TPU Film Coefficient of Friction Test: ASTM D1894 Guide

Corrected by the Teng Yang technical team

Technical Quality and Converting Guide

Running an accurate TPU film coefficient of friction test under ASTM D1894-24 or ISO 8295:1995 requires pulling a 200 g sled across a flat horizontal plane. The square sled measures 63.5 × 63.5 mm. ASTM D1894-24 drives the crosshead at 150 ± 30 mm/min. ISO 8295 operates at 100 ± 10 mm/min. All specimens require conditioning at 23 ± 2 °C and 50 ± 10% relative humidity before material testing. Unlike rigid polyolefin or polyester webs, soft 70A–95A thermoplastic polyurethane (TPU) deforms viscoelastically under normal load. Unmodified glossy TPU films frequently generate sawtooth stick-slip oscillations. Their kinetic friction often exceeds 0.80 to 1.20. This guide shows engineers how to mount thin elastic specimens without stretch distortion, pick the right counterface, and protect thermal lamination peel strength.

Quick Engineering Summary (Key Takeaways)

Baseline TPU friction on unmodified soft glossy grades (70A–85A) reaches static COF (μ s ) of 0.80–1.50+ against 304 stainless steel, while kinetic COF (μ k ) ranges from 0.60 to 1.20. μ_k is in the range of 0.60 – 1.20. Use of a matte chill-roll or a slip-compound reduces μ_k to 0.20 – 0.40.
Standard ASTM D1894-24 vs. ISO 8295:1995 methods both use a 200 g sled (1.962 N normal force, 0.487 kPa pressure). However, ISO 8295 Clause 5.2.5 specifies a 2 ± 1 N/cm spring for static breakaway and covers non-sticky films up to 0.5 mm, whereas ASTM D1894-24 caps film thickness at 0.254 mm (0.010 in.).
For high-speed roll-to-roll lamination, the goal is to achieve a target converting window (μ_k = 0.20 – 0.40) on the roller-contact face. Values less than 0.15 can result in roll telescoping on the rewind mandrel, and values greater than 0.80 can lead to web grabbing and blocking of the roll.
Critical slip vs. peel trade-offs occur if migratory fatty amides (erucamide or oleamide) bloom into a waxy boundary layer during warm-up. To avoid this issue, use of hot-melt TPU films with matte embossing or PET release liners is common.

What Static and Kinetic Coefficient of Friction Mean for TPU Film

Unmodified soft TPU film exhibits a static coefficient of friction (μ s ) of 0.80 to 1.50+ and a kinetic coefficient of friction (μ k ) of 0.60 to 1.20 against stainless steel, whereas matte or slip-modified TPU grades reduce μ k to 0.20–0.40 under ASTM D1894 testing. TPU grades that exhibit a matte or slip surface modify μ_k to values in the range of 0.20 to 0.40 during ASTM D1894 testing. The ratios are dimensionless and are determined by dividing the sliding friction force by the normal load.

The static friction coefficient (μ_s = A_s / B) is the maximum force required to start motion from rest. The kinetic friction coefficient (μ_k = A_k / B) is the average force required to maintain motion or sliding friction at a constant speed. In rigid plastic film and sheeting (e.g. BOPP, PET, etc.) films, surface asperities deform very little under a 200 g sled. However, the behavior of different plastic materials (e.g. soft thermoplastic polyurethane (TPU) film grades) is completely different.

Soft 70A–85A TPU has a low storage modulus at 23 °C. Its surface micro-asperities flatten under contact load. This viscoelastic compliance expands the real area of surfaces in contact (A_r). Tribological studies in ScienceDirect and MDPI Lubricants confirm that polyurethane friction follows interfacial adhesion hysteresis and Schallamach detachment waves. Base polyester and polyether TPU film chemistry also changes frictional properties. Polyester TPU typically shows higher polar dipole tack against bare metal rollers than polyether TPU at equal Shore hardness.

Wound-roll dwell time increases static breakaway resistance. Inside a tightly wound roll, interlayer pressure drives viscoelastic contact creep over days of storage. Short lab sled dwell times (a few seconds under ASTM D1894 Clause 4.6) do not mimic creep behavior of multiple days, as is the case with winding, unless paired with blocking tests.

Table 1: Typical ASTM D1894 Coefficient of Friction Ranges by TPU Film Grade and Surface Finish (200 g Sled, 23 °C / 50% RH)
TPU Film Category	Shore Hardness	Counterface Pair	Typical Static COF (μ_s)	Typical Kinetic COF (μ_k)	Primary Converting Behavior
Soft Unmodified Glossy TPU	70A – 85A	TPU-to-304 Stainless Steel	0.80 – 1.50+	0.60 – 1.20	High tack, severe stick-slip judder, wraps bare steel idler rollers
Medium/Hard Unmodified TPU	90A – 64D	TPU-to-304 Stainless Steel	0.40 – 0.75	0.30 – 0.55	Moderate drag; runs on PTFE or micro-grooved rollers with tension control
Matte-Embossed or Slip-Modified TPU	80A – 95A	TPU-to-TPU (Self) / Steel	0.25 – 0.50	0.20 – 0.40	Smooth web transport across forming collars and guide rollers
Carrier-Backed TPU (PET Release Liner Side)	70A – 90A (on 50–100 µm PET)	PET Liner-to-Steel	0.18 – 0.30	0.15 – 0.25	Stable high-speed unwind and zero elastic stretch prior to liner stripping

