Experimental and numerical investigation of paperboard creasing

Laminated paperboard is widely used in packaging products. It usually consists of multiple layers bonded to each other by starch or adhesion. The indentation of fold lines (creasing) plays a crucial role during the whole converting process. It is important to control delamination and other damage effects to arrive at commercial cartons with high quality. Thus, the aim of this study is to describe the material behavior of a laminated paperboard during the creasing process. The paperboard was considered as a laminate of three different layers, and each was modeled separately with an anisotropic elastic-plastic material model while a cohesive zone approach described the opening behavior in between. The initial yielding was given by the Hill's 48 yield criterion, while the isotropic strain hardening was described by a power law hardening function. To calibrate the material parameters, a sequence of tensile and compression tests was conducted for each layer in different directions to account for the material's anisotropy. Finally, the creasing process was investigated using a two-dimensional plane strain finite element model. (© 2014 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim)     

The effect of mixing methods on the dispersion of carbon nanotubes during the solvent-free processing of multiwalled carbon nanotube/epoxy composites

Several solvent-free processing methods to disperse multiwalled carbon nanotubes (MWCNTs) in bisphenol F-based epoxy resin were investigated, including the use of a microfluidizer (MF), planetary shear mixer (PSM), ultrasonication (US) and combinations. The processed mixture was cured with diethyl toluene diamine. Three complimentary techniques were used to characterize the dispersion of the MWCNTs in cured composite samples: optical microscopy, micro Raman spectroscopy, and scanning electron microscopy (SEM). For sample MF + PSM, optical micrographs and Raman images showed reduced agglomeration and a homogeneous distribution of MWCNTs in the epoxy matrix. SEM analysis of fractured specimen after tensile testing revealed breakage of nanotubes along the fracture surface of the composite. A comparison of the MWCNT dispersion in the epoxy samples processed using different methods showed that a combination of MF and PSM processing yields a more homogeneous sample than the PSM or US + PSM processed samples. Mechanical testing of the composites showed about 15% improvement in the tensile strength of samples processed by the MF + PSM method over other methods. Thermogravimetric analysis (TGA) results showed a small decrease in the onset degradation temperature for poorly dispersed samples produced by PSM compared with the well-mixed samples (MF + PSM). These results strongly suggest that the MF + PSM processing method yield better-dispersed and stronger MWCNT/epoxy composites. © 2012 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys, 2013     

Cyclization of Propargylic Amides: Mild Access to Oxazole Derivatives

The substrate scope, the mechanistic aspects of the gold‐catalyzed oxazole synthesis, and substrates with different aliphatic, aromatic, and functional groups in the side chain were investigated. Even molecules with several propargyl amide groups could easily be converted, delivering di‐ and trioxazoles with interesting optical properties. Furthermore, the scope of the gold(I)‐catalyzed alkylidene synthesis was investigated. Further functionalizations of these isolable intermediates of the oxazole synthesis were developed and chelate ligands can be obtained. The use of Barluenga’s reagent offers a new and mild access to the synthetically valuable iodoalkylideneoxazoles from propargylic amides, this reagent being superior to other sources of halogens.     

Stability and Conversion of Tin Zintl Anions in Liquid Ammonia Investigated by NMR Spectroscopy

Homoatomic polyanions of post‐transition main‐group metals, namely, Zintl anions, are precast in analogous Zintl phases and can react in solution to form new materials. Despite comprehensible reaction approaches, the formed products cannot be planned in advance, as hitherto undetected and therefore disregarded side reactions take place. The outcomes and interpretations of the reactions of Zintl anions are so far based mainly on crystal structures, which only allow characterization of the product that has the lowest solubility. Here we present the results of our investigation of the stability of highly charged tin Zintl anions in liquid ammonia, which is not exclusively based on solution effects but also on the oxidative influence of the solvent. This allows for a deeper understanding of the ongoing processes in solution and opens doors to the directed synthesis of transition metal complexes of Sn₄^4?, here shown by its reactivity towards MesCu.