Effect of Storage Time on the Structure and Mechanical Properties of Starch/Bentonite Nanocomposites

摘要

Thermoplastic starch (TPS), plasticized with glycerol and water, and its nanocomposites containing up to 7.5 parts per hundred resin (phr) pristine bentonite (BT) are prepared by melt compounding. Effects of the BT reinforcement and storage time on the morphology, water content, and mechanical properties of the related TPS nanocomposites are investigated on compression molded specimens. Morphology change is followed by wide-angle X-ray scattering (WAXS) measurements. The presence of BT increases the rate of transformation from A- to V-type crystalline form. It is also found that BT particles hinders the recrystallization (retrogradation) of TPS. BT becomes intercalated in TPS, which is supported by the water used as additional plasticizer for the compounding of maize starch. According to gravimetric measurements, TPS samples lose part of their water content during retrogradation/aging. Both the incorporation of BT and the time of aging result in increased strength and stiffness, however at the cost of elongation at break. This is associated with enhanced strength and stiffness, which is ascribed to a change (from more to less hydrated) in the interphase. According to scanning electron and atomic force microscopy analysis, the reinforcing BT particles are homogenously dispersed on nano and micron scale within the TPS matrix.