In view of their potential applications in sandwich structures, there has been increasing interest in honeycomb networks. Several different types of honeycomb systems have been proposed each exhibiting different mechanical properties. Here we propose a new hexagonal honeycomb structure composed of two different geometrical features: a re‐entrant feature which is known to generate auxetic behavior, and a non re‐entrant feature found in regular hexagonal honeycombs which leads to conventional behavior. This results in a “semi re‐entrant honeycomb” built of alternate conventional and auxetic layers. Finite element analysis and analytical modeling of these honeycombs show that they exhibit a zero Poisson ratio in one direction and a higher than normal Young's modulus in the orthogonal direction. We also show that by virtue of its zero Poisson's ratio, this honeycomb has a natural tendency to form cylindrical shaped curvatures, something which is very difficult to achieve with conventional or auxetic honeycombs.

Three commercial filaments for Fused Deposition Modeling (FDM) were selected to study the influence of polymer formulation on the printing quality and mechanical properties of FDM specimens. The three filaments were all based on polylactic acid (PLA) as the matrix, and they are sold as PLA filaments. The printing quality was tested by printing one complex shape with overhang features. The marked shear thinning behavior for two filaments was observed by rheology. The filaments were also studied by scanning electron microscopy and thermogravimetric analysis (TGA) to unveil their composition. The filaments with the best printing quality showed the presence of mineral fillers, which explained the melt behavior observed by rheology. The tensile testing confirmed that the filled PLA was the best-performing filament both in terms of printing quality and thermomechanical performance, with a p-value = 0.106 for the tensile modulus, and a p-value = 0.615 for the ultimate tensile strength.

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Low molecular weight thermoplastic PES :\ud PEES (polyethersulfone : polyetherethersulfone) copolymer,\ud bearing amine reactive end groups, was blended with a\ud diglycidyl ether of bisphenol A (EPON828) epoxy resins.\ud Two different curing agents, MDEA [methylene bis(2,6-diethylaniline)]\ud and 3,3DDS (3,3-diamino diphenyl sulfone),\ud were used separately to compare flow behavior, curing kinetics,\ud and morphology of the final samples. Emphasis was\ud placed on different phase behaviors of the cured systems,\ud attributed to different solubilities of thermoplastic in the\ud thermoset system as well as to the reactivity of the two\ud curing agents. The presence of PES : PEES was shown not to\ud affect the reaction rate of epoxy blends with respect to the\ud neat resin by the reactive nature of its end groups

Among the different AM techniques, filament-based technology-i.e., fused deposition modeling (FDM)-is the most widely used, and it is also recognized as the best AM technique for functional structures (6). FDM machines can be classified into 2 types: professional and consumer. The professional machines are those produced by the company Stratasys under the trade name Fortus® which, with its founder Scott Crump, developed the original FDM concepts. These machines can operate with acrylonitrile butadiene styrene (ABS) copolymer, nylon (Ny), polycarbonate (PC), and polycarbonate and ABS (PC-ABS), acrylonitrile styrene acrylate (ASA), polyetherimide (PEI) and polyphenylsulfone (PPSF). In recent years, many consumer machines have appeared on the market based on FDM working principles. Consumer machines can operate with poly(lactic acid) (PLA), ABS, polyethylene terephthalate glycol-modified (PETG), Ny and PC.

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This work aimed to review the recent scientific research, focused on the application of recycled fibers, taken from textile waste, in the field of composite materials to fulfill the eco-sustainability requirements of textile manufacturing, and promote actions for a circular economy. The yarns and fabric production represent one of the most polluting processes of the industrial world. The harmful environmental impact of the textile process has been described by reporting the different treatments involving the raw material and the filament fabrication, and concerning the uses of insecticides, fertilizers, and many other chemicals for improving the quality of the final products. In addition, solid textile waste constituted a further additional issue for the environmental sustainability of fabric production. Various strategies have been discussed and in part already adopted by many companies to recover waste fibers and prevent them from ending up in landfills. The alternatives of fiber recycling for composite realization have been presented by reporting several recent studies involving the uses of recycled fibers from the textile waste embedded in different matrices: thermoplastic polymer, thermosetting resins, natural constituents, and concrete in light of specific applications.