Thermoplasticization of High Amylose Starch by Chemical Modification Using Reactive Extrusion |
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Authors: | Jacqueline Stagner Vanessa Dias Alves Ramani Narayan Adelaide Beleia |
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Institution: | 1.Biobased Material Research Group (BMRG),Michigan State University,East Lansing,USA;2.Departamento de Ciência e Tecnologia de Alimentos,Universidade Estadual de Londrina,Londrina,Brazil;3.Lansing,USA |
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Abstract: | Modified thermoplastic high amylose starch (MTPS) was synthesized by reactive extrusion in the presence of maleic anhydride
(MA) as an esterification agent in a twin-screw extruder. The objective of this work was the preparation of reactive thermoplastic
starch in the presence of glycerol and with different amounts of maleic anhydride (MA) and free-radical initiator, in order
to improve processability and reactivity. The concentration of MA added varied from 2 to 6 wt% (of starch + glycerol), and
the free-radical initiator, 2,5-bis(tert-butylperoxy)-2,5-dimethylhexane, also called Luperox 101, varied from 0.1 to 0.5
wt% (of starch + glycerol). Characterization of maleated thermoplastic starch was performed using dynamic light scattering
and thermal analysis. Further, proof of chemically modified extrudate was determined by Fourier transform infrared spectroscopy
and by soxhlet extraction with acetone. The modified high amylose corn starch (20 or 30% glycerol) could be pelletized and
gave pellets that were more transparent than thermoplastic starches not modified with maleic anhydride. There was negligible
change in hydrodynamic radius as the percentage of maleic anhydride increased. However, as the percentage of Luperox 101 increased,
the hydrodynamic radius decreased. It could be inferred that the molecular weight decreased as the percentage of free-radical
initiator increased. Using the maximum temperature in the extrusion process of 165 °C instead of 135 °C caused a decrease
in the hydrodynamic radius, due to the high influence of the temperature profile on the molecular weight of the thermoplastic
starch. The MTPS samples presented higher melting temperatures compared to TPS samples. The soxhlet studies indicated that
the plasticizer, glycerol, was chemically linked to the starch. Using the maximum temperature of 165 °C versus 135 °C in the
extrusion temperature profile resulted in more interaction between glycerol and starch. |
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