Technology & Engineering
Elastomers
Elastomers are polymers with elastic properties, allowing them to return to their original shape after being stretched or compressed. They are widely used in various engineering applications due to their ability to provide flexibility, resilience, and durability. Common examples of elastomers include rubber, silicone, and polyurethane, and they are utilized in products such as tires, seals, and gaskets.
Written by Perlego with AI-assistance
Related key terms
1 of 5
6 Key excerpts on "Elastomers"
eBook - PDF- P.E., Philip A. Schweitzer(Authors)
- 2006(Publication Date)
- CRC Press(Publisher)
5 Elastomers 5.1 Introduction The technical definition of an elastomer , as given by ASTM, states: An elastomer is a polymeric material which at room temperature can be stretched to at least twice its original length and upon immediate release of the stress will return quickly to its original length. More commonly, an elastomer is generally considered to be any material that is elastic or resilient and, in general, resembles natural rubber in feeling and appearance. These materials are sometimes referred to as rubbers . Elastomers are primarily composed of large molecules that tend to form spiral threads, similar to a coiled spring, that are attached to each other at infrequent intervals. As a small stress is applied, these coils tend to stretch or compress but exert an increasing resistance as additional stresses are applied. This property is illustrated by the reaction of an elastic band. The maximum utility of Elastomers, either natural or synthetic, is achieved by compounding. In the raw state, Elastomers tend to be soft and sticky when hot and hard and brittle when cold. Ingredients are added to make Elastomers stronger, tougher, or harder; to make them age better; to color them; and in general, to impart specific properties to meet specific application needs. Vulcanizing agents are also added because the vulcanizing process extends the temperature range within which they are flexible and elastic. Depending on the application of the elastomer, certain specific properties may be required. The following examples illustrate some of the important properties that are required of Elastomers and the typical services that require these properties: 443
eBook - PDFPolymeric Biomaterials
Structure and Function, Volume 1
- Severian Dumitriu, Valentin Popa(Authors)
- 2013(Publication Date)
- CRC Press(Publisher)
478 References ...................................................................................................................................... 478 417 Biocompatibility of Elastomers 14.1.2 M ISCELLANEOUS 14.1.2.1 Definition While they are members of the broad family of polymers, Elastomers behave differently than plastic materials or plastomers. Generally speaking, for materials to be considered Elastomers they must be • Flexible, i.e., have low rigidity (several megapascals) • Highly deformable, i.e., are able to withstand strong deforming forces without ruptur-ing and have an elongation at rupture over 200% while possessing relatively high tensile strength at ultimate elongation • Elastic or resilient, i.e., are able to return to their original shape and size after the deform-ing force is removed and quantitatively release the energy used to deform them (Table 14.1) (Pinchuk 1994). Many so-called biomedical Elastomers do not meet the second criterion. While it is difficult to set an elastic limit beyond which a polymer stops being a plastomer and becomes an elastomer, we will use the broadest medical definition and refer to all polymers with sufficient elasticity to return to their original shape after a substantial deformation as Elastomers (Mardis et al. 1993). However, it will occasionally be more appropriate to talk about elastic polymers than true Elastomers. 14.1.2.2 Classification of Elastomers 14.1.2.2.1 The Various Families of Elastomers There are some 15 families of Elastomers, some of which include 10–20 different grades. Modern polymerization processes increasingly allow the manufacture of customized products that address specific application problems and provide specific elastomeric properties. The current classification system separates Elastomers into four categories (the acronyms are based on the ISO 1629:1995 standard): 1.
eBook - PDF- Saeed Farrokhpay(Author)
- 2023(Publication Date)
- Arcler Press(Publisher)
Advanced Elastomeric Materials 2 1.1. INTRODUCTION Elastomers are exclusive to polymers and display astonishing reversible extensions with minimal permanent set and low hysteresis. They are the perfect polymers free of molecular interactions, chain rigidity, and crystallinity constraints. The usual Elastomers have distinguishing low modulus, however, with poor chemical resistance and abrasion. Theoretical ideas have been developed for their kinetics and thermodynamics, and this information has been made practical for encompassing their properties by the design of molecular and chemical structures, or through adjustment by control of blending, additions of fillers, or crosslinking (Qi et al., 2003, 2004). This chapter provides a review of elastomer theory and the challenging range of properties anticipated. The natural rubber (NR) is an opening material for the institution of chemistries that present damping, higher modulus, and abrasion resistance through co-polymerization and interrelating functional groups. Heteroatoms like fluorine, oxygen (O 2 ), nitrogen, and silicon are displayed to encompass properties and provide chemical resistance. The thermoplastic Elastomers (TPEs) move away from usually cured systems because of the creation of two-phase block copolymers. Lastly, adjustment by filler and the blended systems is well-thought-out, trailed by an introduction in order to shape the memory materials and a short comment on the trends of the future. The diverse and unique properties and performance of the Elastomers remain to be a captivating field for science (Brackbill et al., 1996; Pandey and Mehtra, 2014). An elastomer is a material that can display a quick and large reversible tension in response to stress. Generally, an elastomer is differentiated from the material that displays an elastic response which is a feature of various materials.
