1 Definition and basic properties
An elastomer is a polymeric material characterized by high elasticity and a pronounced ability to recover after deformation. In everyday use, the term usually refers to rubber-like substances that can stretch substantially, absorb energy, and return close to their original dimensions when the load is removed. This combination of flexibility and resilience makes elastomers valuable wherever cushioning, sealing, shock absorption, or repeated bending is required.
Elastomers are distinguished from rigid plastics by their low modulus and from simple viscous materials by their ability to store and release mechanical energy. Their behavior is strongly influenced by molecular architecture, temperature, and the presence of cross-links or physical associations that limit permanent flow.
1.1 Elasticity and viscoelasticity
Elasticity is the tendency of a material to regain its original shape after deformation. In elastomers, this recovery is not perfectly instantaneous, because the polymer chains also show time-dependent movement. This combined response is known as viscoelasticity.
Viscoelastic materials exhibit both elastic and viscous behavior. When stretched, an elastomer can extend significantly, but some of the input energy is dissipated as heat rather than fully returned. The balance between these two responses affects comfort, damping, and durability in practical products.
1.2 Molecular structure
The molecular structure of elastomers typically consists of long, flexible polymer chains with low intermolecular attraction and a disordered arrangement. This flexibility allows chain segments to uncoil and align under stress. Once the stress is removed, the chains tend to recoil because thermal motion favors a more random configuration.
Many elastomers are based on polymers with repeating units that provide chain mobility. The chains are usually above their glass transition temperature during use, which keeps the material soft and deformable. Structural features such as pendant groups, polarity, and backbone saturation also influence flexibility, chemical resistance, and aging behavior.
1.3 Cross-linking and network formation
Cross-linking connects polymer chains into a network that prevents permanent slippage. Without sufficient cross-linking, a rubber-like polymer would flow under load rather than recover its shape. With too much cross-linking, however, the material becomes stiff and loses extensibility.
In conventional rubbers, cross-links are formed during curing through sulfur bridges, peroxides, or other chemical systems. Some elastomers rely on physical networks created by crystalline domains or hard segments. The nature of the network helps determine elasticity, strength, heat resistance, and compression behavior.
1.4 Mechanical behavior
The mechanical behavior of elastomers is defined by their low stiffness, high recoverability, and capacity to undergo repeated deformation. These materials often show nonlinear stress-strain relations, meaning that their resistance to stretching changes as extension increases. Their performance depends on formulation, service temperature, and loading rate.
1.4.1 Tensile strength
Tensile strength is the maximum stress a material can withstand while being stretched before breaking. In elastomers, tensile strength varies widely and is often improved by reinforcement with fillers such as carbon black or silica. A strong elastomer can tolerate substantial force while still remaining flexible.
1.4.2 Elongation at break
Elongation at break describes how far a material can stretch before rupture. Elastomers typically have very high values compared with plastics or metals, which is one reason they are used in dynamic applications. High elongation alone does not guarantee quality, since useful materials must also recover well and resist tearing.
1.4.3 Rebound and hysteresis
Rebound refers to the ability of a material to return energy after deformation, while hysteresis is the energy lost during a loading-unloading cycle. An elastomer with high rebound is efficient and springy, whereas one with higher hysteresis dissipates more energy as heat and can provide better damping. The desired balance depends on whether the application calls for resilience or vibration absorption.
1.5 Thermal and environmental response
Elastomers are sensitive to temperature because their chain mobility changes with heat and cold. At low temperatures, many become harder and less flexible; at high temperatures, they may soften, creep, or degrade. Their performance is also affected by oxygen, ozone, sunlight, moisture, and chemicals in the operating environment.
Environmental resistance depends on polymer type and compounding. Some materials are suited to hot oils or fuels, while others excel in outdoor exposure or electrical insulation. Selection usually involves balancing elasticity against resistance to aging and service conditions.
2 Types of elastomers
Elastomers can be grouped into natural, synthetic, and thermoplastic categories. Each group includes materials with distinct molecular features and processing behavior. Their uses reflect differences in cost, performance, and resistance to heat, chemicals, or wear.
2.1 Natural elastomers
Natural elastomers are obtained from biological sources, usually plant-derived latexes. They are valued for high resilience, good fatigue resistance, and easy processability. Their properties can vary depending on source, purification, and formulation.
