Thermal Conductivity

1. What is thermal conductivity?
2. What is the formula to calculate thermal conductivity?
3. What is the mechanism of thermal conduction in polymers?
4. What materials show thermal conductivity?
5. What factors influence thermal conductivity of polymers?
6. Which instrument measures thermal conductivity of polymers?
7. What test methods measure thermal conductivity of polymers?
8. What are thermal insulation values of several plastics?

What is thermal conductivity?

Thermal conduction is the transfer of heat from one part of a body to another with which it is in contact. The thermal insulating capacity of plastics is rated by measuring thermal conductivity.

Thermal insulation of polymers (thermoplastics, foam or thermoset) is essential to:

• Understand the processing of the material into the final product,
• Establish appropriate applications of the material. For e.g., polymeric foams for insulation.

Note: PUR and PIR can be molded as board materials. They can be used as insulation foams in roofs, plastered walls, sandwich walls, and floors. Unlike metals, plastics do not have free electrons available for conduction mechanisms. Hence, they are poor conductors of heat.

What is the formula to calculate thermal conductivity?

Thermal conductivity is denoted by the letter k. It is calculated using the formula:


Where,

• k is the thermal conductivity of the material [in W/(m·K)]
• Q is the quantity of heat passing through a base area of the sample [in Watts]
• A is the base area of the sample [in square meters]
• d is the distance between two sides of the sample [in meters]
• T₂ is the temperature on the warmer side of the sample [in Kelvin or Celsius]
• T₁ is the temperature on the colder side of the sample [in Kelvin or Celsius]

What is the mechanism of thermal conduction in polymers?

Structural changes in polymers

Thermal conduction in polymers is based on the mechanism of movement of molecules. This occurs across:

• intramolecular bonds and
• intermolecular bonds.

Crosslinking in thermosets & elastomers increases thermal conductivity. This is because the Van der Waals bonds are replaced by valence bonds. Alternatively, a decrease in thermal conductivity can be due to:

• decreasing interbond path length,
• factors causing increased disorder, or
• free volume in polymers.

Crystallinity in polymers

The crystallinity of polymers leads to improved packing of molecules. This in turn increases thermal conductivity.

Amorphous polymers

• They show an increase in thermal conductivity with increasing temperature. This increase is up to the glass transition temperature (Tg).
• Above Tg, the thermal conductivity decreases with an increase in temperature.

Note: For amorphous plastics at 0-200°C, the thermal conductivity lies between 0.125-0.2 Wm^-1K^-1.

Semi-crystalline thermoplastics

• They have a higher thermal conductivity in the solid state than in the melt state. This is due to an increase in density upon their solidification.
• But, in the melt state, the thermal conductivity of these polymers reduces to that of amorphous polymers.

Note: Semi-crystalline thermoplastics have ordered crystalline regions. Hence, they have better conductivity.

What materials show thermal conductivity?

1. Thermally Conductive Thermoplastics — View All Products
2. Thermally Conductive Rubbers — View All Products
3. Thermally Conductive Thermosets — View All Products
4. Thermally Conductive TPEs/TPVs — View All Products

What factors influence thermal conductivity of polymers?

Filler or fiber content

Organic plastics are very good insulators. Thermal conductivity of polymers increases with increasing:

• volumetric filler content or
• fiber content up to 20% by volume fraction.

» Inorganic fillers — They have high thermal conductivity. Thus, they increase the thermal conductivity of filled polymers.

» Gaseous fillers — The incorporation of gaseous fillers in the structure decreases heat conduction. This happens in polymeric foams. This is due to the increase in the number of closed cells in the foam minimizes heat conduction.

Hydrostatic pressure

The thermal conductivity of melts increases with hydrostatic pressure.

Compression of plastics

Compression of plastics imposes the opposite effect on thermal insulation as it increases the packing density of molecules.

Other Factors

The thermal conductivity increases with an increase in:

• density of material
• moisture of material
• ambient temperature

Which instrument measures thermal conductivity of polymers?

The guarded hot plate apparatus is used to measure the thermal transmission properties of homogeneous insulation materials. This is done in the form of flat slabs.

Procedure

1. A solid sample of material is placed between two plates.
2. One plate is heated and the other is cooled or heated to a lesser extent.
3. The temperature of the plates is monitored until they are constant.
4. Thermal conductivity is calculated by using the:
   • steady state temperatures,
   • thickness of the sample, and
   • heat input to the hot plate.

What test methods measure thermal conductivity of polymers?

Thermal conductivity of plastics is generally measured by:

• ASTM C177 — It measures thermal transmission properties. It also measures steady-state heat flux. The measurement is by means of the guarded-hot-plate apparatus.


• ISO 8302 — It determines steady-state thermal resistance and related properties. Guarded hot plate apparatus is used in this case.

What are thermal insulation values of several plastics?

