Sequence-Dependent Compatibilization in PLA/PBAT Blends with Joncryl ADR Chain Extender: Insights from Linear and Nonlinear Rheology for Recycling Efficiency and Melt Stability

Poly(lactic acid)/poly(butylene adipate-co-terephthalate) (PLA/PBAT) blends require compatibilization to reconcile stiffness with ductility, particularly after thermal histories typical of recycling. Epoxy-functional chain extenders (Joncryl ADR) are widely used, yet the interplay between blend sequence and deformation amplitude remains underexplored. We compare four routes, neat, simultaneous dosing (PLA/PBAT/ADR), and two prereaction sequences (PLA + ADR)/PBAT and (PBAT + ADR)/PLA, for PLA-rich (70/30) and balanced (50/50) compositions using small-amplitude oscillatory shear (SAOS) tests, large-amplitude oscillatory shear (LAOS) tests with Fourier-transform (FT) analysis and Chebyshev decomposition, and isothermal time-sweep tests. SAOS results show a composition-dependent optimal route; (PBAT + ADR)/PLA maximizes the linear elasticity in (70/30), whereas PLA/PBAT/ADR is superior in (50/50). Chebyshev e₃ (elastic third-order coefficient) tracks intracycle strain-stiffening driven by long-chain branching and interfacial bridging, while zero-strain nonlinear parameter Q₀ quantifies the overall degree of waveform distortion without distinguishing its elastic or viscous origin; consequently, Q₀ and e₃ can rank materials differently. Time-sweeps results indicate continued reaction for PLA/PBAT/ADR at (50/50) and thermal stability for (PBAT + ADR)/PLA at (70/30). We map these signatures to processing and recycling; the optimal sequences deliver high low-shear melt strength with bounded high-shear dissipation, provided residence time and temperature are controlled to avoid over-reaction.