Measured by ASTM D-648 (ISO 75) test procedures, it is the temperature at which an applied load causes a test bar of the plastic to deflect 0.25mm.  Like other thermal properties, HDT is sensitive to test variables.

in testing a resin for this value, there is particular sensitivity to the annealed/unannealed condition of test specimens.  HDT values therefore should be used only to screen candidate materials, rather than as definitive guides for material selection.

Thermal Conductivity

The thermal conductivity of a material is a measure of the ability to transmit heat through the material.  it is the same as the 'K' factor for insulation and is related inversely to the 'R' value of thermal resistance.

The thermal conductivity is a polymetric material changes as the temperature changes.  As a molecules of the polymer heat up, they vibrate at a higher frequency, enabling more energy in the form of heat to be transfered through the polymer.  For that reason, thermal conductivity is generally reported at at 2 temperature value: -18 Degree Celcius and 100 Degree Celcius.

Coefficient Of Linear Thermal Expansion

The coefficient of linear thermal expansion (CLTE) of any material is the change in the material's length (strain) per unit change in temperature.  As temperature increases, molecular motion within a plastic material increases.  Therefore, the amount of expansion and the value of CLTE increase as well.

Vicat Softening Point

The Vicat softening point measured by ASTM D-1525 (ISO 306) procedures, is the temperature at which a flattened needle of 1mm square cross section, and under a specified constant load, penetrates a specimen of the plastic to the depth of 1mm.  It is useful as a rough comparative guide to a resin's resistance to elevated temperature.

Maximum Use Temperature

The Maximum Use Temperature of a plastic can be expressed as its relative thermal index in maximum degree Celcius, as tested according to Underwriters Laboratory Test Method UL 764b.

When operated at or below its relative thermal index as determined by ageing tests concerning the electrical and mechanical properties, the material should not demonstrate signicant degrading of those properties at that temperature for the intended life of the final product.

Note that different thermal indices may be assigned based on the thickness used and the properties evaluated.

Combustibility

The ignition resistance of a plastic is rated according to Underwriters Laboratory Standard 94 (UL94).  The UL ratings represent the results of two separate tests.  In the ratings from the first test: V-0, V-1, V-2 or HB where V-0 indicates the most ignition resistant material and HB indicates the least resistant.  The rating from the second test (5V), is added to the first rating if the plastic passes the second test.  Thus, a combination of V-0 and V-5 is the highest UL94 rating possible, and HB is the lowest.

Ignition resistant (IR) grades are a large and important segment of the thermoplastic market.

Smoke Generation Limiting Oxygen Index

A limiting oxygen index (LOI) value states the minimum concentration of oxygen, expressed as percent by volume, in a mixture of oxygen and nitrogen, that will support flaming combustion of a material which is initially at room temperature.  A higher value indicates a less flammable material.