ASTM D1894 vs ISO 8295: Standard Test Parameters for Plastic Film and Sheeting

ASTM D1894-24 and ISO 8295:1995 are the primary international standards used to determine the friction of plastic film: ASTM D1894-24 specifies a 63.5 × 63.5 mm square sled weighing 200 ± 5 g, whereas ISO 8295:1995 specifies a 63 × 63 mm square sled (40 cm² area) weighing 200 ± 2 g across a flat horizontal plane. Despite similar normal forces (~1.96 N), differences in crosshead speed, thickness limits, and spring linkage make their results non-interchangeable.

First, crosshead pull speeds differ by 50%. ASTM D1894-24 pulls the sled at 150 ± 30 mm/min (0.5 ft/min) over a 130 mm travel distance, whereas ISO 8295:1995 typically pulls at 100 ± 10 mm/min and connects the sled through an elastic spring (stiffness 2 ± 1 N/cm) during static breakaway testing. Crosshead speeds between 100 and 150 mm/min shift measured TPU friction by 0.05 to 0.18 COF units because viscoelastic shear stress rises with strain rate. Second, specimen thickness limits differ. According to ZwickRoell, ASTM D1894 caps sled specimen thickness at 0.254 mm (0.010 in., per ASTM D883 film terminology). In contrast, ISO 8295:1995 Clause 1.1 covers non-sticky films and plastic sheets up to roughly 0.5 mm thick.

Finally, some engineering guides falsely state that ASTM D1894 permits only film-to-film tests. In reality, ASTM D1894-24 explicitly covers the coefficients of starting and sliding friction of film and sheeting when sliding over itself or other substances. ASTM D1894-24 Clause 4.1.1 also permits heated-plane testing by heating only the horizontal bed while keeping the sled at 23 °C. However, horizontal sled testing remains standard for TPU webs. For ultra-low-COF packaging films (<0.12), for example, labs sometimes perform TAPPI T-815 inclined-plane testing (μ_s = tan θ).

What Is the Difference Between ASTM D1894 and ISO 8295 for TPU Film?

ASTM D1894-24 pulls the 200 ± 5 g sled at 150 ± 30 mm/min on specimens up to 0.254 mm thick. ISO 8295:1995 pulls the 200 ± 2 g sled at 100 ± 10 mm/min on non-sticky films up to 0.5 mm thick. ISO 8295 Clause 5.2.5 also requires an elastic spring linkage (2 ± 1 N/cm stiffness) for static friction, whereas ASTM D1894 permits direct rigid-wire setups.

That linkage difference strongly affects soft TPU. Under ISO 8295:1995 Clause 5.2.5, static friction measurement uses a spring with 2 ± 1 N/cm elasticity. When stick-slip oscillations appear during dynamic friction measurement, ISO 8295 mandates replacing that spring with a rigid connection. ISO 8295 also notes in its scope that horizontal sled testing mainly serves quality control. Lab numbers alone do not fully predict machine runnability without matching line temperature and tension.

Table 2: Parameter-by-Parameter Comparison of ASTM D1894-24 and ISO 8295:1995
Test Parameter	ASTM D1894-24 Specification	ISO 8295:1995 (and GB/T 10006) Specification	Engineering Impact on TPU Film
Sled Footprint & Backing	63.5 × 63.5 mm (40.32 cm²); 3.2 mm medium-density sponge rubber	63 × 63 mm (40 cm², Clause 5.2.2); 3.2 mm elastic felt or foam rubber backing	Distributes 1.962 N normal load evenly across micro-embossed peaks
Sled Mass & Normal Force	200 ± 5 g including mounted specimen (F_N = 1.962 N)	200 ± 2 g (F_N = 1.962 N)	Identical baseline normal load; verify sled mass weekly on a balance
Crosshead Pull Speed	150 ± 30 mm/min	100 ± 10 mm/min	50% speed difference alters viscoelastic shear and stick-slip frequency
Maximum Specimen Thickness	≤ 0.254 mm (0.010 in. per ASTM D883)	Up to ~0.5 mm (Clause 1.1, non-sticky film/sheeting)	Thicker TPU sheets (0.30–0.50 mm) require rigid flat mounting on the sled face
Force Linkage Compliance	Permits the use of a stationary sled with a moving plane or moving sled; direct/spring apparatus	Clause 5.2.5: 2 ± 1 N/cm spring for static force; rigid linkage required if stick-slip occurs in dynamic test	Spring compliance stores elastic energy and amplifies sawtooth amplitude on tacky TPU
Standard Conditioning	23 ± 2 °C, 50 ± 10% RH for ≥40 h (Clause 8.1 per ASTM D618 Procedure A)	23 ± 2 °C, 50 ± 10% RH for ≥16 h (per ISO 291)	Short conditioning (<24 h) misses slow fatty-amide slip blooming

How to Set Up a TPU Film Coefficient of Friction Test Without Stretch Distortion

Setting up a precise and accurate test on thin, low-modulus TPU film (15 µm to 250 µm) requires full-area double-sided adhesive backing, static neutralization, and a 50 mm gauge-mark check (<1% elongation). Standard ASTM D1894 apparatus options include the use of a stationary sled with a moving plane or a sled with a moving crosshead.

