Search results for "Plastics"

Styrene polymerization using nickel(II) complexes as catalysts

2005

International audience; Styrene polymerization is investigated with neutral and cationic Ni(II) complexes, i.e. Ni(bipy)Me-2, 1, Ni(bipy)Br-2, 2, Ni(phen)Br-2, 3, or Ni(Me(2)phen)Br-2, 4, Ni(acac)(2), 5, (bipy = 2,2 '-bipyridine, phen = phenanthroline, Me,phen = 2,9-dimethyl-1, 10-phenanthroline, acac acetylacetonate), activated by [NHMe2Ph][B(C6F5)(4)] or B(C6F5)(3) as cocatalysts, in the presence of AlMe3. The influence on the polystyrene features and the reaction kinetics of the nickel complex and boron activator, the Al/Ni or B/Ni molar ratios as well as the monomer concentration are studied. Catalytic systems derived from 2, 3 or 5 and [NHMe2Ph][B(C6F5)(4)] at a Ni:B:Al ratio of 1: 1:5…

1981

Dynamic-mechanical and dielectric measurements have been performed with some polycarbonate samples. In one set of experiments care was taken to avoid any absorption of moisture. In other sets of experiments, samples were exposed to atmospheric humidity and to boiling water. The glass transition temperature was found to be highly affected by the absorption of water and by the test conditions. Dynamisch-mechanische und dielektrische Messungen wurden an Polycarbonatproben durchgefuhrt. In einer Versuchsserie wurde die Absorption von Wasser vollstandig vermieden, in weitern Versuchen wurden die Proben der Luftfeuchte bzw. kochendem Wasser ausgesetzt. Die Glasubergangstemperatur wurde durch das …

Dual phase titanium alloy hot forging process design: experiments and numerical modeling

2015

Titanium alloys are considered desirable materials when both good mechanical properties and weight reduction are required at the same time. This class of materials is widely used in those fields (aeronautics, aerospace) in which common steels and light-weight materials, e.g., aluminum alloys, are not able to satisfy all operative service conditions. During the last decade, forging of titanium alloys has attracted greater attention from both industrial and scientific/academic researchers because of their potential in providing a near net shaped part with minimal need for machining. In this paper, a numerical model of the forging sequences for a Ti-6Al-4V titanium alloy aerospace component is…

1986

Ultimate tensile properties and dart impact behaviour of coextruded films of LDPE and LLDPE were compared with those of films made from blends of the same resins. The effect of composition and of both blow up ratio and axial draw ratio of the blowing process on film properties was explored. The results indicate that, at least for semicompatible systems like that considered here, films made from blends and coextruded ones have mechanical properties very close to each other. Die Festigkeitseigenschaf ten und das Verhalten beim Kugelfalltest von coextrudiertcn Filmen aus LDPE und LLDPE wurden mit den entsprechenden Eigenschaften von aus Mischungen dieser Polymere hergestellten Filmen vergliche…

Influence of M23C6 carbides on the heterogeneous strain development in annealed 420 stainless steel

2020

Understanding the local strain enhancement and lattice distortion resulting from different microstructure features in metal alloys is crucial in many engineering processes. The development of heterogeneous strain not only plays an important role in the work hardening of the material but also in other processes such as recrystallization and damage inheritance and fracture. Isolating the contribution of precipitates to the development of heterogeneous strain can be challenging due to the presence of grain boundaries or other microstructure features that might cause ambiguous interpretation. In this work a statistical analysis of local strains measured by electron back scatter diffraction and …

Effect of the orientation on the photooxidation behaviour of polymer films

2016

Abstract The effect of the orientation on the photooxidation of polymers is quite controversial. Both improvement of the photo-resistance along the oriented direction and worsening of the photooxidation kinetic have been reported. In this work the effect of the orientation has been investigated on films of PE, PP and PET with different degree of orientation and crystallinity. The results show that the photo-stability, measured from the decay of the elongation at break curve as a function of the irradiation time, improves in the more oriented direction, but this is more and more relevant with increasing the crystallinity degree. It has been hypothesized that the reinforcing action of the ori…

Fluorescence studies of hydrophobically-modified poly(N-isopropylacrylamides) or how to play accordion on a liposome

1991

The coil/globule transition of polymers in solution is a favourite topic of discussion among polymer theoreticians. Here, this phenomenon is used to play a “molecular accordion” built with a thermosensitive polymer anchored to liposomes, a tune which mimics a natural process occuring in cell membranes.

Spatial Demixing of Ring and Chain Polymers in Pressure-Driven Flow

2019

We investigate mixtures of ring and linear polymers in solution at various number ratios, ranging from pure chains to pure rings, and at densities around the overlap concentration. In bulk and at r...

Optical data storage in Langmuir-Blodgett-Kuhn multilayer assemblies of azo-dye side chain LC-polymers

1991

We describe the preparation of LB-films of novel polymers containing azobenzene dye side chains. X-ray refection measurements, surface-plasmon experiments were used to determine the structure of LB-films which had been transferred onto a substrate. Illumination with UV-light causes trans-cis isomerisation of the azobenzene side groups. This effect can be used for optical data storage and will be discussed in detail.

Cell adhesion on UV-crosslinked polyurethane gels with adjustable mechanical strength and thermoresponsiveness

2021

Temperature-responsive polyurethane (PU) hydrogels represent a versatile material platform for modern tissue engineering and biomedical applications. However, besides intrinsic advantages such as high mechanical strength and a hydrolysable backbone composition, plain PU materials are generally lacking bio-adhesive properties. To overcome this shortcoming, the authors focus on the synthesis of thermoresponsive PU hydrogels with variable mechanical and cell adhesive properties obtained from linear precursor PUs based on poly(ethylene glycol)s (pEG) with different molar masses, isophorone diisocyanate, and a dimerizable dimethylmaleimide (DMMI)-diol. The cloud point temperatures of the dilute,…