Cytocompatible 2D Graphitic Carbon Nitride-Modified Polybutylene Adipate Terephthalate/Polylactic Acid Hybrid Nanobiocomposites

Polymer nanobiocomposites (PNCs) prepared with graphitic carbon nitride (GCN) nanosheets in polybutylene adipate terephthalate (PBAT)/polylactic acid (PLA) bioblends were processed using a three-step processing technique that involved: (1) a solution-based GCN exfoliation step; (2) a masterbatching step of GCN in PBAT by solution processing; and (3) a melt-compounding step where the masterbatch was mixed with pristine PLA to delaminate the 2D GCN layers by extrusion high-shear mixing and to deposit them onto the biphasic PLA/PBAT morphology. Due to the partial exfoliation of GCN, this process led to a concurrent presence of three distinct morphologies within the PNCs’ microstructure: (1) Type 1, characterized by an unaltered interface and PLA matrix, with minimal GCN deposition within the PBAT phase; (2) Type 2, distinguished by a diffused and stiff interface with GCN distribution in both the dispersed (PBAT) and matrix (PLA) phases; and (3) Type 3, featuring unmodified interfaces and GCN localization across both PLA and PBAT phases with a stair-like morphological texture. Such a morphological combination generates distinct crack propagation micromechanics, thereby influencing the variability of the plastic deformational behavior of their PNCs. Particularly, the Type 1 morphology enables GCN to act as a secondary stress-dissipating agent, whereas the PBAT domains serve as the primary stress-absorbing sites, contributing to enhanced crack propagation energy requirements. Contrarily, Type 3 (slightly) and Type 2 (predominantly) morphologies invert GCN’s role from stress dissipation to stress concentration due to its localization within the PLA matrix. Differential scanning calorimetry revealed a crystallinity increase in the PNCs until 0.1 wt % GCN, followed by a decline, likely due to agglomeration at higher contents. Thermogravimetric analysis showed that GCN addition improved the thermostability of the bioblends, attributed to the GCN’s nanophysical and pyrolytic barrier effect. Moreover, using both direct and indirect methods, GCN did not impair the biocompatibility of the bioblends as confirmed via cytocompatibility assays.