Search results for "Chemical engineering"
showing 10 items of 5892 documents
Artificial Opals as Effect Pigments in Clear-Coatings
2004
In this paper, we describe the use of artificial opals from polymer beads as effect pigments in transparent industial and automotive coatings. For this purpose, we synthesized monodisperse colloids from fluorinated methacrylates by surfactant-free emulsion polymerization. The fluorinated monomers, in combination with crosslinking, lead to a refractive index contrast, thermal stability, and solvent resistivity necessary for use as effect pigments. After crystallization of the monodisperse polymer beads, crystal flakes with iridescent colors can be obtained. The crystal flakes can act as effect pigments in various transpartent industrial and automotive coatings. due to photonic crystal behavi…
1982
The stress relaxation behaviour after compression yielding of two semicrystalline polymers, a low density polyethylene and an isotactic polypropylene, is investigated. Data taken at several strains, reached with different sample loading rates, are considered. Master curves are obtained by means of dimensionless stress and time measures, similar to those recently adopted for some amorphous polymers. Die Spannungsrelaxation nach Druckbeanspruchung wurde an zwei semikristallinen Polymeren, Polyethylen neidriger Dichte und isotaktischem Polypropylen, untersucht. Die bei unterschiedlichen Deformationen, welche mit unterschiedlichen Beanspruchungsgeschwindigkeiten erreicht wurdern, erhaltenen Erg…
Mechanical Characterization of Polysaccharide/polyaminoacid Hydrogels as Potential Scaffolds for Tissue Regeneration
2011
The mechanical properties of hydrogel scaffolds based on hyaluronic acid (HA) that were chemically crosslinked with α,β-poly(N-2-hydroxyethyl)(2-aminoethylcarbamate)-D,L-aspartamide (PHEA-EDA) were investigated. Variation of these properties as a function of three different PHEA-EDA amounts used to crosslink HA has been related to the reaction efficiency evaluated using a colorimetric assay. Moreover, the amount of unreacted amino groups that was still present in the hydrogels was related to the attachment behavior of human dermal fibroblasts to the hydrogel surface. The mechanical data and biological results suggest the suitability of the investigated hydrogels as scaffolds for the regener…
Large Scale Fractionation of Macromolecules
2004
Access to sufficiently large amounts of material with adequate molecular and chemical uniformity from polydisperse natural products or synthetic materials has been a long-standing challenge to polymer scientists. We have developed a broadly applicable preparative fractionation method consisting of a special kind of continuous extraction removing the easier soluble components from the initial product. It is rendered possible by the use of spinning nozzles throught which a concentrated polymer solution is pressed into a liquid of tailored thermodynamic quality. The initially produced jets of the source phase disintegrate rapidly into minute droplets of typically 50 μm diameter. This efficient…
Modelling the hydrogen-bonding interactions in a copolymer/biodegradable homopolymer blend through excess functions
2008
A recent theoretical approach based on the coupling of both the Flory-Huggins (FH) and the Association Equilibria thermodynamic (AET) theories was modified and adapted to study the miscibility properties of a multi- component system formed by two polymers (a proton-donor and a proton-acceptor) and a proton-acceptor solvent, named copolymer(A)/solvent(B)/polymer(C). Compatibility between polymers was mainly attained by hydrogen- bonding between the hydroxyl group on the phenol unit of the poly(styrene-co-vinyl phenol) (PSVPh) and the car- bonyl group of the biodegradable and environmentally friendly poly(3-hydroxybutyrate) (PHB). However, the self- association of PSVPh and specific interacti…
Characterization of a fiber reinforced semirigid liquid crystalline polymer
1997
In this work, samples of a semirigid Liquid crystalline polymer reinforced with carbon and glass fibers has been characterized. Semirigid liquid crystalline polymers (LCPs) show some advantages with respect to rigid LCPs: in particular lower processing temperatures, and better compatibility with flexible thermoplastics, but also some disadvantages: lower mechanical properties and poor thermomechanical resistance. Both properties can be improved by adding inorganic fillers. Although elastic modulus and tensile strength of the glass fiber filled LCP improve remarkably with increasing the filler content, the same properties for the carbon fiber-filled samples do not increase with increasing ti…
Macro-oriented network of liquid-crystalline polyesters: crosslinking induced by g-irradiation and thermally activated reaction.
2000
Abstract The synthesis of a macro-oriented network from liquid-crystalline polymers, bearing pendant groups with unsaturations, is reported. Virgin polymers are processable to obtain oriented samples, e.g. fibres, which may be crosslinked through thermal activation and/or exposure to γ-radiation. The liquid-crystalline state is “frozen” and the macroscopic anisotropy is preserved even at high temperatures. Compared to virgin fibres, irradiated samples show an enhancement of tensile performances, thus indicating that the main effect of irradiation is crosslinking without significant degradation phenomena.
Ferroelectric block copolymers
1997
A block copolymer consisting of polystyrene and a side chain ferroelectric liquid crystalline polymer was synthesized using polymer analogous chemistry on a monodisperse poly(styrene-b-isoprene). Composition was adjusted to give lamellar microstructure after addition of the mesogenic side groups. If placed in an LC cell without orientation of domains, no ferroelectric response was observed. After shearing the thin film, presumably due to alignment of lamellae, a bistable ferroelectric switching could be detected.
Polymer-polymer interaction parameters in solvent/polymer/polymer ternary systems
1981
Abstract Empirical equations defining the relationships between b23 and χ23 interaction parameters for the ternary systems toluene (1)/poly(dimethylsiloxane), PDMS, (2)/polystyrene, PS, (3) and benzene (1)/PDMS(2)/PS(3) have been determined. The dependences of both interaction parameters on the mean molecular weights of the macromolecular components have also been studied. A single dependence of b23 (or χ23) upon the mean molecular weight is found when both polymeric components have intermediate to high molecular weights. However, that single dependence is not found when the molecular size of polymer (2) is low.