The requisite amount of phosphoric acid was added to maintain the pH value within the range of 2–3. This PVA/PAA/glyoxal solution was stirred vigorously over the course of 2 h at 85 C. The solution was cast on a glass plate (400 mm × 400 mm) to form a 40 m thick film using an applicator. The cast film was dried at 60 C for 24 h.
The thermal behavior of the non-crosslinked and crosslinked PVA films was studied using DSC within the temperature range of 30–300 C using a heating rate of 10 C/min. Thermogravimetric analysis (TGA; Mettler,STARSW) was conducted up to 600 C at a heating rate of 10 C/min under air atmosphere to evaluate the thermal behavior of the films.