Preparation And Properties Of Regenerated Chitin Materials Based On NaOH/Urea Solvent

With the decrease of non-renewable resources,researchers have focused on the development and utilization of natural renewable biomass resources such as cellulose,chitin,and alginic acid.Among them,chitin is a polysaccharide extracted from the shells of marine crustaceans,which is abundant in nature.Due to its renewability,natural antibacterial properties,and biocompatibility,chitin materials are ideal substitutes for petroleum-based materials and are favored by researchers.However,the intermolecular and intramolecular hydrogen bonds in chitin make it difficult to dissolve/melt,thus hindering the development and application of chitin.To solve this problem,researchers have developed a variety of solvent systems to dissolve chitin,including Na OH/CS2 system,copper ammonia solution,NMMO water system,ionic liquid,alkali/urea water system,etc.Among them,the alkali/urea system is simple,efficient and green,which is in line with the development concept of green chemistry.In this work,chitin/cellulose composite film,chitin fiber and flat chitin fiber materials were successfully prepared after dissolving chitin with this dissolution system.,Textile and other fields have good application prospects.This work includes the following three research contents:1.Preparation of chitin/cellulose composite membrane.In this chapter,chitin is used as a raw material,and the alkali/urea system is used as a solvent to dissolve chitin.The chitin solution is doped with different mass ratios of cellulose powder,and the chitin/cellulose is regenerated in a low-temperature 80 wt% methanol coagulation bath.Composite film.The light transmittance of the composite film after doping with particles is not affected,and the light transmittance can still be as high as 90%.Mechanical properties tests show that the strength of the chitin/cellulose composite film can reach 95 MPa,and the elongation at break is 6.3%,which is higher than that of pure The strength of the chitin film increased by 25%,and the elongation at break increased by 186%.The composite membrane has good thermal stability,good chemical stability,no cytotoxicity and good biocompatibility.The composite film has potential application prospects in food packaging and medical materials.2.Preparation of chitin fiber.In the previous chapter,the composite membranes regenerated by low-temperature methanol coagulation bath showed good mechanical properties,while the chitin solution had good stability and spinnability at room temperature.Therefore,the chitin fiber regenerated in the coagulation bath prepared by using chitin solution as the spinning solution with different contents of organic solvent has poor shaping effect.The chitin fibers regenerated in different acidic coagulation baths showed good thermal stability,excellent mechanical properties and could well retain the chemical structure of chitin.The average breaking strength of the chitin fibers prepared in the acid coagulation bath was 96.1 MPa,and the breaking elongation was23.1%.Considering production cost and mechanical properties,sulfuric acid was finally selected as the coagulation bath.During the exploration process,it was found that different concentrations of H had a significant effect on the regeneration rate of chitin fibers.When the H concentration was 2.5 mol/L,the prepared chitin fibers had excellent mechanical properties,with a breaking strength of 100 MPa and a breaking elongation of 21.2%.The strength of chitin fiber is also related to the stability of the coagulation bath system.When the concentration of salt added is appropriate,the chitin fiber regeneration system is stable.By exploring the final selection of H concentration of 2.5 mol/L sulfuric acid and 10 wt% sodium sulfate as the coagulation bath,the mechanical properties of the prepared chitin fibers are the best,with a breaking strength of 95.4 MPa and a breaking elongation of 24.1%.The study also found that with the increase of chitin content,the mechanical strength of the fiber first increased and then decreased.When the chitin content was 4 wt%,it was regenerated in a coagulation bath with H concentration of 2.5 mol/L sulfuric acid and 10 wt% sodium sulfate.The obtained chitin fibers had the best mechanical properties,with a breaking strength of101 MPa and a breaking elongation of 21.2%.The regeneration speed of chitin spinning solution is moderate,and the more stable the coagulation bath system is,the stronger the mechanical properties of the regenerated chitin fibers are.3.Preparation of flat chitin fibers.Coagulation baths with different temperatures and phytic acid contents have a significant impact on the morphology of chitin fibers.At room temperature,as the concentration of phytic acid increases,the flatness of chitin fibers becomes higher.Regeneration in 20 wt% phytic acid coagulation baths results in The flat chitin fiber has good mechanical properties,its dry strength can reach 160 MPa,and its elongation at break is 19%.At the same time,as the temperature rises,the flatness of the fibers is reduced.This shows that only spinning at an appropriate temperature can ensure smooth regeneration of flat chitin fibers.The flat chitin fiber has good thermal stability,mechanical strength,antibacterial properties and other properties,and the fiber has potential application value in the textile field.