Degradation Of Sealant Research Articles

Novel synthetic adhesive as an effective alternative to Fibrin based adhesives.

AIMTo compare a novel, fully synthetic, polyurethane based glue (MAR-1) to fibrin sealant in a partial liver resection rat model.METHODSAfter 50% resection of the lateral left liver lobe in male Wistar rats (n = 7/group/time point), MAR-1, Fibrin or NaCl was applied. After 14, 21 and 90 postoperative days, sealant degradation, intra-abdominal adhesions were scored, and histological examination of liver tissue was performed.RESULTS(Mean ± SEM) (MAR-1 vs Fibrin vs NaCl). Bleeding mass was significantly higher in NaCl (3.36 ± 0.51 g) compared to MAR-1 (1.44 ± 0.40 g) and Fibrin (1.16 ± 0.32 g). At 14 and 90 d, bleeding time was significantly lower in MAR-1 (6.00 ± 0.9 s; 13.57 ± 3.22 s) and Fibrin (3.00 ± 0.44 s; 22.2 ± 9.75 s) compared to NaCl (158.16 ± 11.36 s; 127.5 ± 23.3 s). ALT levels were significantly higher in MAR-1 (27.66 ± 1 U/L) compared to Fibrin (24.16 ± 0.98 U/L) and NaCl (23.85 ± 0.80 U/L). Intrabdominal adhesions were significantly lower in MAR-1 (11.22% ± 5.5%) compared to NaCl (58.57% ± 11.83%). Degradation of the glue was observed and MAR-1 showed almost no traces of glue in the abdominal cavity as compared to the Fibrin (10% ± 5% 14 d; 7% ± 3% 21 d). Survival showed no significant differences between the groups.CONCLUSIONCompared to Fibrin, MAR-1 showed similar hemostatic properties, no adverse effects, and is biocompatible. Further studies on adhesion strength and biodegradability of synthetic sealants are warranted.

Shock releases bile acidinducing platelet inhibition and fibrinolysis

BackgroundMetabolites are underappreciated for their effect on coagulation. Taurocholic acid (TUCA), a bile acid, has been shown to regulate cellular activity and promote fibrin sealant degradation. We hypothesize that TUCA impairs whole blood clot formation and promotes fibrinolysis. MethodsTUCA was exogenously added to whole blood obtained from volunteers. A titration from 250 μM–750 μM was used due to biologic relevance. Whole blood mixtures were assayed using thrombelastography for clot strength (maximum amplitude [MA]) and fibrinolysis (LY30) quantification. Tranexamic acid was used to block plasmin-mediated fibrinolysis. Platelet microfluidics were performed. A proteomic analysis was completed on citrated plasma obtained from a shock and resuscitation rat model. ResultsFibrinolysis increased when 750-μM TUCA was added to whole blood (median LY30 0.08–5.7, P = 0.010) and clot strength decreased (median MA of 53.3–43.8, P = 0.010). The addition of tranexamic acid, to a 750-μM TUCA titration, partially reversed the induced fibrinolysis (LY30: without 7.7 versus with 2.7) and the decrease in clot strength (MA: without 48.2 versus with 53.2), but did not reverse the effects to whole blood levels. Platelet function reduced by 50% in the presence of 100-μM TUCA. Rats had a median 52-fold increase in TUCA, after a shock state that stayed elevated after resuscitation. ConclusionsTUCA reduces clot strength and promotes fibrinolysis. The clot strength reduction is attributable to platelet inhibition. This metabolic effect on coagulation warrants further investigation, as localized areas of the body, with high levels of bile acid, may be at risk for postoperative bleeding.

Experimental Evaluation of Planar SOFC Single Unit Cell With Crofer22APU Plate Assembly

This paper describes an experimental analysis of a planar solid oxide fuel cell (SOFC) single unit cell with Crofer22APU plate assembly. The work reports the electrical behavior of such a system by outlining the time-evolution of contact resistances between the air electrode and the stainless steel plate. Moreover, the stability and effectiveness of a glass-ceramic sealant used to join Crofer22APU interconnector to an anode supported cell is also discussed. The time-evolution of the open circuit voltage was investigated with respect to the eventual sealant degradation or chromium poisoning issues by the metallic interconnector; a rapid voltage degradation at open circuit voltage was measured after 150 h. Chromium poisoning was found to degrade the fuel cell performance, whereas the sealant was chemically and physically stable, as shown by a post-mortem analysis on the cell components.

