Pectin Extraction From Grapefruit Peel And Synthesis And Propercities Of Pectin Madified Compsites

Every year,a large amout of grapefruit peel was generated and wasted owing to consuming grapefruit,so this paper was aimed to reuse these renewable resources.Natural polymer pectin which was existed abundantly in the grapefruit was extracted from the peel.Used as raw material,pectin was grafted with hydrophilic monomer acrylic acid and acrylamide,so a novel compsite pectin-g-p(acrylic acid-co-acrylamide)(PEC/AA)was obtained.At first,the pectin was extracted from the peel of grapefruit by using the technique of microwave extraction-alcohol precipitation.The effect of solid-liquid ratio,extraction pH and extraction time to the yield of pectin were investigated.According to the orthogonal experiment,the optimum extraction conditions were ascertained:solid-liquid ratio 1:20,extraction pH 1.5,extraction time 7min.The degree of esterification to the extracted pection was 65.6%measured by acid-base titration.The pectin formed gel with heavy metal ions:Cu2+、Pb2+、Zn2+.It was observed from the infrared spectrogram that these groups containing O atom were changed or weakened.Then,the composite pectin-g-poly(acrylicacid-co-acrylamide)were synthesized by grafted copolymerization in aqueous solution.The grafted copolymerization was initiated by ammonium persulfate(APS)and N,N-methylene-bis-acry lamide(MBA)was used as the crosslinking agent.The effects of action temperature,amount of APS,amount of MBA and neutralization degree of acrylic acid to the swelling degree were investigated.The maxium of swelling degree was obtained when the conditions were:action temperature 65 ℃,amount of APS 0.8 mg,amount of MBA 1 g,and neutralization degree 80%.The infrared spectroscopy of the compsite showed that pectin was successfully grafted with monomers.The swelling and deswelling behavior and the swelling mechanism of PEC/AA was studied.The results indicated the swelling kinetics of PEC/AA accorded with Schott two-order swelling kinetics model;PEC/AA was very sensitive to pH,its equilibration swelling degrees were increased with increasing of pH in acidic solutions while decresed in alkaline solutions;different swelling behavior of PEC/AA were observed in different solutions:the maxium equilibration swelling degree was obstained in distilled water,then in the tap water,followed by NaCl solution and MgCl2 solution,PEC/AA almost cannot swell in heavy metal solutions.The swelling-deswelling curve were obtained when PEC/AA hydrogel was alternately added into acidic solution and solution or added into Cu2+solution and Na+ solution.At last,the volumetric shrinking kinetics of the PEC/AA hydrogel in heavy metal ion solution were investigated and the volumetric shrinking kinetic constants Kd and the activation energy Ea were estimated.The results indicated that the hydrogel showed responsive volumetric shrinking behavior to all of the heavy metal ions and the volumetric shrinking rate increased with increasing of the concentration of heavy metal ion in solutions;the volumetric shrinking process of the hydrogel could be well fitted with the function Y(t)=Y0+A1exp(-B1/t);the selectivity sequence of the hydrogel for heavy metal ions was Pb2+>Cu 2+>Zn2+>Co2+.