Moisture-Dependent Viscoelastic and Mechanical Response of Thermoplastic Polyurethane after Five Years of Conditioning: Assessing Time–Temperature–Moisture Superposition

Abstract

Dataset for: Moisture-Dependent Viscoelastic and Mechanical Response of Thermoplastic Polyurethane after Five Years of Conditioning: Assessing Time–Temperature–Moisture Superposition Authors Eduards Skukis¹*, Olesja Starkova², Andrejs Krauklis³, Oskars Platnieks¹, Maksims Jurinovs¹, Anton Akulichev⁴, Sergejs Gaidukovs¹* ¹ Institute of Chemistry and Chemical Technology, Faculty of Natural Sciences and Technology, Riga Technical University, P. Valdena Str. 3, LV-1048 Riga, Latvia ² University of Latvia, Institute for Mechanics of Materials, Jelgavas 3, Riga, Latvia ³ digiMEI – Digital Material-Environment Interactions, Institute of Civil Engineering and Woodworking, Faculty of Forest and Environmental Sciences, Latvia University of Life Sciences and Technologies, LV-3001 Jelgava, Latvia ⁴ Nexans Norway AS, Knivsøveien 70, Halden, Norway * Corresponding authors: eduards.skukis@rtu.lv (E. Skukis), sergejs.gaidukovs@rtu.lv (S. Gaidukovs) Abstract This study examines moisture-dependent mechanical behavior and the applicability of time–temperature–moisture superposition after five years of conditioning. A thermoplastic polyurethane synthesized from poly(tetramethylene ether glycol), 1,4-butanediol, and methylene diphenyl diisocyanate-based prepolymer was investigated after conditioning at 20 °C in 75% and 97% relative humidity or water, with specimens stored in sealed bags serving as the comparison. Gravimetric measurements showed equilibrium moisture contents of 1.14, 1.78, and 1.93%, respectively. The infrared absorption bands were broadly similar across conditioning states. Relative to sealed-bag storage, water immersion shifted the glass transition from 7.3 °C to −8.0 °C. At 20 °C and a crosshead speed of 66 mm min⁻¹, water-conditioned specimens exhibited a Young's modulus of approximately 339 MPa and an engineering stress at 50% strain of 23 MPa, compared with 595 MPa and 30 MPa for sealed-bag-stored specimens. Separate time–temperature and time–moisture superposition analyses enabled the construction of master curves for the dynamic mechanical analysis (DMA) storage modulus and tensile stress at 50% strain. Separate temperature and moisture shifts described both DMA and tensile responses, while combined shifting of DMA data at 20 and 50 °C supported time–temperature–moisture superposition over more than seven decades of reduced time in the lower-modulus region. Deviations at short reduced times limited its applicability in the high-modulus regime. The shift factors obtained independently from DMA and tensile tests further suggest the potential of DMA for predicting the rate-dependent large-deformation response within the range where superposition is valid. Sample codes Code Conditioning AW Water immersion, 20 °C AH97 97% relative humidity, 20 °C AH75 75% relative humidity, 20 °C AT20 Control, sealed bag, 20 °C In Mechanical_Properties.csv, AT30, AT40 and AT50 denote control specimens tested at 30, 40 and 50 °C. Files DMA.csv Used for Fig. 3 a, b. Dynamic mechanical analysis (temperature sweep). Columns come in groups of four for each sample (AW, AH97, AH75, AT20): temperature [°C], tan δ [1], storage modulus E′ [MPa], loss modulus E″ [MPa]. The first row below the header gives the units. Rows with tan δ = 20000 and very low E′ (above about 80 °C) are instrument placeholders, not physical data. FTIR.csv Used for Fig. 1 b. ATR-FTIR spectra (absorbance). Wavenumber: cm⁻¹ (700–4000) AW, AH97, AH75, AT20: absorbance for each sample MC_DMA_AT20.csv and MC_DMA_AW.csv Used for Fig. 4. Storage modulus at different temperatures and frequencies, used to build master curves for AT20 and AW. Temperature_C: test temperature (°C) Frequency_Raw_Hz: test frequency E_Storage_Pa: storage modulus Frequency_Shifted_Hz: reduced (shifted) frequency Note: the two files use different scales. In MC_DMA_AT20.csv, both frequency columns are log₁₀(f), and E_Storage_Pa is in MPa. In MC_DMA_AW.csv, both frequency columns are in Hz (linear), and E_Storage_Pa is in Pa. Mechanical_Properties.csv Used for Fig. 3 c, d, e, f and as the basis for the tensile master curves in Fig. 5. Tensile test summary (mean and standard deviation). Speed: crosshead speed (mm min⁻¹): 0.66, 6.6, 66, 660 Condition: AT20, AT30, AT40, AT50, AH75, AH97, AW E_MPa_mean, E_MPa_std: Young's modulus (MPa) Sigma_at_eps_50.0%_MPa_mean, Sigma_at_eps_50.0%_MPa_std: engineering stress at 50% strain (MPa) Time_at_eps_50.0%_s_mean, Time_at_eps_50.0%_s_std: time to reach 50% strain (s) Sorbtion.csv Used for Fig. 2. Gravimetric moisture uptake. t: exposure time (h) sqrt_t: square root of time (h^0.5) AW_1–AW_3, AH97_1–AH97_3, AH75_1–AH75_3: moisture uptake (% by mass) of three parallel specimens per condition. Empty cells mean the specimen was no longer measured. License Creative Commons Attribution 4.0 International (CC BY 4.0): https://creativecommons.org/licenses/by/4.0/