Polylactic Acid/Polybutylene Adipate Terephthalate-Carbon Nanotube Nanobiocomposites with a Segregated Toughening Morphology Yielding Large Ductility for Biocompatible Materials

Selective deposition and encapsulation of nanodispersed multiwalled carbon nanotubes (MWCNT) exclusively within polybutylene adipate terephthalate (PBAT) microdomains in a phase-separated microstructure of 80/20 polylactic acid (PLA)/PBAT polymer nanocomposites (PNCs) were achieved by a three-step processing strategy. The resulting PNC morphology displayed prickly chayote-squash-like domains embedded and distributed within the PLA matrix, which led to an ultratoughening effect in the PNCs at 1 wt % MWCNT, yielding ductility values of 6500 and 50% higher than the virgin PLA and the pristine 80/20 PLA/PBAT blend, respectively. The PBAT microdomains acted as the primary stress-absorbing sites. Moreover, a toughening nanomechanism by MWCNT was proposed to account for the tougher behavior, which delineated the presence of nanotubes with a critical aspect ratio, distribution, orientation, and dispersion, that deflects, pins, and bridges nanocracks, thereby acting as secondary stress-dissipating agents within the domains. The validity of this mechanism was corroborated by the observation of closed-ended and parallel nanocracks in the fractured PNCs’ cross sections. Furthermore, the intermolecular bonding between PBAT and MWCNT through CH–π interactions contributed to the preferential localization of MWCNTs exclusively within the PBAT domains, which constrained the transfer of MWCNT in the brittle PLA matrix during melt mixing, while the presence of interfacial cavitations eliminated the likelihood of interfacial bridging by MWCNT. The presence of shortened MWCNTs exclusively within the PBAT domains decreased the crystallinity of the PLA matrix, restricting the heterogeneous nucleating effect of the MWCNT in PLA as PBAT blocked their effective surface area. The hybrid PNCs developed in this study remained electrically insulative and displayed an ultratough, ultraductile, and cytocompatible behavior, which makes them potential candidates for biomedical and bioelectronic applications.