Coumarin 7

Chemicals from food contact materials migrate into food, leading to a possible health risk for consumers. Other than their bulk material food contact materials often contain printing inks and adhesives. Multi-analyte methods for a large amount of these chemicals in food have not been developed, hampering food safety. A liquid chromatography and a gas chromatography tandem mass spectrometry method to analyze in total 110 food contact chemicals from printing inks and adhesives used on plastic food contact materials was developed and fully validated. Fifty-two food samples packaged in printed and/or multilayered materials were tested using this method. Thirty-nine samples contained at least one of the analytes and 16 different analytes were detected. One finding of caprolactam (at 28 mg/kg) was above the legislative limit. One potential hazard for consumer health was detected, as one sample contained 2-methyl-5-nitroaniline, a potententially carcinogenic compound.

The unique mechanical properties of fibrous networks in biological tissues have inspired the development of synthetic fibrous network hydrogels, yet few polymers can reversibly form such structures. Here, we report the first reversible fibrous network hydrogel composed of synthetic polyelectrolytes with extremely rigid conformation (persistence length is ∼1 µm), made up of double‐helical poly(2,2′‐disulfonyl‐4,4′‐benzidine terephthalamide) (PBDT) and tetrabutylphosphonium bromide ([P4444]Br). The hydrogel exhibits a unique sol–gel transition, triggered by the hydrophobicity increase of [P4444]Br above lower critical solution temperature (LCST). This drives PBDT aggregation into fibrous bundles through electrostatic interactions. These bundles grow and branch into a continuous network, with the molecular rigidity of PBDT's double‐helix conformation being key to gel formation. The hydrogel displays strain‐stiffening mechanical responses akin to biological systems and shows a significant hysteresis (21 °C) between heating and cooling cycles. Uniquely, the effects of salts on the transition temperature deviate from the Hofmeister series, highlighting coordination with sulfonate groups as the dominant factor. Leveraging its modulus change during gelation, the hydrogel was successfully applied as a spray coating on superhydrophobic vertical Teflon surfaces. This study broadens the scope of thermoreversible hydrogels introducing gelation mechanisms for rigid polyelectrolytes and demonstrates their potential in advanced coatings.