Rubber is a material, which can stretch and shrink. It is a polymer. It can be produced from natural sources (e.g. natural rubber) or can be synthesised on an industrial scale. For example, car tires are usually made from Styrene-butadiene or styrene-butadiene rubber (SBR). These materials have good abrasion resistance and good aging stability when protected by additives. In 2012, more than 5.4 million tonnes of SBR were processed worldwide. Many other things are made from rubber, like gloves, tires, plugs, and masks. Natural rubber, also called caucho or caoutchouc, as initially produced, consists of polymers of the organic compound isoprene, with minor impurities of other organic compounds, plus water.
|Phase at STP||solid|
|Ultimate Tensile Strength||5 MPa|
|Yield Strength||15 MPa|
|Young’s Modulus of Elasticity||0.05 GPa|
|Melting Point||177 °C|
|Thermal Conductivity||0.5 W/mK|
|Heat Capacity||1300 J/g K|
Composition of Rubber
Natural rubber is the polymer cis-1,4-polyisoprene. Typically, a small percentage (up to 5% of dry mass) of other materials, such as proteins, fatty acids, resins, and inorganic materials (salts) are found in natural rubber. Polyisoprene can also be created synthetically, producing what is sometimes referred to as “synthetic natural rubber”, but the synthetic and natural routes are distinct.
Applications of Rubber
Rubber moulded products are widely used industrially (and in some household applications) in the form of rubber goods and appliances. Rubber is used in garden hoses and pipes for small scale gardening applications. Most of the tyres and tubes used in automobiles are made up of rubber.
Mechanical Properties of Rubber
Strength of Rubber
In mechanics of materials, the strength of a material is its ability to withstand an applied load without failure or plastic deformation. Strength of materials basically considers the relationship between the external loads applied to a material and the resulting deformation or change in material dimensions. In designing structures and machines, it is important to consider these factors, in order that the material selected will have adequate strength to resist applied loads or forces and retain its original shape.
Strength of a material is its ability to withstand this applied load without failure or plastic deformation. For tensile stress, the capacity of a material or structure to withstand loads tending to elongate is known as ultimate tensile strength (UTS). Yield strength or yield stress is the material property defined as the stress at which a material begins to deform plastically whereas yield point is the point where nonlinear (elastic + plastic) deformation begins. In case of tensional stress of a uniform bar (stress-strain curve), the Hooke’s law describes behaviour of a bar in the elastic region. The Young’s modulus of elasticity is the elastic modulus for tensile and compressive stress in the linear elasticity regime of a uniaxial deformation and is usually assessed by tensile tests.
See also: Strength of Materials
Ultimate Tensile Strength of Rubber
Ultimate tensile strength of Rubber is 5 MPa.
Yield Strength of Rubber
Yield strength of Rubber is 15 MPa.
Modulus of Elasticity of Rubber
The Young’s modulus of elasticity of Rubber is 0.05 GPa.
Hardness of Rubber
In materials science, hardness is the ability to withstand surface indentation (localized plastic deformation) and scratching. Brinell hardness test is one of indentation hardness tests, that has been developed for hardness testing. In Brinell tests, a hard, spherical indenter is forced under a specific load into the surface of the metal to be tested.
The Brinell hardness number (HB) is the load divided by the surface area of the indentation. The diameter of the impression is measured with a microscope with a superimposed scale. The Brinell hardness number is computed from the equation:
Brinell hardness of Rubber is approximately N/A.
See also: Hardness of Materials
Thermal Properties of Rubber
Rubber – Melting Point
Melting point of Rubber is 177 °C.
Note that, these points are associated with the standard atmospheric pressure. In general, melting is a phase change of a substance from the solid to the liquid phase. The melting point of a substance is the temperature at which this phase change occurs. The melting point also defines a condition in which the solid and liquid can exist in equilibrium. For various chemical compounds and alloys, it is difficult to define the melting point, since they are usually a mixture of various chemical elements.
Rubber – Thermal Conductivity
Thermal conductivity of Rubber is 0.5 W/(m·K).
The heat transfer characteristics of a solid material are measured by a property called the thermal conductivity, k (or λ), measured in W/m.K. It is a measure of a substance’s ability to transfer heat through a material by conduction. Note that Fourier’s law applies for all matter, regardless of its state (solid, liquid, or gas), therefore, it is also defined for liquids and gases.
The thermal conductivity of most liquids and solids varies with temperature. For vapors, it also depends upon pressure. In general:
Most materials are very nearly homogeneous, therefore we can usually write k = k (T). Similar definitions are associated with thermal conductivities in the y- and z-directions (ky, kz), but for an isotropic material the thermal conductivity is independent of the direction of transfer, kx = ky = kz = k.
Rubber – Specific Heat
Specific heat of Rubber is 1300 J/g K.
Specific heat, or specific heat capacity, is a property related to internal energy that is very important in thermodynamics. The intensive properties cv and cp are defined for pure, simple compressible substances as partial derivatives of the internal energy u(T, v) and enthalpy h(T, p), respectively:
where the subscripts v and p denote the variables held fixed during differentiation. The properties cv and cp are referred to as specific heats (or heat capacities) because under certain special conditions they relate the temperature change of a system to the amount of energy added by heat transfer. Their SI units are J/kg K or J/mol K.
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