Elastomer Technology Research Articles

Elastomer technology keeps tanks tight

Elastomer technology keeps tanks tight

Thermoplastic Microfluidic Platform for Single-Molecule Detection, Cell Culture, and Actuation

We have developed a multipurpose microfluidic platform that allows for sensitive fluorescence detection on inexpensive disposable chips. The fabrication scheme involves rapid injection molding of thermoplastics, followed by silica deposition and covalent attachment of an unstructured flexible lid. This combines the virtues of elastomer technology with high-throughput compact disk injection molding. Using this technique, the time to produce 100 chips using a single master can be lowered from more than 1 week by standard PDMS technologies to only a couple hours. The optical properties of the fabricated chips were evaluated by studying individual fluorescence-labeled DNA molecules in a microchannel. Concatemeric DNA molecules were generated through rolling circle replication of circular DNA molecules, which were labeled by hybridization of fluorescence-tagged oligonucleotides. Rolling circle products (RCPs) were detected after as little as 5 min of DNA polymerization, and the RCPs in solution showed no tendency for aggregation. To illustrate the versatility of the platform, we demonstrate two additional applications: The flexible property of the lid was used to create a peristaltic pump generating a flow rate of 9 nL/s. Biocompatibility of the platform was illustrated by culturing Chinese hamster ovary cells for 7 days in the microfluidic channels.

Use of a Viscoelastic Model for the Seismic Response of Base-Isolated Buildings

Due to recent developments in elastomer technology, seismic isolation using elastomer bearings is rapidly becoming an acceptable design tool to enhance structural seismic margins and to protect people and equipment from earthquake damage. With proper design of isolators, high-energy seismic input motions can be transformed into low-frequency, low-energy harmonic motions, and the accelerations acting on the isolated building may be significantly reduced. Several alternatives exist for the modeling of the isolators. This study is concerned with the use of a viscoelastic model to predict the seismic response of base-isolated buildings. The in-house finite element computer code, SISEC has been modified to incorporate a viscoelastic spring element, and several simulations are performed. Then, the computed results have been compared with the corresponding observed data recorded at the test facility.

Science and technology of rubber

A.N. Gent, Rubber Elasticity: Basic Concepts and Behavior. R.P. Quirk and M.M. Morton, Polymerization. G. Ver Strate and D.J. Lohse, Structure Characterization in the Science and Technology of Elastomers. B. Erman and J.E. Mark, The Molecular Basis of Rubberlike Elasticity. O. Kramer, S. Hvidt, and J.D. Ferry, Dynamic Mechanical Properties. J.L. White, Rheological Behavior of Processing of Unvulcanized Rubber. A.Y. Coran, Vulcanization. A.I. Medalia and G. Kraus, Reinforcement of Elastomers by Particulate Fillers. W.W. Barbin and M.B. Rodgers, The Science of Rubber Compounding. A.N. Gent, Strength of Elastomers. A.F. Halasa, J.M. Massie, and R.J. Ceresa, The Chemical Modification of Polymers. P.J. Corish, Elastomer Blends. B.P. Grady and S.L. Cooper, Thermoplastic Elastomers. F.J. Kovac and M.B. Rodgers, Tire Engineering. Chapter References. Subject Index.

100% Solids Aliphatic Spray Polyurea Elastomer Systems

Regulations are continually being passed that limit the volatile organic content (VOC) of elastomer coating systems. Because of this restriction, high solids, two-component spray elastomers and coatings are attaining in creases in market interest and sales volume. As this interest grows, the research and development effort focuses on newer and better polymer materials. The development of 100% solids aromatic polyurethane elastomer systems has shown promise with respect to the VOC issues. Recently, a further refined 100% solids spray elastomer system, based on polyurea RIM technol ogy, has also been demonstrated. These systems, like polyurea RIM materials, are based on aromatic isocyanates, aromatic amine chain extenders and amine- terminated polyether resins. In order to take full advantage of the leading edge polyurea elastomer technology, 100% solids aliphatic polyurea elastomer systems have been developed. Amine-terminated polyether resins along with aliphatic isocyanates are incorporated into this next generation of spray elastomer materials. Aliphatic spray polyurea elastomer systems, like the aromatic polyurea elastomer systems, require no catalysts and are extremely fast in reactivity and cure. Due to this fast reactivity and cure, these systems are virtually unaf fected by moisture during processing. Application of the aliphatic polyurea systems is also possible in a variety of temperature ranges with little effect on the reaction profile and cure. Any VOC standards or regulations are easily com plied with due to the 100% solids characteristic. Excellent elastomer physical properties are also noted at varied temperature ranges. Obviously, spray elastomer systems based on this aliphatic polyurea technology are good candi dates for both coating and noncoating-type applications. Recent advances in the aliphatic spray polyurea elastomer technology will be discussed in this paper.

