Polysulfide Rubbers Research Articles

Study of modified thermoplastic elastomers based on polyethylene chlorinated with thiokol rubbers

In this paper has been examined the mechanical properties of thermoelastoplastic polymer materials derived from polyethylene chlorinated with secondary polyethylene. In order to ensure the good performance of the thermoelastoplasts obtained in the external environment, attempts were made to increase their resistance to external influences by modifying them with 1% mass of polysulfide rubbers, and resistance to deformation was determined when studying the properties of the polymer material under UV light for 10 hours.

Photocatalytic Disulfide Bond Coupling by Surface-Reduced Manganese Oxide for Controlled Polysulfide-Based Polymer Synthesis

Manganese oxide (MnO2) is a commonly used vulcanizing agent, which can convert polysulfide oligomers with reactive terminal mercaptans into polymeric networks. Herein, an elegant approach for the fast and facile curing behavior of polysulfide rubbers was disclosed under visible-light irradiation. Photocatalytic disulfide bond coupling of mercaptan end groups can be achieved on MnO2 in the presence of visible-light irradiation. More importantly, compared with pristine MnO2, surface-reduced MnO2 (R-MnO2) with abundant Mn3+ sites and oxygen vacancies exhibited superior vulcanizing performance. Theoretical simulation uncovers that R-MnO2 can facilitate electron transfer due to a narrowed energy band gap and reduce the energy barriers required for photocatalytic disulfide bond formation. This work opens up the potential of using visible light together with surface modification to tune the vulcanizing process and the properties of polysulfide rubbers.

Rapid, efficient and controllable photo-assisted polysulfide sealing over MnO2

δ-MnO2 can achieve rapid, efficient and controllable curing performance for liquid polysulfide rubbers via photo-assistance.

INFLUENCE OF DILUENTS AND PLASTICIZERS ON THE PROPERTIES OF EPOXY-POLYSULFIDE COMPOSITES

It was found that to increase the adhesive and physicomechanical properties of compositions based on epoxy resin and polysulfide rubber (thiokol), cured without heat treatment, it is necessary to carry out a preliminary thioetherification reaction (PRTE) due to the interaction of rubber mercaptan groups and oxirane cycles of epoxy resin at elevated temperatures and then use the product of this reaction to cure at room temperature. Composite materials based on the products of the thioetherification reaction significantly surpass analogs based on mechanical mixtures of epoxy resin and thiokol in terms of cohesive and adhesive strength, deformation capacity, fracture work, and specific impact strength. It is shown that the introduction of both diluents and plasticizers into the products of the preliminary thioetherification reaction of epoxy resins and polysulfide rubbers leads to an increase in the parameters of tensile strength and deformation capacity. The greatest strengthening effect is achieved with the use of oligoesteracrylate MGF-9 and glycidyl ether of diethylene glycol DEG-1, the smallest - with the introduction of the plasticizer EDOS. It was found that the introduction of plasticizers promotes some increase in the adhesive strength, but much less in comparison with the cohesive strength. In this case, the adhesion and cohesive characteristics change antibatically. It has been shown by dynamic mechanical spectrometry that the presence of diluents and plasticizers in epoxy-polysulfide composites leads to a decrease in the temperatures of the maximum values of the tangent of the angle of mechanical losses, loss modulus, the initial and final sections of the transition of the material from the glassy to the highly elastic state, as well as the density of the chemical network in the epoxy matrix.

3D Graphene – sponge skeleton reinforced polysulfide rubber nanocomposites with improved electrical and thermal conductivity

As high performance sealants, polysulfide rubbers (PSR) have been extensive used to seal the tanks of aircraft fuel. Disappointingly, it is easy to produce static electricity due to the movement of fuel, resulting in security issue. In this work, a three-dimensional (3D) RGO-PU foam was constructed by using PU sponge as a template and GO together through hydrothermal reduction. Then the polysulfide rubber composites (RGO-PU/PSR) were fabricated by impregnating 3D RGO-PU framework with liquid polysulfide oligomers (LPO) under vacuum assistance, following by heat treatment. The RGO-PU/PSR composites exhibited improved conductive properties than neat PSR. For example, the volume resistivity of the 0.5 wt%-RGO-PU/PSR composites was 2.6 × 106 Ω·cm, which had a conspicuous 5 orders of magnitude decrease compared to neat PSR. The thermal conductivity of RGO-PU/PSR composite was also enhanced to 0.598 W/(m.k), which raised about 153% compared to the value for neat PSR. It was because that the introduction of 3D RGO-PU foam provided a path for electronic transmission and phonons transfer. In addition, the dielectric properties demonstrated that RGO-PU/PSR composites showed a higher dielectric constant than neat PSR. Furthermore, the polysulfide rubber composites also showed greatly improved compression strength and Young’s Modulus.

