Polyurethane Specimens Research Articles

TSC/RMA study on the depolarization transitions of TDI-based polyurethane elastomers with the variation in NCO/OH content

Thermal behaviors of TDI-based polyurethanes were studied viz. depolarization relaxation transitions by TSC/RMA technique. Two relaxation transitions in T g region were found. One is the T g transition. The other, T global, is the relaxation transition of global nature and dominated by the hard TDI-MOCA segment in an amorphous phase. The observed T g is shifted from the cooperative motion of urethanic matrix dominated by the soft segment to the relaxation transition of the entire global molecular structure. As a result, a merged and widen T g transition range was observed in TSC with supportive observations of a broadened DSC curve for the same specimens. This widened T g transition was further analyzed by thermal windowing technique of RMA. Increases in the following T g temperature ranges of 25°C (−50°C to −25°C), 50°C (−50°C to 0°C), 55°C (−50°C to 5°C) and 60°C (−50°C to 10°C) for 1.6, 2.4, 2.8 and 3.2 NCO/OH ratio specimens were detected in the RMA spectra. The compensation parameters ( T c, log τ c) of polyurethane specimens in order of NCO content are (10.1, −2.85); (39.6, −3.08), (51.8, −3.71) and (85.8, −4.49) for NCO/OH ratios 1.6, 2.4, 2.8 and 3.2, respectively. The T global transition was observed and in association with tangent δ in the DMA measurement.

Gelatin Increases Adherence of Polyurethane Vascular Grafts to Glass Slides

Because polyurethane vascular grafts adhere poorly to glass slides, we investigated the effects of gelatin treatment of the specimen on slide adhesion. Adhesion artifacts seen on glass slides pretreated with gelatin were compared to the number of artifacts seen with untreated glass slides, poly-L-lysine coated slides. and ChernMate slides. Pretreatment with gelatin diminished the number of major and minor artifacts seen on glass slides. Poly-L-lysine coated slides exhibited few major but many minor artifacts. ChemMate slides had the fewest number of major artifacts but had many minor artifacts, comparable to glass slides pretreated with gelatin. There was no significant effect of tissue thickness on the number of artifacts. Inclusion of gelatin in the water bath is a cost-effective treatment to obtain satisfactory routine histology of polyurethane specimens. (The J Histotechnol 21:245–247, 1998)

Crystallinity and morphology of segmented polyurethanes with different soft-segment length

A series of polycaprolactone/4,4′-diphenylmethane diisocyanate/1,4-butanediol (PCL/MDI/BDO) segmented polyurethanes of different compositions was synthesized by solution polymerization. The molecular weight of PCL diols used was in the range of 1600–7000. The crystallinity and morphology of these polymers were studied by using DSC, dynamic mechanical analysis, WAXD, and polarizing microscopy methods. It was found that the crystallinity of PCL prepolymers was depressed in segmented polyurethanes. A lower limit of PCL molecular weight was found, below which the PCL segments were not able to crystallize at the usual processing conditions. This limit of molecular weight is in the range of 2000–3000 and exhibits a slight increase with increasing hard-segment content of polyurethanes. The glass transition temperature related to the PCL segment regions in polyurethane specimens deviated from that of pure amorphous PCL prepolymer to a higher temperature. The deviation resulted from the crystallization of PCL segments and also the influence of hard segments. The formation of hard-segment domains becomes very difficult for polyurethanes having low hard-segment content and short hard-segment length. There is a lower limit of hard-segment content and segment length. Only above that limit do the polyurethanes have enough hard-segment domains acting as physical crosslinks at temperatures above the melting point of the PCL crystals. The structural characteristics of segmented polyurethanes which may exhibit a shape memory effect are also discussed. © 1996 John Wiley & Sons, Inc.

Effects of degeneration on the elastic modulus distribution in the lumbar intervertebral disc.

