Starch esters with improved mechanical properties through melt compounding with nanoclays

Abstract

Biobased nanocomposites were manufactured through the melt intercalation of nanoclays and starch esters synthesized at the Fraunhofer Institute for Applied Polymer Research (TAP) from high amylose starch. Starch acetates (SAs) and starch propionates (SPs) were tested in combination with glycerol triacetate (triacetin) as a plasticizer for concentrations up to 30 and 20 wt %, respectively, with different types of organomodified and unmodified montmorillonites (MMTs). The mechanical properties of injection-molded test bars were determined by a tensile experiment giving the strength, modulus, and elongation of the composites. X-ray diffraction (XRD) analysis and transmission electron microscopy (TEM) were used to study clay dispersion and intercalation/exfoliation. Dynamic mechanical analysis was used to track the temperature dependence of the storage modulus and tan delta behavior of the starch/clay hybrid. Because they were the best performing compositions, SP with 5 wt % plasticizer and SA with 20 wt % plasticizer were filled with 5 wt % nanoclay. For SP, a certain increase in modulus was observed for all clays. However, the strength was practically unchanged, and the elongation decreased in most cases. One exception was found for the 2.5 wt % organomodified clay composition, where the elongation increased. For SA, the addition of 5 wt % nanoclay always increased the strength and modulus, in one case up to 60 and 75%, respectively. In the particular case with 5 wt % unmodified clay, the strength, modulus, and elongation increased by 30, 40, and 1000%, respectively. This was a dramatic improvement in the ductility of the material without losses in the strength and stiffness. XRD and TEM revealed the existence of exfoliated modified clay throughout the starch matrix, whereas for the unmodified case (with the exceptional increase in the elongation), no intercalation was observed

Environmentally friendly polymer nanocomposites using polymer matrices from renewable sources

“…Indeed, regardless of the plasticizer used, the fractional increase in the d -spacing in TPS/ OMMT-CS nanocomposites was twice (108%) as much as that in the TPS/neat MMT nanocomposites (50%) for samples containing 6 wt.% clay. 177 Modifi cation of the starch itself to make it more hydrophobic through substitution of the hydroxyl groups by less hydrophilic functions such as acetate groups 181,185 and propionates 185 has been explored. Acetylation tends to reduce the water solubility index of starch and, as such, is an attractive processing strategy.…”

Evaluation of Viscoelastic Performance and Molecular Structures of Natural Rubber/NBR Blends Reinforced by Carbon Black and Nano-Silica

“…Many efforts have been made to strengthen the material and reduce material losses, and one of the most effective approaches has been the incorporation of fillers [14,15], typically carbon black and silica, into the rubber. Indeed, the inclusion of nano-fillers in elastomer blends provides superior mechanical characteristics compared to the use of micro and macro-fillers, despite a smaller amount of nano-filler ratio [16,17].…”

Hierarchical Structure and Thermal Property of Starch-Based Nanocomposites with Different Amylose/Amylopectin Ratio

“…In addition, the distribution of additive fillers with a high aspect ratio on the nanoscale can substantially lead to the enhancement of mechanical, rheological, gas barrier and optical properties of corresponding nanocomposites [13,14,15]. Such features make nanocomposites as ideal candidates for a broad range of application in high-barrier packaging materials [16].…”