Functionalized GO/polysulfide rubber composites with excellent comprehensive properties based interfacial optimum design

Polysulfide rubbers (PSR) have been widely used as high performance sealants to line or seal aircraft fuel tanks. In this research, liquid polysulfide oligomers-graphene oxide (LPO-GO) nanocomposite was prepared through the mild reaction between liquid polysulfide oligomers (LPO) and graphene oxide (GO) nanosheets, and was dispersed into PSR to obtain LPO-GO/PSR composites. Benefit from the grafting of polysulfide oligomer segments on the surface of GO, good dispersion of LPO-GO in PSR matrix was achieved. The mechanical properties of PSR composites were enhanced by LPO-GO. The elongation at break and tensile strength of the 0.5% LPO-GO/PSR composites were about 70% and 43% higher than that of neat PSR. The dynamic mechanical thermal analysis (DMTA) results showed that the storage modulus of PSR was increased by 206% when 0.5% of LPO-GO was added. The broadband dielectric spectroscopy (BDS) results indicated that LPO-GO was well dispersed in PSR and some phenomena of molecular chain movement in PSR matrix. Study of the reinforcing mechanism showed that a number of thiol groups and S–S bonds had been attached onto the surface of GO after being modified by LPO, which quietly promoted the dispersion of LPO-GO in PSR matrix and strengthened the interfacial interactions between LPO-GO with PSR.

Processing and characterization of silver-filled conductive polysulfide sealants for aerospace applications.

Polysulfide (PS) rubbers have been widely used as high performance sealants to line or seal aircraft fuel tanks. However, safety concerns arise when electrostatic charges are built up due to the motion of flammable fuels. In this report, electrically conductive sealants were designed in order to dissipate these hazardous charges. Silver fillers with various sizes and surface coatings were incorporated into a polysulfide matrix to make conductive sealants. The low electrical conductivity of the sealants led to the assumption that unique filler-resin interactions occurred at their interfaces. To verify this assumption, various characterization methods were employed to investigate the chemical, thermal, morphological, electrical, and mechanical properties of the sealants. In addition, carbon fillers and other room temperature-cured polymer resins were used for comparative study. The systematic analysis revealed that the formation of coordination compounds at silver/PS interfaces could block electron conduction pathways between fillers. Based on the chemical understanding, post cure thermal annealing was utilized to break the coordinated bonds and restore high conductivity (>106 S m-1) of the sealants. Conductivity change as a function of annealing temperature and time was also explored to optimize processing conditions.

Properties and application of rubber-based sealants

Features of the chemical nature, physical state, hardening mechanism, application technology, properties, and main practical fields of application of sealing and tightening materials based on polysulfide and siloxane rubbers are considered. Brands of domestically produced polysulfide and silicon-organic sealants that gained the greatest distribution in engineering and construction are considered. Different technological sealant application methods used in production and repair of various types of machines and equipment are reviewed.

Modification of epoxy resins with liquid polysulfide and carboxylated butadiene rubbers

In this work, we present the results of studying the effect of liquid carboxylated butadiene and polysulfide rubbers on the physicomechanical and adhesive properties of epoxy adhesive compositions with curing agents of different chemical nature—diethylene triamine and polyoxypropylene triamine. It is found that carboxylated butadiene rubbers are more effective modifiers than polysulfide rubbers because they yield a higher complex of properties. It is also shown that the change in the chemical nature of a curing agent has no significant effect on the properties of epoxy-rubber adhesive compositions, which allows one to control their key technological parameters without fear of losing strength characteristics.

Mold making with room temperature vulcanizing silicone rubber

Specimens of all types and sizes can be molded with room temperature vulcanizing silicone rubber (R.T.V.). Mold making procedures, when using R.T.V., differ little from those followed when molding with latex, polysulfide, or polyurethane rubbers. The most important difference is that when using R.T.V. separators are not, under normal circumstances, required either in the making of the mold or in the production of the cast. This allows for the ultimate in surface detail replication in the cast. Thus R.T.V. compounds are ideal for molding small specimens and portions of larger specimens requiring examination using electron microscopy, typically used in vertebrate paleontology for the examination of micro-striations on teeth (for masticatory functions and dietary studies) or bones (for pathologic and taphonomic examinations).

