Investigation Of Constructing Starch-based Polyelectrolyte Functional Membranes Via LbL Assembly

The biodegradable,renewable and biocompatible starch was functionalized by reacting with maleic anhydride or p-aminobenzoic acid to obtain amino-or carboxylic groups-containing starch-based polyelectrolytes?SPE?.Then SPE was applied to conduct layer-by-layer?LbL?assembly with the oppositely charged metal ions,electrolyte or polyelectrolytes to form starch-based polyelectrolyte multilayer film with different functions.Afterward,the structures,properties and generating mechanism of the formed multilayer films were analyzed.The experimental results are summarized as following.1.The feasibility of LbL assembly between starch-based polyanion and metal ions was investigated.Firstly,a starch derivative containing both carbon-carbon double bond and carboxyl group?SC?was obtained through the esterfication between starch and maleic anhydride.Secondly,free radical cross-linking was performed between SC and polyvinyl alcohol-based macromonomer?PVAM?containing both carbon-carbon double bonds and carboxyl groups to generate gels.Then the starch-based gel was maintained in an aqueous solution of copper ions until the equlibrium swollen to provide a positively charged gel.Such a pretreated SC-based gel was adopted as the substrate and immersed alternatively in aqueous solution of SC or SA,rinsed with distilled water,immersed in Cu²⁺or Pb²⁺aqueous solution,and rinsed.This process was repeated until reaching the target layers.The concentrations of metal ions were monitored with UV-visible spectroscopy.X-ray photoelectron spectrometer?XPS?spectra films with the surface of copper ion or SC were recorded to analyze their surface composition.The cross-section of the starch-based multilayer film was examined with a scanning electron microscope?SEM?.The results indicate that the LbL assembly between the polyanion and copper or lead ion is carried as expected.In addition,part of metal ions was replaced with rhodamine B?RHB?to do the same LbL assembly,which also confirms the expected LbL assembly is practicable.2.LbL assembly between polyanion and metal ion was applied to form polysaccharide-based flame retardant coating.Firstly,polyester fabric was pretreated and used as the substrate.Secondly,flame retardant coating was formed through on polyester fabric by aforementioned alternative LbL assembly approach by using aqueous solutions of water-soluble chitosan?WSC?,sodium alginate?SA?and copper ion.The obtained samples were characterized with microscale combustion calorimetry?MCC?,limiting oxygen index?LOI?and thermogravimetric analysis?TGA?.Both the heat release rate?HRR?values and the peak value in HRR?PHRR?of the samples are decreased after LbL assembly.LOI values of the samples are higher than the original fabric.The remained fraction differences between the modified samples and unmodified ones are 1.1%-5.4%.These results suggest that the copper ions and substance containing N element can be introduced via LbL assembly to play the role of flame retardancy.Subsequently,the LbL assembly among cationic and anionic starch-based polyelectrolytes and copper ion were performed to introduce similar flame retardant compositions.The characterization,such as SEM,MCC and LOI,results indicate that the obtained starch-based multilayers are effcitent flame retardant coating as well.3.LbL assembly between starch-based polyelectrolyte and the polyelectrolyte that contained photo-functional groups was performed to construct multilayer with tunablelight-functions.Firstly,theesterficationbetweenSCand4-hydroxyazobenzene was carried out to synthesize azobenzene-containing anionic starch?AZS?.The structures of the starch-based polyelectrolytes were verified with UV-visible spectroscopy,FTIR and ¹HNMR.Secondly,PVAM film was prepared by solution casting and used as substrate.Subsequently,starch-based multilayers with tunable light-functions were formed via aforementioned LbL assembly by immersing in aqueous solutions of AZS and amino starch?AS?or RHB alternatively.The obtained samples exhibited reversible trans-cis photoisomerization when they were subjected to UV and visible light irradiation.The fluorescence of rhodamine B was varied after being LbL assembly with starch-based polyanion.In a word,cationic and anionic starch-based polyelectrolytes that contain amino or carboxylic and azobenezene groups were prepared through common reaction.Starch and PVA were utilizedas raw materials to prepared substrate for examining the LbL assembly between starch-based polyelectrolyte and other components.Then,the mild LbL assembly method was applied to generate flame retardant coating by using copper ion and chitosan or amino starch as effective fire-retardant agents.This technology was also employed to fabricate tunable light-function multilayers by using azobenzene-containing starch-based polyelectrolyte or RHB as light-functional components.As mentioned above,starch-based polyelectrolytes are easily to be prepared and the LbL assembly is able to be performed under ambient temperature as well as using water as medium.Accordingly,what presented here is helpful for developing the applications of starch in the non-toxic and unharmful fields.