PEG-Encapsulated Chitosan Hydrogel Films With Superior Mechanical Durability for Active Thermal Management

To meet high-efficiency thermal management demands in agricultural greenhouses, bio-based chitosan (CS) and polyethylene glycol (PEG) composite hydrogel films (P1–P3) were prepared. By incorporating PEG into the chitosan matrix, the limitation of traditional CS hydrogels—which offer passive insulation but lack active energy storage—was effectively addressed. Experimental results demonstrated that the composite hydrogels possess exceptional thermal stability; after being heated at 60°C for 30 min, the PEG remained firmly locked within the CS network without any leakage. In thermal insulation tests, when exposed to a 200°C heat source, the P3 sample (containing 21% PEG) took the longest time (313 s) for its top surface to reach 60°C, significantly outperforming the neat P0 sample (188 s). In greenhouse simulation experiments, after 2 h of light-induced heating, the P3 group achieved an indoor temperature rise of 15.1°C, exhibiting the strongest thermal storage and release capacity. Regarding mechanical properties, P3 showed the highest mean compressive stress of 75.19 ± 1.60 kPa. Additionally, the transparency of the hydrogels increased with higher PEG content, which is beneficial for greenhouse lighting. This study proves that CS/PEG composite hydrogels offer significant advantages in thermal management and structural durability for agricultural greenhouse film applications.