Starch Based Nanofibrous Films And Pickering Emulsion:Fabrication,Characterization,and Properties

Starch,as a biopolymer produced from natural plants,has been used in many fields,including food industry,agricultural,biomedicine,etc.,due to its biodegradability,safety,non-toxicity,goodbiocompatibility,and environmental-friendly.Recently,the physicochemical properties of starch were improved via different processing technologies or modification methods to develop multifunctional starch-based composites materials,which was conducive to realize the value-added utilization of starch resources.In this work,electrospinning and sulfuric acid hydrolysis were used to fabricate two different shape of starch materials(fibers and granule),respectively.Then,the physicochemical properties of pure starch materials were improved by blending,surface coating and interface modification and endow them novel functional properties,respectively.Subsequently,multifunctional starch-based composite materials were characterized by scanning electron microscopy(SEM),Fourier transform infrared spectroscopy(FTIR),solid-state proton nuclear magnetic resonance(~1H NMR),optical microscopy,X-ray diffraction(XRD),thermogravimetric analysis(TGA),ultraviolet and visible spectrophotometry(UV-Vis).Meanwhile,the application promising of these starch-based composites materials in food packaging and Pickering emulsion are also evaluated.This paper mainly includes follow three parts:(1)Tannic acid/Fe~Ⅲwas incorporated into starch nanofibrous films by blending approach to construct double-crosslinking network structure via non-covalent hydrogen bonding and coordination,which benefit to improve the mechanical strength of starch nanofibrous films and endow them with good biological activity.The results showed that tannic acid/Fe~Ⅲpossess satisfactory compatibility with starch with no significant effect on the morphology of starch nanofibrous films,and could improve the thermal stability.The incorporation of tannic acid endows the starch nanofibrous films with antioxidant activity and antibacterial activity of inhibiting the growth of Staphylococcus aureus.However,the addition of Fe~Ⅲwill decrease the antioxidant activity of the composite films and almost lose the antibacterial activity.Importantly,tannic acid and tannic acid/Fe~Ⅲcan effectively improve the mechanical properties of nanofibrous films.Compared with starch nanofibrous films,the highest tensile strength is 0.88 MPa and 1.01 MPa,which increased by 114.6%and 146.3%,respectively.(2)Surface coating was used to improve the surface properties of starch nanofibrous films through electrospaying acylated tannic acid.Firstly,non-polar fatty acid chains were introduced into tannic acid molecules through acylation reaction to increase its fat solubility.The concentration of butyric anhydride plays a critical role on the synchronous regulation between antioxidant activity and hydrophobicity of tannic acid.The acylation reaction between butyric anhydride and phenolic hydroxyl group of tannic acid can improve hydrophobicity and thermal stability,while retaining some antioxidant activity.Then,acylated tannic acid was coated on the surface of starch nanofibrous film through electrospraying and then rough three-dimensional network pore structural surface was fabricated.Tannic acid with different acylation degree has a positive correlation with the surface hydrophobicity of starch nanofibrous film.which can convert the super hydrophilicity(with water contact angle～0°)of starch nanofibrous film can be transformed into high hydrophobicity(with water contact angle 134.1°).In addition,acylated tannic acid also improved the tensile strength of starch nanofibrous films,up to 0.86 MPa,an increase of 109.8%.(3)Interface modification was used to adjust the interfacial properties of starch nanocrystals in order to improve the interfacial stability of Pickering emulsion.Sodium alginate is combined on the surface of starch nanocrystalline particles through non-covalent hydrogen bonding,which increased its the charge and hydrophobicity and improve the stability of its suspension.High concentration(1.0 wt.%)of sodium alginate can improve the storage stability of the emulsion,and possess excellent p H stability(p H=2-10)and ionic stability(600 m M).The stability of starch nanocrystals was increased due to three aspects.On the one hand,the electrostatic repulsion on the surface of the starch nanocrystals is enhanced,which avoided the aggregate or flocculate of droplets and decreased droplet size.On the other hand,the hydrophobicity improving of starch nanocrystalline,which makes it easier to be absorbed at oil-water interface and decrease the interfacial tension;More importantly,sodium alginate enhances the viscosity of the aqueous phase,and help to form the three-dimensional network gel structure,which limits the movement of droplets.