Both designs are used to measure starting and sliding friction between two materials. Rigid PET film has a tensile modulus above 2,000 MPa. Soft 80A–85A TPU film has an initial modulus of only 10 to 25 MPa. Wrapping a 120 × 120 mm TPU square tightly around sled edges stretches the elastic web. During the 150 mm/min pull, that stored tensile strain recoils against the load cell. It also pushes a buckling wave ahead of the sled. Follow this 6-step lab SOP for determining the coefficient of friction without stretch artifacts:

Step 1 — Condition for ≥40 Hours per ASTM D1894-24 Clause 8.1: Condition all test specimens at 23 ± 2 °C and 50 ± 10% relative humidity for at least 40 hours prior to testing in accordance with ASTM D618 Procedure A. Wear nitrile gloves and hold outer edges only. Skin oils drop local COF by 0.05 to 0.10.
Step 2 – Cut Burr-Free Specimens: Cut the plane specimen to 250 × 130 mm along the machine direction. For thin elastic TPU, cut the sled specimen flush to 63.5 × 63.5 mm, using a fresh rotary blade. Do not fold tacky edges up on the sled sides.
Step 3 – Neutralize Static Charge: Both faces of the film contain dielectric TPU and attract thin webs against the steel bed. That electrostatic attraction inflates initial breakaway force. Pass both faces of the film over an ionizing air bar to mitigate static charge before mounting.
Step 4 – Mount with Full-Footprint Double-Sided PSA: Apply a thin, rigid double-sided PSA tape across the full 63.5 × 63.5 mm sled base and test bed. Carefully lay the TPU film to avoid wrinkles.
Step 5 — Check Zero Pre-Stretch with a 50 mm Gauge Mark: Mark two ink dots 50.0 mm apart in the machine direction before lifting the film. Measure the gap again with a digital caliper after mounting on the PSA tape. Reject any mount showing over 1.0% elongation (>50.5 mm).
Step 6 – Level the Tow Line & Sample at ≥500 Hz: Keep the tow wire parallel to the bed within ±1°. Place the 200 g sled gently onto the track. Hold a consistent 5-second dwell time (ASTM D1894 Clause 4.6), then record force over 130 mm travel across 5 specimens.

Worked Example: Calculating Static COF, Kinetic COF, and Web Roller Drag from Sled Force Readings

A quality lab uses this method for determining the coefficients of friction of plastic on two 50 µm polyether TPU film lots. Each lot slides against a polished 304 stainless steel plane (Ra = 0.2 µm) per ASTM D1894-24. The sled mass B is 200.0 g. That mass produces a normal force F_N = 0.200 kg × 9.81 m/s² = 1.962 N (200 gf).

Sample Lot A (Unmodified Glossy 80A TPU): Across 5 MD specimens, mean peak force A_s is 1.727 N (176.0 gf). Mean sliding force A_k (from 25 mm to 125 mm travel) is 1.354 N (138.0 gf).

Static COF: μ_s = 1.727 N / 1.962 N = 0.88 (SD = 0.031).

Kinetic COF: μ_k = 1.354 N / 1.962 N = 0.69 (SD = 0.024).

Stick-slip spread: Δμ = μ_s − μ_k = 0.19 (ratio μ_s / μ_k = 1.28).
Sample Lot B (Matte Chill-Roll 85A TPU with Non-Migratory Siloxane): Across 5 MD specimens, mean peak force A_s is 0.726 N (74.0 gf). Mean sliding force A_k is 0.569 N (58.0 gf).

Static COF: μ_s = 0.726 N / 1.962 N = 0.37 (SD = 0.012).

Kinetic COF: μ_k = 0.569 N / 1.962 N = 0.29 (SD = 0.009).

Stick-slip spread: Δμ = 0.08 (smooth sliding plateau).
Line Production Translation (1.6 m Wide Laminator Idler): Assume an infeed web tension T₁ = 40 N over a fixed stainless steel bar with a 0.5 rad (28.6°) wrap angle. The capstan equation T₂ = T₁ · e^μ_kθ gives exit tension T₂ = 56.5 N for Lot A (+41% spike, causing web neck-down). Lot B gives T₂ = 46.2 N (+15.5% change, zero necking).

Film-to-Film vs Film-to-Metal Counterfaces and Release Liner Sidedness

Using the wrong counterface in the lab renders the determination of the coefficients useless on the production line. As documented by International Equipments, ASTM D1894 testing involves four surface pairings. These include inside-to-inside (I/I), outside-to-outside (O/O), inside-to-outside (I/O), and film-to-metal (F/M). Each pairing models how one surface slides across a specific machine zone.

