Nanocomposites and nanomaterials

A new way of in-situ preparation of poly(lactic acid)/aliphatic-aromatic copolyesters nanocomposites based on shear induced crystallization
R. Hosseinnezhad, I.Vozniak
Centre of Molecular and Macromolecular Studies, Polish Academy of Sciences, Lodz 90363, Poland
E-mail: wozniak@cbmm.lodz.pl

Polymer nanocomposites are widely used nowadays for various applications because of improved properties when compared to the pure polymers or their blends. As a rule, ready-made nanofibers or nanoparticles dispersed in the matrix are used when producing polymer nanocomposites. Polymer ready-made nanofibers are now produced mostly by electrospinning.
However, it is possible to form polymer nanocomposites directly in the course of extrusion in a single step. In this paper, we present a new way of in-situ preparation of "green", fully polymeric nanocomposites in one step in which the nanofibres of one biopolymer are formed inside the second biopolymer by shear during melt mixing. The solidification of nanofibrous sheared inclusions occurs by shear induced crystallization, all during processing.
Polyesters, such as polylactide (PLA) and aliphatic-aromatic copolyesters (AAC), are good examples as they couple interesting mechanical/thermal properties with biocompatibility and biodegradability.
Poly(lactide) is brittle at room temperature, but shows suitable mechanical features like high yield strength and Young's modulus. Since lactides are sugars fermentation products, another great advantage is that the polymer can be obtained from 100% renewable sources.
Aliphatic-aromatic copolyesters (AAC) containing: butylene terephthalate ester and a mixture of butylene esters: adipate, succinate and glutarate, are instead a rubbery and very ductile materials, with over 1000% of ultimate strain and 200 MPa elastic modulus. The increase of butylene terephtalate comonomer content causes the largest changes to the tensile properties, the higher the content of butylene terephtalate units, the higher the initial modulus of the PBST sample and the higher ultimate strength. However, the elongation at break decreases with the increase of BT co-units .
The studies presented in the paper show that it is possible to generate all-polymer nanocomposites, where the nanofibers of AAC are formed inside the PLA directly during the melt-mixing process and stabilized by shear-induced crystallization.