2.1.1 Natural rubber
Natural rubber is chiefly composed of cis-1,4-polyisoprene obtained from the latex of the rubber tree. It has excellent elasticity, high tensile strength when reinforced, and strong resistance to crack growth. These characteristics have made it one of the most important elastomers in industrial history.
2.1.2 Other naturally derived materials
Other naturally derived elastomeric materials include gutta-percha, balata, and certain latex-based products used in coatings or adhesives. These materials may differ in crystallinity, hardness, and thermal response, which makes them suitable for specialized uses rather than broad general-purpose applications.
2.2 Synthetic elastomers
Synthetic elastomers are produced by chemical polymerization and can be tailored for specific environments. Compared with natural rubber, they often provide better consistency, improved resistance to oils or heat, or enhanced weatherability. Their development expanded the range of practical rubber-like materials.
2.2.1 Styrene-butadiene rubber
Styrene-butadiene rubber is a widely used general-purpose elastomer known for good abrasion resistance and favorable processing characteristics. It is commonly employed in tires, footwear, and molded goods. Its properties can be adjusted by varying styrene content and reinforcement.
2.2.2 Nitrile rubber
Nitrile rubber contains polar nitrile groups that improve resistance to oils, fuels, and many hydrocarbons. This makes it useful for seals, hoses, and gaskets in demanding mechanical environments. Its performance is typically weaker in ozone and weather exposure than in oil resistance.
2.2.3 Neoprene
Neoprene is a chloroprene-based elastomer noted for balanced mechanical properties, moderate chemical resistance, and good weathering performance. It has been used in belts, seals, wetsuits, and protective products. Its combination of resilience and flame resistance supports a wide variety of applications.
2.2.4 EPDM
EPDM is an ethylene-propylene-diene elastomer valued for outstanding resistance to weathering, ozone, and heat. It performs well in outdoor sealing, roofing membranes, and automotive weatherstripping. However, it generally has limited resistance to oils and fuels.
2.2.5 Silicone rubber
Silicone rubber is based on a backbone containing silicon and oxygen atoms, which gives it unusual thermal stability and flexibility over a broad temperature range. It is often used where high and low temperature performance are both important. Medical devices, bakeware, and electrical components are common examples.
2.2.6 Fluoroelastomers
Fluoroelastomers are high-performance materials designed for resistance to heat, fuels, oils, and aggressive chemicals. Their fluorinated structure gives them exceptional stability in harsh environments. They are often selected for seals and components in chemical processing or high-temperature machinery.
2.3 Thermoplastic elastomers
Thermoplastic elastomers combine rubber-like elasticity with thermoplastic processing behavior. They can be softened and reshaped by heating, which simplifies manufacturing and recycling compared with permanently cross-linked rubber. Their structure usually involves physical rather than chemical cross-links.
2.3.1 Styrenic block copolymers
Styrenic block copolymers contain hard and soft segments arranged in blocks that form reversible physical domains. These materials are widely used in adhesives, grips, and flexible consumer products. They offer easy processing and a soft touch.
2.3.2 Thermoplastic polyurethanes
Thermoplastic polyurethanes provide abrasion resistance, flexibility, and a broad range of hardness options. They are common in cable jackets, footwear, hoses, and protective films. Their properties can be tuned by altering the ratio of hard and soft segments.
2.3.3 Copolyester elastomers
Copolyester elastomers offer a balance of elasticity, toughness, and chemical resistance. They are used in automotive parts, sporting goods, and industrial components that need repeated flexing. Their thermal and mechanical behavior often suits demanding molded applications.
3 Manufacture and processing
The manufacture of elastomers begins with polymer production and continues through compounding, shaping, and curing. Processing methods are chosen to achieve the desired balance of strength, flexibility, and durability. Small changes in ingredients or conditions can strongly affect the final material.
3.1 Polymerization and raw material production
Synthetic elastomers are produced through polymerization of monomers using solution, emulsion, or other controlled processes. The choice of route influences molecular weight, chain structure, and distribution of comonomers. Raw material production may also include extraction, purification, and conversion of natural latex into usable forms.
3.2 Compounding ingredients
Compounding blends the base polymer with additives that modify processing and final performance. These ingredients help control hardness, flexibility, aging resistance, color, and cost. The formulation is often tailored to a specific end use.
3.2.1 Fillers
Fillers are added to improve strength, wear resistance, processability, or economy. Reinforcing fillers such as carbon black and silica can greatly enhance tensile properties and abrasion resistance. Non-reinforcing fillers may be used mainly to adjust volume or reduce cost.
