Elastomer

Introduction

An elastomer is a polymer with viscoelasticity (i.e., both viscosity and elasticity) and very weak intermolecular forces, generally having low Young's modulus and high failure strain compared with other materials. The term, a portmanteau of "elastic polymer," is often used interchangeably with rubber, although the latter term is preferred when referring to vulcanized elastomers. Elastomers are typically thermosets (requiring curing) but may also be thermoplastic.

Properties

Elastomers are characterized by their ability to undergo significant deformation under stress and return to their original shape when the stress is removed. This behavior is due to the polymer chains' flexibility, which allows them to stretch and then recoil. Key properties of elastomers include:

**Elasticity**: Elastomers can stretch to several times their original length and return to their original shape.
**Viscoelasticity**: They exhibit both viscous and elastic characteristics when undergoing deformation.
**Low Young's Modulus**: This indicates that elastomers are soft and flexible.
**High Failure Strain**: They can endure significant strain before breaking.

Types of Elastomers

Natural Rubber

Natural rubber, also known as Hevea rubber, is derived from the latex of the rubber tree. It is primarily composed of polyisoprene and is known for its excellent elasticity, resilience, and tensile strength. Natural rubber is used in a variety of applications, including tires, footwear, and adhesives.

Synthetic Elastomers

Synthetic elastomers are man-made and can be tailored for specific properties. Common types include:

**SBR**: Widely used in automobile tires, SBR is known for its abrasion resistance and aging stability.
**NBR**: Resistant to oils and fuels, NBR is used in automotive and aeronautical applications.
**CR**: Also known as neoprene, CR is used in wetsuits, hoses, and gaskets due to its resistance to weathering and chemicals.
**Silicone**: Known for its thermal stability and flexibility, silicone is used in medical devices, cookware, and sealants.

Manufacturing Processes

Elastomers can be processed through various methods, including:

**Extrusion**: The material is forced through a die to create long shapes like tubes and sheets.
**Injection Molding**: The elastomer is injected into a mold where it cools and solidifies into the desired shape.
**Compression Molding**: The material is placed in a heated mold and compressed to form the shape.
**Calendering**: The elastomer is passed through rollers to create thin sheets.

Applications

Elastomers are used in a wide range of applications due to their unique properties. Some of the most common applications include:

**Automotive**: Tires, seals, hoses, and gaskets.
**Medical**: Gloves, catheters, and prosthetics.
**Consumer Goods**: Footwear, elastic bands, and toys.
**Industrial**: Conveyor belts, vibration dampers, and seals.

Chemical Structure

The chemical structure of elastomers consists of long polymer chains with a high degree of flexibility. These chains are typically cross-linked, which provides the material with its elastic properties. The degree of cross-linking can be controlled to tailor the material's properties for specific applications.

Cross-Linking and Vulcanization

Cross-linking is a process that enhances the properties of elastomers by creating bonds between polymer chains. This can be achieved through various methods, including:

**Vulcanization**: A chemical process that involves adding sulfur or other curatives to create cross-links. This process improves the material's elasticity, strength, and resistance to solvents and temperature changes.
**Peroxide Curing**: Uses organic peroxides to form cross-links, providing better heat resistance compared to sulfur vulcanization.
**Radiation Curing**: Uses high-energy radiation to induce cross-linking, often used for medical and aerospace applications.

Thermoplastic Elastomers

Thermoplastic elastomers (TPEs) combine the properties of elastomers with the processing advantages of thermoplastics. They can be melted and reformed, making them recyclable and versatile. Common types of TPEs include:

**SBCs**: Used in footwear, adhesives, and sealants.
**TPU**: Known for its high abrasion resistance and flexibility, used in automotive parts and sports equipment.
**TPVs**: Blend of elastomer and thermoplastic, used in automotive seals and hoses.

Environmental and Health Considerations

The production and disposal of elastomers pose environmental and health challenges. Natural rubber harvesting can lead to deforestation, while synthetic elastomers are derived from petroleum, contributing to fossil fuel depletion. Recycling and developing bio-based elastomers are areas of ongoing research to mitigate these impacts.

Future Trends

Advancements in elastomer technology focus on improving performance, sustainability, and functionality. Innovations include:

**Bio-based Elastomers**: Developing elastomers from renewable resources to reduce environmental impact.
**Smart Elastomers**: Incorporating sensors and actuators for applications in robotics and wearable technology.
**Enhanced Durability**: Improving resistance to wear, chemicals, and extreme temperatures for industrial applications.