Preparation And Characterization Of Modified Pineapple Peel Adsorbent For Metal Ion And Pineapple Peel Cellulose Hydrogel

Pineapple (Ananas comosus L. Merryl) produces 30%-50% peel waste when processed into can and juice foods. Therefore, utilization of pineapple peel waste is a significant topic of resource recycle and environment protection. This work involves in the chemical modification of pineapple peel and hydrogel preparation. With the pineapple peel after bromelain extraction as the raw materials, firstly, it was treated to gain the pretreated pineapple peel fibre (SPPF), or the cellulose was extracted from pineapple peel to obtain the pineapple peel cellulose (PPC); Secondly, in pyridine and dimethyl sulfoxide solvents, a research was carried out on the SPPF and PPC modification through reaction with succinic anhydride respectively to prepare the modified adsorbents. The modified adsorbents were applied in Cu2+, Cd2+ and Pb2+ adsorptions. 1-allyl-3-methylimidazolium chloride (AMIMCl) was used to dissolve PPC to prepare pineapple peel cellulose hydrogel (PPCH). The effects of polyethylene glycol (PEG), polyvinyl alcohol (PVA),к-carrageenan (CN), starch (SH) and insoluble polyvinyl pyrrolidone (PVPP) on the texture and properties of the prepared hydrogels were investigated. The characterization of hydrogels and its primary application in the drug release were also performed. The main results obtained were showed as follows:1,Preparation of adsorbents through modification on SPPF with succinic anhydride in pyridineThe carboxylic function group was proven introduced in the backbone of fibre by modification with succinic anhydride in pyridine. The prepared modified pineapple peel fibre (MPPF-PY) exhibited high Cu2+, Cd2+ and Pb2+ adsorption capacity. The Cu2+, Cd2+ and Pb2+ adsorptions by MPPF-PY depended on initial metal concentration, adsorption time and solution pH value. The adsorption followed the Pseudo second-order kinetics model and the experimental data coincided well with Langmuir model. The maximum adsorption capacities of MPPF-PY were observed at pH 5.4 for Cu2+ (27.68±0.83mg g-1 or 0.44mmol g-1), at pH7.5 for Cd2+ (34.18±1.02mg g-1 or 0.30mmol g-1) and at pH5.6 for Pb2+ (70.29±2.11 mg g-1 or 0.34mmol g-1) respectively. 2,Preparation of adsorbents through modification on SPPF and PPC with succinic anhydride in dimethyl sulfoxideIn dimethyl sulfoxide, SPPF and PPC was chemically modified with succinic anhydride to prepare the modified adsorbents MPPF-DM70 and MPPC-DM70. The modification in dimethyl sulfoxide is more beneficial for introduction of carboxylic function group than pyridine. Elevated the reaction temperature in dimethyl sulfoxide could not only increase the adsorption capacity of the modified adsorbents but also shorten the reaction time. Cu2+, Cd2+ and Pb2+ adsorptions of MPPF-DM70 and MPPC-DM70 well followed the Pseudo second-order kinetics model and Langmuir model. The optimum pH values for Cu2+, Cd2+ and Pb2+ removal exhibited at pH 5.5, 7.5 and 5.5 respectively. The desorption experiments showed that the all Cu2+, Cd2+ and Pb2+ desorption ratios by HCl solution (0.1mol L-1) reached more than 90%. After five circulations of adsorption-desorption, MPPF-DM70 still held more than 75% of its initial adsorption capacity for Cu2+, Cd2+ and Pb2+.3,Preparation of pineapple peel cellulose hydrogels in ionic liquid and their applications in drug releaseAMIMCl was used to dissolve PPC to prepare pineapple peel cellulose hydrogels (PPCH); the effects of PEG, PVA, CN and SH on the texture and properties of hydrogels were investigated. The swelling kinetics of the prepared hydrogels and their release kinetics were also compared in vitro with sodium salicylate (NaSA) as model drug.(1) The results from TPA, FTIR and FESEM analysis suggested the existence of the interaction between the additives (PEG, PVA, CN and SH) and PPC in AMIMCl solutions. The cycle freezing-thawing process improved the texture profile and mechanical properties of hydrogels. Compared with distilled water, ethanol as the detergent could significantly increased the mechanical properties of gels. (2) Equilibrium swelling ratios and swelling kinetics showed that all of the freeze-dried hydrogels exhibited significant higher ESR than the oven-dried hydrogels. The addition of PEG, PVA, CN and SH increased the ESR of the freeze-dried or oven-dried hydrogels. The cycle freezing-thawing process showed little effects on the ESR of the freeze-dried or oven-dried hydrogels. The swelling ratios of hydrogels increased with time extention. These increasing trends were slowed after 540 min, and the swelling reached to equilibrium after 2700 min.(3) The NaSA load ratios and release kinetics showed that all of the freeze-dried hydrogels exhibited significant higher NaSA load ratios than the oven-dried hydrogels. The addition of PEG, PVA, CN and SH increased the NaSA load ratios of the freeze-dried or oven-dried hydrogels. The cycle freezing-thawing process showed little effects on the NaSA load ratios of the freeze-dried or oven-dried hydrogels. For most hydrogels, the NaSA release were in two phases: rapid release phase and slow release phase. After two release phases, the release ratios of NaSA from these hydrogels almost reached to 99-100%.4,Preparation of pineapple peel cellulose hydrogels and PVPP composite hydrogels in ionic liquidHydrogels and PVPP composite hydrogels prepared from pineapple peel cellulose showed differences in characterization and NaSA release. PVPP could improve the mechanical properties and thermal stability of the composite hydrogels. The freeze-dried hydrogels were found exhibiting higher ESR and NaSA load ratios than the oven-dried hydrogels. PVPP addition decreased the ESR and NaSA load ratios of freeze-dried hydrogels but increased the ESR and NaSA load ratios of the oven-dried gels. Oven-drying processing and PVPP addition were found propitious for slowing the NaSA release.