A Highly Ductile Composite of 3D‐Printed Poly(Lactic Acid) With InSe Particles and Flakes as a Filler

ABSTRACT The biodegradable polymer poly(lactic acid) (PLA) is brittle. PLA‐based composites reinforced by indium selenide (InSe) particles or flakes are prepared; each is found to have outstanding plasticity. InSe nanosheets are prepared by sonication of solid InSe in N ‐methyl pyrrolidone, followed by washing/dispersion in ethanol, and subsequent drying. These InSe nanosheets, or in separate studies InSe particles, are mixed with PLA to make composite materials. The PLA composite materials are 3D‐printed into “dogbone” samples that are tensile‐loaded. The optimum dogbone specimen is 1.5 times stronger and 5.5 times tougher than neat PLA specimens prepared in the same way. To the best of our knowledge, this concurrent improvement in tensile strength and toughness has not been achieved before in PLA with any filler type. Finite element analysis, together with experimental analysis of (i) fracture surfaces, (ii) the PLA crystal structure, and (iii) the internal structure by micro‐CT scanning, suggests that the exceptional mechanical performance is due to the intrinsic properties of InSe and, particularly, the emergence of crack shielding and crack deflection at the interfaces of PLA and InSe flakes. These findings indicate that PLA–InSe composites may offer opportunities to broaden the applications of PLA composites, including as load‐bearing materials.