Thursday, November 8, 2007 - 8:55 AM

Polymer-Clay Nanocomposites Of Linear Low Density Polyethylene (Lldpe) and Polyoxymethylene (Pom)

Mahin Shahlari1, Patricia L. Roberts2, Leah A. Leavitt3, Matthew Factor1, and Sunggyu Lee1. (1) Department of Chemical & Biological Engineering, University of Missouri-Rolla, 143 Schrenk Hall, Rolla, MO 65409-1230, (2) Dow Chemical Company, Freeport, TX 77541, (3) NIC Industries, Inc., 7050 6th Street, White City, OR 97503

Polymer-clay nanocomposites involving a blend of two otherwise incompatible thermoplastic polymers were prepared and investigated for the effects of the addition of organically modified clay. Linear low density polyethylene (LLDPE) with melt index (MI) of 20 g/10 min and density of 0.925 g/cm3 and polyoxymethylene (POM) with melt volume rate (MVR) of 8 cm3/10min at 190 C and density of 1.41 g/cm3 at several composition ratios (70/30, 50/50, 30/70) were melt mixed with 5% Cloisite 15A and 5% Cloisite 30B, respectively and their blends were characterized by scanning electron microscopy (SEM), differential scanning calorimetry (DSC), and thermogravimetric analysis (TGA). The LLDPE/POM (70/30) blend nanocomposites incorporating Cloisite 15A showed co-continuous morphology according to the SEM images, while those with Cloisite 30B showed some limited levels of compatibility. Further, Cloisite 15A improved the melting temperature of LLDPE and POM by 2.51C and 2.61C from 122.41C and 161.02C respectively, while Cloisite 30B had no significant effect on LLDPE melting temperature and increased melting temperature of POM by 2.09C. As for the LLDPE/POM (30/70) blends, Cloisite 15A made the two originally incompatible phases indistinguishable, while the blends containing Cloisite 30B showed a significant decrease in the domain sizes. However, the blend samples without organoclay incorporation did not exhibit any compatibility and the dispersed phase was totally segregated.

TGA results showed that addition of Cloisite 15A decreased POM degradation temperature (originally 365.49C) by 72.09C while Cloisite 30B lowered the degradation temperature of POM by 92.43C. There was no significant change observed in PE degradation temperature. The clay compatibility with one or both polymers is shown to make significant difference in blend morphology and compatibilization mechanisms of the polymer-clay nanocomposites are phenomenologically explained in this paper which makes us one step closer to recognize clay as a general compatiblizer. There are very few published studies about LLDPE/POM blends which make this paper more significant; LLDPE in a blend with high percentage of POM could make POM processing much easier, and on the other hand blending a POM with LLDPE could improve mechanical properties of LLDPE.

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