Shape‐Memory Topographies on Nickel–Titanium Alloys Trained by Embossing and Pulse Electrochemical Machining

The two‐way shape‐memory effect (TWSME) in Nickel–titanium (NiTi) alloys is of interest for applications in aerospace, biomedicine, and microengineering due to its reversible shape recovery. In this study, the authors demonstrate two approaches to obtain switchable surface structures using the TWSME. Samples are structured using two surface geometries by either cold embossing, or pulse electrochemical machining (PECM). After planarization, a change from optically smooth to structured and vice versa is observed. The switch is induced through heating and cooling the sample above and below the phase transformation temperature. The protrusions reflect the pattern applied by the two processes. Both methods are promising for preparation of switchable metallic surfaces on larger areas.     

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Low insulin, IGF-I and IGFBP-3 levels in children with Prader-Labhart-Willi syndrome

It is well established that insulin-like growth factor I (IGF-I), insulin-like growth factor binding protein-3 (IGFBP-3) and insulin are low in growth hormone deficiency, but due to their dependence on nutrition, they are elevated in healthy obese children. As the presence of growth hormone deficiency in Prader-Labhart-Willi syndrome (PWS) is still controversial, we studied insulin, IGF-I and IGFBP-3 levels in 19 children with PWS (age range 0.5-14.6 years). Serum concentrations of insulin (SDS: -0.7+/-0.9, P = 0.01) and IGF-I (SDS: -0.7+/-0.8, P = 0.002) were low, but IGFBP-3 (SDS: -0.3+/-1.2, P = 0.2) was normal compared to normal weight age-matched children. Since children with PWS are typically obese, insulin, IGF-I and IGFBP-3 levels should be compared to normal obese children who present increased levels of these hormones. In comparison to data of healthy obese children reported in the literature, not only IGF-I, but also IGFBP-3 levels are low and fasting insulin levels even very low, suggesting a growth hormone deficiency.     

Effect of chemical modification on the thermal and rheological properties of polylactide

Today PLA is one of the most important bioplastics on the market. A disadvantage of commercial polylactide is that it is not readily foamable, due to its low molecular weight, its low melt stability, and the lack of strain hardening effects. Therefore, commercially available polylactide has to be modified. In this study, the effects on properties by adding different modifiers were investigated. Adding of the modifiers and their chemical reaction were performed by means of reactive extrusion on a twin screw extruder. The molecular weight was increased by modifiers, which can be attributed to a changed chain topology. The highest molecular weight was achieved with organic peroxide. The rheological studies show that a changed chain topology can be assumed for the modified PLA. The most pronounced effect on the melt properties—the melt viscosity and also the melt strength—again was observed with the organic peroxide. The melt strength was increased for PLA modified with the organic peroxide. Furthermore, the organic peroxide was the only modifier that enhanced the crystallization rate, which is also favorable for extrusion foaming. POLYM. ENG. SCI., 57:1242–1251, 2017. © 2017 Society of Plastics Engineers     

Development of permanent magnet MnAlC/polymer composites and flexible filament for bonding and 3D-printing technologies

Searching for high-performance permanent magnets components with no limitation in shape and dimensions is highly desired to overcome the present design and manufacturing restrictions, which affect the efficiency of the final devices in energy, automotive and aerospace sectors. Advanced 3D-printing of composite materials and related technologies is an incipient route to achieve functional structures avoiding the limitations of traditional manufacturing. Gas-atomized MnAlC particles combined with polymer have been used in this work for fabricating scalable rare earth-free permanent magnet composites and extruded flexible filaments with continuous length exceeding 10 m. Solution casting has been used to synthesize homogeneous composites with tuned particles content, made of a polyethylene (PE) matrix embedding quasi-spherical particles of the ferromagnetic τ-MnAlC phase. A maximum filling factor of 86.5 and 72.3% has been obtained for the composite and the filament after extrusion, respectively. The magnetic measurements reveal no deterioration of the properties of the MnAlC particles after the composite synthesis and filament extrusion. The produced MnAlC/PE materials will serve as precursors for an efficient and scalable design and fabrication of end-products by different processing techniques (polymerized cold-compacted magnets and 3D-printing, respectively) in view of technological applications (from micro electromechanical systems to energy and transport applications).     

High‐speed melt spinning of various grades of polylactides

Five kinds of polylactides (PLAs), with different D ‐lactide contents and tacticities, were subjected to high‐speed melt‐spinning experiments. In addition to stereochemical purity, the PLA types differed in molecular mass and molecular mass distribution. The properties of the different PLA materials were characterized by thermogravimetry, differential scanning calorimetry, dynamic mechanical analysis, size exclusion chromatography, and ¹H‐NMR and ¹³C‐NMR spectroscopy. The material was spun with a high‐speed spinning process within the range 2000–5000 m/min. The physical and tensile properties of the fibers were determined. The maximum tensile properties of the fibers were a 300 MPa tenacity at an elongation at break of 30% and a tensile modulus of 6.8 GPa. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 91: 800–806, 2004