Coefficient of Friction Testing at Low Temperatures: Methods, Standards, and Applications

Coefficient of friction (COF) testing at low temperatures evaluates how materials behave tribologically when exposed to sub-ambient and cryogenic conditions, providing critical data for packaging, automotive, aerospace, and cold-chain applications. Because friction and wear properties can change dramatically as temperatures drop, low-temperature COF measurement is essential for material qualification, quality control, and product safety. This article explains the principles, sample types, test items, methods, relevant standards, and practical applications of friction coefficient determination in cold environments.

Technical Overview

Coefficient of friction (COF) is a dimensionless value that quantifies the resistance to sliding between two surfaces in contact. It is expressed as the ratio of the tangential friction force to the normal force pressing the surfaces together. The static coefficient of friction (μs) describes the force needed to initiate relative motion, while the kinetic coefficient of friction (μk) describes the force required to sustain sliding at a constant velocity.

Temperature is one of the most influential external factors affecting frictional behavior. At reduced temperatures, polymer chains lose mobility, lubricant viscosity increases sharply, surface condensation and frost formation may occur, and material hardness rises—all of which can shift the COF significantly compared with room-temperature values. A packaging film that runs smoothly on a filling line at 23°C may jam or slip unpredictably in a freezer environment at -30°C. For this reason, low-temperature friction coefficient determination has become a routine requirement in industries such as flexible packaging, cold-chain logistics, automotive winter engineering, refrigeration systems, and aerospace.

Low-temperature COF testing is typically performed by integrating a friction tester or tribometer with an environmental chamber capable of maintaining temperatures from approximately 0°C down to -40°C, with specialized systems reaching -70°C or cryogenic levels below -150°C using mechanical refrigeration or liquid nitrogen cooling. The test records both static and kinetic friction values under precisely controlled temperature, humidity (or dry gas purge), load, and sliding speed conditions.

Testing Samples

Polymer Films and Flexible Packaging Materials

Flexible films such as polyethylene (PE), polypropylene (PP), polyethylene terephthalate (PET), polyamide (PA), and multilayer laminates are among the most frequently tested materials. These films are used in frozen food packaging, ice cream wrappers, and cold-chain pouches, where reliable machinability at low temperature depends on controlled slip properties imparted by slip agents and antiblock additives.

Rubber and Elastomeric Components

Seals, gaskets, O-rings, conveyor belts, tires, and wiper blades made from natural rubber, EPDM, silicone, fluoroelastomers (FKM), or thermoplastic elastomers (TPE) require friction characterization at low temperatures to ensure sealing integrity, traction performance, and wear resistance in cold service conditions.

Engineering Plastics and Sliding Components

Bushings, gears, bearings, guides, and fasteners produced from PA6, PA66, POM, PTFE, PEEK, UHMW-PE, and their filled or lubricated grades are tested to verify friction stability in refrigeration equipment, outdoor machinery, and winter-operated devices.

Metallic and Coated Surface Pairs

Steel, aluminum, anodized surfaces, PVD coatings, and galvanized pairs used in refrigeration hardware, cryogenic valves, and arctic structures can be evaluated for friction changes caused by low-temperature hardening and ice formation.

Lubricants, Greases, and Surface Treatments

Lubricating oils, greases, dry-film lubricants, and release coatings intended for freezers, ski equipment, automotive door mechanisms, and aerospace actuation systems are assessed to confirm that friction performance is retained when viscosity increases at low temperature.

Testing Items

Typical test items and reported parameters for low-temperature friction coefficient determination include:

• Static coefficient of friction (μs) at specified low temperatures (for example, 0°C, -10°C, -20°C, -30°C, or -40°C)
• Kinetic (dynamic) coefficient of friction (μk) under the same temperature conditions
• COF temperature sweeps across a defined range to map friction-temperature behavior and identify transition points such as the brittle point or glass transition influence
• Film-to-film and film-to-metal COF measurements simulating package-on-package and package-on-conveyor interactions
• Friction force curves (force versus time or displacement) to capture stick-slip behavior at low temperature
• Repeat-cycle friction testing to evaluate friction stability after thermal cycling or prolonged cold exposure
• Comparative evaluation before and after cold conditioning, frost/condensation exposure, or accelerated low-temperature aging

Testing Methods

Relevant Standards

Several international and national standards govern friction coefficient measurement, and their principles are extended to low-temperature conditions through the use of environmental enclosures:

• ASTM D1894 – Standard Test Method for Static and Kinetic Coefficients of Friction of Plastic Film and Sheeting
• ISO 8295 – Plastics: Film and Sheeting: Determination of the Coefficients of Friction
• GB/T 10006 – Chinese national standard for determining coefficients of friction of plastic film and sheeting, harmonized with ISO 8295
• ASTM G115 – Standard Guide for Measuring and Reporting Friction Coefficients, applicable to general material pairs
• ASTM G99 – Standard Test Method for Wear Testing with a Pin-on-Disk Apparatus, adaptable to chamber-controlled temperature
• ASTM G133 – Standard Test Method for Linearly Reciprocating Ball-on-Flat Sliding Wear, frequently used with cooled chambers
• ISO 6601 – Plastics: Friction and Wear by Sliding: Identification of Test Parameters
• ASTM D1894 and ISO 8295 modified procedures as commonly referenced in cold-chain packaging specifications

Instrumentation

Testing is performed using a horizontal plane COF tester or a tribometer (pin-on-disk, ball-on-flat, or sled-type configuration) fitted with an environmental chamber. The chamber may achieve low temperatures by mechanical refrigeration, thermoelectric (Peltier) cooling, or liquid nitrogen injection, typically covering ranges from ambient down to -40°C for standard chambers, -70°C for extended refrigeration, and below -150°C for cryogenic configurations. Load cells with temperature-compensated calibration measure the friction force, while integrated thermocouples monitor both the chamber air temperature and the actual specimen surface temperature.

