Wet Chemical Surface Modification And Characterization Of Calcium Metaborate Used As Flame Retardant

Calcium metaborate (CaO·BaO3·nH2O) is a kind of important boron compound, mainly used in alkali-free fiberglass, paint, ceramics, flame retardant and so on. Calcium metaborate can not be well compatible with polymer because of its surface polarity when adding it in polymer as a flame retardant. Therefore, calcium metaborate should be modified by using organic modifier in order to improve its compatibility with organic polymer and enhance the mechanic properties of organic-inorganic composite materials. In this paper, two kinds of different modification processes for calcium metaborate were investigated and several modifiers were employed to modify calcium metaborate in order to improve its surface polarity.In this paper, the reaction of boric acid with calcium hydroxide afforded calcium metaborate hexahydrate at the room temperature. Then, calcium metaborate hexahydrate was dried at140℃for3h to form calcium metaborate dihydrate (CaO·B203·2H20). The obtained products were characterized by chemical analysis, XRD, TG and particle size distribution analysis, some useful information on products, such as composition, phase, losing weight temperature and particle size distribution, were obtained. The XRD result indicated that the afforded calcium metaborate dihydrate was amorphous, and the particle size distribution of the product ranges from20μm to30μm, and the average particle size is24.16μm. The weight loss of calcium metaborate dihydrate is about22%within the range of100-600℃, indicating the removal of two water molecules. Before100℃, the weight loss of calcium metaborate dihydrate is less than3.5%. In order to make the synthesized calcium metaborate dihydrate have a good compatibility with polymer materials, surfactant was used to modify the product by a wet chemical process. Sodium stearate and oleic acid were selected as modification reagents, respectively. The influences of temperature, time, and adding amount of surfactant on the modification of calcium metaborate dihydrate were discussed and the modified calcium metaborate dihydrate was evaluated by FT-IR, contact angle and activation index. The modification result for calcium metaborate dihydrate indicated that the activation index and contact angle of the modified calcium metaborate dihydrate are95.27%and106.3°when10g of calcium metaborate dihydrate was treated at60℃for60min by adding0.5g of sodium stearate, while lOg of calcium metaborate dihydrate was treated at90℃for90min by adding0.5g of oleic acid, the activation index of the modified calcium metaborate dihydrate are95.79%.In addition, in contrast to the above mentioned two-step process, the process for the modified calcium metaborate dihydrate with one-step synthesis/surface modification was also discussed. The activation index of the modified calcium metaborate dihydrate can reach to99.77%and the contact angle of the modified calcium metaborate dihydrate is109.6°with3.0wt.%addition of sodium stearate, while the activation index of the modified calcium metaborate dihydrate can reach to93.94%with2.0wt.%addition of oleic acid. It is noted that the modification effect of one-step process for calcium metaborate dihydrate is better than that of two-step process. The brief modification mechanism was also discussed.