Rapidly polymerized cellulose-based hydrogel pads enabled by bromothymol blue for multifunctional fruit storage

Hydrogel absorbent pads prolong shelf life of foods, but moisture regulation remains challenging. Herein, a bromothymol blue (BTB)-induced ZnCl₂-dissolved cellulose/poly(2-hydroxyethyl acrylate) hydrogel (ZnC/PHEA-B) was developed via rapid free-radical polymerization. BTB concentration gradients (0-80 mg) were established to regulate polymerization behavior and optimize hydrogel performance. BTB accelerated polymerization, reducing the peak-temperature time from 1140 s to 270 s and increasing the peak temperature from 26.1 to 53.3 °C. Based on polymerization behavior, mechanical properties, and functional performance, ZnC/PHEA-4B was identified as the optimal sample. ZnC/PHEA-4B exhibited good mechanical strength (91.3 kPa and 301.5% strain), strong adhesion, resilience, and frost resistance (-137.5 °C). It enabled active moisture regulation with radical-dependent antioxidant and antibacterial activities. When applied as an absorbent pad, it prolonged blueberry shelf life from 4 to 12 days through moisture regulation, antibacterial, radical-dependent antioxidant and mechanical protection.