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Glossary

Abrasion Resistance
This property may be defined as the resistance to abrasive wear. It is very important in retreads, soles and heels, hose, and the covers of conveyor belts and cables.
Acid Resistance
The resistance to action of acid either concentrated or dilute.
Acrylic
Polymer for which resistance to air and hot oil at temperatures above 300°F are required.
Aging
Accelerated aging tests are run on various rubbers to find out in as short a period as possible the destructive influence of light, oxygen, heat and ozone. Natural or shelf aging requires many years for proper evaluation, so accelerated aging tests will give comparative values in short periods of time; however, there is no absolute correlation between natural aging and accelerated aging.
Atmospheric Aging Resistance
The loss of physical properties due to the normal action of its surroundings (weather).
BUNA-S
See SBR.
Butaprene
See Nitrite Rubber.
Butyl
Copolymer of isobutylene and isoprene. (Commonly used for inner tubes.)
Chemigum
See Nitrate Rubber.
Compression Set
This property is similar to permanent set in that it has a tendency to take a permanent deformation under application of stress. It is actually a characteristic of liquids and is sometimes referred to as hot-flow or cold-flow. It is measured (1) as the amount by which a standard test piece fails to return to its original thickness after being subjected to a standard compressive load or deflection for a fixed period of time; or (2) as the distance returned relative to the amount deflected.
Corona Resistance
The ability of rubber acting as an insulator to withstand the effects of high voltage discharge. Indication of failure appears as surface cracks.
Dielectric Properties
The ability of material to resist the puncture due to electrical stress. This property is expressed in terms of volts per MIL thickness.
Durometer
See Hardness.
Elastomer
A term used to describe elastic polymers with rubber-like behavior.
Elongation
The term “elongation” is used to describe the ability of a rubber compound to stretch without breaking. To describe this property as measured it is more accurate to speak of “ultimate elongation” or “elongation at break” since its value, expressed as percent of original length, is taken at the moment of rupture.
EPDM (EPT, NORDEL)
Terpolymer of ethylene-propylene-diene (noted for excellent ozone resistance).
Flame Resistance
The resistance to burning or material that will not support combustion under ordinary conditions.
Flex Cracking
Rubber articles subjected to repeated flexing have been found to develop small cracks on
the surface.
Fluorocarbon
A polymer designed to meet the most rigid requirements. (Viton A, Fluorel) in oils, solvents, synthetic lubricants and corrosive chemicals, at elevated temperatures.
GRS
See SBR.
Hardness (Durometer)
Hardness as a property of rubber stocks is difficult to define except according to the methods used to determine it. These methods measure the resistance of the stock to indentation by the blunt point of a metal rod, ball or needle. Thus the hardness of rubber can best be described as resistance to indentation.Various instruments measure indentation. The most common instrument used on rubber is the Durometer. Several scales are used depending on the hardness range (00, 0, A, B, C, D), but the A scale, ASTM D2240, is used for most compounds. Readings on each scale are from Oto 100. Durometer hardness is a convenient nondestructive method of testing which can also be correlated to other properties such as tensile strength, tensile modulus, plasticity, and resilience. Since indentation hardness is dependent upon elastic modulus and viscoelastic behavior of the compound, rubber compounds which are not completely elastic will “creep” during the test. This creep should be noted as the difference between the initial hardness reading after 15 seconds of engagement with the specimen. A properly noted reading: Durometer A61, creep 4at 15seconds. 73° F.
Heat Resistance
The ability of rubber to retain its useful properties under the destructive influence of heat.
Hydrocarbon Solvents- Aromatic
Solvents having basic benzene structure, usually coal tar types such as benzene, toluene and xylene.
Hypalon
A polymer that is completely resistant to ozone attack under the most extreme conditions; possesses excellent color stability plus the action of acids, bases, and many other chemicals.
Low Temperature Flexibility
The temperature at which the rubber becomes too stiff to function in its intended manner.
Neoprene (GR-M)
A polymer of chloroprene which is prepared from coal, salt and limestone.
Nitrile Rubber (BUNA-N)
Copolymer or butadiene and acrylinitrile. Butadiene generally is derived from petroleum and acrylonitrile from ethylene oxide and hydrogen cyanide. Names for Nitrile rubbers include: Butraprene, Chemigum, Hycar, Perbunan and Paracril.

 

Non-Aromatic
Straight chain organic carbon structures such as petroleum type solvents.
Oxidation Resistance
The ability of rubber to resist the reaction of atmospheric oxygen.
Permanent Set
When a piece of rubber is stretched and released it does not return to its exact original length but comes to rest somewhat longer than it was before stretching. The increase in length of the rubber strip, expressed as per cent of its original length, is termed “permanent set”.
Permeability
Ability or ease in which a liquid or gas can pass through a film of rubber.
PH
Determine the concentration of either an acid or base.
Plasticity
When subjected to sufficient shearing stress any given body will be deformed. If, after the stress is removed there is no recovery, the body is completely elastic. A proper balance between these two factors is required. The three methods most commonly used in measuring the amount of plasticity in an unvulcanized rubber stock are the Williams Plastometer and the Mooney Viscometer and the Firestone Plastometer. These machines measure the plasticity by compression, shear and extrusion respectively.
Polymer
A term used to express the new material formed by a polymerization reaction.
Polymerization
Chemical reaction whereby simple materials, either one or more, are converted to a complex material which possesses properties entirely different than original materials used at the start of the reaction
Polyurethane
An organic material noted for its high abrasion, ozone, corona and radiation characteristics.
Pure Gum State
A non-pigmented, translucent, basic polymer.

 

 

Resilience
Capability of a material to return to its original size and shape after deformation. It is generally expressed in percentage of ratio of energy returned by rubber to the energy used in compressing rubber.
Rubber, Natural
Most commonly used forms are smoked sheet and pale crepe organic material-latex.
S.A.E.
Society of Automotive Engineers.
SBR
Copolymer of Butadiene and Styrene. Butadiene is a gaseous material generally obtained from Petroleum, and Styrene is a reaction product of ethylene and benzene. SBR is an all-purpose type synthetic similar to natural rubber.
Silicone Rubber
A semi-organic material containing a silicone.
Specific Gravity
The ratio of the weight to the given bulk to that of the same bulk of water (solids and liquids).
Tear Resistance
The resistance to growth of a nick or cut when tension is applied to the cut specimen.

(ASTM D-624).

Tension Modulus
The term “modulus” or “stress” is used to denote resistance to being stretched. It is defined as the force in pounds necessary to stretch a piece of rubber, one square inch in cross section, a specified amount. This amount of stretch is normally expressed as a percentage of original length and the “stress” as pounds per square inch at the fixed elongation.
Tensile Strength
The tensile strength of a rubber compound is in its resistance to rupture under tension. It is measured as strength at break and expressed in pounds per square inch of cross section.

This property has an absolute value in some applications where the product is actually subjected to tension in service but, like the other tensile properties, it is most frequently used in evaluating compounding materials on a cooperative basis. In a series of cures with a variable time factor the tensile strength either passes through a maximum or exhibits a marked change in the slope of its curve. Therefore, the tensile strength may be considered either separately or together with the modulus and elongation in defining an optimum state of cure for any specific compound.

Thiokol
An organic polysulfide.