| Cellulose has many excellent characteristics,but it is mainly derived from wood,and China is a country with insufficient total forest resources.The structure of chitin is similar in structure with cellulose and are both natural fiber materials.The main sources of chitin were from wasted lobster or crab shells.Chitin is very likely to replace cellulose materials to alleviate the current situation of forest shortage in China.Due to the strong mutual hydrogen bonding between their macromolecular chains,very few solvents can dissolve them.Therefore,their applications were limited.In order to make better use of these two types of natural degradable bio-sources,it is urgent to find an efficient,low-cost and environment-friendly technology,which can be used for efficient extraction,modification and enhancing the nanofibrillation of chitin and cellulose.Deep eutectic solvents?DES?have various characteristics,such as readily available raw materials,non-toxic or low-toxicity,biodegradable,simple preparation,wide electrochemical operation range,and high ionic conductivity.It was considered as one of the most promising green and designable solvent.In this study,13 types of DES were used for different purpose according to their properties.Firstly,by designing different systems of DES for one-step removal of minerals and protein from lobster shells to realize the extraction of high value-added chitin with different molecular weights.Secondly,further research was focusing on exploring DES that can be used for pretreatment of chitin,cellulose and biomass to produce nanochitin and nanocellulose coupled with mechanical treatment.Finally,DES,which is a multifunctional system,is used to directly disperse cellulose for the preparation of conductive ionic gels,which are used in solid flexible electrolytes for sensors and supercapacitors.The main research content and research results include the following parts:?1?A systematic comparison study was conducted by using five acidic DES?choline chloride/malonate acid,choline chloride/malate acid,choline chloride/lactic acid,choline chloride/levulinic acid and glycerol/hydrochloric acid?at different reaction conditions for extraction of chitin from lobster shell.The results revealed the mechanism of demineralization and deproteinization of lobster shells with acidic DES was clarified.Minerals can react with H+to release CO2,and at the same time the protein can be dissolved in DES or decomposed into amino acids.Compared with the traditional method,DES method showed more efficiently and environmentally friendly with less wasted water.By controlling the reaction condition,different molecular weight chitin could be obtained.For example,choline chloride/malonate acid DES could be used for exaction of high molecular chitin?312 kDa?with good thermal stability and glycerol/hydrochloric acid with acid concentration of 7%could be used for exaction of low molecular weight chitin?55?kDa?.?2?Four different DES systems,choline chloride?ChCl?/urea,choline chloride/thiourea,choline chloride/zinc chloride,and zinc chloride/urea,were used for pretreatment of chitin to produce nanochitin.It was found that the addition of acetic acid or acetic anhydride in choline chloride/zinc chloride could realize the O-acylation and hydrolysis of chitin.By introducing acetyl groups to the surface of chitin,the hydrogen bonding between the chitin molecular chains is weakened,so that the chitin molecular chains become loose,during the ultrasonication treatment the nanofibrillation of chitin is easy to realize.Under the optimal reaction condition,after sonication for 45 min,ca.61.6%with DS?degree of substitution?of 0.23 of chitin nanocrystals were obtained pretreated with acetic anhydride.Under the same conditions,the substitution degree of esterified chitin nanocrystals prepared with cheaper acetic acid was 0.34,and the yield was 62%.The thermal stability of chitin nanocrystals decreased compared with pristine chitin due to the decreased crystallinity and the introduced ester groups.In addition,the yield of chitin nanocrystals in still pending issue for its further application.?3?A DES derived from ferric chloride hexahydrate and betaine chloride?molar ratio of 1:1?was used as hydrolytic media for production of chitin nanocrystals.The synergistic effect of Lewis acid and released Br?nsted acid from betaine hydrochloride enabled an efficient and easy production of chitin nanocrystals.After ultrasonication treatment for only 5 min,the obtained chitin nanocrystals were with an average diameter of 10 nm and length of 268 nm,and a crystallinity of 89.2%with optimal synthesis conditions?at 100°C for 1 h with chitin-to-DES mass ratio of 1:20?.The yield of chitin nanocrystals is up to 88.5%and is 25%higher than using choline chloride/zinc chloride with optimal synthesis condition.The chitin nanocrystals were further investigated as efficient emulsion stabilizers,and they resulted in stable o/w emulsions even at a high oil content of 50%with a low chitin nanocrystals dosage of 1 mg/g.?4?A natural non-toxic biodegradable DES composed of betaine hydrochloride and glycerol was used as a pretreatment medium for swelling and cationic of birch cellulose to prepare cellulose nanofibers with the microfluidization.The cosolvent could readily penetrate into cellulose to swell the fibrillar structure and weaken the interaction within the hydrogen bond network.Moreover,the cationization of glycerol and cellulose by betaine hydrochloride further enhances the swelling process.All of these effects promote the nanofibrillation of cellulose and reduce the energy demand in nanocellulose production.The mole amount of betaine hydrochloride was noted to affect the nanofibrillation process and stability of nanocellulose suspension.A high nanocellulose mass yield of up to 72.5%was obtained with a cationic charge of 0.05–0.06 mmol/g.The thermal stability of nanocellulose is comparable to original cellulose and higher than that of nanocellulose prepared by the sulfuric acid method.The tensile strength of the prepared nanocellulose film is 80-110 MPa.?5?A DES composed of choline chloride and oxalic acid dihydrate was used for partially remove of lignin and hemicellulose from luffa to obtain cellulose rich residue.The residue was further suffered from the ultrasonication treatment for liberation of lignin containing nanocellulose.The DES had a dual purpose:to produce fractions of biomass and to accelerate the nanofibrillation of cellulose.The lignin containing nanocellulose was with residual lignin content of 10.7?%and an average diameter of 28?nm.The self-standing films with tensile strength of 134?MPa,which is 20%higher than the nanocellulose film prepared with betaine hydrochloride/glycerol DES method,and is similar as pure cellulose nanofilms and lignin containing nanocellulose films obtained with common method.?6?A DES was used as electrolyte,polymer matrix solvent and cellulose dispersion medium for preparing ion gel.An ion gel based on a DES was fabricated using free radical polymerization of an acrylamide monomer in a choline chloride/urea/glycerol system.The mechanical properties of the ion gel were reinforced by dispersing cellulose pulp in the DES without losing its conductivity.The obtained ion gel was flexible and strong,and it acted like an elastomer.Its excellent mechanical properties can be ascribed to the formation of a coherent hydrogen bond network between the DES and the polymer matrix.The ion gel was successfully applied as a sensor to monitor the grasping motion of the hand.The ion gel was also applied as a solid-state electrolyte in a symmetric supercapacitor with a wide operating voltage window of 2 V and a high specific capacitance of 161.8 F g-1 at a current density of 0.2 A g-1.It also exhibited a high energy density of 22.47 W h kg-1 at a power density of 0.11 kW kg-1 and outstanding cyclability(95.3%capacitance retention after 2000 cycles at 1.0 A g-1). |
PDF Full Text Request