- Tariq Altalhi, Tariq A. Altalhi(Authors)
- 2022(Publication Date)
- Wiley-Scrivener(Publisher)
One of the family of biodegradable polymer includes biodegradable Elastomers. Essentially, the classification of polymers is outlined into three groups: thermoplastic, thermosets, and Elastomers [13]. Thermoplastics or plastics are the polymers, which become liquid when subjected to thermal or heat treatment. They can be molded or remolded into any shape by dif- ferent processing techniques. They do not crystallize easily to solid state on cooling owing to large ordering of highly entangled molecules present in them. They are amorphous polymers, characterized by glass transition temperature (T g ), at which they transform from glassy to rubbery state [14]. This transition leads to polymeric chain motion which freezes below T g . Thermosets are rigid materials with no chain motion owing to high degree of crosslinking. On the contrary, unlike thermoplastics, Elastomers are intractable, which degrade upon application of heat. Elastomeric poly- mers are crosslinked rubbery polymers that can undergo elastic deforma- tions (stretched to high extensions and recover back upon stress removal) [15]. The cross-linking density is midway between thermoplastics and thermosets, preventing their permanent flow. These elastic polymers can be preferentially used in biomedical field, in pristine or composite form owing to their mechanical compliance and design compatibility [16]. They can be categorized as long-term and medium- or short-term physiological contact or implantation, based on the time of physiological contact [17]. Their promising applicability is attributed to their potential to mimic the Biodegradable Elastomer 337 viscoelasticity of tissues and their obedience toward site without damaging the environs [18]. This chapter aims to endow readers with an updated overview of biode- gradable Elastomers, while providing a brief introduction to test methods of biodegradability, preparation strategy and potential applications of bio- degradable Elastomers.
eBook - PDFFundamentals of Modern Manufacturing
Materials, Processes, and Systems
- Mikell P. Groover(Author)
- 2016(Publication Date)
- Wiley(Publisher)
The word is derived from the Greek words poly, meaning “many,” and meros (reduced to mer), meaning “part.” Most polymers are based on carbon and are therefore organic chemicals. As engineering materials, polymers are relatively new compared to metals and ceramics (see Historical Note 8.1 at www.wiley.com/college/groover). Polymers can be classified into three types: (1) thermoplastic polymers, (2) thermosetting polymers, and (3) Elastomers. Thermoplastic polymers (TP), also called thermoplastics, are solid materials at room temperature, but they become viscous liquids when heated to temperatures of only a few hundred degrees. This characteristic allows them to be easily and economically shaped into products. They can be subjected to this heating and cooling cycle repeat- edly without significant degradation. Thermosetting polymers (TS), or thermosets, cannot tolerate repeated heating cycles as thermoplastics can; when initially heated, they soften and flow for mold- ing, but the elevated temperatures also produce a chemical reaction that hardens the material into an infusible solid. If reheated, thermosetting polymers degrade and char rather than soften. Elastomers (E) are polymers that exhibit extreme elastic extensibility when subjected to relatively low mechan- ical stress. Some Elastomers can be stretched by a factor of 10 and yet completely recover to their original shape. Although their properties are quite different from thermosets, they have a similar molecular structure that is different from the thermoplastics. In popular nomenclature, thermoplas- tics and thermosets are known as plastics and Elastomers are known as rubbers. Thermoplastics are commercially the most important of the three types, constituting around 70% of the tonnage of all synthetic polymers produced. Thermosets and Elastomers share the remaining 30% about evenly. Common TP polymers include polyethylene, polyvinylchloride, polypropylene, polystyrene, and nylon.
eBook - PDF- William F. Hosford(Author)
- 2009(Publication Date)
- Cambridge University Press(Publisher)
20 Polymers Introduction A separate chapter is devoted to polymers because of their engineering importance and because their mechanical behavior is so different from that of metals and ceram-ics. The mechanical response of polymers is far more time dependent than that of crystalline materials. Viscoelastic effects ( Chapter 15 ) are much more important in polymers than in metals or ceramics. The properties of polymers are also much more sensitive to temperature than those of other materials. Changes of molecular orientation with deformation cause large changes in properties and a much greater degree of anisotropy than is observed in metals or ceramics. The phenomena of craz-ing and rubber elasticity have no analogs in crystalline materials. Some polymers exhibit very large tensile elongations. Although a few alloys exhibit shape-memory behavior, the effect is much greater in polymers, more common, and of greater tech-nological importance. Elastic Behavior Elastic strains in metals and ceramics occur by stretching of primary metallic, cova-lent, or ionic bonds. The elastic modulus of most crystals varies with direction by less than a factor of 3. The effects of alloying, thermal, and mechanical treatments on the elastic moduli of crystals are relatively small. As the temperature is increased from absolute zero to the melting point, Young’s modulus usually decreases by a factor of no more than 5. For polymers, however, a temperature change of 30 ◦ C may change the elastic modulus by a factor of 1,000. Elastic deformation of poly-meric involves stretching of the weak van der Waals bonds between neighboring molecular chains and rotation of covalent bonds. This accounts for the fact that the elastic moduli of random linear polymers are often at least two orders of magnitude lower than those of metals and ceramics.
Index pages curate the most relevant extracts from our library of academic textbooks. They’ve been created using an in-house natural language model (NLM), each adding context and meaning to key research topics.
