Polylactide (PLA) was blended by conventional and reactive extrusion with limonene (LM) or myrcene (My) as bio-based plasticizers. As-processed blends were carefully analyzed by a multiscale and multidisciplinary approach to tentatively determine their chemical structure, microstructure, thermal properties, tensile and impact behaviors, and hydrothermal stability. The main results indicated that LM and My were efficient plasticizers for PLA, since compared to neat PLA, the glass transition temperature was reduced, the ultimate tensile strain was increased, and the impact strength was increased, independently of the type of extrusion. The addition of a free radical initiator during the extrusion of PLA/LM was beneficial for the mechanical properties. Indeed, the probable formation of local branched/crosslinked regions in the PLA matrix enhanced the matrix crystallinity, the tensile yield stress, and the tensile ultimate stress compared to the non-reactive blend PLA/LM, while the other properties were retained. For PLA/My blends, reactive extrusion was detrimental for the mechanical properties since My polymerization was accelerated resulting in a drop of the tensile ultimate strain and impact strength, and an increase of the glass transition temperature. Indeed, large inclusions of polymerized My were formed, decreasing the available content of My for the plasticization and enhancing cavitation from inclusion-matrix debonding.

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3D printed neat thermoplastic polymers (TPs) and continuous fiber-reinforced thermoplastic composites (CFRTPCs) by fused filament fabrication (FFF) are becoming attractive materials for numerous applications. However, the structure of these materials exhibits interfaces at different scales, engendering non-optimal mechanical properties. The first part of the review presents a description of these interfaces and highlights the different strategies to improve interfacial bonding. The actual knowledge on the structural aspects of the thermoplastic matrix is also summarized in this contribution with a focus on crystallization and orientation. The research to be tackled to further improve the structural properties of the 3D printed materials is identified. The second part of the review provides an overview of structural health monitoring technologies relying on the use of fiber Bragg grating sensors, strain gauge sensors and self-sensing. After a brief discussion on these three technologies, the needed research to further stimulate the development of FFF is identified. Finally, in the third part of this contribution the technology landscape of FFF processes for CFRTPCs is provided, including the future trends.

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Crystallization kinetics of various blends of poly(lactic acid) (PLA)/polyolefin elastomer (POE) was studied through nonisothermal experimental investigations and theoretical approaches. The PLA/POE blends were prepared in a melt mixing process by using two types of POEs and compatibilizers. The rubber phases used were adopted on the basis of polyethylene (PE) and polypropylene (PP) type olefin elastomers. The effects of two kinds of compatibilizers containing ethylene vinyl acetate copolymer (EVA) and ethylene acrylic ester-glycidyl methacrylate terpolymer (EGMA) on the morphology and various parameters of crystallization of PLA were investigated using scanning electron microscopy (SEM) and differential scanning calorimeter (DSC) measurements, respectively. The morphology investigations on PLA blends containing PP based olefin elastomers showed that the introduction of EGMA compatibilizer into the matrix led to a more than 100% reduction in the size of the rubber droplets. The experimental measurements of crystallization behavior of various PLA/POE blends showed that the POEs and compatibilizers could cause a fall in the initial crystallization temperature more than 13 °C. The theoretical approaches used for studying the kinetics of crystallization of PLA in the presence of various POEs and compatibilizers indicated a decrease in the crystallinity of PLA and a 64% reduction in the activation energy compared to the neat PLA. The results suggest that the largest variation in the crystallization kinetic parameters of PLA was resulted from the PP based olefin elastomer and EGMA compatibilizer.