Preparation Of Intercalated Mg/Al-ldhs And Effect On Thermal Behavior For Poly(vinyl Chloride)

This paper studied the synthesis of hydrotalcite, a new type of inorganic thermal stabilizer, and its effect on thermal behavior of poly(vinyl chloride). Preparation conditions, structure and properties of hydrotalcite had been intensively explored in this article. Because hydrotalcite is non-toxic,green and environmentally friendly, it is expected to replace the traditional heat stabilizers.The impact of reaction temperature, crystallization temperature and the molar ratio of reactants on the preparation of hydrotalcite were investigated by single factor rotation method. It showed that the best synthetic route of Mg Al-LDHs was, the best molar ratio of Mg2+/ Al3+ was 3:1 and the best molar ratio of Na2CO3 /Na OH was 1.6:1, acid and alkali solutions were heated at 90℃ and the p H value maintained between 9-11, after the dropping(2-3 seconds per drop), kept stirring for another 2h with 400 r/min stirring speed, after the suspension had been precipitated and cooled, the reaction solution was aged at 65℃ for 18 h, filtered with deionized water to neutrality and then dried in vacuum at 80℃ for 12 h. The white solids obtained were ground into a fine powder. The best synthetic route of Zn Al-LDHs was : the best molar ratio of Zn2 +/ Al3 + was 2:1 and the best molar ratio of Na OH/Na2CO3 was 1.5, acid and alkali solutions were simultaneously added dropwise slowly into the flask(stirring vigorously) which contained 50 ml deionized water at 70℃ and the p H value maintained at around 10, after the dropping(2-3 seconds per drop), kept stirring for another 2-3h with the stirring speed of 400 r/min; and then the reaction solution was aged at 70℃ for 24 h, filtered with de-ionized water to neutrality and then dried in vacuum at 75℃ for 18 h. The white solids obtained were ground into a fine powder.Mg Al-LDHs intercalated with CO(NH2)2, NH4 Cl and NH3·H2O were prepared by co-precipitation and XRD, FT-IR, WAXS and SEM techniques were employed for characterization. The results indicated the layer-layer spacing of LDHs were enlarged by 0.169, 0.285 and 0.227 ? with the intercalation of CO(NH2)2, NH4+and NH3, respectively. The effects on thermal stability and degradation behavior of synthesized LDHs with mole ratios of Mg/Al/urea=3:1:1, Mg/Al/NH4Cl=3:1:1.5 and Mg/Al/NH3·H2O=3:1:0.5 were investigated by Congo Red Method and thermogravimetric analysis(TGA) from 25~800℃ under N2. The TGA and DTA results showed, by incorporating 5% Mg Al-CO(NH2)2 LDH, the dehydrochlorination temperature of PVC composites is 12℃ higher than Mg Al-NH4+ and Mg Al-NH3 LDHs. Mg Al-NH3 LDH enhances the ending temperature of the first degradation stage of PVC composites by 8℃ compared with Mg Al-LDH. The thermal stabilization time for PVC of Mg Al-LDH is 18.5min. The best thermal stabilization time for PVC of Mg Al-CO(NH2)2 LDH, Mg Al-NH4+LDH and Mg Al-NH3 LDH were respectively 31.5min, 38 min and 43 min.In addition, a series of Zn Al-LDHs intercalated with CO(NH2)2, NH4 Cl and NH3·H2O were prepared, all of the samples were tested by Congo Red Method, and part of the samples were characterized by XRD, FT-IR. The results showed that the thermal stabilization time for PVC of Zn Al-LDH was 18 min; after intercalation with urea, NH4 Cl and ammonia, thermal stabilization time for PVC were respectively up to 32 min, 37.5min and 41 min, and at the same time the layer spacing were respectively increased by 0.422, 0.146 and 0.325 ?.PVC/hydrotalcite composite film was prepared by casting method. Five kinds of PVC composite film including the film without the addition of hydrotalcite and added respectively with Mg/Al-LDHs, Mg/Al/urea-LDHs, Mg/Al/NH4Cl-LDHs, Mg/Al/ ammonia-LDHs were produced. Thermal stability of the composite film was tested by Congo Red Method and oven aging method. Limiting Oxygen Index for PVC / hydrotalcite composites were tested as well. The results showed that the thermal stabilization time for the filmwithout the addition of hydrotalcite were 10 min, and the thermal stabilization time for the film added respectively with Mg/Al-LDHs, Mg/Al/urea-LDHs, Mg/Al/ NH4Cl-LDHs, Mg/Al/ammonia-LDHs were increased to 19 min, 32 min, 38 min, 44 min. The oven aging results were consistent with Congo Red results. LOI value for the filmwithout the addition of hydrotalcite were 29.6, when added with Mg/Al-LDHs, Mg/ Al/urea-LDHs, Mg/Al/NH4Cl-LDHs, Mg/Al/ammonia-LDHs, the LOI value were respectively as high as 30.8, 33.8, 34.4, 34.8.