Standard Test Method for Static and Kinetic Coefficients of Friction of Plastic Film and Sheeting - PDF

Introduction

ASTM D1894 is the standard test method used to determine the static and kinetic coefficients of friction (COF) of plastic films and sheeting when sliding over themselves or other surfaces. This test is essential for understanding the handling, stacking, converting, and processing behavior of plastic materials, especially in packaging, manufacturing, and consumer goods applications.

This guide provides a complete explanation of how to perform ASTM D1894, including the test setup, equipment, specimen preparation, parameters, and result interpretation. Following this method ensures accurate evaluation of the slip resistance of films and sheet materials.

Overview of ASTM D1894

ASTM D1894 evaluates two key frictional properties:

• Static Coefficient of Friction (μs) – the force needed to start sliding.

• Kinetic Coefficient of Friction (μk) – the force needed to maintain motion after sliding has started.

Both measurements help assess whether a material is too slippery (which may cause misalignment or instability) or too tacky (which may lead to feeding or stacking problems).

Equipment and Materials

1. Universal Testing Machine (UTM) or Friction Tester

• A tensile testing machine equipped with a horizontal sliding friction table and capable of maintaining a constant crosshead speed is used.

• Alternatively, a dedicated coefficient of friction tester may be used.

• Load cell capacity is typically 10 N to 50 N, depending on film thickness and frictional properties.

2. Test Platform

• A flat, level, low-friction platform on which the base specimen is secured.

• Surface should be smooth and clean for consistent contact.

3. Sled

• A weighted sled of 200 ± 5 g with a smooth, flat bottom surface.

• A film sample is wrapped or adhered to the sled’s underside.

• The sled is attached to the testing machine using a flexible, low-stretch cable or string.

Specimen Preparation

1. Conditioning
   All specimens should be conditioned in a controlled environment of 23 ± 2°C and 50 ± 5% RH for a minimum of 40 hours prior to testing.

2. Sample Dimensions
   Cut both base and sled film samples to 63 mm wide × 130 mm long (2.5 in × 5 in).
   Ensure samples are free of wrinkles, folds, and surface contaminants.

3. Orientation
   The direction of film movement (machine or transverse) should be noted and kept consistent for all test replicates.

Test Procedure

1. Mount Base Specimen
   Affix one specimen securely to the horizontal platform using tape or vacuum suction to prevent movement during testing.

2. Mount Sled Specimen
   Attach another specimen to the underside of the sled using double-sided adhesive tape or static cling.

3. Place Sled on Base
   Gently position the sled on top of the base specimen with no external pressure.

4. Connect Sled to UTM
   Attach a flexible cable between the sled and the tensile tester’s crosshead.

5. Run the Test
   Move the crosshead horizontally at a speed of 150 ± 30 mm/min (5.9 ± 1.2 in/min) over a sliding distance of at least 130 mm (5 in).

6. Measure Forces
   Record:

   • The peak force required to initiate motion (used for static COF)

   • The average force during steady sliding (used for kinetic COF)

Calculation of Results

Static Coefficient of Friction (μs):

Static COF = Static Force (N) ÷ Weight of Sled (N)

For example:
If the peak static force = 0.40 N, and the sled weighs 2.00 N, then:
Static COF = 0.40 ÷ 2.00 = 0.20

Kinetic Coefficient of Friction (μk):

Kinetic COF = Average Sliding Force (N) ÷ Weight of Sled (N)

For example:
If the average sliding force = 0.30 N, and the sled weighs 2.00 N, then:
Kinetic COF = 0.30 ÷ 2.00 = 0.15

Reporting Requirements

The final test report should include:

• Type and thickness of film

• Direction of test (machine or transverse)

• Surface preparation method (self-to-self, coated to uncoated, etc.)

• Environmental conditions (temperature and humidity)

• Mass of sled used

• Static and kinetic coefficients of friction (average of multiple tests)

• Number of replicates (typically 3–5)

• Notes on any visual observations (e.g., film sticking, tearing)

Applications of ASTM D1894

• Flexible packaging (e.g., snack bags, pouches)

• Plastic liners and bags

• Label films and sheets

• Shrink wrap and stretch wrap

• Laminate films

• Automotive and electronic films

By measuring COF, manufacturers can ensure optimal machine performance, stackability, and consumer usability of plastic products.

Best Practices and Tips

• Always clean the sled and platform between tests to avoid residue affecting results.

• Perform tests in the same direction (machine or transverse) across all samples for consistency.

• If the film has different sides (e.g., coated vs. uncoated), test each side against itself and opposite side to understand variation.

• Repeat tests with multiple sleds and operators to reduce human error.

Conclusion

ASTM D1894 is the industry-standard method for quantifying static and kinetic friction in plastic film and sheeting. It provides valuable data for material development, quality control, and process optimization in packaging and plastics industries.

By using the correct grips, sled, test platform, and loading rate, manufacturers can achieve consistent, reliable friction measurements that help improve film processability, user experience, and final product quality.