Typical Test Procedure

• Specimen preparation: Samples are cut to the dimensions required by the selected standard, and surfaces are cleaned as specified to remove contaminants that could alter results.
• Conditioning: Specimens are preconditioned in the chamber at the target temperature for a sufficient dwell time (commonly 30 minutes to several hours) to ensure thermal equilibrium throughout the material thickness.
• Test setup: The sled or counter-body of defined mass and contact area is placed on the specimen, applying the standard normal force.
• Measurement: The drive system initiates relative motion at the specified speed, and the force transducer records the peak force (static) and the average sustained force (kinetic).
• Calculation: The coefficients are computed by dividing the measured friction forces by the normal force (μs = Fs/N; μk = Fk/N).
• Repetition: Multiple runs (typically at least three to five per condition) are performed, and results are reported as mean values with standard deviations.
• Reporting: The test report documents the material pair, temperature, humidity or purge-gas condition, normal load, sliding speed, contact geometry, and all measured COF values.

Key Considerations for Low-Temperature Measurement

Moisture management is critical: condensation and frost on cooled surfaces can artificially raise or lower measured friction. Chambers are commonly purged with dry nitrogen or operated at controlled low dew points to ensure reproducible results. Load-cell thermal drift must be corrected through calibration at temperature, and sufficient thermal soak time must be verified because thick or low-conductivity specimens may remain warmer than the chamber air. Stick-slip phenomena, which intensify in many polymer systems at low temperature, should be captured with high-speed data acquisition and discussed in the report.

Applications

Low-temperature coefficient of friction testing supports numerous industries and product categories:

• Cold-chain and frozen food packaging: Verifying that films, pouches, and cartons maintain machinable friction on high-speed vertical form-fill-seal and case-packing equipment operating in chilled production rooms.
• Automotive engineering: Qualifying door seals, window channels, weatherstrips, brake components, and interior mechanisms for reliable operation in winter climates down to -40°C.
• Aerospace and defense: Evaluating actuator materials, seals, and lubricants subjected to high-altitude and polar low-temperature environments, including cryogenic propellant system components.
• Refrigeration and HVAC: Confirming friction performance of sliding parts, drawer rails, gaskets, and conveyor elements inside freezers and cold storage facilities.
• Oil, gas, and arctic infrastructure: Assessing pipeline coatings, sealing materials, and structural sliding interfaces exposed to extreme cold.
• Medical and laboratory products: Ensuring that packaging for refrigerated biologics, vaccines, and diagnostic kits feeds and opens predictably in cold environments.
• Sports and consumer goods: Characterizing ski bases, snowboard surfaces, cold-weather footwear outsoles, and winter outdoor equipment.

FAQ

Why does the coefficient of friction change at low temperatures?

At low temperatures, polymer materials become harder and less compliant, reducing real contact area but increasing surface adhesion characteristics; slip agents in films may migrate more slowly to the surface; lubricant viscosity rises sharply, altering boundary and hydrodynamic lubrication regimes; and frost or ice formation can introduce new interfacial layers. The net effect may be an increase or decrease in COF depending on the material system, which is why direct measurement is essential.

What temperature range can be achieved in low-temperature COF testing?

Standard environmental chambers typically operate from room temperature down to -40°C, extended refrigerated systems reach approximately -70°C, and cryogenic tribometers using liquid nitrogen can operate from -150°C down to -196°C. Accredited third-party laboratories can advise on the most appropriate range for a given application and standard.

Which standard should be used for plastic film friction testing?

ASTM D1894 and ISO 8295 (with its Chinese counterpart GB/T 10006) are the most widely applied methods for plastic film and sheeting. For rigid material pairs, ASTM G115 provides general guidance, while ASTM G99 and ASTM G133 cover pin-on-disk and reciprocating tribometry that can be adapted to chamber-controlled low temperatures.

How long should specimens be conditioned at the low temperature before testing?

Conditioning time depends on specimen thickness and thermal conductivity, but a minimum soak of 30 minutes after the specimen surface reaches the set point is common; thicker or multi-layer samples may require several hours. Surface-attached thermocouples are recommended to confirm that the actual contact interface has reached thermal equilibrium.

How is frost and condensation controlled during testing?

Chambers are purged with dry nitrogen or dry air, or the entire test section is enclosed in a sealed, dehumidified environment so that water vapor cannot condense and freeze on the specimens. This ensures the measured friction reflects the material pair rather than an ice interlayer.

What sample size and quantity are needed for a typical test?

For film testing per ASTM D1894 or ISO 8295, specimens are typically prepared as a sled-mounted piece (for example, 63.5 mm square) and a larger stationary plane sample (approximately 250 mm by 130 mm). A minimum of three to five valid runs per temperature condition is recommended for statistical reliability; accredited third-party laboratories can confirm exact sample requirements based on the selected method.