Thermal conductivity is the intrinsic property of a material relating to its ability to conduct heat through conduction without overall motion. Conduction occurs due to a temperature gradient creating higher molecular energy and movement from hot to cold areas. Thermal conductivity is defined quantitatively as the amount of heat transmitted through a material of a given thickness with a certain area, due to a temperature difference. It is important for manufacturing and processing fibers where heating and cooling rates impact orientation and properties, as well as applications where fiber thermal comfort and advanced composites rely on heat dissipation capacity. A material's thermal conductivity depends on numerous factors like temperature, pressure, density, chain orientation, crystallinity, and can vary significantly with changes in these conditions.

1. Thermal conductivity
• Ther al o du ti ity λ is the i tri si property of a aterial hi h relates
its ability to conduct heat. Heat transfer by conduction involves transfer of
energy within a material without any motion of the material as a whole.
Conduction takes place when a temperature gradient exists in a solid (or
stationary fluid) medium. Conductive heat flow occurs in the direction of
decreasing temperature because higher temperature equates to higher
molecular energy or more molecular movement. Energy is transferred from
the more energetic to the less energetic molecules when neighboring
molecules collide.
• Thermal conductivity is defined as the quantity of heat (Q) transmitted
through a unit thickness (L) in a direction normal to a surface of unit area (A)
due to a u it te perature gradie t ΔT) under steady state conditions and
when the heat transfer is dependent only on the temperature gradient. In
equation form this becomes the following:
• Thermal Conductivity = heat × distance / (area × temperature gradient)
λ = Q × L / (A × ΔT) Thermal conductivity is measured in watts per kelvin-
eter W·K−1 · −1)

2. Importance
• Thermal conductivity of man made fibers is an
important thermal property in regards to
manufacturing, processing and applications.
• In manufacturing, subsequent cooling or annealing
may also be controlled by heat transport properties of
polymer, which eventually give the molecular
orientation and therefore physical properties of fiber.
• One example is crystalline polymers, for which the
structural and morphological features may be
significantly changed with the speed of cooling.

3. • Heating and cooling rates of fiber/fabric in various
processing (heat setting, ironing etc) depend on
this property.
• Thermal comfort of garments in cold/summer
seaso depe d o o stitue t fi ers’ o du ti ity.
• There are lot of advance fiber composite materials
are produced based on heat dissipation capacity of
fibers.
• MMF typically have intrinsic thermal conductivity
much lower than those for metals or ceramic
materials, and therefore are good thermal
insulators.

4. • Dependency of conductivity
• Temperature, pressure, density of polymer, orientation of
chain segments, crystal structures, degree of crystallinity, and
many other factors may significantly affect thermal
conductivity of polymers.
• Generally, with increase in temperature, thermal conductivity
for amorphous polymers increases gradually in the glassy
region and decreases slowly or remains constant in the
rubbery region.
• For crystalline polymers, thermal conductivity decreases
steadily with the increase in temperature below the melting
point. At temperature above the melting point, it behaves in a
similar way as amorphous polymers