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In this study, the possibility of using a layered silicate-reinforced polylactic acid (PLA) in additive manufacturing applications was investigated. In particular, the aim of this work was to study the influence of printing temperature in the 3D printing process of PLA/clay nanocomposites. For this reason, two PLA grades (4032D and 2003D, D-isomer content 1.5 and 4, respectively) were melt-compounded by a twin screw extruder with a layered silicate (Cloisite 30B) at 4 wt %. Then, PLA and PLA/clay feedstock filaments (diameter 1.75 mm) were produced using a single screw extruder. Dog-bone and prismatic specimens were 3D printed using the FDM technique at three different temperatures, which were progressively increased from melting temperature (185–200–215 °C for PLA 4032D and 165–180–195 °C for PLA 2003D). PLA and PLA/clay specimens were characterized using thermogravimetric analysis (TGA), dynamic mechanical analysis (DMA), differential scanning calorimetry (DSC), and tensile tests. Moreover, the morphology of the 3D printed specimens was investigated using optical microscopy and contact angle measurements. The different polymer matrix and the resulting nanocomposite morphology strongly influenced 3D printed specimen properties. DMA on PLA/clay filaments reported an increase in storage modulus both at ambient temperature and above the glass transition temperature in comparison to neat PLA filaments. Furthermore, the presence of nanoclay increased thermal stability, as demonstrated by TGA, and acted as a nucleating agent, as observed from the DSC measurements. Finally, for 3D printed samples, when increasing printing temperature, a different behavior was observed for the two PLA grades and their nanocomposites. In particular, 3D printed nanocomposite samples exhibited higher elastic modulus than neat PLA specimens, but for PLA 4032D+C30B, elastic modulus increased at increasing printing temperature while for PLA 2003D+C30B slightly decreased. Such different behavior can be explained considering the different polymer macromolecular structure and the different nanocomposite morphology (exfoliated in PLA 4032D matrix and intercalated in PLA 2003D matrix).

Additive manufacturing (AM) is a promising technology for the rapid tooling and fabrication of complex geometry components. Among all AM techniques, fused filament fabrication (FFF) is the most widely used technique for polymers. However, the consistency and properties control of the FFF product remains a challenging issue. This study aims to investigate physical changes during the 3D printing of polylactic acid (PLA). The correlations between the porosity, crystallinity and mechanical properties of the printed parts were studied. Moreover, the effects of the build-platform temperature were investigated. The experimental results confirmed the anisotropy of printed objects due to the occurrence of orientation phenomena during the filament deposition and the formation both of ordered and disordered crystalline forms (α and δ, respectively). A heat treatment post-3D printing was proposed as an effective method to improve mechanical properties by optimizing the crystallinity (transforming the δ form into the α one) and overcoming the anisotropy of the 3D printed object.

ABSTRACT:The curing kinetics and chemorheology of a low-viscosity laminating system, based on a bisphenol A epoxy resin, an anhydride curing agent, and a heterocyclic amine accelerator, are investigated. The curing kinetics are studied in both dynamic and isothermal conditions by means of differential scanning calorimetry. The steady shear and dynamic viscosity are measured throughout the epoxy/ anhydride cure. The curing kinetics of the thermoset system is described by a modified Kamal kinetic model, accounting for the diffusion-control effect. A chemorheological model that describes the system viscosity as a function of temperature and conversion is proposed. This model is a combination of the Williams-Landel-Ferry equation and a conversion term originally used by Castro and Macosko. A good agreement between the predicted and experimental results is obtained.

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This work focuses on the possibility of improving performance properties of polyamide-layered\ud silicate nanocomposite films for packaging applications by using, as alternative matrix, a statistical copolymer of\ud the nylon-6 having a partially aromatic structure. Nanocomposites at different silicate loadings (commercial organomodified\ud montmorillonite) were produced by cast-film extrusion using three polyamide matrices: nylon-6 and\ud two copolyamides with similar chemical structure but different molecular weights. Oxygen barrier and mechanical\ud properties of the produced films were investigated and correlated to their nanostructure through analytical techniques\ud sensitive to different aspects of the same morphology, such as TEM, rheological, and dynamic-mechanical analyses.\ud Permeability data were interpolated on the basis of different theoretical approaches, from which a quantitative\ud indication on exfoliation and orientation levels of silicate layers in the matrices was obtained. TEM images at\ud different magnifications were used to empirically evaluate the average length-thickness ratio of silicate platelets\ud and to verify the correspondence with aspect ratios and order parameters calculated by data fitting. A strong\ud correlation between nanomorphology and properties was observed in the different nanocomposite systems and\ud all the three matrices exhibited performance improvement with increasing the silicate content. Nanocomposite\ud films based on the copolyamide with higher molecular weight displayed more exfoliated regions and a preferential\ud orientation of silicate layers, leading to the most significant oxygen barrier improvements and the best mechanical\ud propertie