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At least 1,351 records · Page 75Linked to original sources
PubMed1999

NMR microscopy of polyurethane foams.

NMR microimaging has been applied to the characterization of foam materials, in order to understand their properties and gain deeper insight into their structures. The structure of "open cell" foams can be visualized with sufficient resolution to obtain the size and shape of cells, as well as their spatial distribution within specimens. Statistics of cell sizes have been calculated from NMR microscopy and are in good agreement with results obtained from electron microscopy. We demonstrate that the local density of foams, which are parameters largely inaccessible by other analytical methods, readily can be determined by NMR microscopy.

Construction Materials↗
PubMedDate not supplied

Selective adsorption of serum albumin on biomedical polyurethanes modified by a poly(ethylene oxide) coupling-polymer with cibacron blue (F3G-A) endgroups.

A tri-block-coupling polymer, "PEO-MDI-PEO" ["poly(ethylene oxide)-4,4'-methylene diphenyl diisocyanate-poly(ethylene oxide)", abbreviated "MPEO"], was used to react with a triazine dye, Cibacron Blue F3G-A (ciba), in an alkaline environment. The product of this nucleophilic reaction was a penta-block-coupling polymer, "ciba-PEO-MDI-PEO-ciba" (abbreviated "cibaMPEO"). The cibaMPEO-modified poly(ether urethane) (PEU) surfaces were prepared by dip-coating and detected by XPS. The surface enrichment of both ciba endgroups and poly(ethylene oxide) spacer-arms was revealed. On the modified surfaces, bovine serum albumin (BSA)-adsorbing experiments were carried out, respectively, in the low and high BSA bulk-concentration solutions, and accordingly, the methods of radioactive (125)I-probe and ATR-FTIR were, respectively, employed for the characterization. The competitive adsorption of BSA and bovine serum fibrinogen (Fg) in the BSA-Fg binary solutions was also studied using a (125)I-probe, and through which the reversibly BSA-selective adsorption on cibaMPEO-modified PEU surfaces was confirmed. Finally, the improvement of blood-compatibility on the modified surfaces was verified by the plasma recalcification time (PRT) test.

Adsorption↗
PubMed2003

Short- and long-term releases of fluorocarbons from disposal of polyurethane foam waste.

Several halocarbons having very high global warming or ozone depletion potentials have been used as a blowing agent (BA) for insulation foam in home appliances, such as refrigerators and freezers. Many appliances are shredded after the end of their useful life. Release experiments carried out in the laboratory on insulation foam blown with the blowing agents CFC-11, HCFC-141b, HCF-134fa, and HFC-245fa revealed that not all blowing agents are released during a 6-week period following the shredding process. The experiments confirmed the hypothesis that the release could be divided into three segments: By shredding foam panels, a proportion of the closed cells is either split or damaged to a degree allowing for a sudden release of the contained atmosphere in the cell (the instantaneous release). Cells adjacent to the cut surface may be only slightly damaged by tiny cracks or holes allowing a relative slow release of the BA to the surroundings (the short-term release). A significant portion of the cells in the foam particle will be unaffected and only allows release governed by slow diffusion through the PUR cell wall (the long-term release). The magnitude of the releases is for all three types highly dependent on how fine the foam is shredded. The residual blowing agent remaining after the 6-week period may be very slowly released if the integrity of the foam particles with respect to diffusion properties is kept after disposal of the foam waste on landfills. It is shown by setting up a national model simulating the BA releases following decommissioning of used domestic refrigerators/freezers in the United States that the release patterns are highly dependent on how the appliances are shredded.

Air Movements↗
PubMed2006

Influence of single versus double hydrogen-bonding motif on the crystallization and morphology of self-assembling carbamates with alkyl side chains: model system for polyurethanes.

The difference in the morphology and crystallization aspects of hydrogen-bond-mediated self-assembling systems with single and double hydrogen-bonding motifs is studied here with carbamates as an example. These carbamates have alkyl side chains of various lengths, from C(4) to C(18). The biscarbamates with double hydrogen-bonding sites and symmetric substitution of alkyl segments show a significantly different morphological behavior as compared to the N-octadecyl carbamate alkyl esters (ref 5, referred to as simple carbamates henceforth) with a single hydrogen-bond motif and asymmetric substitution of alkyl side chains. In contrast to the simple carbamates in which no significant difference was found in the spherulite size from C(4) to C(12), with the biscarbamates we find that the spherulitic size, rate of growth of spherulites, and rate of crystallization show a maximum with an alkyl chain length of C(8). This is rationalized in terms of the relative contributions of the hydrogen-bond and van der Waals interaction energies. Oriented X-ray diffraction patterns from the fibrils of the spherulites lead to a model for the growth patterns of the hydrogen-bond planes and the molecular orientation in the spherulites.

Carbamates↗
PubMed1986

Severe fibrous epicarditis after microporous polyurethane (Mitrathane) cardiac patch implantation.

Several materials have been used for pericardial closure after open heart surgery. Mitrathane is a recently introduced material designed for use in the cardiovascular system. A case of severe epicarditis after implantation of a Mitrathane cardiac patch for pericardial closure is presented. This epicardial reaction rendered the exposure of the heart at reoperation extremely difficult. This is a complication not reported to date with this new material. Thus, careful evaluation of Mitrathane is needed before extending its use to larger series.

Adult↗