The thermal behavior of multifunctional polyvinyl alcohol/polyurea hybrid hydrogel prepared from oligomers with urea linkage

An innovative hybrid hydrogel with antibacterial properties and high heat resistance has been developed. This new hydrogel is created by crosslinking urea linkage oligomer (ULO) with PVA polymer.

The ULO is produced through a condensation reaction in a molten state, using sulfamic acid, phosphorous acid, and urea. The polymer film is prepared in an aqueous environment by mixing the materials, molding, and applying heat pressing.

The characterization of hydrogel was reported using an SEM microscope, ion chromatography technique, FT-IR, DSC, TGA, and LOI analysis. After heat pressing and crosslinking, polyurea networks, mineral salt particles; ammonium sulfate, phosphates, nitrates, and melamine are identified through the polymer layer, and the heat resistance of polymer films is enhanced. The study focused on the products generated during the pyrolysis process. Flammable volatile gases released from the samples were affected by the amounts of raw materials used and the production conditions. The most flammable gases from PVA decomposition include acetaldehyde, 2-butenal, and 2,4-hexadienal. The active and combustible gases from urea and its oligomers are cyanic acid and cyanamide. These samples' thermal pyrolysis enthalpy was calculated from the DSC curve and discussed. The modified polymer demonstrates excellent flame-retardant properties, with an LOI of 48 % and a char content of 37.28 % at 500 °C. The mechanism by which this urea oligomer controls ignition through the dilution of volatile gases, the production of a resistant foam coating, and the formation of carbon char remains debatable.