Time-dependent accuracy of elastomer impression materials. Part II: Polyether, polysulfides, and polyvinylsiloxane

T here are currently four basic types of elastomer impression materials in use in the dental profession: (1) silicone rubbers which polymerize by a condensation reaction, (2) polysulfide (mercaptan) rubbers, (3) polyethers, and (4) silicones which polymerize by an addition reaction. The latter have been introduced relatively recently and are also called polyvinylsiloxanes. The basic properties of these materials have been reviewed by Craig’ and Phillips.’ Two clinical advantages of these materials over reversible and irreversible hydrocolloids are that (1) multiple dies may be made from repetitive pours of a single impression and (2) the clinician can wait for an extended time period to pour the stone cast after making the impression. In addition, elastomers can be metal plated for the production of electrodeposited metal dies. There is disagreement in the literature regarding the superiority of dimensional stability between polysulfide rubbers and condensation silicones.:‘-” Polyether has been suggested as being more dimensionally stable when compared with its predecessors,‘. 7. ” and the polyvinylsiloxanes have recently claimed even superior accuracy and stability over polyethers.‘, ” The purpose of this study was to make a quantitative comparison of the accuracy and dimensional stability of representative products in each class by

Characterization of the setting process in dental polysulfide rubbers.

SYNOPSIS IN INTERLINGUA CHARACTERISATION DEL PROCESSO DEL PRISA IN CAUCHUS DENTAL A POLYSULFURO.—Le characteristicas del prisa de cauchus dental a polysulfuro esseva studiate per viscometria extrusional. Quando le reagente de prisa esseva addite, le fortia extrusional (F) cresceva exponentialmente con le tempore, i.e., F = Aexp(kt). Per contrasto con le situation in alginatos e cauchus a silicona, nulle prestemente identificabile tempore del initiation del processo de prisa esseva trovate. Le parametro k characterisava le intensitate del prisa. Illo dependeva del temperatura, e le energia de activation esseva circa 12 kilo-calorias per mol. Le parametro k esseva relativemente insensibile pro le concentration del reagente de prisa. Isto contrastava marcatemente con le comportamento de cauchus a silicona. Le characteristicas del processo de prisa es explicabile a bases chimic.

Low Temperature Expansion of Polysulfide Rubbers

Abstract A novel method for producing a cellular cured rubber product at room temperature has been developed. Pourable liquid polysulfide polymers are treated with a conventional oxidizing curative and selected water-sensitive or oxidation-sensitive blowing agents. Standing at ambient temperature the viscous liquid mixture gradually “rises” and cures to form a finely porous cellular rubber product. Conventional curatives employed include oxidizing agents such as lead peroxide and cumene hydroperoxide. These convert terminal or pendant thiol groups in the polysulfide polymer chains to chain-connecting disulfide linkages. Water is a byproduct of the curing reaction. In the presence of water-sensitive blowing agents such as, (1) metal salts of azodicarboxylic acid or, (2) metal hydride compounds the water produced in the cure reacts to form copious amounts of nitrogen or of hydrogen. Alternatively, oxidation-sensitive blowing agents such as p, p′-oxybis-(benzene sulfonyl hydrazide) react directly with the oxidizing curative to form nitrogen gas. The blowing reactions are concurrent with cure and efficient and controllable expansion can be achieved. The unique process offers possible economies and special properties in applications of liquid polysulfide rubbers as potting compounds, joint sealants, solvent resistant forms, and cold casting compounds.

Organic Sulfides and Polysulfides. VI. Reactions of Metallic Oxides with Polysulfide Rubbers

Abstract 1. Both mercaptides and disulfides were obtained by the reactions between benzyl mercaptan or tolyl mercaptan with zinc oxide or lead oxide. Qualitatively, mercaptides were formed from benzyl mercaptan easier than from tolyl mercaptan, and lead oxide reacted with mercaptan easier than zinc oxide with mercaptan. From the fact that no metallic sulfide was present, disulfides were likely formed from the oxidation of mercaptans by air. 2. The mono- or disulfides of the benzyl and tolyl series did not react with zinc oxide or lead oxide. 3. Neither tolyl tri- nor tetrasulfide reacted with zinc oxide, but benzyl tri- and tetrasulfide reacted with zinc oxide to give zinc sulfide. In the case of benzyl trisulfide, hydrogen sulfide, stilbene and benzaldehyde were formed, and in the case of tetrasulfide, we found the formation of hydrogen sulfide, stilbene, benzaldehyde and sulfur. 4. The tri- and tetrasulfide of both the benzyl and tolyl series reacted with lead oxide and they gave lead sulfide and organic disulfide. That is, they were desulfurized by lead oxide. In these reactions the benzyl series was more reactive than the tolyl series and the tetrasulfide was more reactive than trisulfide in the same series. 5. Lead oxide reacted with polysulfide easier than zinc oxide. 6. From the results of reactions between metallic oxide with mercaptan or other sulfide, it was concluded that the vulcanization mechanism of polysulfide rubber by metallic oxide is the reaction represented by Equations (1) to (4), the products being converted to high polymer without formation of a network of polysulfides.