Novel thin wire paint and sealant degradation sensor

Very thin corrosion sensors have been developed to detect the degradation of paints and sealants and for application in bolts and joints to detect the ingress of the environment due to failure of corrosion protection coatings. The sensors are based on thin insulated wires that have had the insulation removed over small regions by laser micro-machining. The sensors can be interrogated with very simple instrumentation, such as an Ohm meter, however, in this paper we have used a low power, networked sensor interface developed at the Defence Science and Technology Organisation. This paper presents the fabrication of the sensors, theoretical sensor responses and experimental results from sensors deployed on bare metal and under paint, and then exposed to salt water.

Study of Weatherability of Construction Sealants with Novel Testing Method

Abstract Although construction sealants are used for all kinds of construction joints such as static joints with little movement, dynamic joints with thermal or seismically induced movement, and so on, the general test methods employed in the evaluation of the weatherability of construction joint are based on weathering test without movement. In November of 2000, AIJ (Architectural Institute of Japan) established a subcommittee chartered with developing an accelerated weathering test method, which enables the determination of the durability of waterproofing materials and sealants. In this activity, we evaluated the weatherability of sealants with a new test method using newly developed test specimens, which enable exposing the cured sealants to compression and extension at the same time in a single test specimen. In this paper, we report the interim test results, which cover twelve months of natural weathering and 3500 hours artificial weathering with xenon lamp and carbon flame weathering device. In this evaluation, we confirm that the surface degradation of sealants is accelerated by the additional movement cycles, and the differences in the degradation among the sealants are becoming observable.

Artificial Weathering and Cyclic Movement Test Results Based on the RILEM TC139-DBS Durability Test Method for Construction Sealants

Abstract The purpose of this study was to assess the effect of artificial weathering and cyclic movement in a laboratory test based on the RILEM Technical Recommendation (RTR) “Durability Test Method for Curtain Wall Joint Sealants.” Eleven sealants being used in Japan were tested, including two silicones, two silicon-modified polyethers, two polysulfides, two polyurethanes — each as one- and two-part products — one two-part silicon-modified polyisobutylene, one two-part urethane cure acrylic, and one one-part water-borne acrylic. The two-part polyurethane, the two-part urethane-cure acrylic, and the one-part water-borne acrylic were also evaluated with and without painting the sealant surface. Test specimens were prepared using anodized aluminum and mortar as substrate materials; primers were used for all sealant/substrate combinations as recommended by the manufacturers. All sealant specimens were conditioned according to Method A. The durability test, consisting of weathering and thermo-mechanical cycling, was carried out both with and without the influence of fatigue cycling. The durability cycles were repeated three times. Weathering was conducted in a fully automatic weathering machine using a xenon arc light source. Sealants without painting were observed to chalk and craze at an earlier stage in the durability cycles than the ones with painted surfaces, confirming the effectiveness of painting the sealant surface in protecting organic sealants from aging. A substantial difference in the behavior of sealants was observed for exposures with and without fatigue cycling, confirming the importance of fatigue cycling in the degradation of sealants. In order to obtain a good correlation between accelerated weathering and actual service performance, a proper balance of degradation factors is essential.

Experimental results obtained with proposed RILEM durability test method for curtain wall sealants

Over the past six year, RILEM TC 139-DBS has been developing a RILEM Technical Recommendation (RTR) for a durability test method for curtain wall joint sealants. As the committee started to converge towards the final test method, the importance of evaluating the behaviour of a set of sealants under comparative conditions became apparent in order to validate the proposed durability test method. This paper provides a summary of the results obtained with the procedure described in the April 1999 draft. The study shows that the test method is able to differentiate between products with regard to their resistance to accelerated ageing and mechanical cycling. The type of failure and the changes in surface appearance obseved during the test regime are similar to those observed in actual service conditions. Sealant degradation resulting from the durability cycles was slower than had been anticipated for most sealant systems. The dynamic conditioning procedure (movement during cure) reduced joint durability for some of the tested products, but increased it for others. The fatigue cycling clearly accelerated sealant degradation.

