Search results for " Plastic"
showing 10 items of 3463 documents
Multi-Arm Star Poly(L-lactide) with Hyperbranched Polyglycerol Core
2007
Biocompatible multi-arm star block copolymers based on poly(L-lactide) (PLLA) have been prepared by a core-first approach, using hyperbranched polyglycerol (PG), a polyether polyol, as a polyfunctional initiator. The molecular weight of the hyperbranched initiator-core was varied from 2 200 to 5 200 g mol -1 , molecular weights of the resulting multi-arm stars were in the range of 6 700-107 000 g mol -1 (NMR), depending on the amount of dilactide (LA) added. Various monomer/initiator ratios have been employed in the Sn-catalyzed LA polymerization in order to vary the length of the lactide arms from DP n (arm) = 2 to 20 units. Detailed NMR analysis using conventional and 2D-NMR techniques (e…
A quantitative investigation on the thermoelastic effect of CFRP laminates
2009
The thermoelastic effect on CFRP laminates with various lay-ups is investigated. A thick low crimp unidirectional fabric reinforcement is adopted. The measured thermoelastic signal is compared with predictions from two analytical models based on the meso-mechanical bulk properties of the lamina and on assuming a strain witness behaviour of the surface resin rich layer.
Mercury(II) removal from aqueous solution by sorption onto alginate, pectate and polygalacturonate calcium gel beads. A kinetic and speciation based …
2013
Abstract Gel beads of calcium alginate, pectate and polygalacturonate salts have been tested as sorbent materials for mercury(II) removal from aqueous solutions. Physico-chemical properties of gel beads, defined by SEM–EDX, TGA and texture and density analysis, were correlated with gel beads sorption capacity towards Hg 2+ ion. A speciation study in aqueous solution was carried out to define the strength of interaction of mercury ion with the polymers investigated and to assess the more suitable experimental conditions to achieve the best effectiveness of Hg 2+ sorption by gel beads. On the basis of the speciation study, pH values in the 3–5.5 pH range were considered appropriated for mercu…
New amphiphilic terphenyl liquid crystals for the preparation of highly ordered ultrathin films
1991
Four new amphiphilic liquid crystals have been synthesized, in which terphenyl was used as the mesogenic unit. In order to enable the formation of Langmuir Monolayers at the air/water-interface, the molecules were equipped with slightly polar headgroups such as esters or a carboxylic acid group. All compounds can be transferred onto solid substrates. In addition, it is possible to prepare freely suspended films of at least one compound in the temperature range of the smectic phases. The phases of the different states, bulk, monolayer, freely suspended film, and Langmuir-Blodgett multilayers have been investigated by means of monolayer isotherms, optical textures, differential scanning calor…
A compact Raman microprobe/microscope: Analysis of polydiacetylene Langmuir and Langmuir-Blodgett films
1991
A compact Raman microprobe/microscope has been developed which contains no wavelength dispersive elements. Multilayer dielectric filters, tuned by rotation, provide sufficient wavelength selectivity for taking Raman spectra and forming Raman images of samples as small as 1 μm in diameter. The application of the instrument is demonstrated by Raman spectra and images of polydiacetylene Langmuir and Langmuir-Blodgett films.
Stereospecific Polymerization of Isoprene with Nd(BH4)3(THF)3/MgBu2 as Catalyst
2004
The neodymium trisborohydride Nd(BH 4 ) 3 - (THF) 3 (THF = tetrahydrofuran) has been used as a catalyst precursor for isoprene polymerization for the first time. Associated to an excess of Al(Et) 3 , the resulting catalyst is moderately active, giving a mixture of cis- and trans- polymer. Addition of a stoichiometric amount of MgBu 2 to Nd(BH 4 ) 3 (THF) 3 affords a stereospecific catalyst providing trans-1,4-polyisoprene, more than 96% regular. That dual component Nd/Mg system also shows a better efficiency and good control of the molecular weights. A molecular structure is tentatively attributed to a bimetallic active species, based on 1 H NMR experiments.
Effect of the remaining lanthanide catalysts on the hydrolytic and enzymatic degradation of poly-(ε-caprolactone)
2003
Poly-(e-caprolactone) is a biodegradable polymer, which can be used for both medical and environmental applications. Due to its multiple applications the synthesis of such a polymer has been attracting an increasing attention in the past few decades. In our work, the polymers were synthesised by bulk polymerisation, using different lanthanide halides as initiators. The lanthanide derivatives are known as very active catalysts in the ring-opening polymerisation of cyclic esters. Moreover, they are not toxic in comparison of catalysts, which are usually used for this synthesis. In this paper, the influence of the lanthanides on both the hydrolytic and enzymatic degradation of the PCL obtained…
Unusual finite size effects in the Monte Carlo simulation of microphase formation of block copolymer melts
1995
Extensive Monte Carlo simulations are presented for the Fried-Binder model of block copolymer melts, where polymer chains are represented as self and mutually avoiding walks on a simple cubic lattice, and monomer units of different kind (A, B) repel each other if they are nearest neighbors (e AB > O). Choosing a chain length N = 20, vacancy concentration Φ v = 0,2, composition f = 3/4, and a L × L × L geometry with periodic boundary conditions and 8 ≤ L ≤ 32, finite size effects on the collective structure factor S(q) and the gyration radii are investigated. It is shown that already above the microphase separation transition, namely when the correlation length ζ(T) of concentration fluctuat…
X-ray scattering studies of the structure of aqueous hydroxy-propylcellulose solutions
1991
X-ray diffraction studies have been undertaken on aqueous solutions of hydroxy propylcellulose (HPC) over a wide range of the scattering vector Q. The experiments revealed only modest differences in local structure on a distance scale ca. 5–300 A despite the fact that they covered concentrations generally interpreted as ranging from the isotropic (35.1 wt %) to the anisotropic liquid crystalline (LC) phase (53.5 wt %). Several models were used to interpret the small-angle scattering data, and each gave similar structural parameters and extrapolated intensities (Q → 0) for both solutions. Peaks were observed with d-spacings ca. 12–17 A in both materials. Wide-angle x-ray scattering (WAXS) sh…
Orientation of polybutadiene chains in a thermoplastic elastomer
1996
The orientation of polybutadiene chains in thermoplastic elastomers based on hydrogen bonding complexes is investigated under uniaxial deformation by two-dimensional small-angle neutron scattering (SANS), deuteron magnetic resonance spectroscopy (2H-NMR), optical birefringence and infrared dichroism spectroscopy (FTIR-D). While SANS probes orientation on the length scale of the radius of gyration,2H-NMR, birefringence and FTIR-D monitor orientation on a segmental scale. The deformation of the elastomer chains appears to be affine on the different length scales.