Mechanism of Vulcanization of Polysulfide Rubbers

Abstract This investigation was carried out to discover the terminal group present in polysulfide rubbers of the kind represented by Thiokol Type FA and the chemical reactions involved in the standard vulcanization recipe. Hydroxyl groups were found to be present as terminals on these polysulfide rubbers. The effects on vulcanization of omitting the compounding ingredients normally used, of varying the amounts of zinc oxide, substituting other metallic atoms for zinc, and of using diisocyanates were studied, and the mechanism was deduced. Knowledge of the end groups present in the polymer chain is helpful in planning supplementary experiments to try to discover the chemical reaction involved in the cure with zinc oxide. It also makes it possible to look intelligently for improved vulcanizing agents for these polysulfide polymers.

Brief-Mechanism of Vulcanization of Polysulfide Rubbers

Brief-Mechanism of Vulcanization of Polysulfide Rubbers

Mechanism of Vulcanization of Polysulfide Rubbers

Mechanism of Vulcanization of Polysulfide Rubbers

Chemorheology of Polysulfide Rubbers

Abstract Experimental results indicate that the socalled “cold flow” of polysulfide rubbers is almost certainly chemical rather than physical in nature. The term chemorheology has been adopted to describe this chemical type of plasticity. The experimental method employed in this investigation was the measurement of relaxation of stress in stretched rubber samples held at a constant elongation. The changes in relaxation rate produced by changing the molecular structure of the rubber (by cross-linking), by incorporating carbon black, by illuminating with ultraviolet light, and by treating the rubber with various chemical agents, such as sulfur, a thiol, and agents that destroy thiol groups, were studied by this method. From the results of the above experiments and from additional considerations, it is concluded that the chemical reaction responsible for cold flow is an intermolecular exchange reaction, and that this exchange reaction is probably an exchange between a terminal thiol group of one chain and a disulfide linkage of an adjacent chain.

Stress-Time-Temperature Relations in Polysulfide Rubbers

Abstract Polysulfide rubbers of various internal structures have been investigated by measurements of continuous and intermittent relaxation of stress and by creep under constant load at temperatures between 35° C and 120° C. Continuous stress relaxation measurements indicate that these rubbers obey approximately the simple Maxwellian law of relaxation of stress, which indicates that one definite type of bond in the network structure is responsible for stress decay. The activation energy for the relaxation process in each of the polysulfide rubbers is nearly the same, indicating that the same type of bond is responsible for the relaxation behavior of all the polysulfides investigated. In contrast to hydrocarbon rubbers, oxygen is not the cause of high temperature relaxation in polysulfide rubbers, nor does heating in air at moderate temperatures for times comparable to the relaxation time produce changes in physical properties as determined by modulus or by appearance of the samples. Several possibilities regarding the mechanism of the relaxation process and the type of bond involved are considered in the light of the experimental results.

Stress-Time-Temperature Relations in Polysulfide Rubbers

Polysulfide rubbers of various internal structures have been investigated by measurements of continuous and intermittent relaxation of stress and by creep under constant load at temperatures between 35°C and 120°C. Continuous stress relaxation measurements indicate that these rubbers approximately obey the simple Maxwellian law of relaxation of stress, which indicates that one definite type of bond in the network structure is responsible for stress decay. The activation energy for the relaxation process in each of the polysulfide rubbers is nearly the same, indicating that the same type of bond is responsible for the relaxation behavior of all the polysulfides investigated. In contrast to the hydrocarbon rubbers, oxygen is not the cause of high temperature relaxation in polysulfide rubbers, nor does heating in air at moderate temperatures for times comparable to the relaxation time produce changes in physical properties as determined by modulus or by appearance of the samples. Several possibilities regarding the mechanism of the relaxation process and the type of bond involved are considered in the light of the experimental results.