Essential Work of Fracture of Bio-Polyamides and Clay Composites

Fully (PA10.10) and partially (PA6.10) bio-based polyamides were extruded in a film casting machine. A modified montmorillonite (Cloisite 30B) was also added to the bio-PAs in a preliminary extrusion step to increase the thermal, mechanical and barrier properties. Despite the materials are interesting for a possible industrial development in the packaging field, data concerning mechanical performances are rare in the literature. Thus, tensile tests were carried out on extruded films. The modified clay increased the rigidity, yield strength and decreased the deformation at break. To better understand this behavior, the Essential Work of Fracture (EWF) protocol was applied to the films. The ligament length was in the range from 5 to 22 mm. The specific work of fracture (wf) was obtained as well as the essential (we) and non-essential (wp) work of fracture were extrapolated. Clay did not significantly affect the work required for the onset of crack propagation (we) in PA6.10 while it was decreased in PA10.10. The plastic item (β·wp) of both PAs was increased with clay. The clay particles acted as stress concentration points, which promoted cavitations and thus induced relatively large local deformation. Consequently, the mechanical work content necessary to generate the plastic flow was increased, leading to a higher wp value.