Synergistic Combination of Metal Stearates and b-Diketones with Hydrotalcites in Poly(vinyl chloride) Stabilization

摘要

A synergistic effect of synthetic hydrotalcites as long term stabilizer with metal soaps (the mixture of calcium and zinc stearate) and metal acetylacetonates on dehydrochlorination of PVC has been studied. A proper balance between color stabilization and HCl scavenging capacity has been obtained. Hydrotalcite was prepared by hydrothermal treatment and characterized by EDX, XRD, FTIR, TGA, and SEM techniques. The material is reasonably crystalline and suggests a relatively well ordered sheet arrangement with crystallite size 24.87 nm. The interlayer water content was calculated from the TGA curves and the suggested formula is Mg0.76 Al0.24(OH)2(CO3)0.12 0.5H2O. Synergism in PVC stabilization has been studied by measuring the HCl evolution during the processing at 180 C. Oven aging method was used to study the color stabilization at higher temperature. PVC sheet with different formulation was prepared using Labcoater and subjected to oven for different time interval. The color development (polyene formation) on oven ageing was recorded using UV_visible spectroscopy. UV_visible studies shows that an average sized polyene gives pale yellow color, whereas red or brown color was developed due to long range polyene (n _ 10_14) sequences. Hence, the HCl evolution depends on the rate of dehydrochlorination but color depends on the kind of polyene formed. Mechanism of stabilization suggests that adsorption and ion exchange, both phenomenon, are responsible for hydrotalcites as long term stabilizers. The acetylacetonate complex too substitute allylic chlorides and inhibit formation of long polyene responsible for darkening. A clear effect of synergism has been observed.