Preparation Of Surface Coated Nano-Antimony Oxide With Melamine-Formaldehyde Resin And Study Of Flame Retardant Property In Flexible PVC

Nano-antimony trioxide and nano-antimony pentoxide surface coated with melamine-formaldehyde (MF) resin were prepared and used to fill flexible polyvinyl chloride (PVC). The uncoated and coated nano-antimony oxide samples were characterized by means of X-ray diffraction, transmission electron microscopy (TEM) and Fourier transform infrared spectrometry (FT-IR). The flame retardant behavior of flexible PVC filled with uncoated and coated nano-antimony oxide was evaluated based on oxygen index (OI) measurement and differential thermal analysis. The tensile strength of flexible PVC filled with uncoated or coated nano-antimony oxide of different dosage was determined. The main contents and research results are as follows:1. Preparation of nano-antimony trioxideNano-antimony trioxide was prepared via coordination precipitate in the presence of fluorine ion. The effects of reaction conditions including concentration of fluorine ion and antimony ion, temperature, and molecular weight of surface modifying agent on the size of Sb₂O₃ particles were investigated in detail; and the optimal synthetic condition was established. It has been found that in the absence of fluorine ion, as-synthesized nano-antimony trioxide consists of cubic and orthorhombic crystalloid. With increasing content of fluorine ion, the content of orthorhombic crystalloid in as-synthesized nano-antimony trioxide tends to gradually decrease, and orthorhombic crystalloid disappears at a F to Sb molar ratio of 1 : 1. Besides, the grain size of as-synthesized nano-antimony trioxide tends to decrease with decreasing concentration of antimony ion; and nano-antimony trioxide obtained at an antimony ion concentration of 0.025 mol/L has a grain size of about 80～200 nm. Moreover, the temperature for synthesizing nano-antimony trioxide is suggested to be 30℃; and PEG-6000 with fine mesh structure seems to result in a narrowed grain size distribution.2. Preparation of antimony trioxide surface coated with melamine-formaldehyde resin and its application in PVCNano-antimony trioxide surface-coated by melamine-formaldehyde (MF) resin was prepared and used to fill flexible PVC. The microstructure and chemical feature of as-prepared antimony trioxide surface coated with MF resin were analyzed by means of TEM and FT-IR. Uncoated and coated nano-antimony trioxides were separately filled into flexible PVC; the tensile strength and flame retarding behavior of resultant filled PVC composites were examined. It has been found that flexible PVC filled with 5% (mass fraction) coated antimony trioxide has an OI of 30.0%, much higher than 23.8%, that of unfilled PVC. Since the content of nano-antimony trioxide in coated nano-antimony trioxide is 25.2%, the actual content of nano-antimony trioxide in PVC filled with 5% surface-coated nano-antimony trioxide is as low as 1.26%, but its flame retarding efficiency is comparable to that of PVC doped with 3.55% Sb₂O₃, corresponding to a decrease of Sb₂O₃ dosage by 64.5%. This indicates that the dosage of Sb₂O₃ as a flame retardant in PVC can be significantly decreased by surface-coating with MF resin, which contributes to save the resource of antimony and alleviate possible impact of flame retardants on environment.3. Preparation of antimony pentoxide surface coated with MF resin and its application in PVC Colloidal antimony pentoxide was prepared via an oxidative reflux route. Resultant colloidal antimony pentoxide was surface-coated with melamine-formaldehyde resin. The microstructure and chemical feature of antimony pentoxide surface-coated with MF resin were analyzed by means of TEM and FT-IR. The effect of the surface-coated antimony pentoxide on the tensile strength and flame retarding behavior of flexible PVC was investigated. It has been found that flexible PVC doped with 5% surface-coated antimony pentoxide has an increased OI of 28.3% than the unfilled one (23.8%). Since the content of antimony pentoxide in the surface-coated antimony pentoxide is 34.2%, the actual content of antimony pentoxide in flexible PVC filled with 5% surface-coated nano-antimony pentoxide is as low as 1.7%, but its flame retarding efficiency is comparable to that of PVC doped with 4.8% Sb₂O₅, corresponding to a decrease of Sb₂O₅ dosage by 64.1%. This indicates that the dosage of Sb₂O₅ as a flame retardant in PVC can be significantly decreased by surface-coating with MF resin, which contributes to save the resource of antimony.