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Biodegradable Polymer /Clay Nanocomposites Based on Poly(Butylene Adipate-co-Terephthalate) and Poly(Lactic Acid)

Mahin Shahlari and Sunggyu Lee. Department of Chemical & Biological Engineering, Missouri University of Science and Technology, 143 Schrenk Hall, Rolla, MO 65409

Modification of biodegradable plastics and the expansion of their application by methods that would not affect the biodegradability of the material can play a major role in today's world movement toward environmentally friendly products. Advancements in processing and modification make biodegradable plastics more capable of competing with non-biodegradable materials.

Poly(butylene adipate-co-terphthalate) (PBAT) is a biodegradable polymer with high ultimate elongation but low modulus. This paper demonstrates that the addition of nano-sized clay can improve the modulus without significantly decreasing the tensile strength and biodegradability of the PBAT , while offering enhanced blendability with a rigid biodegradable polymer as a conceivable means to improve the PBAT's modulus.

Poly(butylene adipate-co-terephthalate) was melt mixed with 3 wt.% and 5 wt.% Cloisite 15A which is organically modified Montmorillonite. This process resulted in nanocomposites with higher moduli than those of the neat PBAT samples. A further increase in the modulus of the PBAT was achieved by blending it with poly(lactic acid) (PLA) in addition to Cloisite 15A. Samples containing 10, 20, or 50% PLA and 5 % clay were melt compounded with a twin screw extruder. The samples were then prepared as films and injection molded parts. The morphologies of the blends were examined using scanning electron microscopy (SEM), and the thermal properties of the blends were tested using Differential Scanning Calorimetry (DSC) and Thermal Gravimetric Analyzer (TGA). X-Ray Diffraction (XRD) was used to investigate the intercalation and dispersion of clay layers in the polymer matrix.

The addition of 5 wt. % and 3 wt. % Cloisite 15A increased the Young's modulus and flexural modulus of PBAT by 57.5% and 36.5%, respectively. DSC results revealed slight changes in the melting temperature of PBAT nanocomposites but significant changes in PLA melting and cold crystallization upon presence of clay particles in the blend. According to the XRD results, the clay layers were intercalated in both the PBAT and the PBAT and PLA blend. Finally, the addition of clay to the PBAT and PLA blend decreased the PLA phase domain size significantly, thus providing morphological evidence for enhanced compatibility.

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