Abstract. In this work the effect of multiple reprocessing was studied on molecular structure, morphology and properties of poly(lactic acid)/hydrotalcites (PLA/HT) nanocomposites compared to neat PLA. In addition, the influence of two different kinds of HT -organically modified (OM-HT) and unmodified (U-HT) -was evaluated. Thermo-mechanical degradation was induced by means of five subsequent extrusion cycles. The performance of the recycled materials was investigated by mechanical and rheological tests, differential scanning calorimetry (DSC), intrinsic viscosity measurements and SEM observation. The results indicated that the best morphology was achieved in the systems incorporating OM-HT. On increasing the extrusion reprocessing cycles, the properties showed behavior due to two opposite effects: i) chain scission due to thermo-mechanical degradation and ii) filler dispersion effect resulting from multiple processing. In particular, at low reprocessing cycles, both tensile and rheological properties seem to be mainly affected by HT dispersion, especially when OM-HT was added. After five reprocessing cycles, on the contrary, chain scission, i.e. thermo-mechanical degradation, dominated. As regards the effect of the presence of organic modifier in HT, the results indicated that this variable apparently did not affect the macroscopic performance of the nanocomposites, especially at high reprocessing cycles.

The time evolution of organoclay particle size and volume fraction, as well as the shear viscosity, are measured in-line for a series of Poly(lactic acid)/organoclay composites, using a rheo-optical die coupled to a prototype modular corotating twin screw extruder. The small angle light scattering patterns and light attenuation recorded during transient experiments indicate that clay dispersion develops through melt intercalation between the clay galleries, thereby expanding the aggregates size, and eventually leads to aggregates break-up, i.e., exfoliation. The simultaneous recording of shear viscosity also indicates that smaller viscosities promote a faster melt intercalation and exfoliation but hinder the extent of clay dispersion. The methodology used in the present study validates the well accepted mechanism for clay dispersion and can be applied straight away for the monitoring of PNC manufacturing during practical production.