About Plastics and Rubber

What is Plastic?

Plastics and plastic materials are organic, synthetic or processed polymers that are supplied as raw materials or stock shapes. They typically consist of thermoplastic or thermosetting resins and can be made into many forms. Stock shape forms include sheets, plates, rods, tubes, films, or extruded profiles. Often, thermoplastic resins are supplied as pellets for feeding into molding machines or extrusion presses. Thermosets may be supplied as two-part liquid resins such as epoxies, or as a non-flowing mass premixed with fiber reinforcement. Polyester bulk molding compounds (BMC) are an example of this latter form. Water-based resins, water-born resins and latex products are plastics and plastic materials that consist of resin or polymer droplets that are dispersed and suspended in a water carrier or solvent.

There are many material types and grades for plastics and plastic materials. Cure type or cure technology is also an important consideration. Material types include monomers and intermediates, binders and base polymers, composite materials, thermoplastic materials, thermosets and crosslinked materials, semi-finished shapes, fabricated shapes, and resins and compounded raw materials such as pellets and liquids. Electrical and electronic materials, optical grade materials, and self-lubricated or bearing-grade plastics and plastic materials are also available. With regard to cure type or cure technology, choices include air setting or film drying, anaerobic, thermoplastic or hot melt, thermosetting or cross-linking, room-temperature curing or vulcanizing, and pressure sensitive adhesive (PSA). Plastics and plastic materials that are cured with ultraviolet light (UV) are also available, as are reactive resins, single-component products, and two-component systems.

With plastics and plastic materials, the term “material system” refers to the chemical or polymer system type. Examples include acetal, acrylonitrile-butadiene-styrene (ABS), acrylic, bismaleimide (BMI), cellulosic, epoxy (EP), ethylene copolymer, fluoropolymer, ionomer, liquid crystal polymer (LCP), and ketones such as polyaryletherketone and polyetheretherketone (PEEK). Choices for plastics and plastic materials also include phenolics and formaldehyde resins, polyamide, polyamide, polyimide, polybutadiene, polycarbonate (PC), polyethylene, polyethylene terphthalate (PET), and polybutylene terphthalate (PBT). In addition, plastics and plastic materials may contain polyester, vinyl ester, polyether block amide (PEBA) resins, polyetherimide, polyolefin, polyphenylene oxide (PPO), polypropylene (PP), polysulphide, polysulphone, or polyphthalamide. Products made of silicone, styrene, styrene copolymer, and vinyl are also available.

Plastics and plastic materials carry many different specifications. Categories include material type or grade, cure type or technology, material system, and (if applicable) filler material. Thermal properties, mechanical properties, electrical and optical properties, and processing and physical properties are also important considerations. Thermal properties for plastics and plastic materials include use temperature, deflection temperature, thermal conductivity and coefficient of thermal expansion (CTE). Tensile strength, tensile modulus, and elongation are important mechanical parameters. Electrical and optical properties include electrical resistivity, dielectric strength, dielectric constant or relative permittivity, index of refraction, and transmission. Viscosity, melt flow index (MFI) and water absorption are processing and physical properties to consider when selecting plastics and plastic materials.

(Article Courtesy of GLOBALSPEC – The Engineering Search Engine)

 

 

What is Rubber?

An elastomer is an elastic material which, at room temperature, can be stretched and, when released, returns to within 90% of its original dimensions and shape within a period of time. Engineered Elastomers are a group of tough, rubber-like materials which are designed to perform in certain predictable ways when subjected to defined application stresses. They are most commonly used to manufacture mechanical parts which solve commercial/industrial problems involving impact, vibration, shock, pressure, corrosion, wear, abrasion and noise.

Rubber & Urethane elastomers are very unique materials. No other compound can duplicate their range of desirable properties. Unlike other engineering materials such as plastic or metal, rubber and urethane elastomer often do not have as clearly defined design criteria. This is because there are so many interdependent variables which effect performance. Successful rubber material selection often relies heavily on the designer’s application experience. Although there may be comparatively few “types” of rubber but there are infinite variations of factors which effect material performance, such as formulation, hardness, chemical compatibility, dynamic and static forces, mechanical properties, temperature, abrasion, part geometry, installation technique and cost — just to name a few.

Due to this complex interaction, it is critical that our elastomer recommendations be rigorously tested in actual application so that performance assumptions may be checked against the application’s unique variables as well as approved by the customer.

What is Rubber?

“Rubber” refers to elastomeric compounds that consist of various monomer units forming polymers that are heat cured (vulcanized). Polymers are long molecular chains that are connected together (cross-linked) to improve their toughness and resilience. The base monomer (or monomers, when blended) is used to classify the type of rubber. For example: Neoprene, SBR or Nitrile.

Rubber correctly refers to the natural gum rubber produced from the sap of the Hevea tree (latex). However it is more commonly used by our customers to describe any material with “rubber-like” elastomer properties. This includes synthetic rubbers and often polyurethanes are referred to as “polyurethane rubber”.

What is a Rubber Compound?

Engineered Rubber is composed of many different ingredients that include the base monomer, vulcanization agents, modifiers, fillers and plasticizers. The addition of modifiers improves physical properties and performance. The “compound” is the complete package of ingredients blended into a formula to offer specific desirable properties.

Identifying Rubber

Many rubber materials look and feel visually similar and are black in color. In fact, some specialty grades are colored black for the purpose of preventing people from guessing what their beneficial properties may be. In other cases, materials which are traditionally black, such as Nitrile and EPDM can be tinted bright colors like Red, Orange and Blue; color alone is a very poor method of identifying materials. The only sure method of determining what a particular sample may be is laboratory analysis; this is a very expensive and time consuming process. Therefore, we often make educate assumptions about customer samples based on application details, past performance and a simple burn test, which can provide indications of the elastomer type based on odor and flame behavior.

Why Does Rubber Act “Rubbery”?

An elastomer is made of two linked parts; a very viscous liquid encapsulated within an elastic solid. The polymeric chains in rubber tend to be very long and flexible which results in an entangled mass of contorted chains. Under load an elastomer is stretched causing these tangled chains to uncoil. They recoil to their original shape when the force is released. Therefore, elastic rebound or rubbery behavior is observed, giving rubber its resilient reputation.

To learn more about designing mechanical components with plastics or rubber, please contact our service team to discuss your application.