Chemical Modification Of Starch And Its Application As An Adsorbent Material

Starch is a plant biopolymer which is cheap abundant and has many applications in food and non-food industries.However,in the native form,its applications are limited due to shortcomings,such as loss of viscosity and thickening power upon cooking,retrogradation characteristics,absence of certain groups responsible for a particular function,etc.So,in order to reduce its limitations and improve its applications,modification of starch is necessary.It can be modified by several ways like chemical modification and physical modification but the most important one is the chemical modification.The different chemical modification techniques used for starch are grafting,cross-linking,esterification,etherification and dual modification.Some of the important applications of modified starches are adsorbents for the removal of dyes,ammonia and phenol.Dyes in the effluents of industries,are very harmful to environment and living organisms as these dyes cause different diseases while some dyes are carcinogenic.Similarly,ammonia and phenol are also among the harmful toxicants which are mostly inhaled through smoking.The different diseases caused by phenol are cancer,coordination impairment,convulsions,respiratory failure,coma,kidneys disorders,and muscle weakness.The different diseases caused by ammonia are pulmonary fibrosis,bronchitis,chemical pneumonitis,dyspnea,laryngospasm,noncardiogenic pulmonary edema,headache respiratory failure and irritation to skin,eyes,nose and throat.Besides these direct effects,ammonia increase addiction towards cigarette.Different methods used for the removal of these toxicants are flotation,chemical precipitation,electrochemical deposition,ion exchange and adsorption.Adsorption is the best method to get rid of these toxicants as other methods has certain limitations like waste of chemicals,poor settlement and non-selectiveness.Activated carbon is considered as a good adsorbent but its use is limited due to non-selective adsorption and regeneration problems.Similarly the synthetic polymeric adsorbents are non-biodegradable and non-renewable and may act as secondary pollutants.Starch may prove an excellent substitute for these adsorbents because it is biodegradable and environmentally safe.However,native starch are rarely used directly as an adsorbent due to its less adsorption ability for dyes,ammonia and phenol.In order to improve its adsorption capability towards dyes,ammonia and phenol,it needs to be modified chemically.So,here in the first project,carboxymethyl starch-g-polyvinylpyrolidones(CMS-g-PVPs)were synthesized by grafting polyvinylpyrolidone(PVP)on carboxymethyl starch(CMS)using azobisisobutyronitrile(AIBN)and potassium persulphate(KPS)as initiators.The grafting percentage of the different CMS-g-PVPs was determined by simple weighing method.The modified starch(CMS-g-PVP-5)with maximum grafting percentage was further characterized by elemental analysis,Proton nuclear magnetic resonance(1H NMR)and Fourier transform infrared(FT-IR)spectroscopy.Crystallinity of CMS-g-PVP-5 was analyzed from its x-ray diffraction(XRD)pattern and thermal properties of this modified starch were analyzed by thermogravimetric analysis(TGA)and differential thermal analysis(DTG).The TGA and DTG curves were also used to confirm the grafting percentage.CMS-g-PVP-5 was then used for the adsorption of Rhodamine 6G(dye)from wastewater under different pH,temperature,adsorbate dose and adsorbent concentration.This modified starch showed good adsorption ability with maximum adsorption efficiency of 363.95 mg/g towards Rhodamine 6G.CMS-g-PVP-5 was also applied for the adsorption of ammonia gas and proved to be an exciting adsorbent for ammonia adsorbing 0.820 mmol of ammonia at maximum.In the second project,different types of starch phosphates(SPs)were synthesized by treating starch with monosodium phosphate(NaH2PO4)and disodium phosphate(Na2HPO4)under different conditions like difference in Na2HPO4 to NaH2PO4 ratio,salt to anhydroglucose unit(AGU)of starch ratio,reaction time,starch morphology and reaction temperature.The synthesized SPs were characterized by phosphorus-31 nuclear magnetic resonance(31P NMR)and FT-IR spectroscopy.The phosphorous contents in each type of starch phosphate were determined by energy dispersive x-ray(EDX)spectroscopy.Crystallinity of the prepared samples was analyzed by XRD while thermal properties of the synthesized SPs were analyzed by TGA and DTG.These SPs were then used for the adsorption of Rhodamine 6G from wastewater under different conditions and showed excellent adsorption efficiencies towards Rhodamine 6G(with maximum adsorption%of 94.31%(SP2),96.85%(SP8)and 96.74%SP10)).These SPs were also used for the adsorption of ammonia and phenol from gaseous mixtures of the argon-ammonia and argon-phenol,respectively and showed good adsorption towards ammonia(with adsorption efficiency of 5.40 × 103 mmol/g(SP2),5.68 x 103 mmol/g(SP8)and 