| This paper using corn starch as material with plasticizer and cross-linking agent,aimed at the preparation of the starch film with certain pore structure and mechanical strength by adding CaCO3 as pore-former,for using as a food freshness indicator label.First of all,by analyzing the material of corn starch,it was found that the content of amylase was 24.04%and the remaining was amylopectin,it indicated that amylopectin was higher in corn starch.Through DSC analysis,the glass transition temperature of starch was reduced by adding glycerol;From the XRD analysis,glycerol could destroy the crystal structure and hydrogen bond of starch,which made the starch plasticized and the film forming better.By conditional experiments the best film compositions were gained at the addition of starch 5.5 g the glycerol content of 35%w/w starch,the glutaraldehyde content of 3 5%w/w starch,under this addition,the best mechanical properties with tensile strength of 501.8 N/m,the lowest water vapor permeability of 2.71 ×10-9 g.s-1.m-1.Pa-1 showed that the film had lower sensitivity to water and the best hydrophobility with the contant angle of 92.3 °than the other films.Secondly,the feasibility of improving hydrophobicity of starch film was subjected to discuss,through the infrared spectrogram analysis,stearic acid and starch were combined to form a composite substance,not just a kind of a mixture.From the XRD analysis,stearic acid and starch were formed into the V-crystal structure.When the optimal addition of stearic acid was 0.04 g by the conditional experiments,the mechanical properties of the composite film was best.And because of the presence of stearic acid,a highly hydrophobic oil film could be formed on the surface of the starch film,which greatly improved the hydrophobic property of starch film.And then the pore forming property of the film was discussed,a solution with restricted volume of 100ml was made under the optimum film-forming conditions with the addition of starch 5.5 g,the stearic acid 0.04 g,the dispersed CaCO3 of 0.1 g/100ml.Both of CaCO3/starch film and CaCO3/starch/stearic acid film had good film-forming properties.CaCO3/starch film was processing by hydrochloric acid of lmol/L,the reaction time of 25 s;CaCO3/starch/stearic acid film was processing by hydrochloric acid of 1 mol/L,the reaction time of 30 s,the tensile strength of these two films were 365.7 N/m and 380.21 N/m,the contact angles were 89.18° and 88.43°,respectively,both had high strength and low water sensitivity.And in this condition,according to calculation results,the porosities of the two films were 16.45%and 10.56%,respectively.From the variation of the porosity with different processing time,it could be concluded that the pore size of the films could be controlled by adjusting the processing time.The comparison of two films indicates that with the addition of stearic acid,the film showed a certain hydrophobic state,and this also made the porosity of the film decreased.Finally,the increments of the surface area(pore size)of CaCO3/starch film and CaCO3/starch/stearic acid film were 82.9078 m2/g and 53.8056 m2/g respectively;the increments of the pore volume were 0.095841 cm2/g and 0.053396 cm2/g respectively;the increments of the pore size were 1.7403 nm and 0.9749 nm.were higher than CaCO3/starch/stearic acid film,it indicated that the pore forming effect of the film without stearic acid was better,but the tensile strength of CaCO3/starch film was 287.9 N/m-389 N/m,was poor than 361.3 N/m-402.4 N/m of CaCO3/starch/stearic acid film.So how to achieve a good result that on the premise of the starch film possessed good mechanical properties,the porosity of the film could be much more increased,the research need to be improved. |
PDF Full Text Request