High Efficiency And Low Cost Preparation Of Starch Nanoparticles And Investigation Of Their Flocculation Behavior

Nanoparticles are defined as the particulate dispersions,colloida l particles and solid particles with a size in the range of 10-1000 nm.At the nano-scale,properties of particles can be significantly different from the original bulk material.Starch is a natural,renewable,and biodegradable polymer produced by many pla nts as a source of stored energy.A growing interest has been aroused in synthesis of starch-based nanoparticles for applications in various aspects,such as reinforcements for nanocomposites,delivery systems for drugs,nanoencapsulations for food ingredients and additives,and adsorbents for heavy metalions.Size and size distribution of starch nanoparticles are of paramount importance for the applications mentioned above,and high efficiency and low cost preparation of size controlled SNPs t is the basis of their applications.In this paper,amylose and potato starc h were used to prepare starch nanoparticles by precipitation.Ultrasound and ?-amylase was applied to treat amylose and potato starch aqueous solutions aimed at lowering viscosity of the solutions and altering molecular weight and distribution of starch.The factors affecting the size and distribution of starch nanoparticles prepared by preicipitation were investigated.Thenafter,modified starches(cationic starch,carboxymethyl starch and amphoteric starch)were used to prepare modified starch nanoparticles via precipitation.The effects of the new groups in starch on the size and distribution of starch nanoparticles were investigated.Finally,the cationic starch and cationic starch nanoparticles were used as flocculants.The influence of pH of simulated water,substituting degree of cationic starch and its nanoparticles on flocculation behavior was investigated.The main results are as follows:(1)Amylose aqueous solutions and potato starch aqueous solutions were treated with ultrasounic for various periods of time and amylose nanoparticles(ANPs)and potato starch nanoparticles(SNPs)were prepared via nanoprecipitation.Results showed that after 30 min ultrasonic treatment,apparent viscosity of 5wt.% amylose solution and potato starch solution were decreased from 1136 and 1628 mPa s to 13.9 and 16 mPa s,respectively.At the same time,the molecular weight of amylose and potato starch decreased.Therefore,high concentration amylose and potato starch solution(up to 5wt.%)after ultrasonic treatment could be used to prepare smaller ANPs and SNPs with more uniform size.The SNPs with mean size of 95 nm could be obtained from 5wt.% potato starch solution after 30 min ultrasonic treatment.Moreover,the ultrasonic treatment of starch solutions eliminated the influence of starch solution/non-solvent(S/NS)volume ratio on size of SNPs,making it possible to prepare SNPs with less non-solvent.After 30 min ultrasonic treatment,SNPs with 77 nm were obtained by adding 3wt.% potato starch solution into 2 times volume of ethanol.Scanning electron microscopy(SEM)results showed that ANPs and SNPs prepared by nanoprecipitation were spherical.X-ray diffraction(XRD)results indicated that effect of the ultrasonic treatment on crystalline structure of ANPs and SNPs was negligible.The results of fourier transform infrared spectroscopy(FTIR)showed that ultrasonic treatment had no effect on the molecular structure of starch.This study not only offers a convenient and easily controllable methodology to prepare SNPs with small size and narrow distribution through precipitation,but also provides an approach to produce SNPs with high efficiency and low cost.(2)?-amylase was used to treatment amylose and potato starch solutions aimed at altering the chain length distribution of amylose and potato starch.ANPs and SNPs were prepared by nanoprecipitation.The effects of chain length distribution of amylose and potato starch,concentration of amylose and potato starch solutions on the size and structure of starch nanoparticles were investigated.The chain length distributions of amylose and potato starch were analyzed by size exclusion chromatography(SEC)and fluore scence assisted carbohydrate electrophoresis(FACE).The results of the study indicated that the critical factor to control the size of ANPs prepared via nanoprecipitation was chain length of amylose instead of the concentration of amylose solution.However,the concentration of amylose solution affected the distribution of ANPs,the smaller the concentration,the narrower the distribution.When hydrolysis degree of amylose was 52.8%,mean size of ANPs decreased from 206.4nm to 102.7nm.The results of SNPs prepared via precipitation showed that the amylose content in potato starch may affectted the distribution of SNPs,the lower the amylose content,the wider the distribution.SEM results showed that all of ANPs and SNPs prepared by nanoprecipitaion appeared spherical.XRD results indicated that effect of the ?-amylase treatment on crystalline structure of ANPs and SNPs was negligible in the investigated range.(3)Modified SNPs were prepared via precipitation by using cationic starch,carboxymethyl starch and amphoteric starch.The results showed that small amount of charge in starch gave rise to smaller and more uniform SNPs prepared via nanoprecipitation.However,beyonda certain amount,the increase of steric resistance for starch molecular agglomeration resulted in an increase in the size of SNPs.XRD results confirmed that with increase of substituting degreeof starch,starch molecules could not be arranged neatly to form the structure of the starch.The results of FTIR showed that the chemical structure of the modified starch changed,and there were characteristic peaks of the modified group in the corresponding region.(4)Cationic starch and cationic starch nanoparticles were used as flocculants to flocculate kaolin.The effect of substituting degree of cationic starch and its nanoparticles on the flocculation ability of kaolin was investigated.The results showed that both cationic starch and cationic starch nanoparticles had certain flocculation ability to kaolin.Under acidic condition,the flocculation ability of the flocculants was better than that under neutral condition,and the amount o f flocculant needed to reach the maximum transmittance wasless.When the cationic starch nanoparticles were used,the amount of used flocculants to reach the maximum transmittance of the supermatant was smaller than that of cationic starch.The effect of size of cationic starch on flocculation behavior decreased with increase of the substituting degree of cationic starch.Electric neutralization played a primaryrole in the flocculation process and other flocculation mechanisms played a synergistic role.The adsorption kinetics of the cationic starch nanoparticles to kaolin followed pseudo-second kinetics equation.