Local elastic moduli of sliced intervertebral disc specimens were studied after establishing the relation between the elastic modulus and indentation behaviors by model tests using polyurethane specimens. This study presents a method to quantify the distribution of compressive elastic moduli in the lumbar intervertebral disc and to clarify the effects of degeneration on the distribution. No study has been performed to evaluate the distribution of axial compressive elastic moduli, which is supposed to relate previous biomechanical, biological, and biochemical findings regarding the intervertebral disc. Local compressive elastic moduli of the intervertebral disc were estimated by indentation tests. To evaluate the distribution of elastic moduli, indentation tests were performed at nodal points of a 10 mm x 10 mm network on a specimen. Nine cadaveric lumbar discs (L3-L4 and L4-L5) with various degrees of degeneration were tested. The age of subjects ranged 39 to 90 years (mean, 58.4 years). The distribution of elastic moduli in normal discs was symmetric about the midsagittal plane. The mean elastic modulus in the nucleus pulposus was 5.8 kPa and those of the anterior and posterior anulus fibrosus were 110.7 and 75.8 kPa, respectively. The elastic moduli in the lateral portions were the lowest in the normal anulus, and were close to the values of the nucleus. Compared to normal discs, degenerated discs showed irregular distributions of elastic moduli. The elastic moduli of the degenerated nucleus were higher than those in normal discs. The distribution of elastic moduli is much different between discs with and without degeneration.

Microwave Plasma Reactions of Imidazole on Polyurethane Elastomer Surfaces: A Spectroscopic Study

Recently initiated studies concerning surface modifications of poly(dimethylsiloxanes) using microwave plasmons were extended to polyurethane (PU) surfaces. However, when the same experimental conditions used in the closed and open flow microwave plasma reactors were applied, no chemical bonding of imidazole molecules to PU surfaces was detected. In order to facilitate the imidazole−urethane surface reactions, PU specimens were immersed in an imidazole-containing methylene chloride solution and exposed to Ar microwave plasmons. This approach appears to be successful in creating chemically stable imidazole species attached to PU surfaces. Imidazole molecules are bonded to PU surfaces through the CN bond opening of imidazole, to create C−O−C surface bonds. Analysis of the imidazole−urethane linkages was accomplished using attenuated total reflectance Fourier transform infrared spectroscopy and revealed that the same surface structures on PU surfaces, but different concentration levels of imidazole at variou...

Accurate Real Area of Contact Measurements on Polyurethane

Theoretical models describing the contact of rough surfaces have been developed for at least three decades. Experimental verification, however, has not been straightforward up till now, since current measurements suffer from large inaccuracies, often 100 percent or worse. In this paper a new method, based on autofocus techniques, is applied with an accuracy better than 15 percent. Measurements are presented for the contact of a rough polyurethane specimen in contact with a smooth glass plate. It was not yet possible to conclude whether the real area of contact is proportional to the contact load, but the results show the forming of contact agglomerations, which becomes significant at 10 percent real area of contact. Asperity interaction appears to be important, even at low loads. However, one or both of these facts are often not considered in present contact models, questioning their reliability.

Biostability of a non-ether polyurethane.

A new type of medical grade polyurethane elastomer, based upon an ether-free macroglycol, has been developed by VASCOR, Inc. Prior research conducted by others has indicated that an ether-free urethane should be inherently immune to biodegradation and environmental stress cracking. Specimens of the experimental polyurethane, along with positive and negative control materials, were formed into tubing, mounted on mandrels, and implanted in rabbits. After being exposed to the in vivo environment for six months, the specimens were explanted and examined with scanning electron microscopy. No indication of degradation was observed in the experimental polymer or negative control specimens, whereas severe microcracking was seen in most of the positive control specimens.

Viscous properties of solutions of branched polyurethanes

It has been ascertained that branches in polyurethane (PU), having a length commensurate with the length of the linear section of the macromolecule, cause the effect that the viscosity of solutions of such polymers is reduced in the concentration region up to 20 wt.%. It has been established that, for the solutions of the polyetherurethanureas investigated, this reduction in viscosity agrees with theoretically calculated values. It is suggested that the nature of the rigid block polymer affects the viscous properties of PU solutions. It has been shown that, for PU solutions, the character of the flow curves is connected with the structure of the polymer chains. It is suggested that the form of the flow curve depends upon the molecular weight distribution of the polymer for linear PU specimens under certain conditions.

Flow Through a Deformable Porous Material

A model is presented to describe the one-dimensional flow of an incompressible fluid through a deformable porous material. The model is based on the Forchheimer extension of the Darcy law for flows through incompressible media, where the Forchheimer coefficients are functions of the local stress. Experiments to determine the stress-dependence of the coefficients for polyurethane foam specimens are described. The coefficients are then used in the model to predict the mass flow rate through long polyurethane specimens as a function of the applied pressure difference across the material. The predictions of the model are compared with experimental observations.

Kinetics of acoustic drying of capillary-porous materials

Investigations have been made of the drying of quartz sand and specimens of foam polyurethane in an acoustic field. The layerwise distribution of moisture and temperature during elimination of moisture is given.