications,this study focused on improving the gel properties of agar and optimizing bioactivity of carrageenan oligosaccharides through the structure designing on the molecular scale.1)The preparation and properties of the tough,seawater-tolerated agar composite hydrogelsThe unstable gel property and poor mechanical strength of the traditional agar gel restricted its practical application.Inspired by the synergistic effect of multi-scale structures,we introduced nano-clay to construct the composite network structure at the molecular level,and fabricated agar/polyisopropylacrylamide/clay composite hydrogels by photoinitiation polymerization.Tensile tests showed that agar,clay and iso-propylacrylamide(NIPAM)had synergetic effect on the mechanical properties of the composite gel,and the optimum ratio was agar 2.5 wt%,NIPAM 10 wt%,clay 30 wt%in water.More important,agar significantly enhanced the mechanical strength of the composite gel in seawater.The results of swelling tests and salt-tolerance experiments further proved that the increasing agar content notably enhanced the stability of the composite hydrogel,reduced the degree of swelling in ultrapure water and the degree of contraction in seawater.In addition,the results of heating tests showed that the interpenetrating double network structure of agar composite hydrogels evidently enhanced the structural stability and improved the thermal stability.Transmission electron microscopy and scanning electron microscopy analysis showed that the clay interspersed among the network served as physical cross-linkers,and composite hydrogel formed a stable ternary interpenetrating network,resulting in excellent mechanical properties,salt tolerance and high temperature resistance.2)Preparation and characterization of environmental friendly agar composite hydrogel-coated mesh for oil/water separationOn the basis of the above work,taking advantage of high stability and tough strength of the agar composite hydrogel,agar-based composite membrane with interfacial micro/nanostructure was prepared by coating agar composite hydrogel on metal mesh.The SEM tests showed that agar hydrogel was successfully coated on the micron metal mesh,forming a micro/nano composite interface,which increased the roughness of the surface of the mesh.Furthermore,the contact angle tests showed that the hydrogel-coated mesh possessed superhydrophilic,underwater superoleophobic properties,and the oil contact angle underwater was 150°± 1°.Oil/water separation experiments and infrared oil measuring instrument(IOMI)test results showed that the separation efficiency of the agar composite membrane above 250 items reached 98%with different types of oil,oil concentration,pH and salt concentration.The stable oil/water separation performance of the agar composite membrane has great practical value in marine environmental protection,sewage,oily wastewater of food processing and other fields.3)Investigations of microwave-assisted ?-Carrageenan oligosaccharides preparationCarrageenan is sulfate galactan with special structure,and it has great potentials for medicine application owing to its good bio-activities.However,the low solubility and absorption of carrageenan limit the applications in medicine due to its high molecular weight.In this study,the simple and controllable method of microwave-assisted acid degradation was used to prepare carrageenan oligosaccharides with low molecular weight,which improved the solubility absorbability and bioactivity of carrageenan.The molecular weight of the degradation products was analyzed by high performance liquid chromatography(HPLC).To explore the optimal conditions for the preparation of low molecular weight ?-carrageenan oligosaccharides facilely and efficiently,the orthogonal experiment L9(33)based on the factors of pH,temperature and time were applied.The experimental results showed that the optimal pH,temperature,time for degradation reaction were 2.50,110?,20 min respectively.Compared to the degradation by microwave oven,the molecular weight distribution of the degradation products was more uniform.At the same time,by selecting different reaction conditions,we obtained carrageenan oligosaccharides with polymerization degree between 5 and 15(molecular weight of 1800 u?5400 u).The controllable preparation of low molecular weight carrageenan oligosaccharides was achieved and can be applied on subsequent modifications and pharmacodynamics studies.