| Pineapple?Ananas comosus L.Merryl?can produce 30%50%of waste residue after serving as fresh fruit or being processed into canned foods and juices.Pineapple peel mainly consists of cellulose,hemicellulose,lignin and pectin.In this work,pineapple peel was used as the basic research material to isolate cellulose,and the isolated cellulose was modified to prepare different types of hydrogels composites.The structure,swelling,smart response characteristics and the applications of methylene blue adsorption and enzyme immobilization of the prepared hydrogels were investigated.The resulting findings can provide basic supports for the high-value utilization of agricultural waste resources.The main research contents and results of this work are concluded as follows:Part ?:Study on modification of pineapple peel cellulose and hydrogels preparation in ionic liquidHydrogels based on pineapple peel cellulose?PPC?and sepia ink were synthesized by homogeneous acetylation of cellulose in ionic liquid 1-butyl-3-methylimidazolium chloride?BmimCl?under no addition of catalysts.The acetylation reaction processed successfully without adding any catalysts.After the reaction,the cellulose crystal type was changed from cellulose I to cellulose II.Sepia ink was evenly distributed on the surface of hydrogel and improve the thermal stability.The hydrogel prepared within 3 h of acetylation reaction,80°C of acetylation reaction temperature,4:1 of acetic anhydride/AGUPPCPC molar ratio and 20%of sepia ink addition amount showed better methylene blue adsorption performance,up to147.41mg/g,while for the hydrogel without addition of sepia ink,which was only 53.72 mg/g.The methylene blue adsorption of the hydrogels followed pseudo-second-order kinetic model and belonged to the chemical adsorption.Novel pH-sensitive hydrogels were synthesized by grafting of acrylic acid onto PPC and addition of kaolin and sepia ink in ionic liquid BmimCl.Sepia ink and kaolin were uniformly distributed in the prepared hydrogels and then enhanced the thermal stability of the hydrogels.The swelling behavior of the hydrogels conformed to Schott's second-order kinetic model and exhibited pH sensitive characteristics.The hydrogel with addition of 10%kaolin and 20%sepia ink showed better adsorbing ability,with 153.85 mg/g of adsorption capacity and95.45%of adsorption ratio,respectively.The pseudo-second-order kinetic model fitted well with the experimental results,indicating the adsorption was chemisorption behavior.Part ?:Study on preparation and swelling response characteristics of pineapple peel carboxymethyl cellulose-based smart hydrogelsThe smart superabsorbent hydrogels were synthesized by grafting acrylic acid and acrylamide onto pineapple peel carboxymethyl cellulose?PCMC?with the introduction of carclazyte.After the introduction of carclazyte,the swelling ratio of the prepared hydrogel increased from 420.17 to 515.24 g/g in distilled water,and 28.03 to 37.89 g/g in 0.9%NaCl solution.The swelling dynamic mechanism of the hydrogel was explained well by Fickian diffusion and Schott's pseudo-second-order models.The swelling of the prepared hydrogels exhibited obvious sensitivities to pH,salt and solvent.The hydrogels showed a high swelling ratio in the urea solution,showing potential applications in the agricultural field such as slow-release fertilizer and water-retaining agent.Natural polyelectrolyte composite hydrogels with multiple-responsive characteristics were prepared in the solutions composed of PCMC,gelatin?GL?and sodium alginate?SA?,via cross-linking with CaCl2 and glutaraldehyde solutions.As PCMC increased,the pore-like wrinkles on the surface of the hydrogel and swelling ratio increased.The prepared hydrogels exhibited the swelling dynamic mechanism well-agreed with the Fickian diffusion and Schott's pseudo second order models,and had obvious pH sensitivity and salt sensitivity.When a DC electric field was applied,the hydrogels exhibited obvious deformation and bending behavior,showing reversible electric field sensitivity.The bending degree of the hydrogels was related to the concentration of the electrolyte NaCl solution,pH value and electric field strength.This multiple-responsive characteristic was conducive to application as potential biomaterials such as drug delivery systems,biosensors and artificial muscles.Part ?:Study on preparation and application of pineapple peel carboxymethyl cellulose composite hydrogelsThe hydrogels PCMC/PVA/SBA-15 were prepared by repeated freeze-thaw method using PCMC and polyvinyl alcohol?PVA?as raw materials and SBA-15 as a functional material.Papain was immobilized in the prepared hydrogel by physicial adsorption and glutaraldehyde cross-linking.The PCMC,PVA and SBA-15 formed a crosslinked structure due to their strong hydrogen bonding interaction.SBA-15 was found to play a role as porogen,and the hydrogels with addition of PCMC showed a more uniform and larger pore-like morphology.The addition of PCMC and SBA-15 also improved the thermal stability of hydrogels.The preparation parameters of hydrogels influenced the activity of the immobilized papain.The optimal papain immobilization conditions were as follows:papain concentration3 mg/mL,pH 6.5,glutaraldehyde concentration 0.75%,and crosslinking time 1.5 h.The obtained immobilized papain exhibited obvious pH sensitivity.Compared with the free papain,the immobilized papain showed enhanced pH,thermal and storage stability.The hydrogels were prepared by the repeated freeze-thaw cycles,using PCMC and PVA as basic materials and graphene oxide?GO?and bentonite as inorganic particle additive.By virture of hydrogen bonds formed between PVA,PCMC,GO and bentonite,GO and bentonite uniformly dispersed in the hydrogel network,acting as physical cross-linkers.GO and bentonite promoted the formation of porous structure of the hydrogels and improved the thermal stability and swelling ratio.The hydrogels exhibited pH-sensitive swelling,showing a maximum swelling ratio at pH 8.0.The methylene blue adsorption capacity was influenced by temperature,pH value and dye concentration.Introducing graphene oxide and bentonite into the hydrogels evidently enhanced the methylene blue adsorption capacity.The hydrogel exhibited good cycling performance on methylene blue adsorption.After four cycles,the hydrogels still retained 92.76%of its original adsorption capacity.The adsorption process conformed to the pseudo-second-order kinetic model and Langmuir isotherm model. |
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