| In this paper, the cellulose and hemicellulose were extracted and separated from pineapple peel. The extraction of hemicellulose crude polysaccharide from pineapple peel via alkali-extracting and ethanol-precipitating method and ultrasound-assisted extraction were optimized through orthogonal experiment. The hemicellulose extracted from pineapple peel was then purified through DEAE-Cellulose(OH-) column. The characteristics of the purified pentosans was also compared and studied.The optimal processing conditions for pineapple hemicellulose polysaccharides extraction with alkali-extracting and ethanol-precipitating method showed as extracting time of 2h, 1:10 ratio of material 7%NaOH (w/v), 40℃.The yield of hemicellulose and content of pentosans reached to 41.3% and 73% respectively. While the optimal processing of ultrasound-assisted extraction showed as ultrasonic power 160w, ultrasonic time 90min, concentration of NaOH 2%, alkali extracting temperature of 25℃. The yield of hemicellulose and content of pentosans reached to 45.3% and 72.3% respectively.Three purified hemicellulose polysaccharides were obtained through DEAE-Cellulose(OH-) column. The contents of pentosans reached to 3.3%,78.6%和67.9% respectively. The purified hemicellulose polysaccharides were proven as a typical polysaccharide FT-IR spectrum profile; the hemicellulose polysaccharides-2 was then purified through GPC and two purified pentosans were obtained and their Mp 93468D, 9042D respectively and Mw 166889D, 11837D respectively.The pineapple peel, pineapple crown and pineapple pulp were modified through etherification and amination. The adsorption characteristics and conditions were studied though the adsorption on Direct Red 4B, Reactive Dark Blue B and Vat Yellow G. The changes of the modified products were revealed through FTIR spectrum and SEM. Meanwhile, the adsorption mechanistic and thermodynamic properties of modified cellulose from pineapple peel were studied. The characteristics of cellulose in pineapple peel and its modified products were compared through FTIR, X -ray diffraction, DSC and SEM.The result shows that the adsorption ability of modified pineapple peel, pineapple crown and pineapple pulp exhibited much higher than the unmodified pineapple peel, pineapple crown and pineapple pulp. The adsorption velocity of the modified products on the dyes exhibited as pineapple crown,pineapple peel,pineapple pulp. Direct Red 4B was found easier to be removed than Reactive Dark Blue B and Vat Yellow G. from waste water by modified pineapple peel, pineapple crown and pineapple pulp. The modified pineapple peel showed the optimum pH4～10 for Direct Red 4B adsoption,pH2～6 for Reactive Dark Blue B adsorption and pH2～9 for Vat Yellow G adsorption. The change of related groups in FTIR spectrum and the change of surface on the SEM pictures indicated that the etherification and amination reactions took place.The studies of kinetics of adsorption on the modified pineapple peel fiber showed that: the adsorption was in accord with Lagrange pseudo first-order model. The adsorption was proven as the chemical style.The isothermal adsorption of modified cellulose was in accord with Freundlich isothermal adsorption model. The thermodynamic parameters showed that the adsorption of modified cellulose was automatic, entropy production and endothermic process. The studies on structure and characterization showed that there was an increase on the heat resisting property and a basically unchange on the degree of crystallinity of modified cellulose. The FTIR spectrum and SEM pictures indicated that the etherification and amination reactions took place on the cellulose in pineapple peel. |
