Exfoliation And Esterification Of Expanded Graphite And Its Application Of Polyvinyl Alcohol Film

Hydrothermal exfoliation technique was used to treat expanded graphite with cationic surfactant acting as intercalating agent in alkaline water and ethanol medium respectively. Then the exfoliated graphite prepared in the ethanol dispersion reacted with phosphorus oxychloride in toluene. Finally the esterified and exfoliated graphite was used to improve the flame retardant of poly(vinyl alcohol). The crystallinity, crystallite size, and morphology of exfoliated and expanded graphite, the functional groups and surfactant attachment on exfoliated and expanded graphite surfaces were investigated with X-ray diffraction, infrared spectroscopy, Raman spectroscopy, field scanning electron microscopy, and thermo-gravimetric analysis. The flame retardations of the esterified and exfoliated graphite and the modified graphite reinforced poly(vinyl alcohol) film were characterized with microcone calorimetry. In addition, the reinforcing effect of the hydrothermally exfoliated graphite on the cast PVA film was investigated. The following main conclusions can be obtained.(1) The cationic surfactant cetyltrimethyl ammonium bromide(CTAB) demonstrated best exfoliation, such as, 97.6% of expanded graphite was exfoliated(also known as amorphous structure), and 1.8% of expanded graphite was intercalated with CTAB acting as intercalating agent dispersed in alkaline ethanol system, whereas, 87.6% of expanded graphite was exfoliated and 12.4% of expanded graphite was intercalated in alkaline water system.(2) The hydroxyl groups were implemented onto the exfoliated and expanded graphite surface after hydrothermal treatment both in alkaline water and ethanol media. The weight loss of ca. 30-75% appeared in the temperature range of 100-240 degree Celsius, corresponding to the loss of the adsorbed and intercalated surfactants hydrothermal treated both in alkaline water and ethanol media as well. In addition, all the exfoliated and intercalated graphite treated by cationic surfactants showed excellent reinforcing effect for the cast polyvinyl alcohol film, among them, tetradecyl imethyl benzyl ammonium chloride was most effective.(3) Phosphate was resulted by reacting exfoliated graphite prepared in the ethanol dispersion with phosphorus oxychloride in toluene. The esterified graphite presented strong weight loss ca. 50-60% in the temperatures of 200-600 degree Celsius, corresponding to decomposition of phosphate. The esterified graphite also gave doublet heat release peaks in the microcone calorimetry, and this implied the carbonization due to catalytic dehydration of phosphoric acid. The esterified graphite improved the flame retardation of PVA film.The characteristic and innovation of the thesis:(1) The hydrothermally exfoliated and esterified graphite was used to improve the flame retardant of polyvinyl alcohol film.(2) The Raman spectroscopy and X-ray diffraction were used to interpret the structure and components of the exfoliated and intercalated of the expanded graphite, and the hydrothermal treatment not only produce the exfoliated expanded graphite(also named as amorphous structure) and the intercalated expanded graphite, but also crack down the graphitic plane size.