Potassium Sorbate-Modified Adhesive Layers in Greaseproof Cardboard Inserts: Mechanical Performance, Migration Behaviour and Technological Validation

Paper- and cardboard-based food-contact materials require solutions that combine mechanical integrity, controlled migration and technological simplicity. This study evaluated greaseproof cardboard inserts in which the aqueous adhesive layer was modified with sodium alginate, chitosan or potassium sorbate. Initial formulation screening comprised eight concentrations (0.5–4.0% (w/w)) for each modifier, with ten adhesive-joint strength measurements per formulation (240 measurements in total). Overall migration to modified polyphenylene oxide (MPPO; Tenax®) was determined at an additive concentration of 4.0% (w/w), using ten measurements per modifier. Further experiments evaluated adhesive application side, adhesive dosage (9 and 15 g·m−2), creasing intensity (0–20 crease lines), and potassium sorbate concentrations of 4.30, 4.55 and 4.90% (w/w). Among the tested modifiers, potassium sorbate combined relatively high mechanical performance with lower overall migration: normalised breaking force remained within 144.2–181.6 N·m−1 across the initial screening range, and overall migration at 4.0% (w/w) was the lowest among the three modifiers (3.61 ± 0.38 mg·dm−2). Additional migration validation yielded 4.678 ± 0.292 and 4.779 ± 0.158 mg·dm−2 for the 4.30 and 4.55% formulations, respectively, whereas the 4.90% formulation showed substantially higher migration (8.737 ± 0.204 mg·dm−2) and reduced breaking force below the internal technological acceptance criterion. Increasing adhesive dosage from 9 to 15 g·m−2 significantly increased migration within both investigated exposure protocols. The 4.30–4.55% (w/w) potassium sorbate range was identified as a preliminary technological window under the investigated conditions. Given the limited number of independent production batches and the absence of formal statistical optimisation, this interval should not be interpreted as a statistically established optimum or a generalisable formulation limit. Antimicrobial efficacy and shelf-life extension were not investigated.