Preparation And Characterization Of Thermoplastic Starch

Degradable plastic based on starch is one of the effective means to solve white pollution,but the processing performance of starch is poor,because there are a large number of intramolecular hydrogen bonds in its molecules,forming a stable crystalline structure,limiting The application range of starch,so how to weaken the hydrogen bond inside the starch and destroy the crystalline structure of the starch is the focus of research.This paper is divided into two parts,the preparation of amorphous starch and the plasticization of amorphous starch.In addition,the starch used in this study was ordinary corn starch.The preparation of amorphous starch mainly involves two steps of gelatinizing starch with hot water,destroying the crystalline structure of starch and precipitating amorphous starch with alcohol.Hot water gelatinization starch makes it amorphous,mainly to study the influence of water amount on starch gelatinization amorphous.Under the condition that other conditions remain unchanged,the starch ratio of water is 1:1,1:3,1:4 and 1:5,respectively,and the starch is gelatinized with four different amounts of water.After the gelatinization process is completed,the samples are taken out,and then Dry the sample,grind the sample,and use it later.Alcohol precipitation of amorphous starch,mainly to study the effect of different types of alcohol on the crystalline structure of amorphous starch.After gelatinizing starch with a suitable amount of water and destroying its crystalline structure,methanol,ethanol,and three mixed alcohols were selected respectively（methanol/ethanol equals 1:1,methanol/ethanol equals 1:3,methanol/ethanol equals1:7）The amorphous starch is precipitated with alcohol,then the sample is filtered,then dried,and then ground into powder for use.Then the experimental results are analyzed and studied by polarized light microscope,SEM,XRD,solid NMR and other characterization tests.The conclusions are as follows:（1）Starch/water ratio of 1:3 and starch/water ratio of 1:4 is a better ratio of gelatinized amorphous,under this ratio of gelatinized amorphous,Polarizing cross phenomenon of starch basically disappears,and the particles are broken less.。XRD also proved that the A-type crystalline structure of starch was basically destroyed,and solid NMR also showed that the A-type crystalline structure of starch was destroyed completely.（2）The sedimentation effect of ethanol on amorphous starch is the best,the amorphous starch particles in the solution are evenly dispersed,and the amorphous starch is easy to powder after filtration and drying.Methanol precipitates amorphous starch granules,and the granules flocculate in the solution.After filtration and drying,the amorphous starch is easy to agglomerate.（3）Combined with the experimental situation and XRD analysis,it is easier to form V-shaped crystals in methanol precipitation gelatinized amorphous starch,and at the same time,high-temperature drying is also more likely to lead to the formation of V-shaped crystals.The plasticization of amorphous starch mainly involves two processes: exploring the reasonable amount of plasticizer and using plasticizer to plasticize amorphous starch,that is,the preparation of thermoplastic starch.To explore the reasonable amount of plasticizer,mainly to explore the reasonable amount of glycerol and urea.Combined with the previous preliminary experiments,it was determined that in the aqueous solution system,（the mass ratio of starch is 5%～55%,and 5% is a gradient）glycerol and（the mass ratio of starch is 3%～24%,3% is a gradient）urea was subjected to gelatinization amorphous experiment.After the process was over,the sample was taken out,then dried,and then the sample was ground and used for later use.The preparation of thermoplastic starch is mainly to plasticize amorphous starch with an appropriate amount of plasticizer,and to study the ability of thermoplastic starch to resist recrystallization.After obtaining a reasonable amount of plasticizer.The glycerol,urea and amorphous starch are blended in three proportions,wherein the amorphous starch is the amorphous starch after alcohol precipitation and drying,and the three proportions are respectively 50%（accounting for the mass ratio of the amorphous starch）glycerol+non-crystalline starch,40% glycerol + 10% urea +amorphous starch,40% glycerol + 15% urea + amorphous starch.Then,at 135℃,the blended thing is hot-pressed into a film,sealed and stored for later use.Taking these three ratios can not only ensure a good plasticizing effect,but also will not make the plasticizer exceed the standard in single amount.Then the experimental results are analyzed and studied by polarized light microscope,SEM,EDS and XRD diffraction characterization test.The conclusions are as follows:（1）Taking starch quality as a reference,the reasonable amount of plasticizer glycerol is 40%-50%,and the reasonable amount of urea should not exceed18%.In addition,excessive use of plasticizer will lead to plasticizer overflow.Or the plasticizer itself crystallizes out and so on.（2）The XRD analysis of thermoplastic starch films found that the addition of glycerin plasticizer will lead to the formation of V-shaped crystals to a certain extent,but the proper addition of urea plasticizer can inhibit the formation of V-shaped crystals.（3）After placing the films with the three ratios for 30 days,the crystallinity was measured,and it was found that the crystallinity did not increase by more than 1%,so it indicated that the obtained films had a certain anti-crystallization ability.The three ratios were 50 % glycerol thermoplastic starch（TPS）,40% glycerol + 10% urea TPS,40% glycerol + 15% urea TPS.