Browsing by Subject "Nanostructures--Mechanical properties"

Now showing 1 - 1 of 1

Effects of polymer-organoclay interactions and processing methods on nanocomposite structure and properties
(2006) Chavarria, Florencia; Paul, Donald R.
Polymer-layered silicate nanocomposites based on polyamide, thermoplastic polyurethane, and polyolefin matrices and several organoclays were prepared by melt processing. The effects of types of matrices, organoclay structures, silicate layer charge, and processing conditions on the morphology and mechanical properties of nanocomposites were analyzed to obtain a greater understanding of the exfoliation process. Polyamide structure strongly influences the degree of platelet dispersion and mechanical property enhancement; nylon 6 nanocomposites show superior clay dispersion and matrix reinforcement than nylon 66 nanocomposites. The affinity of nylon 6 for the organoclay appears to be greater than that of nylon 66, which must be related to some aspect of their differences in chemical structure. Mixing conditions created by twin screw extruders also have significant effects on morphology and properties of nylon 6 nanocomposites. Mixing the molten polymer with the organoclay under low shear, and applying a medium level of shear throughout the extruder for a longer residence time leads to high platelet dispersion and matrix reinforcement. Mixing the solid polymer with the organoclay under high shear leads to short particle lengths and lower matrix reinforcement; this is believed to be due to attrition of clay platelets under these conditions. Nanocomposites formed in a DSM micro-compounder yield similar morphologies and modulus trends than conventional twin screw extruders. The affinity between polymer and organoclay is also critical to produce high platelet dispersion and mechanical property enhancement. It is determined, to some extent, by the polarity of the polymer and the degree of silicate surface coverage given by the clay layer charge and the organoclay structure. Organoclays with reduced layer charge lead to lower exfoliation and modulus enhancement of nylon 6 and polypropylene-based nanocomposites than organoclays with no layer charge reduction; this was attributed to heterogeneities in layer charge and charge distribution produced during the charge reduction process. Thermoplastic polyurethane nanocomposites show similar trends than nylon 6 nanocomposites regarding organoclay structure, i.e., a higher exfoliation and matrix reinforcement was observed for organoclays with one alkyl tail that provide less coverage of the silicate surface. In the case of polyurethanes, the high affinity of the matrix for hydroxy ethyl functional groups appears to aid clay dispersion.