Elastomeric Sealants Research Articles

Crack Length of Elastomeric Sealants and Their Service Life in Contrasting Canadian Climates: Effects of Climate Change.

The longevity of polymer-based sealant and jointing products, including elastomers, significantly depends on the level of exposure to sunlight and joint movement. These factors are particularly crucial in the application of polymers in construction due to their susceptibility to degradation under environmental conditions. For instance, diurnal cycles of contraction and dilation, arising from daily temperature fluctuations, impose significant stress on sealants and joints, impacting their durability over time. The elastic nature of polymeric sealants enables them to endure these cyclic mechanical loads. Athough there is considerable information on sealant durability obtained from laboratory accelerated aging, there is limited knowledge about the effect of climatic factors using historical and projected weather data on the durability and expected service life of these products. This study employed the Shephard crack growth model to predict the performance of sealants in a Canadian context; the crack growth and time-to-failure of hypothetical silicone sealants were investigated across 564 locations, for which historical climate data were obtained from 1998 to 2017, including gridded reanalysis data for the period of 1836-2015. The historical climate data were classified into four climate categories, and crack growth was estimated based on historical climatic data within the valid range for the Shephard model, revealing that locations in colder climates with lower levels of precipitation typically exhibit higher cumulative crack growth. The impact of climatic variation and environmental stressors on the longevity of sealants in the context of climate change was also investigated using future projected data.

Effects of Prestrain on the Nonlinear Viscoelastic Properties of a Model Sealant

Abstract Elastomeric sealants are nonlinear viscoelastic materials that exhibit the Mullins effect. As a result, the behavior of a sealant depends on the previous history of strains the sample has seen. To deal with this issue, characterization tests like ASTM C1735, Standard Test Method for Measuring the Time Dependent Modulus of Sealants Using Stress Relaxation, subject the specimen to a specific strain history before measuring properties. To gain a better understanding of this history effect, this article studied a model sealant where the nonlinear viscoelastic properties were measured after a variety of strain histories ranging from no exposure to strain before the test to the history specified in ASTM C1735. The results provide insight into how strain history affects properties, supports information for the ASTM characterization test, and adds knowledge on the nature of the Mullins effect.

Failure of elastomeric sealants under tension and shear: Experiments and analysis

The mechanical behaviour of two elastomeric fuel tank sealants was investigated. Laboratory tests were conducted on two sealants, an epoxy cured polythioether and a manganese cured polysulfide. Tensile, planar tension and torsion tests were performed to characterize and understand the response of the sealants under quasi-static loading. Single lap joint tests in tension were also carried out using four different sealant layer thicknesses and two types of adherend (aluminium and steel). The adherends were either primed with an epoxy primer or otherwise conventionally treated (e.g. grit blasted). Experimental results showed a decrease in joint strength with increasing sealant layer thickness. Emphasis was given to the understanding of the failure and the prediction of the strength of the single lap joints. Predicted failure loads were derived by analytical calculations and finite element simulation of the joints.

The Mechanism of Adhesion Improvement of Elastomeric Silicone Sealants to Difficult-to-Bond Polymeric Substrates through Reactive or Interpenetrating Molecular Brushes

Abstract High-quality and durable adhesion of elastomeric adhesives to metallic, ceramic, and organic substrates is essential to a broad range of industries, e.g., building and construction, automotive, electronic, aerospace, biomedical, and others. The principles of engineering substrate surfaces through grafted connector molecules are discussed in this paper. In particular, two important modes of interaction for surface-grafted “molecular brushes” are investigated and experimentally verified. It is demonstrated that the inclusion of silicone- and/or amine-terminated graft molecules, such as silanes or polyethyleneimines, at polymer interfaces, results in the formation of strong molecular bridges between a range of organic substrates and elastomeric sealants leading to significantly improved bonding. The technology has been successfully adopted by global automotive industry for improving adhesion of a variety of adhesives and coatings to polyolefinic substrates.

Substrate Durability Guidelines Used in Silicone Structural Attachment

Abstract This paper sets forth a procedure for evaluating substrates for durability for use in conjunction with structural silicone glazing (SSG). Lap shear and peel adhesion specimens are evaluated after exposures to various conditions using a modified ASTM C794-06, “Standard Test Method for Adhesion-In-Peel of Elastomeric Joint Sealants,” and ASTM C961-06, “Standard Test Method for Lap Shear Strength of Sealants.” Conditions of exposure include water, sodium hypochlorite (bleach), acetic acid (vinegar), salt fog, UV florescent accelerated weathering device (UVFl), ultraviolet light (UV) exposure, and heat. Evaluation of substrates and the interfaces are completed after tensile testing and visual surface analysis. The silicone structural glazing adhesive used in this evaluation is a high modulus high strength material intended to place the maximum load at the interface. Substrates evaluated include steel, anodized aluminum, galvanized steel, extruded rigid polyvinyl chloride (PVC), glass reinforced thermoplastic resin (fiberglass), and polyvinylidene fluoride (PVDF) painted aluminum. These evaluated substrates are tested to this procedure to show differences in performance and suggest a minimum time frame required for testing. The results and guidelines set forth in this paper provide the foundation for a practice and or a substrate specification for use in conjunction with structural silicone attachment methods.