In engineering discussions on Reddit r/AskEngineers, several practitioners explain that rubbing two surfaces of the same polymer together leads to greater static friction than sliding polymer against metal. If two TPU surfaces come into contact (F/F), there is interdiffusion of polyurethane chains across the interface. When one surface is TPU and the other is 304 stainless steel (film-to-metal), metal surface roughness (Ra) controls real contact area.

Side-by-side comparisons of carriers are only part of the story. Higher demands on sidedness apply to carrier-backed hot-melt adhesive film and some optical aliphatic TPU film constructions. A laminate attached to a 75 µm PET release liner has two surfaces with different frictional characteristics. The PET carrier back shows a low μ_k of 0.15 to 0.25 against steel guide bars. The exposed TPU adhesive face may show μ_k of 0.45 to 0.95. If the supplier tests only the PET liner face, your laminator can still jam at the first bare TPU roller after liner removal.

Should You Test TPU Film-to-Film or Film-to-Metal Coefficient of Friction?

Test both pairings to match your converting line. Request film-to-film (inside-to-outside) COF to prevent roll blocking, telescoping and die-cut stack sticking. Request film-to-metal COF for 304 stainless steel (Ra = 0.2 to 0.4 µm) to predict drag across unheated guide rollers and forming collars.

When reporting COF for 90° pulling angle, expect 0.05 to 0.15 COF differences for MD vs. TD. Draw-induced alignment during extrusion creates localized differences in COF.

Machine direction (MD) and transverse direction (TD) COF should always be reported in pairs.

Table 3: Converting Zone Counterface & Sidedness Selection Matrix
Converting Process Zone	Interacting Surfaces in Contact	Required ASTM D1894 Test Pair	Target μ_k Specification Window
Jumbo Roll Unwind & Storage	TPU Top Face vs. Back Face (or PET Liner Back)	Film-to-Film (Inside-to-Outside, MD)	0.20 – 0.45 (prevents both telescoping and blocking)
VFFS Forming Collar & Guide Chutes	TPU Active Web Face vs. 304 Stainless Steel	Film-to-Metal (304 SS plate, Ra = 0.2–0.4 µm)	0.20 – 0.38 (heated plane per Clause 4.1.1 if collar is warm)
Post-Strip Adhesive Lamination Infeed	Bare Hot-Melt TPU Face vs. Idler / Spreader Rollers	Film-to-Metal (or PTFE-coated plate)	≤ 0.45 on bare steel; use PTFE sleeves if μ_k > 0.50
Die-Cut Sheet Stacking & Medical Drape Pick-and-Place	Cut TPU Sheet Face vs. Adjacent TPU Sheet	Film-to-Film (Inside-to-Inside & Outside-to-Outside)	0.22 – 0.40 (ensures single-sheet vacuum pick without double-feeding)

Diagnosing Stick-Slip Sawtooth Curves and Viscoelastic Test Artifacts

When soft TPU slides against the bed, the load-cell trace usually looks like a sawtooth pattern. As explained by both Mecmesin and Instron, accurate cof testing requires separation of true polymeric stick-slip from setup errors.

In flexible packaging QC, International Equipments notes a widely used diagnostic rule of thumb: when the static and kinetic coefficients ratio exceeds μ_s / μ_k > 1.5, films exhibit stick-slip judder. The film hesitates, jerks forward, and grabs again. Other tribological studies on TPU by Hausberger et al. (2010) show that stick-slip boundaries also shift with normal load, sliding speed, and filler content. ASTM D1894-24 Clauses 4.4, 4.6, and 4.7 also note that static breakaway peaks depend on film age, loading rate, pre-start dwell time, and load-cell response rate.

If your testing instrument samples force at only 10 to 50 Hz, they miss the millisecond static breakaway spike (A_s). Instron specifies a 5 kHz capture rate on its 2530 Series low-capacity load cell (accurate to 0.02 N) to record fast breakaway peaks. Use the 4-Trace COF Curve Diagnostic Grid to help classify force curves before accepting a lab report.

Table 4: The 4-Trace COF Curve Diagnostic Grid for TPU Film Testing
Force-Displacement Curve Signature	Physical Root Cause	Valid Material Property or Invalid Test Artifact?	Corrective Action per ASTM D1894-24
Trace 1: Periodic Sawtooth Oscillation (Regular peaks & drops with ΔF > 0.30 N across 130 mm travel)	Viscoelastic adhesion-detachment cycling (Schallamach waves) amplified by spring compliance	Valid Material Behavior (if rigid linkage used); report μ_s, mean μ_k, and amplitude Δμ	Replace ISO 8295 spring with rigid connection (Clause 5.2.5); switch TPU to matte finish or siloxane slip
Trace 2: Overshoot Spike Followed by Steep Drop (Initial spike >2× plateau in first 3 mm)	Slack in the tow wire or dropping the sled onto the film before pull start	Invalid Test Artifact (inflates reported static friction μ_s by 25%–60%)	Remove tow-line slack to 0.05 N pre-load; enforce standard 5 s dwell time (Clause 4.6)
Trace 3: Rising Ramp Where μ_k > μ_s (Force climbs steadily from 10 mm to 130 mm)	Unbacked thin TPU stretching in-plane and bunching into a wave ahead of the sled	Invalid Test Artifact (measures film plowing, not sliding friction of plastic film)	Discard run; mount specimen with full-area double-sided PSA tape; verify <1% pre-stretch
Trace 4: Erratic High Spikes Mid-Travel (Sudden 0.4–0.8 N jumps at random points)	Cut-edge elastomeric burrs dragging, dust particles, or fingerprint oil patches	Invalid Test Artifact (exceeds SD ≤ 0.02 repeatability limit)	Clean steel bed with isopropanol; re-cut sled square with fresh rotary blade; deionize static

