Preparation Of Modified Mg-Al Hydrotalcite And Its Effect On Thermal Stability Of PVC

Hydrotalcite (called Layered Double Hydroxides, abbreviated as LDHs) is a kind of anionic compound with layered structure. Owing to its alkalinity, interlayer ion exchange ability and memory effect, hydrotalcite has been widely used as catalyst,adsorbent, PVC flame retardant and heat stabilizer. In this paper, MgAl-CO3-LDHs was prepared by co-precipitation method, and the effects of modification methods and modifiers on its structure and properties were also investigated.Firstly, the synthesis process of MgAl-CO3-LDHs was optimized by the single factor method. Using the thermal stability time of PVC as the evaluation index, the effects of synthesis method, dropping rate of alkali solution, pH, temperature and time of synthesis and hydrothermal crystallization were discussed in co-precipitation process. The optimum process conditions were as follows: dropping rate of the NaOH and Na2CO3 mixed solution is 1 drop/s at a constant pH of 11, the reaction is condected at 50? for 2h and then at 180? hydrothermal crystallization for 18 hours.The results showed that the synthesized MgAl-CO3-LDHs could significantly improve the thermal stability of PVC, and the thermal stability time was more than 1 times higher than that of non-adding.Secondly, the roasting reduction method and the pillared intercalation method were used to modify MgAl-CO3-LDHs. Zinc stearate, sodium stearate and terephthalic acid were used as modifiers. The results showed that the performene of the product modified by the pillared intercalation method was better than that by the roasting reduction method. Zinc stearate and terephthalic acid were successfully inserted into the interlayer of hydrotalcite and the thermal stability of PVC was improved.Finally, using zinc stearate as modifier, the MgAl-CO3-LDHs in different states modified by the pillared intercalation was investigated. The results showed that the performene of the product obtained from the dry and wet LDHs cake was better than that LDHs slurry. Considering the energy consumption, the optimum method to modify the MgAl-CO3-LDHs wet cake was the pillared intercalation modification by using zinc stearate as modifier. The static thermal stability time of PVC with the modified hydrotalcite stabilizers was higher than that with the unmodified hydrotalcite stabilizers by a factor of 1.5.