Tendencies in the application of elastomeric sealants in aircraft construction and prospects of the improvement of their properties

Results of the application of sealants based on polysulfide and organosilicon elastomers developed in VIAM are reported. Methods for the considerable improvement of their properties in view of developing sealants of new generation are demonstrated.

Analysis of the Effects of Interference and Sealant on Riveted Lap Joints

Much of the fatigue damage in aircraft structures can be linked to the stress concentration arising at the rivet/skin interface in fuselage lap joints. Fatigue damage can degrade the strength of the structure and reduce structural integrity. Elastomeric adhesives and sealants are applied to the lap joints before riveting to prevent entry of moisture, thus, preventing corrosion. The effect of the sealant on the residual stress state resulting from the rivet interference and subsequent load transfer has not been investigated. A three-dimensional finite element model of the riveting process is simulated to determine the effects of interference and sealant on the induced stresses. Both implicit and explicit finite element techniques are utilized to model the process. The finite element simulation is validated initially for both techniques with experiment. The analysis with sealant shows an increase in the residual hoop stress for the majority of the cases in comparison to the results without sealant.

建築用シーリング材

建築用シーリング材

Silyl-Terminated Polyurethanes for Construction Sealants

Abstract Construction sealants produced through the curing of silyl-terminated oligomers (STO) display properties similar to conventional polyurethanes, but they possess several distinct advantages. This paper provides a state-of-the-art review of silane-functional polymers for sealants in construction. Properties of silyl-terminated polyurethanes (STPU) are compared with traditional polyurethanes as well as silyl-terminated polyether (STPE) sealants. Urethane prepolymers, prepared from the reaction of a diisocyanate and a conventional polyol, are end-capped with an organo-functional silane. As a consequence, there are no free isocyanate molecules in the sealant. These sealants show improved adhesion to glass, UV stability, and weatherability. Sealants based on STPU chemistry are presently in use for industrial and transportation applications, which require medium to high modulus. Current work explores methods to reduce the modulus and increase elongation while retaining good cohesive properties. STPU sealants have been prepared with varying isocyanates, polyols, and silanes. They have been evaluated in accordance with several ASTM tests, including those in the ASTM Standard Specification for Elastomeric Joint Sealants (C920). The glass-transition temperatures and rheological characterizations of STO-based sealants are presented. Correlations are made between these fundamental material properties and the sealant's behavior in use, as measured by ASTM test methods. These measurements could provide a method for identifying candidate formulations that are expected to pass more extensive ASTM testing. These material characterizations as well as the results of mechanical property testing are compared for selected STPU, STPE, polyurethane, and silicone sealants.

Application of extreme value analysis to crevice corrosion

Extreme value statistics have been applied to the crevice corrosion front that advances under elastomeric seals to aluminum surfaces. The exponential cumulative extreme value distribution provided an accurate description of the distribution of corrosion fronts quantified by tracing. Extreme value analysis can be applied to seals of small test samples to estimate the most probable maximum corroded depths of larger structures and, thereby, required seal widths. Variations in the calculated most probable maximum corroded depths introduced by subjectivity in tracing are considered. Crevice corrosion kinetics were determined using sets of fixtures salt spray tested for 2–60 days. These fixtures were assembled with 2024-T3 or 380 cast aluminum and silicone adhesive, ethylene–propylene–diene monomer, or Viton rubber elastomeric sealants. An empirical power law function was used to model the most probable maximum corroded depth under the seals versus test time. For tight seals to smooth surfaces, the dependence on time varied as t p with p=0.35–0.40, which is similar to the time dependence obtained in pitting corrosion studies.

Standard operating procedure (SOP) for the quantitative determination of organic silicon compounds at the surface of elastomeric sealants

Elastomeric sealants may contain organic silicon compounds. The use of these sealants for housings for electronic components is harmful for the reliability of electric contacts inside. In order to prevent electronic components from malfunction, quality control of elastomeric sealants is required. An analytical procedure developed to fulfil this requirement was developed. It is based on electron spectroscopy for chemical analysis (ESCA). Information on the silicon compounds existing at the surface of elastomeric sealants is provided by this method. Silicon in organic and inorganic compounds can be differentiated with the help of Si 2p photoelectron spectra. Quantitative results can be obtained too. The uncertainty budget of the quantitative procedure is estimated.

Monitoring crosslinking and polymerization of elastomeric adhesives and sealants by dynamic mechanical analysis at 100 kHz

A technique has been developed for measuring the stiffness and damping of a thin layer of sealant, encapsulant, or adhesive as it goes through the chemical processes of polymerization and crosslinking at various temperatures, and transforms from the liquid to solid state. The technique can be used to study elastomeric liquids since high frequency vibrations (100 kHz) are used so that viscoelastic changes and crosslinking can be followed even in the liquid state. The method allows us to monitor polymerization as well as crosslinking, related to E″ and E′ respectively, and can only be determined if both stiffness and phase are measured. The equipment can be used for either technological or research applications.

