Study On The Organically Modified Layered Double Hydroxides And Their Application In PVC

Layered double hydroxides (LDHs), also named as anionic clays or hydrotalcite-like compounds, have a remarkable property that a variety of anionic species can be inserted as guests into the interlamella of the LDHs, especially beneficial organic anions, to form a large variety of new functional materials. Recently, Layered double hydroxides have attracted the attention of many researchers because of their potential application in the field of catalytic, adsorption, UV absorption, drug controlled release and polymer additives. Light transmittance of films could be improved by adding anti-dripping agent, therefore, it plays an important role in the agricultural production. At present, anti-dripping agent has some shortcomings, for example, the persistent period is short, lacking of compatibility between anti-dripping agent and other additives and the thermal insulation performance of film is very poor, and so on. In this paper, the surfactant was intercalated into Mg-Al-LDH interlayer by traditional co-precipitation method to form an organic-inorganic composite anti-dripping agent, and the possible effect factors were investigated.1. A series of APG-LDHs were synthesized by co-precipitation method. The optimum preparing conditions are pH 9, the mass ratio of APG/[Mg(OH)2+Al(OH)3] = 1/4 and the molar ratio of Mg/Al is 2. Besides electrostatic interaction, the driving forces of intercalation and assembly for APG molecules is hydrogen bonding between APG molecules and hydroxyl group of the host layers or interlayer water molecules. The interlayer APG molecules were arranged with a tilting angle between layers through hydrogen bonding, the range of the angleθis approximately between 48.6°~54.8°. Thermal decomposition temperature of APG between LDH layers increase about 40℃than pure APG, due to the strong host-guest interaction and the shielding effect of LDH layers.2. Mg–Al layered double hydroxide (Mg–Al LDH) was modified with lauric acid, myristic acid, hexadecanoic acid, stearic acid and sodium dodecyl sulfonate by co-precipitation method, and the resulting materials were characterized. The possible arrangement of surfactant in LDHs interlamellar space was also illustrated. The optimum modifier was selected as carrier of organic-inorganic composite anti-dripping agent. Comparison of performances of the resulting materials, we found that lauric acid is the optimum modifier. The interlayer surfactant molecules are arranged as a bilayer with a tilting angle. In addition, the d-spacing of myristic acid-LDHs increased to 3.71 nm and 4.37 nm indicating two types of arrangements are possible, and so does hexadecanoic acid-LDHs. The optimum preparing conditions for lauric acid-LDHs are the temperature are 30℃, the molar ratio of Mg/Al is 2 and pH 9.3. Organic-inorganic composite anti-dripping agent (Span20-lauric acid-LDHs) was synthesized by re-assemble method, and the resulting materials were fully characterized. The results showed that surface organophilic modification can improve surface tension of Span 20-lauric acid-LDHs and induced uniform dispersion of Span 20-lauric acid-LDHs in PVC matrix. In addition, Span20 has two types existing form: surface adsorption and interlayer intercalation, therefore, the surface hydrophilicity of film was improved markedly and the interfacial tension between water and film was decreased significantly by adding Span20-lauric acid-LDHs. In other words, anti-drop property of the film could be significantly improved. In addition, organic-inorganic composite anti-dripping agent can improve the insulation performance and visible light transmittance of films.