Alloplastic Implants for Men

Recent advances in medical grade elastomer technology empower plastic surgeons to enhance specific body parts, thereby performing body sculpting. This article examines alloplastic implants for large body soft-tissue augmentation, namely pectoralis major enlargement, calf augmentation, and buttock enhancement.

Osseointegration in maxillofacial prosthetics. Part II: Extraoral applications

The application of osseointegrated fixtures to the cranial skeleton for facial prosthesis retention marks a revolutionary step in the search for the perfect soft tissue replacement. They allow present elastomer technology to be used to its greatest potential by protecting surface coloration, eliminating adhesive-induced base material degeneration, and allowing the long-term retention of fine, but weak peripheral margins. Although not all facial defect patients are candidates for this approach, the concept as applied in our present experience has proved to be a valuable replacement for available adhesive systems.

Current Trends in Fluoroelastomer Development

Abstract Recent advances in the automotive, petroleum, and energy-related industries have created applications for high-performance elastomers, which often require chemically resistant elastomers with improved high-temperature operating capability. Fluoroelastomers are uniquely capable of withstanding high temperatures in conjunction with aggressive chemicals, fuels, and lubricants. While a number of reviews concerning fluoroelastomers have been published in the last three years, this paper will concentrate on recent developments that have improved fluoroelastomers to meet the requirements of new high-performance applications. Three types of fluorine-containing elastomers—fluorocarbon, fluorosilicone, and fluoroalkoxyphosphazene (phosphonitrilic)—are commercially available. The fluorocarbon elastomers have the highest fluorine content, with general grades having between 53 and 70% fluorine. The high fluorine content of these specialty elastomers imparts exceptional resistance to attack by fuels, oils, and corrosive chemicals. The excellent resistance to high-temperature aging for extended periods of time results in a temperature use range of −46 to 320°C. Fluoro-carbon elastomers are produced in the United States by 3M (“Fluorel” Brand fluoroelastomer) and Du Pont (“Viton” Brand fluoroelastomer) and outside the United States by Montedison (Italy, “Technoflon” Brand fluoroelastomer), Daikin (Japan, “Daiel” Brand fluoroelastomer), and Asahi Glass (Japan, “Aflas” Brand elastomer, a copolymer of tetrafluoroethylene and propylene). Fluorosilicone and fluoroalkoxyphosphazene elastomers contain 30–40% fluorine. Although the fluorine content of these elastomers is less than that of fluorocarbon elastomers, it is high enough to provide moderate chemical resistance to many fluids. The flexible nature of the heteroatoms of the polymer chain backbone in fluorosilicone and fluoroalkoxyphosphazene elastomers results in excellent low-temperature flexibility, giving them a temperature use range of −54 to 230°C. Fluorosilicone elastomers are produced by Dow Corning (“Silastic”) and General Electric (“FSE”), while fluoroalkoxyphosphazene elastomers are produced by Firestone (“PNF”). This paper is a discussion of developments in fluorocarbon elastomer technology that have led to successful use in demanding applications which require high-performance elastomeric parts. Typical properties of fluorocarbon elastomers and improved properties resulting from cure system development and variations in the fluorine content of this type of elastomer will be presented. Applications for fluorocarbon elastomers in the automotive, petroleum, and energy-related industries will be illustrated.

