Nanocomposites of starch mixed esters and MMT: Improved strength, stiffness, and toughness for starch propionate acetate laurate

Novel starch mixed esters were compounded with nanoclays through a melt intercalation method. Two organo-modified clays and one unmodified clay with varying percentage of plasticizer (triacetin, TA) were used. The effect of clays on the tensile, dynamic mechanical and impact properties of the nanocomposites was investigated. The dispersion and orientation of the silicate layers in the polymer matrix was characterized by using transmission electron microscopy (TEM) and wide angle X-ray scattering (WAXS).For a propionate rich system (StPrAcLau) with 10 wt% TA ductility could be improved considerably by using 2.5 wt% of organo-modified clay. Charpy impact strength was increased 5 times reaching 15 kJ/m2. In contrast to unmodified clay, good dispersion was found with TEM for organo-modified clays while WAXS revealed the presence of tactoids consisting of 4-5 silicate layers and a preferred orientation of the platelets parallel to the sample surfaces along the injection molding direction.