Anions Control And Surface Modification Of Hydrotalcite Type PVC Heat Stabilizer

Hydrotalcites are one kind of compounds with supramolecular layered structure.Owing to their advantages such as acid-base adjustability,non-toxicity,and low cost,they can be used as a new variety of PVC heat stabilizers.Moreover,they are expected to replace the traditional heat stabilizers such as lead salts,metallic soaps and organic-tin.However,the modification is exceedingly desirable for magnesium-aluminum hydrotalcites due to their strong hydrophilicity,poor dispersibility and compatibility in PVC,and insufficient thermal stability.Firstly,Mg Al-X LDH(X=CO₃^2-,NO₃^-,Cl^-,and SO₄^2-)with different intercalated inorganic anions were prepared by co-precipitation method.The structure of the samples were characterized by X-ray diffraction,FT-IR,XPS,SEM and BET specific surface analysis.The effects of the dosage ratio of Mg to Al and interlayer anions on the adsorption of HCl and the thermal stability of PVC were investigated by adsorption and thermal stability experiments,and the mechanism of thermal stability was explored.The results showed that the as-obtained samples exhibited a regular hexagonal sheet shape with a high crystallinitie,and illustrated a narrower particle size distribution of about 120-275nm.The interlayer counterion had a great influence on their adsorption of HCl and the thermal stability of PVC.In addition,it was found that the greater adsorption capacity of HCl onto Mg Al-X LDH was,the better thermal stability of PVC/Mg Al-X LDH composites had.The orders of adsorption amount and thermal stability followed the consistent sequence:the dosage ratio of Mg to Al of 3>2>4,and nterlayer counterionadsorption and pore adsorption of HCl released from the thermal degradation of PVC that limited the autocatalytic dehydrochlorination and improved the thermal stability of PVC.Secondly,Mg Al-CO₃ LDH with the dosage ratio of Mg to Al of 3 was modified with terephthalic acid.The effects of crystallization time,crystallization temperature,p H,and types of solvents on the performance of PTA-Mg Al-CO₃ LDH were discussed.The results showed that the PTA-Mg Al-CO₃ LDH had the best performance using 10%?vol?ethylene glycol?EG?aqueous solution as the medium,crystallized at 150?and p H of 7for 8h.Compared with unmodification Mg Al-CO₃ LDH,Congo red time and static heat aging time of PVC can be increased by 38.5%and 48.0%,respectively.XRD and FT-IR results showed that terephthalic acid entered into the interlayer of hydrotalcite and partially replaced the original carbonate ions.The interlayer terephthalic acid improved the compatibility of hydrotalcites and PVC,increased the active sites on the surface of the hydrotalcites and enhanced the adsorption ability to HCl.So,the initial thermal stability and long-term thermal stability of PVC have been greatly improved.Finally,Mg Al-CO₃ LDH with the dosage ratio of Mg to Al of 3 was modified with sodium stearate.The effects of crystallization time,crystallization temperature,stirring time,stirring temperature,p H,and types of solvents on the performance of St-Mg Al-CO₃LDH were discussed.The results showed that the St-Mg Al-CO₃ LDH had the best performance using 20%?vol?EG aqueous solution as the medium,co-precipitated at40?for 2h and crystallized at 130?and p H of 7 for 8h.The surface activation degree of St-Mg Al-CO₃ LDH can reach 99%.Compared with unmodification Mg Al-CO₃ LDH,Congo red time and static heat aging time of PVC can be increased by 24.1%and 48%,respectively.XRD and FT-IR results showed that the interlayer anions of the St-Mg Al-CO₃ LDH were still carbonate ions.Sodium stearate was only adsorbed on the surface of the St-Mg Al-CO₃ LDH,which improved its hydrophobicity and the compatibility of hydrotalcite with PVC.