Highly transparent and flame‐retardant polyvinyl alcohol membranes crosslinked with 2‐methyl‐2,5‐dioxo‐1,2‐oxaphospholane.

In the present paper, crosslinked polyvinyl alcohol (PVA) membranes with high transparency and excellent flame retardancy were obtained by blending 2‐methyl‐2,5‐dioxo‐1,2‐oxaphospholane (OP) with a PVA water solution at the molecular scale. Fourier transform infrared spectrometry and differential scanning calorimetry were used to investigate the crosslinking reaction. The surface morphology and micromechanical assessments of the membrane were examined using nanoindentation. The limited oxygen index (LOI) and vertical flame microscale combustion calorimetry, thermogravimetric analysis, scanning electron microscopy (SEM), energy‐dispersive spectroscopy (EDS), and x‐ray photoelectron spectroscopy (XPS) were employed to evaluate the flame retardancy and reveal the corresponding mechanisms. It was found that OP reacted with PVA below 120°C. The crosslinked membranes have a rougher surface and higher hydrophilicity and lower hardness and modulus than pure PVA does. The crosslinked membranes exhibit enhanced flame retardancy and high transparency. The membrane passes the UL 94 V 0 rating with an LOI of 27.6% and achieves a transmittance of 90.2% when the OP content is 20 wt.%. The SEM, EDS, and XPS results demonstrate that the interaction between OP and PVA effectively promotes the formation of a continuous and stable char in the condensed phase. [ABSTRACT FROM AUTHOR]