| The small size effect of starch nanomaterials gives it higher surface energy and has the characteristics that inorganic nanomaterials do not have,such as biocompatibility,bio-regeneration and biodegradability.Starch nanomaterials are often used as film filler,Pickering emulsion stabilizer,active ingredient delivery carrier and fat substitute.The common methods of preparing starch nanomaterials have some problems,such as high environmental pollution,low efficiency,and high energy consumption.Therefore,exploring a green and efficient preparation method of starch nanomaterials has become a research hotspot.Among them,natural deep eutectic solvent（NADES）is a new green solvent,which has great potential in the pretreatment of natural polysaccharide-based nanomaterials.In addition,due to the hydrophilicity of starch nanomaterials,it is easy to aggregate to form micron aggregates in the preparation of food packaging materials or Pickering emulsions,such as pH and salt ion concentration,which limits its application.Therefore,waxy maize starch（WMS）was treated with NADES composed of choline chloride and oxalic acid,and starch nanoplatelets（SNP）were successfully prepared.Then,the effects of pH and salt ion concentration on the aggregation behavior of SNP in aqueous system were studied.Finally,SNP was blended with methylcellulose（MC）,M20,A4C and A4M at pH of 3～7.Methylcellulose/starch nanoplatelets（MC-SNP）nanocomposite films were prepared by solvent casting method,and the effect of SNP on the physical and chemical properties of MC-SNP nanocomposite films was studied.The results showed that:（1）SNP with carboxyl group on the surface were successfully prepared by treating WMS for 2h with NADES composed of choline chloride and oxalic acid dihydrate（molar ratio 1:1）.At the same time,various modern detection methods were used to monitor the physical and chemical properties of the samples with different treatment times obtained in the process of treating WMS with NADES.It was found that with the extension of treatment time,WMS was degraded,which showed that the molecular weight（Mw）and particle size of the sample gradually decreased,and the yield decreased significantly.In addition,with the extension of reaction time,the absolute value of Zeta potential increases,resulting in the increase of the stability of suspension.The results of Fourier transform infrared spectroscopy（FTIR）showed that,compared with WMS spectrum,a new stretching vibration peak of C=O group appeared at 1725 cm-1,and its intensity increased with the increase of treatment time,which was consistent with the results of conductometric titration.X-ray diffraction（XRD）analysis showed that with the extension of treatment time,the crystal form of NADES treated samples remained unchanged,but the relative crystallinity decreased.Thermogravimetric analysis（TGA）showed that,compared with WMS,NADES treated samples had a new weight loss stage at 253℃due to the oxalate half-ester group on the surface.No new peaks were detected in X-ray photoelectron spectroscopy（XPS）of NADES treated samples,indicating that NADES treatment did not introduce any new elements into starch.（2）Under the conditions of different pH and salt ion concentration,it is found that when the pH range of SNP suspension was 3～10,only slight stratification is observed within 72 h,and the turbidity of SNP suspension has no significant change.When pH was 2 and 11,SNP precipitated rapidly,and the turbidity decreased significantly after 110 min and 4 h,respectively.In the presence of salt ions,the SNP suspension aggregate in a short time.When the NaCl concentration in the sample increases from 2.5 mM to 10 mM,the time of precipitation of SNP suspension is shortened from 24 h to 1 h,and the turbidity decreases sharply.The particle size results showed that when the pH range was 3～7,the particle size of SNP suspension did not change significantly within 72 h,while the particle size of SNP increased significantly in a short time under the conditions of low pH,alkaline and salt ions.SEM results show that in the initial state,SNP was well dispersed in aqueous solution in the range of pH of 2～11,showing a single dispersion state.The average size of SNP adsorbed（0.9μm）by each other at low pH.When pH was 5,there was no obvious agglomeration of SNP within 72 h.Under alkaline conditions,SNP aggregates to form micron-sized agglomeration.（3）When SNP and MC were blended at pH 3～7,it was found that the addition of SNP had a significant effect on the physical and chemical properties of three different MC-SNP nanocomposite films.Compared with pure MC films,the nanocomposite films with 15%SNP have better mechanical properties and barrier properties,especially A4C-15%SNP nanocomposite film.The rheological results show that all samples except M20 show as shear thinning behavior.SEM results showed that SNP had good compatibility with A4C,dispersed relatively evenly in A4C-15%SNP nanocomposite film,and formed obvious micron-sized agglomeration in M20-15%SNP and A4M-15%SNP nanocomposite films.FTIR results showed that the interaction between MC and SNP formed hydrogen bonds,which may be the reason for the enhancement of mechanical properties of nanocomposite films.XRD patterns showed that the addition of SNP changed the crystal structure of M20-15%SNP nanocomposite film,while had no effect on A4C-15%SNP and A4M-15%SNP.TGA results showed that compared with MC pure films,MC-SNP nanocomposite films showed three weight loss stages,which was mainly related to the oxalate half-ester groups on the surface of SNP. |
PDF Full Text Request