Influence of the Solidification Process on the Mechanical Properties of Solid-State Drawn PCL/Sepiolite Nanocomposite Tapes

In this research, poly(epsilon-caprolactone) (PCL) was melt-mixed with sepiolite nanoclays in a twin-screw extruder. In a subsequent step, the extruded films were drawn in the solid state to highly oriented nanocomposite films or tapes. A twin-screw extruder equipped with a Sultzer mixer for improved mixing in combination with a bench top drawing unit was used to prepare oriented nanocomposite tapes of different sepiolite loading and draw ratios. In order to study the influence of the solidification step on the drawability of the materials, different cooling procedures were applied prior to drawing. Optical microscopy images showed that slow or fast solidification using different chill rolls settings (open or closed) for the cast films resulted in different morphological conditions for subsequent drawing. The addition of sepiolite nanofillers led to nucleation and faster crystallization kinetics and oriented tapes which deformed by homogenous deformation rather than necking. The addition of sepiolite significantly improved the mechanical properties of both undrawn and drawn PCL tapes and Young's modulus (1.5 GPa) and tensile strength (360 MPa) for composites based on 4 wt% sepiolite were among the highest ever reported for PCL nanocomposites. Interestingly, samples cooled with open chill rolls (slow crystallization) showed the highest modulus while solidification with closed rolls (fast crystallization) showed the highest tensile strength after drawing.