2.1. Material Processing
Thermoplastic starch blends with zein were prepared with starch/zein w.w-1 ratios of 100/0, 80/20, 50/50, 20/80 and 0/100. The content of glycerol was 22% by weight of the total weight of polymers (starch and zein), on a dry basis.
Starch, zein and glycerol were weighed separately, pre-mixed in a beaker and the resulting mixtures then processed at 160 °C in a Haake Rheomix 600 batch mixer connected to a torque rheometer, with the rotors operating at 50 rpm. The mixing time used for all preparations was 6 minutes, since higher mixing times leads to starch degradation. The materials thus obtained were pressed for 5 minutes at 160 °C with a force of 0.2 MPa, to produce 150 x 120 x 2.5 mm molded sheets. These sheets were conditioned for four weeks at 22 ± 3 °C at a relative humidity (RH) of 52 ± 2%, prior to characterization. Glycerol losses were negligible, since the processing temperature was kept under the glycerol boiling point and no exudation was observed during processing.
2.1. Material ProcessingThermoplastic starch blends with zein were prepared with starch/zein w.w-1 ratios of 100/0, 80/20, 50/50, 20/80 and 0/100. The content of glycerol was 22% by weight of the total weight of polymers (starch and zein), on a dry basis.Starch, zein and glycerol were weighed separately, pre-mixed in a beaker and the resulting mixtures then processed at 160 °C in a Haake Rheomix 600 batch mixer connected to a torque rheometer, with the rotors operating at 50 rpm. The mixing time used for all preparations was 6 minutes, since higher mixing times leads to starch degradation. The materials thus obtained were pressed for 5 minutes at 160 °C with a force of 0.2 MPa, to produce 150 x 120 x 2.5 mm molded sheets. These sheets were conditioned for four weeks at 22 ± 3 °C at a relative humidity (RH) of 52 ± 2%, prior to characterization. Glycerol losses were negligible, since the processing temperature was kept under the glycerol boiling point and no exudation was observed during processing.
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