Edge of Practice · Short-Cycle Experiment

TPU Segmental Network Decoupling Test

Mechanical equivalence masking reset-resistant segmental reconfiguration and barrier divergence in thermoplastic polyurethane

Hidden Assumption

Separability: in thermoplastic polyurethane (TPU), passing mechanical acceptance tests (tensile strength, modulus, elongation) certifies equivalence of transport and barrier performance; segmental hydrogen bond network rearrangement cannot induce substantial permeability changes without corresponding mechanical signature.

Why This Assumption Persists

Industry acceptance practices privilege tensile and abrasion metrics because they are fast, standardized, and user-visible. Segmental hydrogen bonding and soft–hard domain topology are presumed to track mechanical integrity, not functional barrier behavior. Once mechanical specification is met, permeability is rarely re-verified, reinforcing the presumption that mechanical and transport states are inseparable.

Minimal Falsification Experiment

Material

  • Single production lot of ether-based TPU film or plaque (no fillers, blends, or plasticizers; batch verified)
  • Prepare 50 identical, standardized specimens

Condition History Induction

Divide specimens into five groups (n = 10):

  • Group A: No treatment (baseline control)
  • Group B: Moderate humidity soak (75% RH, 72 h)
  • Group C: Cyclic humidity (25% ↔ 75% RH, 12 h per step, 6 cycles)
  • Group D: Static sub-yield tensile pre-strain (15% of yield, held 24 h, then unloaded)
  • Group E: Combined humidity cycling (as Group C) + sub-yield pre-strain (as Group D), synchronized

No group may exceed yield or display any visible deformation. All groups equilibrate 48 h at 25 °C, 50% RH before testing.

Mechanical Indistinguishability Gate

Test 5 specimens per group. Require:

  • Yield strength and UTS within ±3% of control mean
  • Modulus and elongation within ±5%
  • No whitening, cracking, or necking

Groups failing any criterion are excluded from further analysis; only mechanically indistinguishable sets advance.

Functional Proxy — Barrier / Transport

On remaining 5 specimens per group, measure WVTR or OTR using the same fixture, randomized order, under standardized test conditions.

Molecular Proxy — Segmental State

Run DMA temperature sweep on matched specimens. Record tan δ peak position and width in the soft-segment Tg region.

Reversibility Strike (Post-Divergence)

For any group showing barrier or molecular divergence, apply reset anneal:

  • 80 °C × 24 h, dry air, no load
  • Re-equilibrate 48 h at 25 °C, 50% RH
  • Repeat permeability and DMA testing

Primary Readout

  • Discontinuous or threshold shift in transport (≥30% change in WVTR/OTR or non-monotonic jump)
  • Accompanied by ≥5 °C tan δ shift or ≥20% peak broadening (DMA)
  • All while mechanical parameters remain matched to control

Pass / Fail Threshold

The assumption fails if any treatment group:

  • Passes the mechanical indistinguishability gate
  • Shows ≥30% transport property change (WVTR/OTR) versus control
  • Shows ≥5 °C shift or ≥20% broadening of tan δ in the soft-segment region
  • Retains divergence after standardized reset anneal

Embarrassing Flip Condition

Discovery that TPU remains fully within mechanical specification while undergoing reset-resistant segmental network reconfiguration that silently alters barrier functionality directly falsifies separability. Mechanical testing alone is disqualified as a proxy for environmental, chemical, or transport equivalence.

This experiment is fixed at publication and revised only by explicit versioning to preserve epistemic continuity.

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