Current Perspectives on Silicone Rubber Technology

Abstract This perspective embraced many factors that are important in understanding silicone elastomer technology and the reasons for the unique properties that they exhibit. The fact that they possess the lowest transition temperatures for any known polymer qualify them as a viscoelastic polymer that can be converted to an elastomer by crosslinking. Important also is the fact that the polymer molecules are predominantly linear prior to vulcanization, which allows high extensibility when the chemical crosslinks are in the desirable range of 100–400 mer units. Siloxane chemistry is uniquely different from hydrocarbon chemistry primarily because silicon is more electropositive than carbon, and the siloxane bonds possess more ionic character. Intermolecular forces for polydimethylsiloxane based elastomers are much lower than hydrocarbon polymer based elastomers. These polymers exhibit unusually high chain flexibility, easy rotation of pendant organic groups attached to silicon, and more free volume at ambient conditions than other polymers. These properties contribute to the lower Tg values and less change in properties (e.g., viscosity of polymers, elastomer modulus and strength) with temperature, compared with organic elastomers. Additional properties that contribute to the unique properties of silicone elastomers are low surface energy, excellent oxidative and thermal resistance formulatibility to provide excellent resistance to hydrolysis and rearrangement of siloxane bonds, easy modification of solubility characteristics by substitution of different organic groups on silicon, and the use of simple chemistry alterations that allow a range of molecular weights for making high and low consistency compositions that can be crosslinked either at elevated or room temperature conditions by a variety of reactions. The unusually high degree of reinforcement obtained with silica fillers compared with nonreinforced silicone polymers is a result of excellent polymer filler bonding which consists of largely physical bonds with some chemical bonds also being present after exposure to elevated temperature curing conditions. The combination of the above mentioned properties contribute to the fact that silicone elastomers have become important engineering materials that find hundreds of difficult-to-satisfy applications. Based on the excellent potential for continued technology advancement for silicone elastomers, it is believed that substantial future growth of this family of elastomers will occur.

Recent Developments in Urethane Elastomers and Reaction Injection Molded (RIM) Elastomers

Abstract The chemistry and technology of urethane elastomers has advanced rapidly since their inception in Europe in the late 1930'a and early 1940's. The earliest elastomers were Vulkollan, developed by I. G. Farbenindustrie (IGF) and Vulcaprene, developed by Imperial Chemical Industries (ICI). IGF developed a casting process for Vulkollan, while the processing of Vulcaprene was carried out on conventional rubber equipment. While these elastomers were crosslinked, new types of urethane elastomers were developed which were thermoplastic in nature and allowed processing by means of conventional thermoplastic processing equipment. Urethane elastomers were also developed in various other forms such as latices, solutions in organic solvents, poromeric sheets, spandex fibers, sealants and caulks (consisting generally of low modulus elastomers), and expanded or micro-cellular elastomers. Omitting spandex fibers and poromerics, urethane elastomers can be classified according to the method of processing by which they are produced:

Elastomer Structures and ‘Cold Crystallization’

Abstract In a great number of applications an ideal elastomer should satisfy, to a certain extent, both of the following requirements: (1) nearly instantaneous crystallization upon application of strain (strain induced crystallization) and (2) slow or no crystallization when cooled at the temperature of maximum crystallization rate (cold induced crystallization). A noteworthy case of (2) is elastomer crystallization in a strained state. The connection between the points (1) and (2) has not been clearly understood up to now, but it is known that some crystallizable elastomers fulfil the requirements of both (1) and (2) better than others. From an experimental point of view, cold induced crystallization kinetics are substantially easier to measure than those of very fast strain induced crystallization. The phenomenon of cold induced crystallization in natural rubber, NR, has been known since the very beginning of elastomer technology and the tendency of natural rubber to crystallize by cooling has been overcome by crosslinking it with sulphur (vulcanization) without impairing its ability to crystallize by stretching (Goodyear, 1836). The synthesis of cis-polyisoprenes (IR) and cis-polybutadiene (BR) of different microstructural purity (different cis content) gave the possibility of changing the crystallization rate. It has also been reported that the very fast cold crystallization of trans-polypentenamer (TPA) could be reduced by lowering the trans content. The same fact had been observed earlier for trans-polychloroprene. There is a general agreement in postulating that the reduction of the crystallization rate, obtained either by cross-linking or by chain regularity reduction, can be linked with the lowering of the melting point. In both cases the low level of structural defects introduced in the chains does not affect the glass transition temperature in such a way as to vary the crystallization rate. The aim of this paper is to emphasize the importance of the variations of the glass transition temperature and melting point on the elastomeric cold crystallization rate and the way these may be used in planning new elastomer structures.