How TPU Film COF Controls Roll-to-Roll Converting, Web Tracking, and Blocking

In high-speed roll-to-roll lamination, a value of kinetic coefficient of friction (μ_k) in the range of 0.20 to 0.40 on the roller-contact face works well; values less than 0.15 result in roll telescoping, and values greater than 0.75 to 0.80 result in web stretching, wrinkling and blocking.

Evaluating how a material will slide across guide bars helps determine line speed limits and protects product quality. Many buyers assume a lower coefficient of friction always improves packaging efficiency. Packaging World and Viking Masek state that flexible webs require balanced frictional forces. The inner surface must have slip properties for easy sliding over forming collars and spreader bars. However, drive nips and wound layers must have sufficient grip to avoid lateral roll shift.

Remember ISO 8295:1995’s scope caution as well. Room-temperature horizontal sled testing ensures baseline consistency, but heated converting lines change film behavior. When TPU passes over a warm guide roller at 40–55 °C, soft segments soften and contact area rises. Use The 4-Band Roll-to-Roll COF Window below—a converting decision matrix mapping kinetic COF bands (<0.18, 0.20–0.40, 0.45–0.75, >0.80) to unwind tension, roller wrap, telescoping, and blocking across bare vs liner-carried TPU films—to match ASTM D1894 numbers to your converting line.

Table 5: The 4-Band Roll-to-Roll COF Window and Sub-Tier Converting Matrix for TPU Films and Laminates
COF Tier & Film Category	Kinetic COF Band (μ_k, ASTM D1894)	Classification Model	Roll-to-Roll Web & Winding Behavior	Primary Defect Risk & Process Action
Band 1A: Ultra-Slip Over-Bloomed TPU	<0.18 (0.10 – 0.15)	Severe Over-Lubrication	Wound layers slide laterally under pallet vibration; drive nips lose traction	Roll telescoping (conical roll ends) and print misregistration; cut amide masterbatch
Band 1B: Low-Friction PET Carrier Liner	<0.18 (0.15 – 0.18)	Borderline Carrier Slip	Zero roller drag on steel chutes; requires higher core chuck brake tension	Slight edge weave at high deceleration; add 0.15 wt% silica anti-block to carrier back
Band 2A: High-Speed VFFS & Collar Web	0.20 – 0.40 (0.20 – 0.28)	Optimal Fast-Collar Slip	Glides over 304 SS forming collars and spreader bars at 40–80 m/min	Minimal defect risk; ideal for automated packaging applications and DTF film transport
Band 2B: Standard Textile Lamination Web	0.20 – 0.40 (0.28 – 0.35)	Optimal Lamination Slip	Balanced roller release and nip traction; zero tension spikes during unwind	Standard release window for matte-embossed or siloxane-modified 85A–95A TPU
Band 2C: Precision Die-Cut & Sheet Stack	0.20 – 0.40 (0.35 – 0.40)	Controlled Stack Slip	Clean single-sheet vacuum pick-and-place without double-feeding or sliding	Verify MD/TD standard deviation SD ≤ 0.02 across 5 specimens per lot
Band 3A: Semi-Matte Unmodified Medium TPU	0.45 – 0.75 (0.45 – 0.55)	Moderate Roller Drag	Noticeable friction on fixed guide bars; stable on low-inertia driven idlers	Keep web spans short (<0.8 m); monitor width neck-down on thin gauges (<35 µm)
Band 3B: Warm-Chute Elastomeric Web	0.45 – 0.75 (0.55 – 0.65)	Elevated Drag Zone	Capstan tension builds rapidly across wrap angles above 45°	Wrap fixed steel bars with PTFE tape or switch to micro-grooved aluminum idlers
Band 3C: Soft Unlined 80A–85A TPU Web	0.45 – 0.75 (0.65 – 0.75)	Upper Tension Limit	Requires closed-loop load-cell dancer control to stop elastic elongation	Width shrinkage (>2%) and diagonal wrinkles; consider removable PET carrier liner
Band 4A: High-Tack Glossy Elastomeric TPU	>0.80 (0.80 – 1.10)	Critical Stiction Zone	Severe sawtooth stick-slip judder; web grabs bare steel chutes and hesitates	Web snap and registration jump; apply matte chill-roll embossing (Ra = 1.5–2.5 µm)
Band 4B: Ultra-Soft Unlined Hot-Melt TPU	>0.80 (1.10 – 1.50+)	Severe Roll Blocking	Adjacent wraps cold-weld under winding pressure; cannot unwind unsupported	Mandatory extrusion onto 50–100 µm PET release liner or anchored siloxane compound

Lowering TPU Film COF Without Killing Hot-Melt Peel Bond Strength

Lowering TPU friction is easy when the film only acts as an outer cover. Additives trap adhesion when TPU needs to seal, RF-weld, or laminate to fabric. The wrong additive passes ASTM D1894 checks and causes delamination three weeks later.

