Synthesis, Characterization and O₂ Permeability of Shape Memory Polyurethane Films for Fresh Produce Packaging

The aim of this work was to investigate the effect of film formulations in an effort to obtain a fresh produce packaging film with increased temperature sensitivity for gas permeability. Series of shape-memory polyurethane (SMPU) were synthesized using poly(ethylene glycol) (PEG), 1,6-hexamethylene diisocyanate, 1,4-butanediol and castor oil (CO) and casted into films. The changes in thermal, viscoelastic, shape-memory properties and oxygen permeability of the films were studied. The polyurethane films with 1500 g mol⁻¹ PEG showed a phase transition temperature (switching temperature) between 20 and 27°C. The SMPU consisting of 50/50 CO/PEG had a log E′ value of 8.32 Pa and showed good elasticity as low density polyethylene. SMPU prepared from 1500 g mol⁻¹ PEG with 50/50 CO/PEG and 40/60 butanediol/(PEG + CO) ratios showed excellent shape-memory properties with shape recovery ratio >85% and shape fixity ratio >90%. This film had higher oxygen permeability and showed up to 67% increase in Q₁₀ value for oxygen permeability compared with commercial packaging films like low density polyethylene. This film can be used to develop smart packaging with increased thermally responsive gas permeability to similar levels observed in respiration rates of fresh produce.