THERMOPLASTIC POLYURETHANE FILMS REINFORCED WITH CARBON NANOTUBES: THE EFFECT OF PROCESSING ON THE STRUCTURE AND MECHANICAL PROPERTIES

The influence of the main film production technologies, i.e. chill-roll extrusion and film blowing on the structural characteristics and mechanical performances of films based on a commercial thermoplastic polyurethane resin reinforced with carbon nanotubes has been studied. Structural investigations by means of X-ray diffraction and FTIR spectroscopic analysis have shown how the different processing conditions determine the mutual arrangement of soft and hard domains characteristic of the polyurethane matrix as well as the orientation and the final distribution of the included nanotubes as confirmed by electron microscopy observations. The higher the carbon nanotubes content, the higher the content and the size of segregated hard domains. Furthermore the film blowing process, characterized by relatively longer cooling times with respect to the extrusion process, allows a better self-assembly of hard domains maximizing the interdomain distance and, apparently, ensuring a worse distribution of the filler. By focusing on samples with 0.5 wt.% of carbon nanotubes, an increase of the tensile modulus with respect to neat TPU ones, approximately equal to 90% and 30% has been shown for flat and blown films, respectively. Morphological and structural considerations have provided a reasonable explanation of the mechanical behavior exhibited by the investigated films.