Standard polyolefin films and sheets rely on fatty-acid amides like erucamide and oleamide at 0.05-0.30 wt% (500-3,000 ppm), as noted in EPA HERO and Plastics Engineering studies. These small molecules are insoluble in the cooled polymer. After extrusion, they bloom to the air-polymer interface and form a lubricating layer.

As shown in studies by SilikeTech and ResearchGate, fatty-acid amides cause three major problems in wound films and laminates:

Wound-roll cross-layer migration: Due to winding tension, molecules from the sealant face migrate to the outer corona face.
Interfacial weak boundary layers on bonding faces: Excess amide precipitates as white powder. That waxy film blocks polyurethane wetting under thermal bonding film lamination parameters.
Extrusion thermal volatility and die build-up: At TPU extrusion temperatures (175–210 °C), low-MW amides volatilize and condense on chill rolls.

To avoid migratory wax bloom, modern TPU formulations use anchored copolymer polysiloxanes (US Patent 6,759,487 B2 and WO 2018/226591 A1), amorphous silica anti-block, or physical matte chill-roll texturing. Use The 5-Route Slip-vs-Peel Trade-Off Matrix below to protect your hot-melt adhesive film melting point and thermal activation window.

Can COF vary with time or environment?

Yes, COF for TPU film varies from 0.15 to 0.40 due to migration of slip agents. In amide-modified films, erucamide continues diffusing to the surface over 24 hours to 4 weeks. Higher storage temp (35-40 °C) further supports this process and COF reduction. Warm 35–40 °C storage accelerates this bloom and drops COF rapidly, whereas unmodified soft TPU rolls gain static friction as winding pressure flattens asperities.

Data from International Equipments illustrate this phenomenon. A freshly extruded amide-modified film drops from COF = 0.65 at 0 hours to 0.45 at 6 hours, 0.22 at 24 hours, and 0.18 at 72 hours. For critical bond applications, 24 hour ASTM D1894 tests must be paired with 14-day T-peel adhesion testing at 40 °C.

Table 6: The 5-Route Slip-vs-Peel Trade-Off Matrix for TPU Films
Friction-Control Route	Physical / Chemical Mechanism	Typical μ_k Achieved	Storage Drift & Bloom Risk	Impact on Hot-Melt Peel & Printability	Best Application Decision Rule
Route 1A: Migratory Erucamide (C22 Amide, 0.05–0.15 wt%)	Blooms to surface over 24–72 h to form a boundary wax layer	0.18 – 0.30	High: Continuous migration above 35 °C; cross-transfers in wound rolls	Negative at high dosing: Waxy bloom degrades T-peel bond, RF welds, and ink wetting	If single-layer non-bonded film → acceptable. If laminated or printed → verify with 14-day peel aging check.
Route 1B: Fast-Bloom Oleamide (C18 Amide, 0.05–0.12 wt%)	Diffuses rapidly within 6–24 h to lubricate outer film surface	0.15 – 0.25	Very High: High volatility at 185 °C extrusion; severe die-lip condensation	Severe bond loss: Forms weak boundary layer that blocks polyurethane thermal wetting	Avoid on hot-melt adhesive TPU films; restrict to disposable non-laminated packaging wraps.
Route 2A: Anchored Copolymer Polysiloxane (SILIMER Series)	Alkyl chains anchor into TPU matrix while siloxane segments lubricate	0.20 – 0.32	Very Low: Non-migratory across layers; stable in summer and winter	Minimal impact: Preserves heat-seal strength, optical clarity, and printing	If unsupported TPU needs permanent low COF without powder bloom → primary additive choice.
Route 2B: UHMW Siloxane Masterbatch (1.0–2.5 wt% Loading)	Dispersed ultra-high-MW siloxane domains reduce metal chute drag	0.22 – 0.35	Low: High molecular weight prevents cross-layer transfer in tight rolls	Safe for thermal bonding: Retains ≥90% peel bond strength after 40 °C aging	Best for high-speed VFFS forming collars and stainless steel guide chutes.
Route 3A: Inorganic Silica Anti-Block (Amorphous SiO₂, 2–5 µm)	Micro-asperity peaks hold adjacent film layers apart	0.32 – 0.48	Zero: Inorganic particles cannot migrate in solid TPU	Safe for bonding: Melts flat under heated nip press; slightly raises haze	If stopping blocking on 85A–95A translucent TPU → use 0.15–0.35 wt% loading.
Route 3B: Dual Siloxane + Silica Anti-Block System	Combines micro-roughness spacing with non-migratory surface lubrication	0.20 – 0.30	Zero bloom drift: Stable COF from 24 hours through 6 months storage	High bond retention: Preserves adhesive wetting while preventing roll blocking	Ideal for export sea-freight jumbo rolls exposed to 40–50 °C container temperatures.
Route 4A: Fine Matte Chill-Roll Embossing (Ra = 1.2–1.8 µm)	Light surface texture reduces real contact area A_r against rollers	0.30 – 0.42	Zero until melted: Purely physical texture; zero chemical bloom	100% Bond Retention: Texture melts flat above TPU activation temperature	If 100% pure TPU chemistry is required with semi-clear optics → preferred physical route.
Route 4B: Deep Matte Chill-Roll Texturing (Ra = 1.8–2.5 µm)	Pronounced micro-peaks break vacuum suction on polished steel plates	0.25 – 0.36	Zero storage drift: Unaffected by humidity or warehouse heat cycles	100% Bond Retention: Collapses completely under flatbed press or hot-air weld	Best for additive-free medical barrier drapes and high-peel textile adhesive webs.
Route 5: Removable PET Release Liner (50–100 µm Carrier Film)	PET carrier handles web tension and roller sliding until stripping	0.15 – 0.25 (PET side)	Zero on carrier: Protects soft TPU from roll pressure and dust	100% Bond Retention: Virgin adhesive TPU face exposed right before nip	If ultra-soft (65A–80A) or thin (<30 µm) hot-melt TPU film → mandatory architecture.