5.91 × 103 mmol/g(SP10))and phenol(adsorption efficiency of 2.56 mmol/g(SP2),2.39 mmol/g(SP8)and 2.70 mmol/g(SP10)).In third project,different types of starch-g-polymethacrylic acids(S-g-PMAAs)were prepared by grafting of methacrylic acid(MAA)on starch using different conditions like different amount of initiator(KPS),different mole ratio of MAA to starch AGU and different morphologies of starch.The synthesized S-g-PMAAs were characterized by 1H NMR spectroscopy.Two of these S-g-PMAAs,S-g-PMAAl which was found to have maximum content of grafted PMAA and S-g-PMAA5 which was synthesized from porous starch,were further characterized by FT-IR spectroscopy.Crystallinity of the S-g-PMAA1 and S-g-PMAA5 was checked by XRD analysis and their thermal properties were determined from their TGA and DTG curves.The surface morphology of normal starch,porous starch and S-g-PMAA5 was checked from their SEM images.Finally,normal starch,S-g-PMAAl and S-g-PMAA5 were used for the adsorption of gaseous ammonia and gaseous phenol.The modified starches were found to have good adsorption efficiencies towards ammonia and phenol(S-g-PMAA1;342.5 mmol(ammonia)and 8.08 mmol(phenol)and S-g-PMAA5;348.5 mmol/g(ammonia)and 21.46 mmol/g(phenol)).As,S-g-PMAA5 was synthesized from porous starch with large surface area,it showed higher adsorption efficiency for ammonia and phenol than S-g-PMAA1.Both the modified starches can be used in cigarette filters as additives to reduce the concentration of hazardous ammonia and phenol from the cigarette smoke.In fourth project,SP was first prepared by treating starch with NaH2PO4 and Na2HPO4 at 170?.This SP was further treated with different amount of acrylic acid in the presence of KPS to prepare three different types of starch phosphate-g-polyacrylic acids(SP-g-PAAl,SP-g-PAA2 and SP-g-PAA3).These SP-g-PAAs were then characterized by 1H NMR and FT-IR spectroscopy.Integration results of the 1H NMR spectra of the SP-g-PAAs showed that SP-g-PAA3 had the highest amount of PAA,followed SP-g-PAA2 and SP-g-PAAl,respectively.Crystallinity of starch,SP and the SP-g-PAAs was checked from their XRD analysis.The XRD analysis showed that SP and SP-g-PAAs had amorphous nature which revealed that starch has lost its crystallinity after modification.The thermal properties of the modified samples were checked by TGA and DTG which also confirmed the successful grafting of PAA on SP.Finally the SP-g-PAA1,SP-g-PAA2 and SP-g-PAA3 were utilized for ammonia and phenol adsorption.SP-g-PAA3 which had the highest PAA content,showed the highest adsorption efficiency towards ammonia and phenol(ammonia;7.47 mmol/g and phenol;1.02 mmol/g)which was followed by SP-g-PAA2(ammonia;5.73 mmol/g and phenol;0.9 mmol/g)and SP-g-PAA1(ammonia;2.33 mmol/g and phenol;0.61 mmol/g).These adsorbents could effectively be used as additives in cigarette filter to reduce the concentration of these harmful ammonia and phenol in the cigarette smoke.In fifth project,five different types of carboxymethyl starch-g-poly acry lic acids(CMS-g-PAAs)were synthesized by using different initiators(KPS and AIBN),different mole ratio of acrylic acid to CMS AGU and different amount of water.Grafting ratio showed that suitable initiator for grafting of PAA on CMS was KPS.Similarly,the suitable ratio of acrylic acid to CMS AGU for grafting PAA on CMS was 29.94.The modified CMS prepared with lower amount of water(100 mL)showed higher grafting ratio than the modified CMS prepared with higher amount of water(150 mL).Three types of modified CMSs,CMS-g-PAAl,CMS-g-PAA3 and CMS-g-PAA4 were selected for further characterization and application for ammonia and phenol adsorption.The 1H NMR spectroscopy and FT-IR spectroscopy confirmed the successful grafting of PAA on CMS.Crystallinity of CMS and the three modified CMSs was checked by their XRD analysis.The XRD analysis showed that CMS had crystalline nature.After modification the crystallinity of CMS was almost completely lost.The thermal properties of CMS and the modified samples were checked by TGA and DTG.The thermal analysis also gave information about the successful grafting of PAA on CMS.Finally the modified CMSs were further used for the adsorption applications of ammonia and phenol from the gaseous stream.It was found that CMS-g-PAA4 showed the highest adsorption efficiency(0.352 mmol/g)towards ammonia.CMS-g-PAA1 showed the intermediate adsorption efficiency(0.3 mmol/g)and CMS-g-PAA3 showed the least adsorption efficiency towards ammonia(0.285 mmol/g).Similarly,for the adsorption of phenol,CMS-g-PAA4 showed the highest adsorption efficiency(0.18 mmol/g)while CMS-g-PAAl and CMS-g-PAA3 had similar adsorption efficiency(0.06 mmol/g).On the basis of experimental findings,it was concluded that modified starch can be used for the adsorption of dyes from water,and ammonia and phenol gaseous stream.These modified starches can also be used on industrial scale in the cigarette filters as additives to reduce the concentration of ammonia and phenol.