Dichotomy of crystalline and amorphous polyester-clay nanocomposites

5 Dichotomy of crystalline and amorphous polyester-clay nanocomposites 

Polyesters include a range of crystalline and amorphous materials similar to that of polyamides. Additional polyester types include unsaturated polymers that can be dissolved into reactive solvents such as styrene and methyl methacrylate that participate with the unsaturated polyester in peroxide crosslinking or will crosslink ambiently as coatings that have been dissolved in unreactive solvents. 

An amorphous polyester-montmorillonite nanocomposite prepared from condensation of 2,2,4,4-tetramethyl-l,3-cyclobutanediol, 1,3-propanediol, and dimethylterephthalate produced unexpected mechanical properties [45]. Cloisite 20A was melt blended with the polymer at 2.5,5, and 10 wt.% with a Haake HBI System 90 drive attached to a Rheomex CTW 100 twin-screw extruder. The r/min of the extruder was 60 and the temperature was 120°C. The test samples were prepared in two different injection molders. The test samples from the polyester-montmorillonite composite at 5% Cloisite 20A content were prepared with a Demag Ergotech 35 at 150°C with a pressure range of 10000 to 11000 psi. The test samples from the polyester-montmorillonite composites with 2.5, 5.0, and 10% Cloisite 20A content were prepared with a mini-jector molding machine at a temperature range of 190-200°C. 

WAXS indicated an intercalated composite. The modulus values for the 5% loaded composite are indicative of an intercalated composite (a 12% increase above the pure polymer value of 8.66x10 Pa). A Halpin-Tsai calculation for a 3% loaded composite predicts a 63% increase in modulus for a fully exfoliated montmorillonite composite with the particles ahgned in the direction of applied stress. The unexpected result is the dramatic increase in percent elongation to failure 

The other sample type did not have this region. The sample with the separate region had a modulus of approximately 12.38 x 10 Pa and a percent elongation to failure similar to the pure polymer (82.8% for the composite and 68% for the pure polymer). An example of the sample without the distinct region at the surface had a modulus of 11.56 x 10 Pa and a percent elongation to failure of 365.3%. 

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