COF Testing Equipment, Lab Costs, and the 7-Item TPU Film RFQ Specification

After selecting a low-friction slip route, third-party ASTM D1894 testing typically costs \$150 to \$400 per 5-specimen sample set at commercial polymer labs. In-house horizontal benchtop COF testers range from \$2,500 to \$15,000, and universal testing machine sled fixtures cost \$900 to \$2,500, making benchtop units cost-effective at 15+ lots monthly.

Buyers doing 2 to 5 qualifications a year tend to go to an ISO/IEC 17025 accredited lab (Petro-Lubricant Testing Labs or Intertek). Converters with daily quality testing needs buy lab testing equipment to catch blocking or bloomed lots before they jam a line, especially if evaluating coefficient of friction test equipment.

Generally, modern quality control laboratories are faced with two primary hardware setups:

Modular UTM Horizontal Sled Fixture (\$900–\$2,500 attachment): Plants that already own a universal testing machine (Instron, ZwickRoell zwickiLine, or Mecmesin MultiTest-i) can mount an ASTM D1894 horizontal plane table, low-friction pulley, and 200 g sled. Pair the fixture with a 5 N to 50 N load cell sampling at ≥500 Hz.
Standalone Dedicated Benchtop COF Tester (\$2,500–\$15,000): Benchtop units include microprocessor-based analyzers with a digital display. Common models include a standard co-efficient of friction tester, a cof-01 coefficient of friction tester (from Cell Instruments, Labthink, Pacorr, or Presto), or a precision coefficient friction tester from Thwing-Albert (FP-2265), Testing Machines Inc. (32-76e), or Mark-10. Each unit measures static and kinetic friction across a programmable range of testing speeds.

Table 7: Comparison of TPU Film COF Testing Options and Typical 2026 Commercial Costs
Testing Route	Representative Equipment / Providers	Typical Cost (USD)	Key Technical Specifications	Best Fit For
Accredited Third-Party Lab Test	ISO 17025 Polymer Testing Labs (Petro-Lubricant, Intertek, SGS)	\$150 – \$400 per 5-specimen sample set (+ \$50–\$100 for custom metal counterface)	Full ASTM D1894-24 or ISO 8295 report with 24–40 h conditioning, MD/TD mean, SD, and force traces	Annual vendor qualification, dispute arbitration, or TPU film grade selector validation
UTM COF Fixture Attachment	Instron 2810-005, ZwickRoell COF Fixture, Mecmesin Peel/Friction Table	\$900 – \$2,500 (fixture only; requires existing UTM frame)	200 g sled, low-friction pulley, 5–100 N load cell (0.02 N resolution), 500–5,000 Hz software capture	Plants that already run ASTM D882 tensile and ASTM D1876 T-peel tests on a UTM
Dedicated Benchtop COF Tester	Thwing-Albert FP-2265, TMI 32-76e, Mark-10, Labthink COF-01, Cell Instruments	\$2,500 – \$15,000 (depending on heated plane & PC software)	Microprocessor-based drive (100 & 150 mm/min), digital display, optional Clause 4.1.1 heated bed	Daily extrusion QC and high-volume roll-to-roll converting incoming inspection

Why Supplier TDS Sheets Omit COF—And How to Specify It in Your RFQ: Common technical specifications from global TPU producers (Covestro Platilon, Lubrizol Pearlbond, Argotec/Mativ, American Polyfilm) and custom extruders (Teng Yang) list Shore hardness, tensile strength, melting point, and peel strength. Lot-by-lot COF is rarely printed on a generic TDS. Measured friction is affected by a number of variables including chill-roll finish and gauge, metal counterface, and PET liner backing.