On-site non-destructive test for sealants

The degradation of sealants is defined as a change in physical properties caused by chemical reaction involving bond breaking in the backbone of macromolecules, and hence causes deterioration in the functionality of the polymeric material properties, such as elastic recovery and hardness. Currently, there is still no successful technique of determining the elastic recovery of in-situ sealant on building facades. Specifications and standards available are basically concerned with quality control in the manufacturing, and testing of new formulated products, and the design and application of sealants. They do not reflect and give adequate indications of the status of working sealants. Furthermore, the conventional laboratory testing techniques are tedious, time consuming and often destructive, which make them unsuitable for in-situ testing. This paper discusses the development of an on-site non-destructive testing technique to assess the performance of sealants on building facades. Assessment was made of the sensitivity, reliability and applicability of the tester. This is achieved by carrying out tests on various generic types of high-performance sealants subjected to natural and artificial weathering.

Sealant Degradation during Crack Sealing of Pavements

Application practices of bituminous hot-poured crack sealants, typically used to effect repairs on pavements, were monitored in the field and heating conditions were reproduced in the laboratory. From viscometry, thermogravimetry, and tensile testing measurements, it was found that sealants degrade upon heating at recommended installation temperatures. Consequently, given the level of product degradation observed from laboratory evaluations, it is not expected that a consistent low temperature sealant performance could be obtained in the field. These conclusions help explain the number of premature sealant failures that exist despite the fact that these materials may be in accordance with the requirements in ASTM D 3405.

Applicability of infrared spectroscopy for sealant degradation studies

The degradation under various accelerated weathering conditions of one and two part polyurethane, one and two part polysulphide was studied using FTIR spectroscopy. Sealants cast in rectangular aluminium moulds were exposed to various accelerated weathering conditions. FTIR spectra and elastic recovery were monitored up to 35 days. For polyurethane (one and two parts), the FTIR spectra show that the degradation of sealant as indicated by the reduction of elastic recovery could be due to hydrolysis of urethane linkage and chain degradation. On the other hand, polysulphide (one and two parts) degraded extensively with the formation of epoxy ring and broadening of CH2 deformation band indicating chain degradation.

Evaluation of Sealands Using Infrared Spectroscopy

High performance sealants are widely used in joints of curtain walling on building facades. Although highly polymeric, these sealants are susceptible to degradation due to environmental factors such as ultraviolet, moisture, heat and others. The most important property being the mechanical elastic recovery. The degradation under various accelerated weathering conditions of one and two part polyurethane, one and two part polysulphide was studied using Fourier Transform Infrared Spectroscopy (FTIR) spectroscopy. Sealants were cast in a rectangular aluminium mould and cured under ambient conditions. The sealants were then exposed to four accelerated weathering conditions, namely weatherometer (QUV), oven aging at 70°C, water immersion at 25°C and 70°C. FTIR spectra and elastic recovery were taken at a time up to 35 days. The results show considerable degradation and reduction in elastic recovery after weathering. For polyurethane (one and two parts), the FTIR spectra show that the degradation of sealant as indicated by the reduction of elastic recovery could be due to hydrolysis of urethane linkage and chain degradation. On the other hand, polysulphide (one and two parts) degraded extensively with the formation of epoxy ring and broadening of CH2 deformation band indicating chain degradation.

Organic Curing Agents for Polysulfide Sealants. III. A Mechanistic Interpretation of the Thermal Degradation of Nitrile Oxide-Cured Polysulfide Sealants

Sealants obtained by cure of polysulfide liquid polymers with aryl bis ( nitrile oxides) possess the thiohydroximic acid ester structural feature. Unexpectedly these materials were found to exhibit poor thermal stability: when heated at 60° they soften within days and liquefy in 3 weeks. Products obtained with excess nitrile oxide degraded faster than those produced with equimolar amounts of reagents. Interpretations considered included (A) dissociation of the thiohydroximic acid group, (B) reaction between nitrile oxide and a reactive centre in the polysulfide structure, and (c) addition of nitrile oxide to the side chain. It was shown that neither of the first two possibilities was applicable. Moreover, spectroscopic studies demonstrated that, after an initial rapid addition between nitrile oxide and thiol , a second slower reaction occurred which consumed additional nitrile oxide. Although aldehyde oximes and a- chloro oximes do not participate in such processes unless catalysts are present, thiohydroximic acid derivatives were shown to react with nitrile oxides at ambient temperature to form 1,2,4-oxadiazole 4-oxides and alkyl thiol . For the case of a polysulfide sealant the equivalent rupture of a C-S bond to form the thiol involves cleavage of the polymer backbone. Continuation of the process would lead to degradation of the sealant. These observations were supported by thermal analysis studies on the polysulfide sealants and model polymers.