Molecular-level side chain engineering on comb-shaped sulfonated poly(ether ether ketone) equilibrium-modified atmosphere packaging membrane

Abstract

In the fabrication of equilibrium-modified atmosphere packaging (EMAP) membranes, precise control over the membrane properties can be achieved by manipulating their chemical and chain structures. This study synthesized four types of comb-shaped sulfonated poly(ether ether ketone) (SPEEK)-based EMAP membranes, incorporating tertiary amines, imidazole, dodecyl chains, and methoxy polyethylene glycol terminal pendants via a sulfonamide electrophilic substitution reaction. These functionalized pendants acted as “valves” to modulate the membrane properties, with the “valve” size controlled by the grafting degree of each substituent and its microstructures. Among these engineered membranes, the SPEEK-12C-25 membrane, with moderate 12-C side chains, exhibited the best overall performance. It demonstrated robust mechanical strength (tensile stress >218 MPa), controllable hydrophilicity and dimensional stability across temperatures, favorable visible light transmittance (T > 85 %), and UV shielding (S_UVA > 84 %, S_UVB > 99 %). Notably, the well-defined hydrophilic/hydrophobic microphase separation structure within its matrix (characteristic separation length (d) value of 2.94 nm) provided a second-phase selective gas transport pathway, optimizing gas permeability and the CO₂/O₂ separation coefficient (5.51). Furthermore, these features facilitated rapid air balance within the packaging and timely removal of moisture to prevent water vapor condensation, allowing the packaged cherry tomatoes to maintain 88.70 % of their weight, 53.10 % of firmness, 97.30 % of total soluble solids, and controllable levels of titratable acidity, phenolic, and flavonoids content. Evidently, understanding the underlying principles of molecular-level engineering for the SPEEK side chains is critical for designing EMAP materials with optimal overall performance.