| Calcium borate (xCaO·yB2O3·nH2O) is one of the important chemical materials and products. It can be widely used in glass, paint, steel, ceramics industries, etc. In addition, it also can be applied in flame retardants, nonlinear optical materials, agricultural, antiseptic and medicine industries, etc. The synthesis of calcium borate depends on many conditions, such as raw materials, pH value, process route, etc. In order to develop caicium birate as a high-quality halogen-free flame retardants with less cost, the superficial polarity features of calcium borate should be modified based on its physical and chemical characteristics. The affinity and compatibility of calcium borate with polymer minerals would be improved when modifying calcium borate and the mechanical properties of polymer materials can also be enhanced when adding modified calcium borate. With the filling of the modified calcium borate into the organic materials, the production cost of polymer minerals can be reduced and the application field of calcium borate can be also widened. In addition, the industrial value and economic value of calcium borate is expected to rise.In this paper, calcium borate was synthesized with using boric acid and calcium hydroxide as raw materials by a hydrothermal synthesis, the influences of raw material ratio, solid to liquid ratio, reaction time and reaction temperature on the type, particle size and yield of calcium borate were studied, respecyively. The perferred reaction conditions were acquired. Calcium borate obtained by hydrothermal synthesis was characterized by XRD, TG/DTG, SEM, chemical analysis and particle size distribution analysis. Many useful physics and chemistry information, such as the type of calcium borate synthesized, temperature of weight loss, the distribution of particles size, were provided for screening a proper flame retardant. The suitable synthesis conditions are as follows:reaction temperature 160℃, raw materials' B2O3/CaO molar ratio 1.7, liquid to solid ratio 6 and reaction time 4h. Pure preceite was synthesized under these conditions. The contents of B2O3 and CaO in the synthesized preceite are 47.65wt% and 30.41wt%. The weight loss of preceite is about 17.40% between 110 and 600℃, indicating removing 7 water molecules, and the weight loss of preceite is less than 2% before 200℃. The average particle size of preceite is about 5.96μm and particle size distribution is mainly between 3 and 8μm。The priceite was modified using sodium stearate as a modification reagent by a wet chemical process. Effects of temperature, time, surfactant addition and liquid to solid ratio on the modification of priceite were discussed. In addition, modified priceite was evaluated by FT-IR, SEM, contact angle, activation index and suspension performance in water. The preferred modification conditions for priceite was achieved when priceite was treated at 80℃for 75min with a liquid to solid ratio of 3 by adding 5wt.% of sodium stearate. The activation index of the modified priceite can reach to 97.16% and the contact angle of the modified priceite is up to 121.23°. In addition, the process for the modified priceite with one-step hydrothermal synthesis/surface modification was also discussed. The activation index of the modified priceite can reach to 86.80% and the contact angle of the modified priceite is 104.9°with 4.0wt.% of sodium stearate addition.The colemanite of Turkey was characterized by chemical analysis, XRD, TG/DTG and particle size distribution analysis. The raw colemanite, ball milling colemanite, different modifiers and different modification method were investigated in the process of modification. The modified products were characterized by FT-IR, contact angle, activation index and SEM. Results showed that when the colemanite was treated at 80℃for 75min with a liquid to solid ratio of 2 by adding 2.0wt.% of sodium stearate, the activation indexes of modified raw colemanite and modified ball milling colemanite were 45.95%, with a contact angle at 129.3 0 and 64.95%, with a contact angle at 112.7°, respectively. The activation index of colemanite modified by NDZ-311 with ball milling was also reached to 67.85%, with a contact angle at 85.6°. In addition, the modification mechanism was also discussed. The modified calcium borates were filled into EVA, and the mechanical properties of the composite materials were tested. The composite materials were then burned and surface morphologies were observed by microscope.
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