Thermoresponsive films are favorable for the packaging of fresh fruits and vegetable products as their gas permeabilities increase to a greater extent than commercial films when temperature abuse occurs during refrigerated storage. Thermoresponsive polyurethane (PU) films were synthesized from polyethylene glycol (PEG) with three different molecular weights (400, 1000, and 1500 g mol⁻¹), castor oil (CO) with two different proportions (30 and 50 %, CO/PEG ratio) and a constant level of 1,4-butanediol (BDO). The effects of these compositional factors on the thermal, mechanical, physical, structural, and gas barrier properties of the films were investigated. Melting temperatures (T_m) of the PU films varied from 25 to 29 °C and decreased with CO content. Glass transition temperatures (T_g) of the films were all below −32 °C and decreased by increased CO content. PU films with 1500 g mol⁻¹ PEG and 30 % CO/PEG ratio had better shape memory (R_r) and shape fixity (R_f) properties than others. O₂ permeabilities of the PU films were in the range of 1.99–7.25 barrer while their CO₂ permeabilities were between 10.3 and 18.3 barrer. The temperature sensitivity of the gas permeabilities of the PU films was higher than that of a commercial LDPE film, which makes them more appropriate for fresh produce packaging. Nevertheless, PU films were mechanically weaker and they had higher water vapor permeability compared to the LDPE film. These properties of the PU films need further improvements for potential packaging applications.

A thermoplastic polyurethane (PU) polymer was synthesized, casted into films, and specific and overall migration (OM) tests were applied. A new method with gas chromatography–flame ionization detector was proposed to measure specific migration (SM) of 1,4-butanediol from the PU film. OM values in the four established simulants were under the legal limits. Determination of 1,4-butanediol migrating from PU film to the three established simulants showed maximum SM result as 1.5 mg/kg which was far below the legal limits. Therefore, the PU film has a good potential as a safe food contact material. Moreover, the analytical method used for determination of SM of 1,4-butanediol resulted in good analytical characteristics and detection limits at ppm level.