The Properties Of Natural Rubber Coagulated By In-situ Prepared Mg（OH）₂/Al（OH）₃

Magnesium hydroxide (Mg(OH)2) and aluminum hydroxide(Al(OH)3) are widely used as inorganic flame retardant in the flame retardant field of polymer. Skim latex is a by-product when produce rubber latex concentrate. As the high content of ammonia and low content of rubber particles, the most common way to coagulate skim latex is to add sulfuric acid (wt10%) which is so corrosive that it can endanger personal and equipment safety. In industry, Mg(OH)2and Al(OH)3are prepared by ammonia react with MgCl2and AlCl3. This paper added MgCl2and AICl3solution into skim rubber to coagulate it. The effect of coagulation and properties of skim rubber will be studied.The effects of addition of MgCl2solution, ammonia dosage in skim latex on the coagulation were studied. The results show that a small amount of MgCl2can not effectively coagulate skim latex, it only get small rubber particles. Overdosage of MgCl2can easily cause too much Mg(OH)2in limited space, which results in local coagulation of the skim latex, therefore, it reduce the recovery rate of rubber. It is bad for coagulation if skim latex contain too much ammonia. Considering about the domestic productive technology, the ammonia in skim latex is below0.3%. So, the best formula to coagulate skim latex is to add8ml MgCl2solution (1M) per100g skim latex.Same dosage of MgCl2and AlCl3solution and their mixed solution were added into skim latex. The coagulation and properties of rubber were studied, the results show that AlCl3solution can not coagulate skim latex well, it only get small rubber particles, which need microwave radiation to form the complete coagula. There is also bad coagulation when the AlCl3ratio in mixed solution was greater than one-third. Rubber coagulated by mixed solution of MgCl2and AlCl3with the volume ratio of1:1has the maximum tensile strength, tensile strength of rubber coagulated by MgCl2and AlCl3was similar to coagulation by sulfuric acid, rubber coagulated by microwave radiation with NaCl has the lowest tensile strength. When MgCl2and AlCl3with the volume ratio of4:1, rubber get the best ageing property, the second is coagulated by mixed solution with ratio of3:1the third is coagulated by MgCl2alone. While, rubber which obtain Mg(OH)2and Al(OH)3has better aging properties than rubber coagulated by sulfuric acid. By analyzing the physicochemical properties of rubber coagulated by different solution found that indictors have already reached to the Level2standard skim rubber expect ash content. The data of dynamic mechanical properties show that rubber coagulated by AlCl3has the highest modulus of elasticity; rubber coagulated by MgCl2was higher than coagulated by sulfuric acid, which indicates that rubber coagulated by Mg(OH)2and Al(OH)3remains complete of internal structure and hindered the free movement of rubber molecules.The effects of different of generated amounts of magnesium hydroxide and the different of added amounts of surfactant on coagulation and properties of rubber were studied. The results show that Mg(OH)2is not enough to evenly disperse in rubber if to add small amount of MgCl2, on the contrary, large amount of MgCl2will cause aggregation of Mg(OH)2. Both will decrease the mechanical property of rubber. Rubber will get best mechanical property when10-15phr Mg(OH)2was generated. The maximum decomposition rate declined and the residue increased obviously when they contain more Mg(OH)2, so, more Mg(OH)2, rubber enjoys better thermo stability. Surfactant is beneficial to get smaller size Mg(OH)2and improve its dispersion in rubber, but it cannot be added too much. The mechanical property declined obviously when added more than0.1phr. The results showed that when the content of surfactant was0.05phr, rubber has the best mechanical property, Mg(OH)2has smaller particle size and distributed more uniform.