Cure of elastomeric building sealants

AbstractThe cure of a range of elastomeric building sealants is investigated by measuring tack‐free time and hardness under a range of laboratory test regimes and under natural exposure. Temperature, relative humidity and ultraviolet light were noted to have an interactive effect on cure, although the influence of these factors varied between the different sealant types studied. The investigation identifies laboratory conditions which are favourable to cure, and these are compared with cure conditions specified in standard tests.

Chemistry and Technology of Polysulfide Sealants

Abstract The highly reactive terminal mercaptans of liquid polysulfide polymers can be converted into high molecular weight products very easily at ambient temperatures by oxidation or by reaction with other active polymers. Polysulfides have excellent solvent resistance, predictable cure, good low-temperature performance, good weathering, and excellent adhesion to many substrates. This combination of properties has given polysulfide polymers a modest but significant position as specialty polymers since their commercialization in 1929. Polysulfide sealants have found wide acceptance in industries, e.g., construction, aircraft, automotive, marine, and insulating glass. In fact, polysulfide sealants were the first elastomeric sealants used in the construction industry and continue today, to a large extent, the standard against which other sealants are compared. Polysulfide sealants, although facing strong challenges by silicones and polyurethanes, continue to be the dominant segment of the elastomeric sealant market [1–6].

Sealants for solar collectors

Elastomeric sealants employed in thermal solar collectors are subjected to extremely harsh conditions. In order to function properly for long periods of time, they must exhibit good resistance to environmental factors such as high and low temperature extremes, oxygen, ozone, water, and ultraviolet radiation. Several types of candidate elastomers consisting of fluorocarbon, silicone, acrylic, ethylene-acrylic, ethylene-propylene terpolymer, and butyl and chlorosulfonated polyethylene were subjected to extensive testing. Results are reported on outgassing characteristics during thermal aging and on retention of such physical properties as compression set, elongation, and tensile strength. Relative hydrolytic stabilities of these materials are also discussed. 1 ref.

The Use of Elastomeric Sealants in Concrete Paving

Close observation indicates that a very substantial number of reported adhesive failures in elastomeric pavement joint sealants are actually the result of concrete failure by spalling. This spalling can be reduced by more careful protection and preparation of the substrate. This paper is a critical evaluation of past performance with close examination of reasons for failures and design proposals for improved performance, resulting in superior, long range concrete paving performance.

Metering High Viscosity Elastomers

This article describes processing equipment for elastoplastics. Equipment models described are in production on such applications as construction application for deck coatings and pavement joint sealing, elastomer moldmaking, encapsulation of electrical and electronic devices. Advances are being rapidly made in other industries, too. Automobile manufacturers, for example, are installing windshields and back lights with a polysulfide material, replacing the conventional rubber gasket. Aircraft manufacturers operate central “Sealant Cribs” to supply in-plant locations with elastomeric sealants for sealing of integral fuel tanks. With manufacturers guaranteeing product performance for 5 and 10 years, automatic metering and mixing equipment is becoming an integral part of the manufacturing process in many industries.

Hydrofluorocarbon High-Temperature Integral Fuel Tank Sealants

Abstract Supersonic aircraft in the Mach 3 range have increased temperature requirements for many materials of construction. One of the most critical problem areas is the integral fuel tank where state-of-the-art elastomeric sealants no longer meet those requirements. New sealants resistant to hydrocarbon fuels at temperatures in excess of 500° F are urgently needed. A high temperature integral fuel tank filleting sealant has been developed based on a mixture of high and low molecular weight hydrofluoroearbon polymers. This sealant has a solids content of 85 per cent and cures at modest temperatures. It is a one component system stable for several weeks at ambient temperatures and for longer periods if refrigerated. The sealant exhibits good room temperature and high temperature mechanical properties both before and after aging in hydrocarbon fuel and fuel vapor at temperatures up to 500° F. A typical formulation showed an increase in tensile strength and better than 50 per cent retention of elongation after 1000 continuous hours exposure to fuel vapor at 500° F. Adhesion to metal substrates is good and samples have resisted rupture and loss of adhesion when pressurized at 500° F for 1000 hours. This is only an interim solution to the critical fuel tank sealant problem in Mach 3 aircraft. Research is continuing to improve its useable life and to eliminate a possibly serious corrosion problem with titanium substrates. It must be emphasized, however, that sealants based on hydrofluorocarbons, fluorosilicones, and other available elastomers can at best provide interim solutions to the high temperature sealant problems and that new base polymers, such as the triazine and polyether elastomers currently being developed by the Air Force Materials Laboratory, are needed to provide sealants which completely meet requirements.