To get consistent quality products and avoid sea-freight blocking, include The 7-Field TPU Film COF Purchase Specification in your purchase order when you request a custom TPU film sample and technical review.

The 7-Field TPU Film COF Purchase Specification (RFQ & COA Checklist)

Field 1 — Test Standard & Pull Speed: Specify ASTM D1894-24 at 150 ± 30 mm/min or ISO 8295:1995 at 100 ± 10 mm/min. State whether the static linkage uses a rigid wire or a 2 ± 1 N/cm spring.
Field 2 — Exact Surface Pair & Counterface Roughness: Define Film-to-Film (Inside-to-Outside) for roll winding stability. Specify Film-to-Metal (304 Stainless Steel, Ra = 0.2–0.4 µm) for machine chutes.
Field 3 — Carrier Liner Sidedness & Mounting Method: State which face is tested (Bare TPU Adhesive Face vs. PET Release Liner Face). Mandate full-area double-sided PSA backing with <1% pre-stretch for films ≤100 µm.
Field 4 — Conditioning & Post-Extrusion Age Window: Require 23 ± 2 °C and 50 ± 10% RH for ≥24 hours per ASTM D618. Record hours elapsed since extrusion on the COA.
Field 5 — Target μ_s / μ_k Acceptance Window & Dispersion Limit: Specify both static and kinetic bounds (e.g., μk = 0.22–0.38, μs ≤ 0.50, SD ≤ 0.02 across n = 5 MD specimens). Add Clause 4.1.1 heated-plane temperature if collars exceed 40 °C.
Field 6 — Slip Architecture & Migration Restriction: Specify Matte chill-roll finish, PET carrier liner, or Non-migratory siloxane modifier. Prohibit unapproved migratory fatty-amide dosing on bond-critical grades.
Field 7 — Paired Post-Aging Peel Retention Gate: For thermal bonding grades, require ≥85%–90% T-peel bond strength retention after 14 days at 40 °C roll aging alongside the COF report.

Frequently Asked Questions

What is a normal coefficient of friction for TPU film?

Unmodified thermoplastic polyurethane (TPU) film typically shows a static coefficient of friction (μ s ) between 0.80 and 1.50+ against stainless steel under ASTM D1894. Harder grades, 90 Shore A and higher, and slip compounded or textured TPU films run much lower. Modified grades provide a kinetic COF of between 0.20 and 0.45 for roll-to-roll conversion.

Why is my kinetic coefficient of friction higher than static COF during an ASTM D1894 test?

When a kinetic COF exceeds static COF on a TPU film test, then viscoelastic stick-slip or sled edge plowing is occurring, rather than steady sliding. During a test, the 200 g sled has to move soft TPU against a stainless-steel bed. As the 200 g sled moves, soft TPU adheres to the bed and builds high dynamic shear resistance. Unbacked, thin film TPU can also form a surface wave in front of the sled. This sled plowing action builds an average sliding force greater than the breakaway force.

Does lowering TPU film COF with slip agents reduce hot-melt lamination peel strength?

Yes, using a migratory slip additive, such as erucamide or oleamide, reduces hot-melt peel-bond strength. Migratory slip additives, such as fatty amides, bloom to the film surface and form a waxy layer. In thick or warm rolls, the waxy layer forms a weak boundary layer that blocks substrate wetting and reduces thermal bonding. Thus, for bond-critical films, matte texturing or PET release liners should be used.

How often should COF testing be performed in TPU film production?

Run ASTM D1894 or ISO 8295 COF testing at initial grade qualification and after any resin, slip masterbatch, or chill-roll change. When migratory slip agents are used, test both freshly conditioned rolls (24 h) and 7-to-14-day aged rolls.

Can a universal tensile testing machine run an ASTM D1894 coefficient of friction test?

Yes, a universal testing machine (UTM) can run ASTM D1894 and ISO 8295 tests at 100 to 150 mm/min using a 200 g sled when equipped with a horizontal plane table and a low-friction pulley. The setup uses a 200 ± 5 g rubber-backed sled and a low-capacity load cell (5 N to 50 N). Sampling at 500 Hz or higher captures the initial static breakaway peak accurately.

Which TPU film manufacturers supply slip-controlled grades with batch COF test reports?

Specialty TPU film extruders and hot-melt adhesive film manufacturers—including Teng Yang (tengyangfilm.com), Covestro (Platilon), Argotec/Mativ, and American Polyfilm—supply custom TPU film constructions for textile and industrial lamination. Standard technical data sheets normally list hardness, tensile strength, melting point, and peel adhesion rather than lot-by-lot COF. Buyers requiring tight roll-to-roll slip control should specify the counterface, ASTM D1894 or ISO 8295 pull speed, carrier liner format, and paired peel-retention limits directly in the purchase order.