Click to find polymer you are looking for:
A-C     |      E-M     |      PA-PC     |      PE-PL     |      PM-PP     |      PS-X

Polymer Name	Min Value (W/m.K)	Max Value (W/m.K)
ABS - Acrylonitrile Butadiene Styrene	0.130	0.190
ABS Flame Retardant	0.173	0.175
ABS High Heat	0.200	0.400
ABS High Impact	0.200	0.400
ABS/PC Blend 20% Glass Fiber	0.140	0.150
ASA - Acrylonitrile Styrene Acrylate	0.170	0.170
ASA/PC Blend - Acrylonitrile Styrene Acrylate/Polycarbonate Blend	0.170	0.170
ASA/PC Flame Retardant	0.170	0.700
CA - Cellulose Acetate	0.250	0.250
CAB - Cellulose Acetate Butyrate	0.250	0.250
CP - Cellulose Proprionate	0.190	0.190
CPVC - Chlorinated Polyvinyl Chloride	0.160	0.160
ECTFE	0.150	0.150
EVOH - Ethylene Vinyl Alcohol	0.340	0.360
FEP - Fluorinated Ethylene Propylene	0.250	0.250
HDPE - High Density Polyethylene	0.450	0.500
HIPS - High Impact Polystyrene	0.110	0.140
HIPS Flame Retardant V0	0.120	0.120
Ionomer (Ethylene-Methyl Acrylate Copolymer)	0.230	0.250
LCP - Liquid Crystal Polymer Glass Fiber-reinforced	0.270	0.320
LDPE - Low Density Polyethylene	0.320	0.350
LLDPE - Linear Low Density Polyethylene	0.350	0.450
MABS (Transparent Acrylonitrile Butadiene Styrene)	0.170	0.180
PA 11 - (Polyamide 11) 30% Glass fiber reinforced	0.330	0.330
PA 11, Conductive	0.330	0.330
PA 11, Flexible	0.330	0.330
PA 11, Rigid	0.330	0.330
PA 12, Flexible	0.330	0.330
PA 12, Rigid	0.330	0.330
PA 46 - Polyamide 46	0.300	0.300
PA 6 - Polyamide 6	0.240	0.240
PA 6-10 - Polyamide 6-10	0.210	0.210
PA 66 - Polyamide 6-6	0.250	0.250
PA 66, 30% Glass Fiber	0.280	0.280
PA 66, 30% Mineral filled	0.380	0.380
PA 66, Impact Modified, 15-30% Glass Fiber	0.300	0.300
PA 66, Impact Modified	0.240	0.450
PAI - Polyamide-Imide	0.240	0.540
PAI, 30% Glass Fiber	0.360	0.360
PAI, Low Friction	0.520	0.520
PAR - Polyarylate	0.180	0.210
PARA (Polyarylamide), 30-60% glass fiber	0.300	0.400
PBT - Polybutylene Terephthalate	0.210	0.210
PBT, 30% Glass Fiber	0.240	0.240
PC (Polycarbonate) 20-40% Glass Fiber	0.220	0.220
PC (Polycarbonate) 20-40% Glass Fiber Flame Retardant	0.210	0.390
PC - Polycarbonate, high heat	0.210	0.210
PE - Polyethylene 30% Glass Fiber	0.300	0.390
PEEK - Polyetheretherketone	0.250	0.250
PEEK 30% Carbon Fiber-reinforced	0.900	0.950
PEEK 30% Glass Fiber-reinforced	0.430	0.430
PEI - Polyetherimide	0.220	0.250
PEI, 30% Glass Fiber-reinforced	0.230	0.260
PEKK (Polyetherketoneketone), Low Crystallinity Grade	1.750	1.750
PESU - Polyethersulfone	0.170	0.190
PET - Polyethylene Terephthalate	0.290	0.290
PET, 30% Glass Fiber-reinforced	0.330	0.330
PETG - Polyethylene Terephthalate Glycol	0.190	0.190
PFA - Perfluoroalkoxy	0.190	0.260
PI - Polyimide	0.100	0.350
PLA - Polylactide	0.110	0.195
PMMA - Polymethylmethacrylate/Acrylic	0.150	0.250
PMMA (Acrylic), High Heat	0.120	0.210
PMMA (Acrylic) Impact Modified	0.200	0.220
POM - Polyoxymethylene (Acetal)	0.310	0.370
POM (Acetal) Low Friction	0.310	0.310
PP - Polypropylene 10-20% Glass Fiber	0.200	0.300
PP, 10-40% Mineral Filled	0.300	0.400
PP, 10-40% Talc Filled	0.300	0.400
PP, 30-40% Glass Fiber-reinforced	0.300	0.300
PP (Polypropylene) Copolymer	0.150	0.210
PP (Polypropylene) Homopolymer	0.150	0.210
PP, Impact Modified	0.150	0.210
PPE - Polyphenylene Ether	0.160	0.220
PPE, 30% Glass Fiber-reinforced	0.280	0.280
PPE, Flame Retardant	0.160	0.220
PPS - Polyphenylene Sulfide	0.290	0.320
PPS, 20-30% Glass Fiber-reinforced	0.300	0.300
PPS, 40% Glass Fiber-reinforced	0.300	0.300
PPS, Conductive	0.300	0.400
PPS, Glass fiber & Mineral-filled	0.600	0.600
PS (Polystyrene) 30% glass fiber	0.190	0.190
PS (Polystyrene) Crystal	0.160	0.160
PS, High Heat	0.160	0.160
PSU - Polysulfone	0.120	0.260
PSU, 30% Glass fiber-reinforced	0.300	0.300
PTFE - Polytetrafluoroethylene	0.240	0.240
PTFE, 25% Glass Fiber-reinforced	0.170	0.450
PVC, Plasticized	0.160	0.160
PVC, Plasticized Filled	0.160	0.160
PVC Rigid	0.160	0.160
PVDC - Polyvinylidene Chloride	0.160	0.200
PVDF - Polyvinylidene Fluoride	0.180	0.180
SAN - Styrene Acrylonitrile	0.150	0.150
SAN, 20% Glass Fiber-reinforced	0.200	0.320
SMA - Styrene Maleic Anhydride	0.170	0.170