Toughening of poly(lactic acid) without sacrificing stiffness and strength by melt-blending with polyamide 11 and selective localization of halloysite nanotubes

Abstract

This paper aims at improving the mechanical behavior of biobased brittle amorphous polylactide (PLA) by extrusion melt-blending with biobased semi-crystalline polyamide 11 (PA 11) and addition of natural halloysite nanotubes (HNT). The structure and properties of PLA/PA11/HNT blends were studied in terms of morphological, thermal and mechanical properties. The morphological analysis of the PLA/PA11/HNT blends shows a strong interface between the two polymeric phases due to hydrogen bonding, and the migration of HNTs towards PA 11 phase inducing their selective localization in one of the polymeric phases of the blend. A “salami-like” structure is formed revealing a HNTs-rich tubular-like (fibrillar) PA11 phase. Moreover, HNTs localized in the dispersed phase acts as nucleating agents for PA11. Blending PLA (80 wt.%) and PA11 (20 wt.%) increases PLA ductility (elongation at break, ɛr, is multiplied by more than 20), however at the slight expense of strength and stiffness. Further addition of HNTs (2 wt.%) further increases ductility (ɛr reaches 155 %, i.e. it is multiplied by more than 40) whereas tensile strength and modulus of PLA are unchanged and impact strength is more than doubled. The toughening mechanism is discussed based on the combined effect of resistance to crack propagation and nanotubes load bearing capacity due to the existence of the fibrillar structure. Thus, blending brittle PLA with PA11 and HNT nanotubes results in tailor-made PLA-based compounds with enhanced ductility without sacrificing stiffness and strength.