This study addresses the mechanical behavior of lattice materials based on flexible thermoplastic polyurethane (TPU) with honeycomb and gyroid architecture fabricated by 3D printing. Tensile, compression, and three-point bending tests were chosen as mechanical testing methods. The honeycomb architecture was found to provide higher values of rigidity (by 30%), strength (by 25%), plasticity (by 18%), and energy absorption (by 42%) of the flexible TPU lattice compared to the gyroid architecture. The strain recovery is better in the case of gyroid architecture (residual strain of 46% vs. 31%). TPUs with honeycomb architecture are characterized by anisotropy of mechanical properties in tensile and three-point bending tests. The obtained results are explained by the peculiarities of the lattice structure at meso- and macroscopic level and by the role of the pore space.

In situ formation of polymer nanofibrils during compounding with a second polymer followed by their immediate solidification due to shear induced crystallization for two pairs of polymers is described. Sustainable green biopolymer–biopolymer nanocomposites of polylactide (PLA) were then fabricated based on two copolyesters forming nanofibrils during shearing: poly(butylene adipate-co-succinate-co-glutarate-co-terephthalate) (PBASGT) and poly(butylene adipate-co-terephthalate) (PBAT). The shear induced crystallization allowed solidification of PBASGT or PBAT nanofibers immediately under applying a high shear rate without subsequent cooling. The melt memory unveiling as a self-nucleation facilitated shear-induced crystallization. Formation of nanofibril-matrix morphology led to an exceptional combination of strength, modulus and ductility. In situ SEM observation of the tensile test revealed crazing as a dominant mechanism for PLA deformation. However, addition of PBASGT or PBAT resulted in intensified crazing followed by shear banding. Increase of PBASGT or PBAT concentration promoted the brittle-to-ductile transition of the PLA matrix. At the same time, PBAT or PBASGT nanofibers span PLA craze surfaces and at large strain, when PLA craze tufts get broken, they bridge the craze gaps resulting in an increase of both strength and plasticity of PLA.