3.2.2 Plasticizers
Plasticizers lower stiffness and improve flexibility, especially at lower temperatures. They can also aid mixing and processing by reducing viscosity. The choice of plasticizer affects compatibility, migration risk, and long-term performance.
3.2.3 Vulcanizing agents
Vulcanizing agents create the cross-links that convert a raw rubber compound into a durable elastomeric network. Sulfur systems are common for many rubbers, while peroxides and other agents are used for specific polymers. The curing chemistry has a major effect on heat resistance, elasticity, and set behavior.
3.2.4 Antioxidants and stabilizers
Antioxidants and stabilizers slow degradation caused by oxygen, heat, ozone, light, and other environmental factors. They help preserve flexibility and service life during storage and use. Different additives are selected according to the polymer’s vulnerability and expected exposure.
3.3 Mixing and milling
Mixing distributes ingredients uniformly throughout the polymer. It is often carried out in internal mixers or on two-roll mills, depending on batch size and material type. Good dispersion is essential for predictable properties and avoids weak spots in the finished product.
3.4 Shaping methods
After compounding, elastomer materials are formed into the desired shape. Shape-making techniques must preserve uniformity and avoid entrapped air, contamination, or premature curing. The choice of method depends on product geometry and production volume.
3.4.1 Extrusion
Extrusion forces material through a die to produce continuous shapes such as tubing, profiles, and wire coatings. The process is well suited to long, uniform products. It often precedes curing or cooling steps that stabilize the shape.
3.4.2 Molding
Molding forms elastomers in closed cavities under heat and pressure. Compression, transfer, and injection molding are widely used for parts such as seals, grommets, and vibration components. Molding offers precise dimensional control and complex shapes.
3.4.3 Calendering
Calendering passes material through heated rollers to produce sheets or coat fabrics and other substrates. It is used for rubberized textiles, liners, and layered assemblies. Thickness and surface quality can be carefully controlled.
3.5 Curing and vulcanization
Curing transforms a shaped compound into its final elastomeric state. This step develops the network structure that provides resilience and dimensional stability. The curing method must match the polymer chemistry and intended service conditions.
3.5.1 Sulfur vulcanization
Sulfur vulcanization is a classic method used especially with unsaturated rubbers. Sulfur creates bridges between polymer chains, improving elasticity and reducing flow. The process remains important because it produces a well-balanced combination of strength and flexibility.
3.5.2 Peroxide curing
Peroxide curing forms carbon-carbon cross-links and is often chosen for materials needing better heat stability or resistance to compression set. It is used with selected synthetic elastomers and silicone systems. The resulting network can be more stable in high-temperature service.
3.5.3 Radiation curing
Radiation curing uses energetic radiation to generate cross-links in suitable polymers. This method can be useful for precise processing and specialized products. It is less common than sulfur or peroxide systems but valuable in particular industrial settings.
4 Material properties and testing
The usefulness of an elastomer depends on measurable properties that describe hardness, strength, deformation, and durability. Testing ensures that a compound meets design requirements before it is put into service. Standardized measurements also support comparison between materials.
4.1 Hardness
Hardness indicates resistance to indentation and is commonly measured on scales suited to soft polymers. It helps predict whether a material will feel firm, cushion well, or maintain shape under pressure. Hardness selection is important in seals, footwear, and rollers.
4.2 Compression set
Compression set is the permanent deformation remaining after a material has been compressed for a period and then released. A low compression set is desirable for gaskets, O-rings, and seals that must retain contact pressure. It reflects both formulation and curing quality.
4.3 Tear resistance
Tear resistance measures the ability to resist crack initiation and propagation. Elastomers with high tear resistance are better suited to parts that experience sharp edges, repeated flexing, or mechanical abuse. This property is particularly important in membranes, belts, and dynamic seals.
4.4 Abrasion resistance
Abrasion resistance describes how well a material withstands surface wear from rubbing or sliding. It is a critical property for tires, conveyor components, footwear soles, and industrial rollers. Reinforcement often improves abrasion performance.
4.5 Chemical resistance
Chemical resistance refers to the ability to maintain properties when exposed to oils, solvents, acids, bases, or other reactive substances. Different elastomers respond very differently to the same chemical. Material selection therefore depends heavily on the expected service environment.
