Preparation And Characterization Of Hydrogels Based On Pineapple Cellulose And Hemicellulose And Its Application

In this study, cellulose and hemicellulose were extracted from pineapple residue and used to prepare composite hydrogels with different solvent systems and the structures of the prepared composite hydrogels were characterized by a series of modern detection methods. The research can be helpful to recycling pineapple residue in high value. The specific results are concluded as follow:(1) Celluloses and hemicelluloses were isolated and extracted from pineapple peels by alkaline peroxide treatment. Four different kinds of cellulose(C0, C1, C2, C3) and four kinds of hemicellulose components(H1, H2, H3, H4) were obtained respectively. The structure of cellulose and hemicellulose were characterized by a series of detection methods including IC, FT-IR, TGA, DSC. The results showed that hemicellulose and lignin could be effectively removed by alkaline peroxide treatment. IC analysis indicated that cellulose C3 with the highest purity, contained above 93% of glucose. TGA and DSC showed that cellulose C3 exhibited good thermostability with a maximum decomposed temperature at 335.8℃ and a molten exothermic peak at 128.8℃. Four hemicelluloses were similar in structure, composed of arabinose, glucose, galactose, xylose. More linear hemicelluloses were extracted with the increasing concentration of alkaline. TGA and DSC showed that hemicellulose H3 had a maximum pyrolysis rate at 285.2℃and a strong melting exothermic peak at 124.5℃.(2) Pineapple cellulose was prepared into regenerated cellulose hydrogel by dissolving it in ionic liquid. The effects of cellulose content, cellulose component and ionic liquid type on the texture of prepared regenerated hydrogels were investigated. The results showed that the prepared composite hydrogel exhibited optimal texture behaviors when pineapple peel cellulose with content of 4% was dissolved in BMIMCl. The characterization analysis revealed that the purity of cellulose was further improved and the crystalline status could be changed from cellulose I to cellulose II with the degree of crystallinity slightly decreasing and the thermal stability declined to some extent during the process of forming regenerated hydrogel.(3) Composite hydrogels were prepared by mixing cellulose with inorganic adsorbent(activated carbon, carclazyte, bentonite, attapulgite, kaoline) in ionic liquid BMIMCl and its methylene blue adsorption experiments in aqueous solution were performed. TPA, FT-IR, SEM, TGA were used to characterize the structures of the prepared composite hydrogels. The results showed that attapulgite/cellulose composite hydrogel exhibited the highest adsorption capability for methylene blue and the adsorption kinetics was accord with pseudo second-order model. FT-IR and SEM ananlysis suggested that inorganic adsorbent didn’t participate chemical reaction but were imbedded in network structures of the prepared composite hydrogels. TPA and TGA revealed that the addition of inorganic adsorbent into hydrogel could greatly improve the texture properties and thermal stability of the hydrogel.(4) Porous pH sensitive hemicellulose-grafted-poly(acrylamide) hydrogels were prepared in water system using PEG as the pore-foaming agent. The effect of cross-linking agent content, monomer ratio, molecular weight and amount of PEG on the equilibrium swelling rate and texture of the prepared hydrogels was investigated. The structures of hydrogels were characterized by TPA, FT-IR, SEM, TGA methods. The results revealed that cross-linking agent content and monomer ratio could greatly impact the equilibrium swelling rate and texture of the prepared hydrogels while molecular weight and content of PEG showed no effect. Harder texture and lower swelling rate of the prepared hydrogels were observed as more cross-linking agent and higher monomeric ratio were used. SEM and swelling analysis showed that the prepared hydrogels had porous structure and sensitivity to change of pH value. Swelling kinetics performance in different pH solutions indicated that the swelling behavior of the prepared hydrogels complied to Fickian diffusion Model at initial phase and fitted to Schott Model during the whole swelling process. FT-IR suggested that acrylamide was grafted to hemicellulose successfully and PEG was found not to involve in polymerization.