| This research was supported by the project of “The Eleventh Five-Year” NationalScience and Technology Support Program of China, which was the key technology oflarge-scale production and application of Konjac Glucomannan (2007BAE42B04) andthe Postgraduate Innovation Fund sponsored by Southwest University of Science andTechnology, which was the Plasticization of starches containing varying amylose contentand their application studies (Grant No.12ycjj09). Starch is one of the most promisingnatural polymers because of its inherent biodegradability, annual renewal and itsoverwhelming abundance. In this study, three different types starches (differentamylase/amylopectin ratio) were used to prepare thermoplastic starch (TPS) and theeffect of amylase/amylopectin ratio on the physicochemical properties of TPS wereinvestigated. Furthermore, comparative blends of poly (butylene succinate)(PBS) andWTPS, NTPS and PTPS were prepared for investigating the effect of starch type andPBS content on the properties of PBS/TPS blends. We hope our efforts in the currentwork may shed some light on the developing of full-starch materials and controlling theproperties of starch-based materials by adjusting the starch type used. The results wereconcluded below:(1) Amylose content was determined using the iodine adsorption method and theamylose content of waxy corn starch, normal corn starch and pea starch is0%,27%and49%, respectively. Amylose and amylopectin were separated from cornstarch bybutanol recrystallization method. The morphologies, crystal structure and thermalproperties of native cornstarch, amylose and amylopectin were determined usingmicroscopy with ordinary and polarized light, scanning electron microscopy (SEM),X-ray diffraction (XRD), differential scanning calorimetry (DSC) andthermogravimetric analysis (TGA). It was found that native cornstarch was nearlygranular spheres, but amylose and amylopectin were irregular in shape. Nativecornstarch showed typical A-type patterns, which also corresponds to thebirefringence under polarized light, while the amylase showed V-type patterns and amylopectin showed no crystal structure respectively. Analysis of diagrams of DSCsuggested that all samples had a melting temperature which was very close todecomposition temperature and a unique big endothermic peak was detected fornative corn starch. The TGA results showed that the sequence of initial thermalstability for the samples was corn starch> amylose> amylopectin. The dissimilaritiesin both molecular chain structures and the state of molecular chain aggregation wereused to explain the distincts in their physico-chemical properties.(2) The results of plasticization of starches containing varying amylose content byglycerol showed that, as the amylose content increased from0to49%, themaximum torque increased from about8.2to25.1N·m, respectively and a longerplasticizing time was required to achieve the equilibrium torque value. Theseresults suggested that the plasticization and processing of waxy corn starch weremore easily performed than normal corn starch. Meanwhile, SEM studies showedthat the higher the amylose content, the more heterogeneous of the plasticizedstarch fracture surface, which is consistent well with the torque rheologicalanalysis. The water absorption of TPS was decreased with the increasing ofamylose content and the adsorption process was found to followpseudo-second-order kinetics for the first time. The ambient humidity andstanding time all affect the hygroscopicity of TPS. The dynamic rheologicalbehaviors of these three TPS were various with varying amylose content andelastic response is more obvious with the amylose content increasing. It can beconcluded that the resulting properties of TPS depend on the degree ofplasticization, which is primarily governed by the types of starch used.(3) The results demonstrate that the crystalline structure and fracture surfacemicrostructure of PBS/TPS blends depend on the starch type as well as PBScontent. The melt flow rate (MFR) results indicate that the incorporation of PBS,even at a low content, greatly ease the processability of TPS. Based on the resultsfrom tensile testing, it can be concluded that PBS contributes to improve thestrength and extensibility, while decreasing the rigidity, of the blends. In addition,compared with the NTPS/PBS blends and PTPS/PBS blends, the combination of PBS and WTPS could gain some excellent performances such as goodprocessability, superior mechanical properties and higher water resistance. It isalso showed that morphological variations are found as a function of the masscomposition of the blends’ components. The the temperature of maximum weightloss rate (Td) of PBS decreases with increasing the TPS content and both thestarch type and PBS content can affect the thermal stability of PBS/TPS blends.When the mass ration of PBS≤40, the dynamic rheological behavior of the blendswas mainly attributed to TPS phase and the NTPS/PBS and PTPS/PBS blends hadhigher storage modulus (G’) and complex viscosity (η*) than WTPS/PBS blends.When the mass ration of TPS/PB≥60, PBS phase played an important role for thedynamic rheological behavior of the blends, while the TPS phase did an auxiliaryfunction. It can be concluded that the resulting properties of TPS/PBS blendsdepend on the degree of TPS’ plasticization and the blend ratio.There is a correlation between starch type and properties of TPS/PBS blends asthe the amylose content can affect the properties of TPS. As a result, choosing rawmaterials (amylose/amylopectin ratio) among different starches may be one of thekey methods to control the properties of TPS/PBS blends. This method is simplerthan chemical modification, which is very conducive to mass production andpopularization. |
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