4.6 Weathering and ozone resistance
Weathering resistance covers the effects of sunlight, moisture, temperature changes, and outdoor exposure. Ozone resistance is especially important for materials under strain, since ozone can cause cracking in susceptible rubbers. Additives and polymer choice both influence long-term outdoor durability.
4.7 Standard test methods
Standard test methods provide consistent ways to measure elastomer properties such as tensile strength, hardness, compression set, and aging behavior. These procedures make it possible to compare materials and verify quality. Industry standards also help ensure that products perform predictably in use.
5 Applications
Elastomers are used in many sectors because they combine flexibility, resilience, and practical manufacturability. Their applications range from high-volume consumer goods to precision industrial and medical components. In many cases, the material is chosen for both performance and comfort.
5.1 Transportation
Transportation systems rely on elastomers for damping, sealing, grip, and wear resistance. These materials reduce noise and vibration while helping components maintain reliable contact. Their broad use reflects the need for parts that can endure repeated motion and varying temperatures.
5.1.1 Tires
Tires are among the most visible elastomer products. They depend on rubber compounds reinforced for traction, durability, and heat resistance. Tire performance requires a careful balance of grip, rolling resistance, wear, and flexibility.
5.1.2 Bushings and mounts
Bushings and mounts isolate vibration and allow controlled movement between connected parts. They are used in vehicles and machinery to reduce shock transfer and improve comfort. Their formulations often emphasize fatigue resistance and compression behavior.
5.1.3 Seals and hoses
Seals and hoses must remain flexible while resisting leakage, pressure changes, and environmental stress. Elastomer choice depends on temperature, fluid compatibility, and mechanical load. These components are essential in engines, fluid systems, and many industrial assemblies.
5.2 Consumer products
Consumer goods often use elastomers for comfort, grip, and durability. Their soft texture and elastic recovery make products easier to handle and more pleasant in daily use. Design considerations frequently include appearance as well as function.
5.2.1 Footwear
Footwear commonly incorporates elastomers in soles, midsoles, trims, and protective features. These materials provide cushioning, traction, and resistance to wear. Different formulations are chosen for athletic, casual, or work-related uses.
5.2.2 Sporting goods
Sporting goods use elastomers in grips, balls, protective gear, and elastic components. The materials contribute rebound, shock absorption, and control. Their performance can affect both comfort and equipment handling.
5.2.3 Elastic bands
Elastic bands rely on stretchability and repeated recovery. They are simple but useful products made from rubber or thermoplastic elastomers. Their function depends on consistent elasticity and resistance to aging.
5.3 Industrial uses
Industrial applications demand reliability under mechanical stress, heat, vibration, and chemical exposure. Elastomers are valued for their ability to form tight seals and absorb motion. Many parts are designed for long service life in demanding environments.
5.3.1 Gaskets and O-rings
Gaskets and O-rings provide sealing between surfaces to prevent leakage of fluids or gases. They must maintain contact pressure while tolerating compression and temperature changes. Material selection is guided by the medium being sealed and the service conditions.
5.3.2 Rollers and conveyor components
Rollers and conveyor components often use elastomer coverings for traction, wear resistance, and product handling. These parts must resist abrasion and sustain repeated contact. The surface properties of the elastomer can improve transport efficiency.
5.3.3 Vibration isolators
Vibration isolators reduce the transmission of oscillation between machines, structures, or mounted equipment. Elastomers are useful because they deform under dynamic loading and dissipate energy. Their effectiveness depends on stiffness, damping, and frequency response.
5.4 Medical and specialty uses
Medical and specialty applications often require cleanliness, biocompatibility, and precise control of softness. Elastomers may be selected for transparency, sterilization resistance, or tactile qualities. In such uses, formulation and processing are especially important.
5.4.1 Medical tubing
Medical tubing uses elastomers that remain flexible, resilient, and suitable for fluid transfer. Depending on the application, the material may need to resist kinking, repeated bending, or sterilization procedures. Smooth surface finish and purity are also important.
5.4.2 Gloves
Gloves made from elastomeric materials provide barrier protection and dexterity. They are used in medical, laboratory, and industrial settings. The choice of material affects comfort, puncture resistance, and tactile sensitivity.
5.4.3 Soft-touch components
Soft-touch components include grips, overmolds, buttons, and handles designed to feel comfortable and secure. Thermoplastic elastomers are often used because they can combine softness with efficient manufacturing. These parts also enhance control and reduce slippage.
