Measuring the Thermal Conductivity of Polymers

C-Therm TCi Analyzer - Polymer ApplicationPolymers are a unique field of science with application in many industries. Polymers can be found as components for such things as electronics, explosives, household items, thermoelectrics, insulation, packaging and many others. Researchers in the polymer sector are constantly improving these materials to not only better their thermophysical properties but also their density, strength and mechanical properties.

Thermal conductivity plays a key role in the development of these polymers. Researchers experiment with various composite additives in polymers in order to either increase or decrease the thermal conductivity of the material. Researchers in the packaging industry may seek lower thermal conductivity polymers in order to create more insulative packaging materials. Whereas researchers in the electronics industry may experiment with composites to increase thermal conductivity values in order to prevent overheating in the electronic systems.

The C-Therm TCi Thermal Conductivity Analyzer provides the optimal solution for measuring Polymers & Composites as it is the only commercial instrument that offers the versatility to test the thermal conductivity of solids, liquids, powders, pastes, and textiles.

C-Therm TCi Thermal Conductivity and Effusivity Analyzer

              C-Therm TCi Thermal Conductivity Analyzer

Case Highlight #1:

Measuring the Thermal Conductivity of Anisotropic or Oriented Samples

C-Therm’s TCi thermal conductivity measurement is based on the modified transient plane source (MTPS) technique. The MTPS method provides a fast, highly-accurate, and easy way to measure the thermal conductivity of both isotropic and anisotropic samples. For this reason it has become a very popular tool for rapid quality control in the manufacturing of conductive polymers with oriented glass fibres and other fillers for improved heat transport. 

With C-Therm's patented one-sided sensor, clients enjoy the added benefit of not having to mock up specific samples for thermal conductivity testing.  The only requirement is to cover the active 18-mm diameter surface area of the sensor. The figure below illustrates the testing of tensile bars. The bars were described as a polymer resin with carbon fibres heavily oriented in the in-plane direction, and were already produced for testing the tensile strength of the material.  The grip section provided sufficient contact area for the through-plane thermal conductivity measurement.  The limited 4mm thickness of the bars required multiple samples to be clamped together for the in-plane measurement.  In being able to use tensile bars for testing both the through-plane and in-plane thermal conductivity, this saves the client time and money in ensuring the product is meeting the critical performance attributes for heat transport.


Table:  Measuring the Anisotropic Thermal Conductivity of a Polymer
  Through-Plane    In-Plane       
Thermal Conductivity (W/mK) 1.32 2.587

Case Highlight #2:

Investigation of Expandable Polymeric Microspheres for Packaging Applications

This case highlight investigates the feasibility of incorporating expandable polymeric microspheres into polyolefin films for food packaging application. There is also a focus on the ability of the microsphere-loaded film to reduce the weight of the packaging materials and to improve their thermal insulation, mechanical, and barrier properties.

The graph below features the thermal conductivity data acquired using the TCi. Both their thermal conductivity and thermal effusivity of the multilayer HDPE microsphere films decreased with increasing microsphere loading levels. The addition of 1% microsphere loading resulted in an 80% decrease in thermal conductivity. Overall, with the addition of up to 5% microsphere loading it was found that the polyolefin films would be lighter for ration packaging, would reduce cost through the use of less resin to produce the same thickness of film and could improve the thermal insulation for the pouches.


Case Highlight #3:

Measuring the Thermal Conductivity of a Polymer Melt by Transient Line Source (TLS) Technique

Thermal conductivity provides vital information for reliable process simulation of extrusion and injection moulding processes.
Injection molding is the most commonly used manufacturing process for the fabrication of plastic parts. The plastic is melted in the injection molding machine and then injected into the mold, where it cools and solidifies into the final part.
Figure1- Plastic Injection Molding
The thermal conductivity of molten plastics is an important material property from the point of view of plastics processing since it affects temperature distribution and cooling behavior of the melt.  Accurate thermal conductivity characterization of the polymer feedstock supports increased productivity and better quality of finished product.  It is vital for reliable process simulation of extrusion and injection moulding processes.
Figure 2 - C-Therm's Transient Line Source (TLS) sensors provide a robust, efficient, and accurate capability to measure the thermal conductivity of polymer melts according to ASTM D5930.  (L:  Sensor and Sample Vessel  R:  C-Therm TCi Thermal Conductivity Analyzer)
Historically, the setup parameters for such operations were discovered iteratively through trial-and-error and based on the experience of the operator’s “feel” for the equipment.. In modern process development, it is expected to predict the polymer’s behavior during unit operations with the aid of rheological modelling. Polymer manufacturing processes can be optimized in a rational way using such a model – but a model is only as good as the data it’s built on. The thermal conductivity of the polymer feedstock from its initial state (often powdered or pelletized), through the melt transition, and then again as it cools to the melt, is a key thermophysical parameter for such processes, as it dictates important process parameters like heating rate and cooling time needed to avoid undesirable flaws such as blistering, burn marks, warping or sink marks.
Industry has standardized on measuring the thermal conductivity of thermoplastics via the Transient Line Source method C-Therm offers as part of its TCi Thermal Conductivity Analyzer modular instrument. C-Therm’s TLS sensor operates in accordance with industry standard ASTM D5930.  Using a TLS sensor and a sample vessel, as seen above, a powdered polymer may be melted in a bath or dry thermal chamber, then its thermal conductivity measured through the melt transition, and again as it re-solidifies.
Figure 3- Thermal Conductivity Test Results of Polyamide 12      
A sample of powdered polyamide 12 (above), a thermoplastic material commonly used in injection molding, was measured for its thermal conductivity at 125°C, 150°C, and 200°C using the C-Therm TCi Thermal Conductivity Analyzer with a Transient Line Source (TLS) sensor.
C-Therm’s TLS system provides researchers and manufacturing engineers in the polymer sector with a reliable, easy-to-use solution for measuring polymer melts.  The TLS option on the C-Therm TCi can also be bundled together with the broader capabilities the MTPS sensor offering ever greater versatility in testing all types of materials including solids, liquids, powders and pastes with a thermal conductivity range of 0 to 500 W/mK. 


Source:Schirmer Cheney, S., Thellen, C., & Ratto, J. (2012). Investigation of Expandable Polymeric Microspheres for Packaging Application. US Army Natick Soldier R&D Center.