Preparation,Characterization And Rheological Properties Of Chitin Regenerated From Phosphoric Acid

Chitin is highly crystalline biopolymer with poor solubility in water and common solvents due to the presence of strong intermolecular and intramolecular hydrogen bonds,which discourages its application in the food industry.Herein,native chitin was dissolved in concentrated phosphoric acid to disrupt its crystalline structure,followed by regeneration in water to produce nanostructured regenerated chitin in high yield.The effects of preparation condition on the structure and rheological properties of resulting regenerated chitin was studied.Chitin,water and concentrated phosphoric acid were mixed at a ratio of 1:3:50(w/v/v)to a homogeneous state,and incubated at 5? for 12 h,25 ? for 5 h or 15 h,50? for 0.5 h,1 h or 2 h,respectively,and diluted with water to regenerate the chitin.The regenerated chitin was characterized by scanning electron microscopy,transmission electron microscopy,Fourier transform infrared spectroscopy,X-ray diffraction and solid nuclear magnetic resonance spectroscopy.The yield of regenerated chitin prepared at 5? was constantly high,and the yields prepared at 25? or 50? decreased with the increase of treatment time.The degree of polymerization of regenerated chitin decreased with the increase of treatment time.5?-12 h and 25?-5 h regenerated chitin were fiber-like with diameter about 25 nm.25?-15 h,50?-0.5 h and 25?-1 h regenerated chitin were spherical with size ranged from 200 to 500 nm.50?-2 h regenerated chitin showed irregular morphology with extensive aggregation.The chemical structure of all regenerated chitin were not affected by phosphoric acid treatment significantly,and their degree of substitution of phosphoric acid were less than 1.00%.In comparison with native chitin,the regenerated chitin had decreased crystallinity and altered crystal structure.Rheological testing demonstrated typical shear thinning and weak thixotropic behavior in regenerated chitin.5?-12 h regenerated chitin had higher apparent viscosity than others.5?-12 h and 25?-5 h regenerated chitin demonstrated a typical gel characteristic,and three stages viscosity-shear rate curve:shear thinning-platform area or shear thickening-shear thinning,in which ionic strength,pH and temperature had little influence.Viscoelastic analysis confirmed ionic strength and pH had no influence,but increasing temperature decreased the storage modulus,which was explained by the weakening or disruption of intermolecular interactions,such as hydrogen bonds and Van der Waals forces.