6 Degradation and durability
Elastomers gradually change over time due to heat, oxygen, light, mechanical cycling, and chemical exposure. Degradation can alter flexibility, strength, color, and sealing performance. Understanding these processes is essential for designing durable products.
6.1 Thermal aging
Thermal aging occurs when prolonged heat causes changes in polymer structure and additives. The material may harden, lose elasticity, or become brittle. Higher temperatures generally accelerate aging, though the rate varies with polymer type and stabilizer package.
6.2 Oxidation
Oxidation is a chemical reaction with oxygen that can break chains or create additional cross-links. It often leads to embrittlement, surface cracking, and loss of performance. Antioxidants help slow the process, but they cannot eliminate it entirely.
6.3 Ozone cracking
Ozone cracking affects susceptible elastomers exposed to ozone, especially when under tension. Small cracks may appear on the surface and grow with continued stress. Some formulations resist this damage much better than others, particularly those designed for outdoor use.
6.4 UV degradation
Ultraviolet radiation can trigger chemical changes in elastomers, leading to discoloration, embrittlement, and surface deterioration. Outdoor products often require protective additives or inherently stable polymers. Coverings, pigments, and stabilizers may extend service life.
6.5 Chemical attack
Chemical attack occurs when solvents, fuels, acids, bases, or other agents interact with the polymer. Effects may include swelling, softening, extraction of additives, or loss of strength. Resistance depends heavily on molecular structure and formulation.
6.6 Fatigue and wear
Fatigue results from repeated loading and unloading, while wear arises from friction and contact. Both processes can shorten the life of elastomer components, especially in dynamic systems. Good design reduces stress concentration and selects materials suited to cyclic service.
7 Recycling and sustainability
The recycling of elastomers is more complicated than that of many thermoplastics because conventional rubber is cross-linked and does not melt cleanly. Sustainability efforts focus on reuse, material recovery, alternative feedstocks, and longer product life. Formulation and product design can greatly affect environmental impact.
7.1 Reprocessing challenges
Cross-linked elastomers are difficult to remelt and reshape because their network structure remains intact after heating. This limits straightforward mechanical recycling. As a result, recovery often involves grinding, blending, or using the material in lower-value applications.
7.2 Recycling of thermoplastic elastomers
Thermoplastic elastomers are easier to recycle because they soften when heated and can be reprocessed. This advantage supports material recovery and manufacturing scrap reuse. Their recyclability is one reason they are attractive in some consumer and industrial products.
7.3 Devulcanization of rubber
Devulcanization aims to break or loosen cross-links in vulcanized rubber so the material can be reused. It is technically challenging because the goal is to preserve useful polymer chains while restoring processability. Successful methods can reduce waste and recover value from scrap rubber.
7.4 Bio-based elastomers
Bio-based elastomers are derived wholly or partly from renewable raw materials. They are being developed to reduce dependence on fossil resources and to broaden sustainable material choices. Their performance must still meet the mechanical and durability requirements of practical applications.
7.5 Environmental considerations
Environmental considerations include raw material sourcing, energy use in manufacturing, service-life efficiency, and end-of-life disposal. Longer-lasting products can reduce replacement frequency and waste. Material selection increasingly considers both technical performance and lifecycle impact.
8 Historical development
The history of elastomers reflects the progression from natural plant-derived materials to engineered synthetic systems. Improvements in chemistry, processing, and reinforcement transformed rubber from a useful curiosity into an essential industrial material. Modern elastomer engineering builds on this long development.
8.1 Early natural rubber use
Early users of natural rubber valued its waterproofing, flexibility, and resilience. It was employed in simple goods long before industrial processing methods were established. However, untreated natural rubber was limited by temperature sensitivity and poor dimensional stability.
8.2 Vulcanization
Vulcanization was a major advance that made rubber more stable, durable, and practical. By creating cross-links, it reduced tackiness and flow while improving elasticity and service life. This development enabled the growth of many rubber industries.
8.3 Development of synthetic rubbers
Synthetic rubbers emerged as chemistry and industrial production advanced. They provided alternatives to natural rubber and offered specialized resistance to oils, heat, weather, and chemicals. This diversification expanded the use of elastomers in transportation, industry, and consumer goods.
8.4 Modern elastomer engineering
Modern elastomer engineering focuses on precise material design for specific performance targets. Researchers and manufacturers can tailor molecular architecture, reinforcement, and curing systems to suit demanding applications. The result is a broad family of materials spanning soft consumer products to high-performance industrial components.