Synthesis And Modification Of Starch-based Materials And Its Applications In Pharmaceutical Excipients

The medicinal film coating is a layer of polymer film coated on the surface of a drug core,used for coloring,protecting and beautifying.Film coating materials are applicable to drug tablets,dropping pills,pellets and so on.At present,cellulosic material is widely used for film coating,which usually associate with economic drawbacks.In contrast,starch is a promising film coating material owning to the low-cost,sustainable and good film forming properties.However,the barrier and mechanical properties of the film prepared directly from pure starch are usually unsatisfied,and further improvements are needed.Hence,the starch modifications are essential to increase the performance of the obtained starch film.In this work,potato starch was initially oxidized followed by further esterification to obtain the esterified starch.Then the modified starch-montmorillonite composite film was prepared by film casting method using montmorillonite as the strength agent.The mechanical properties,oxygen permeability,water vapor transmission rate and transparency of the obtained composite membrane were tested in detail.Also characterizations such as infrared spectroscopy(FTIR),scanning electron microscopy(SEM)and X-ray diffraction(XRD)were used to analyze the microstructure and morphology of the prepared composite film.The experimental results are as follows:1.After comparing the mechanical properties of prepared film from potato starch,cassava starch,corn starch,amylose,waxy starch and banana starch,we tended to select potato starch as the raw material to conduct this research.Because the potato starch film had the highest mechanical properties,then was the cassava starch,and the amylose,waxy starch film had worst mechanical properties.2.The viscosity of starch paste decreased with the increasing of reaction time at a certain oxidization temperature.When the reaction temperature was 30℃ or 40℃,the mechanical properties of starch film increased at first and then decreased as thereaction time continued to increase.The prepared starch film tended to have a larger tensile strength under a lower reaction temperature if the viscosity was kept almost the same.But the reaction temperature had little effect on the elongation at break.So the reaction temperature was selected as 30℃.In addition,the starch film had largest mechanical properties after oxidation at 30℃ for 4 hours,so the oxidation conditions were determined as follows: the temperature was 30℃,the oxidant dosage was 5m L,the reaction time was 4h and the starch mass content was fixed as 35wt%.3.The esterification of oxidation potato starch was demonstrated by IR spectrum with obvious adsorption peak at 1729.92 cm-1,which is assigned to the carbonyl groups after esterification treatments.Besides,esterification degree increased with the prolonging of reaction time and the increasing dosage of esterifying agent.The film would have a largest mechanical properties after the oxidized potato starch was esterified by using 6wt% esterifying agent for 1 hour.Furthermore,the transparency of the starch paste was almost constant when the reaction time and dosage of esterifying agent were promoted to a certain degree.Taken together all of these observations,we finally selected the esterifying condition as follows: the esterification time was 1h,the dosage of esterifying agent was 6wt%,and the reaction temperature was fixed at 30℃.4.The tensile strength of the composite film was increased when 0.1wt% of montmorillonite was used,while the elongation at break was kept almost constant.Importantly,the transparency of starch paste remained unchanged,possibly owning to the much less dosage of montmorillonite.The hydroxyl groups on the starch molecules were replaced by acetyl groups after esterification treatment,which in turn would promote the water resistance property of the starch-based films.Additionally,both of the water and oxygen resistance properties of the obtained composite films could be improved after the recombination of esterified starch with montmorillonite,which should be contributable to the pore blocking of the starch molecular network by montmorillonite layered structures.