Liquefaction Of Chitin,Shrimp Shells And Researching The Preparation And Properties Of Liquefied Products Based Composite Membranes

Chitin is widely found in shrimp,crab shells,and is the most abundant nitrogen-containing organic polymer in the natural world and the second largest biomass resource after Iignocellulose.The annual global production of shrimp,crab shells and other marine products as much as 6-8 million tons of waste,most of which are disposed of as rubbish,causing waste of resources and environmental pollution.Exploring their use of resources is imminent.In this paper,commercial chitin,chitin extracted directly from shrimp shells and shrimp shells as raw materials,which were pretreated by ball milling,diethylene glycol(DEG)as liquefied solvent,concentrated sulfuric acid as catalyst,the resulting liquid mixture was roughly separated into two portions:the real products of the reaction(liquefied ball-milled chitin LBMC,liquefied ball-milled extracted chitin LBMC',or liquefied ball-milled shrimp shells LBMS)and the remaining unreacted DEG.Through GPC,HPLC,1H NMR,13C NMR,MS and other detection and analysis methods to separate and identify the small molecular substances and higher boiling point liquefied products,the possible reaction mechanism in the liquefaction process was deduced.Finally,different amounts of LBMC,LBMC,LBMS and polyvinyl alcohol were blended to prepare blend membranes.Combined with tensile properties test,Fourier transform infrared spectroscopy(FTIR),X-ray diffraction spectroscopy(XRD),scanning electron microscopy(SEM),X-ray photoelectron spectroscopy(XPS),thermogravimetric analysis(TG)and other detection methods to detect and characterize the properties of the blend membranes,the degradation and antibacterial properties of the blended film were also tested.The main eontents and conclusions of this article are as follows:In the DEG system,the optimum liquefaction conditions were obtained as:liquid-solid ratio of 7:1,reaction temperature of 160°C,reaction time of 120 min,and the catalyst dosage accounted for 50 wt%of the raw material.Under these conditions,chitin liquefaction yield reached to 92%,extracted chitin liquefaction yield was as high as 96%,and shrimp shells liquefaction yield was 20%.FTIR,GPC analysis of liquefied products showed that LBMC,LBMC',LBMS relative molecular mass Mw and deacetylation DD values were determined as 7192 and 86-0%,8219 and 88.7%,9711 and 57.9%,respectively.The resulting mixture was subjected to rotary evaporation to remove the unreacted liquefied solvent,and a lower boiling point product which was successfully distilled off together with the liquefied solvent and the remaining higher boiling point liquefied product were obtained,respectively.By means of fractionation,extraction and column chromatography,the main product in the low boiling point products and nitrogen containing product were identified as 2-(2-hydroxyethoxy)ethyl acetate(HEEA)and(2-hydroxyethoxy)ethoxy-2-acetamido-2-deoxyhexopyranoside(HEADP)by HPLC-MS and confirmed by 1H NMR,13C NMR.FTIR,GPC and NMR correlation characterization of liquefied products with higher boiling point further explained that the depolymeri/ation and deacetylation reaction occurred in the process of liquefaction.In addition,through the analysis of high and low boiling point products,a plausible mechanism for product formation was proposed.Compared with the pure PVA membrane,the mechanical properties,thermal stability,water solubility and antibacterial properties of the blend membrane prepared by LBMC,LBMC',LBMS and polyvinyl alcohol have been greatly improved.The blend membrane with the best overall performance was 12%liquefied products/PVA film,respectively.Surprisingly,all the measured properties of LBMC/PVA,LBMCf/PVA and LBMS/PVA blend membranes were comparable,and even some of properties of the latter were slightly superior than those of the former,which will provide a new solution for the direct use of seafood waste.