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A novel strategy adaptive to 3D printing of stereo-complexed polylactide matrix for simultaneous toughness and stiffness was designed. Stereo-complexation is a potent way to enhance both aqueous stability and heat resistance of polylactide, but also aggravates brittleness problem of polylactide. Though poly(butyleneadipate- co -terephthalate) elastomer with epoxidized compatibilizer improved stiffness and toughness of common polylactide, their effectiveness on mechanical and crystallization properties of stereo-complexed polylactide remained unknown. More importantly, incorporation of above techniques into 3D printing kept a fundamental challenge. Both stereo-complexation of polylactide and co valent coupling of polylactide and poly(butyleneadipate-co-terephthalate) by epoxidized compatibilizer are easy to occur when preparing the filaments for printing, impeding the following 3D printing procedure. The hypothesis for this research is that controlled hierarchical crystallization and reaction in three thermal processes could ensure simultaneous toughness and stiffness, and complete stereo-complexation in polylactide matrices. Reinforcing effects of a selected epoxidized compatibilizer, POSS (epoxy)8 , on crystallinities, thermal properties, mechanical properties and morphologies were systematically studied. Such a strategy not only removed the obstacles in incorporating stereo-complexation and coupling techniques of polylactide into 3D printing, but also revealed the mechanism to produce high-performance 3D printed polylactide matrix via hierarchical crystallization and reaction. • A novel strategy adaptive to 3D printing of stereo-complexed PLA was designed. • Hierarchical crystallization and reaction ensured feasibility of the strategy. • Improvement in composite ductility coincides with increase in strength. • Reinforcing effects of epoxidized POSS on PLA properties were systematically studied. • Complete stereo-complexation was achieved in 3D printed PLA matrices. [ABSTRACT FROM AUTHOR]

A novel strategy adaptive to 3D printing of PLA matrix for complete stereo-complexation was designed. Stereo-complexation has been demonstrated for its effectiveness in simultaneously improving aqueous stability and heat resistance of PLA. However, current techniques could not be directly incorporated into 3D printing of stereo-complexed PLA since stereo-complexed crystallites are easily formed before printing. High printing temperatures are thus required but decompose PLA materials at the same time. The hypothesis for this research is that controllable hierarchical crystallization in three thermal processes, the filament preparation, 3D printing and post annealing, could ensure feasibility of the strategy and a 100% stereo-complexation level in PLA matrices. Effects of extrusion, ambient and annealing temperatures on material structures were analyzed via WAXD, DSC and DMA. Resistance to hydrolysis and heat of the 3D printed PLA matrix was evaluated under practical conditions. It was showed that homo-crystallites anchored molecular chains of PLA during the post-annealing process for a high retention of tensile properties, while stereo-complexed crystallites provided stronger intermolecular interactions for improved hydrolytic and thermal resistance. This novel strategy via incorporating controlled hierarchical crystallization into 3D printing would enrich the fabrication and exploration of high-performance 3D printed PLA materials. • A novel strategy adaptive to 3D printing of stereo-complexed (sc) PLA was designed. • Hierarchical crystallization in three thermal processes ensured feasibility of the strategy. • Effects of homo- and sc-crystallites on PLA properties were systematically studied. • 100% sc-level was achieved in 3D printed PLA matrices. • 3D printed sc-PLA exhibited strong resistance to both hydrolysis and heat. [ABSTRACT FROM AUTHOR]

PLA bio-composites reinforced by oligo(d -lactic acid) grafted chitosan has been developed for simultaneously improved ductility, strength and modulus. Brittleness problem greatly limits the applications of PLA, a polymer derived from corn. Various methods have been developed to solve the brittleness problem. Unfortunately, these methods have their limitations, such as sacrifice of strength and modulus of PLA, use of toxic chemicals and high costs. Bio-based elastomers such as chitosan also have poor compatibility with PLA, leading to poor mechanical properties. The hypothesis for this research is that CS-g-oligo(D-LA) particles with good ductility could form strong interfacial interactions with PLLA matrix. Reinforcing effect of CS-g-oligo(D-LA) particles on PLLA matrix was systematically studied. Compatibility and intermolecular interactions between CS-g-oligo(D-LA) particles and PLLA matrix were studied by SEM, DSC and 13C NMR analyses. The reinforcing mechanism was summarized. Due to effective transfer of stress from PLLA matrix to the strong but ductile skeletons of CS-g-oligo(D-LA), ductility, strength and modulus of PLLA bio-composites were substantially improved. This novel reinforcing strategy via formation of strong interactions between enantiomeric lactyl units would enrich the fabrication and exploration of high-performance PLA-based bio-composites. Unlabelled Image • PLLA bio-composites reinforced by oligo(D-LA) grafted CS are developed. • Improvement in composite ductility coincides with increase in strength and modulus. • Such result is due to good properties of grafted CS and its compatibility to PLLA. • A small addition of oligo(D-LA)-g-CS is enough to achieve good reinforcing effect. [ABSTRACT FROM AUTHOR]