Correlating structure and viscoelastic behavior of 3D‑printed PLA/PHA blends: Experimental and simulation

Abdullah, Kardo Khalid and Krizsma, Szabolcs and Széplaki, Péter and Molnár, Kolos (2026) Correlating structure and viscoelastic behavior of 3D‑printed PLA/PHA blends: Experimental and simulation. MATERIALS TODAY COMMUNICATIONS, 54. No. 115546. ISSN 2352-4928

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Abstract

Polylactic acid (PLA) is widely used in 3D printing, but its brittleness limits its use in shape-memory applications. Polyhydroxyalkanoates (PHA) are more flexible and crystalline, yet their thermal instability complicates processing. To overcome these limitations, we blended PLA with two semi-crystalline PHA grades: PLA/PHAS (70/ 30 wt%) and PLA/PHI (70/30 wt%) to combine printability with tailored thermal and viscoelastic properties. Filaments were melt-extruded and printed by fused filament fabrication. Oscillatory melt rheology at the printing temperature (220 ◦C) showed that the blends exhibited higher elasticity than neat PLA. Scanning electron and atomic force microscopy revealed that neat PLA exhibited a smooth, single‑phase surface, whereas both blends showed a phase‑separated matrix–droplet morphology with spherical PHA domains. Differential scanning calorimetry confirmed immiscibility through two distinct glass transitions (PHA‑rich near 3–4 ◦C, PLA‑rich near 54–55 ◦C). Both blends showed lower cold‑crystallization enthalpies than printed PLA, indicating that the PHA phase hinders the mobility of the PLA chains. X‑ray diffraction showed that pure PLA formed only mesomorphic domains (< 1 nm), while the blends developed hierarchical crystalline structures containing large lamellae (24–29 nm) alongside smaller crystallites (~6–7 nm). A Prony-series finite element model, calibrated using time–temperature superposition from creep test data, accurately predicted linear viscoelastic behavior below the glass transition, remaining reliable up to 40 ◦C for PLA/PHAS and 45 ◦C for PLA/PHI. These results demonstrate that blending PLA with PHA enables tunable crystalline structures and predictable viscoelasticity, supporting the development of biomaterials with a functional thermal response.

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