Recent advances in elastomer technology for UHV applications

Recent advances in elastomer technology for UHV applications

Elastomer structures and ‘cold crystallization’

Abstract In a great number of applications an ideal elastomer should satisfy, to a certain extent, both of the following requirements: (1) nearly instantaneous crystallization upon application of strain (strain induced crystallization) and (2) slow or no crystallization when cooled at the temperature of maximum crystallization rate (cold induced crystallization). A noteworthy case of (2) is elastomer crystallization in a strained state. The connection between the points (1) and (2) has not been clearly understood up to now, but it is known that some crystallizable elastomers fulfil the requirements of both (1) and (2) better than others. From an experimental point of view, cold induced crystallization kinetics are substantially easier to measure than those of very fast strain induced crystallization. The phenomenon of cold induced crystallization in natural rubber, NR, has been known since the very beginning of elastomer technology and the tendency of natural rubber to crystallize by cooling has been over...

Recent advances in elastomer technology for UHV applications

The advances made in vacuum-oriented elastomer performance during the development of the latest UHV compatible elastomer (Kalrez†) are briefly reviewed by correlating their chemical character with the physical characteristics of relevance to UHV technology. Total pressure and mass spectral data on the degradation characteristics of Kalrez and of the latest Viton† (E 60C) shows the superior performance of the first and establishes it from this point of view to be in a class on its own for UHV oriented applications.

Radioisotope Methods of Analysis and Characterization of Elastomers

Abstract Radioactivity applied to rubber technology encompasses such diverse areas as the effect of radiation on elastomers, use of strong gamma and beta sources for process control, and isotope methods to measure tire tread wear. These applications of radioisotopes have received considerable attention in recent years and the principles and techniques have been discussed extensively in both reviews and original papers. Significant contributions, however, have also been made in advancing elastomer technology through analytical use of radioisotopes of carbon, hydrogen, sulfur, and other beta-emitters, as well as by special radioisotope techniques. This survey discusses recent advances achieved with beta-emitters in vulcanization, diffusion, dispersion, adsorption, coagulation, and determination of functional groups in polymers. In addition, the value of activation analysis and other radioisotope investigative methods for characterization of elastomers is shown.

Role of Computers in Elastomer Research

Abstract Computer usage has spread so rapidly in recent years that these instruments are almost considered to be common tools. Publications may make only casual reference to the computer's role in the investigation or they may omit such reference altogether, if the use was routine in nature. Consequently the literature on elastomer research and technology does not fully represent the growing importance of this extension to human capabilities. Enough references are available, however, to show that computers have penetrated into many areas of rubber science. The aims of this article are, therefore, to review some computer applications that have been made and to indicate potential uses. Perhaps both of these aims can be served by first considering the nature of computers and the type of problem solving for which they are uniquely adapted.

Physico-chemical aspects of elastomer technology for UHV applications

Physico-chemical aspects of elastomer technology for UHV applications

Some Neglected Problems in the Rheology of High Polymers

Abstract In accordance with custom, I have been asked, as a Goodyear Medalist, to address the Division of Rubber Chemistry of the American Chemical Society on the subject of my past work in the science and technology of elastomers. Hoping that I have correctly understood your desires, I shall now give you an informal, anecdotal story of some of this work. Going beyond this story of the past I shall also sketch, as I now see them, certain related unsolved problems, some of which have been rather neglected. While keeping in mind that detailed mathematics and theoretical argument would be inappropriate and even unwelcome on this occasion, I shall endeavor, with very little mathematics, to stimulate some of you to initiate programs of research on some of these problems, if you have not already done so. First let me tell you how, without realizing it, I became a rheologist. When I was employed by the United States Rubber Company in the fall of 1928, my first assignment was to study rubber plasticity, or the flow properties of crude rubbers and raw compounded stocks. When I was told of this problem in a conference with my group leader, Dr. Roscoe H. Gerke, there was a third person present, Dr. Ernest J. Joss, a physical chemist. Dr. Joss had only shortly before been given the same assignment; but with my appearance in the group, he was permitted to drop this work and give his full time to more congenial tasks. At the conference he turned over to me some talced strips of pale crepe which had been cut from a batch on a laboratory mill after various milling times. I knew nothing about rubber at that time; and if I had been asked to guess what these samples were, I could only have replied that they looked like fillets of sole sprinkled with flour and ready for the frying pan. The rheologieal testing devices for raw rubber that were available at that time were of two forms, the compression plastometer and the extrusion plastometer. I quickly decided that neither of these was suitable for the purpose, which, as I conceived it, was to measure the flow behavior of raw rubbers or stocks in their working condition as exhibited on a mill or calender or in a tuber.