Preparation Of Environmental Friendly Thermal Stabilizers And Their Applications In PVC

Poly(vinyl chloride) (PVC) is the world's three general-purpose resin which is widely used due to its good performance in respect of mechanical behaviour as well as low price. However, PVC suffers from poor thermal stability, it undergoes extensive dehydrochlorination which results in severe discoloration and loss of mechanical properties. Therefore it is necessary to add thermal stabilizers in order to improve its thermal stability. However, the conventional thermal stabilizers generally contain lead, chromium and other toxic metals which will be environmental pollution. In recent years, the developments of environmentally friendly thermal stabilizers have become a necessity because environmental issues have become increasingly prominent.First of all, oleic acid, formic acid and peroxide were used to synthesize epoxidized oleic acid. Afterward, epoxidized calcium (zinc) oleate was synthesized by double decomposition reaction. Investigation of thermal stability of epoxidized calcium (zinc) oleate was investigated by means of congo red test, conductivity test, visual color comparison, thermo gravimetric analysis (TGA) test, FTIR analysis and mechanical analysis. The results showed that epoxidized zinc oleic acid ester was an initial-term thermal stabilizer, which can absorb the released HCl, react with the labile chlorine atoms in PVC chain and prevent further dehydrochlorination. However, an undesirable effect of the stabilizing action of epoxidized zinc oleic acid ester was the production of ZnCl2, which can promote the sudden dehydrochlorination of PVC. There was a fast exchange reaction between ZnCl2 and epoxidized calcium oleic acid ester, where the active epoxidized zinc oleic acid ester was regenerated and the undesir able ZnCl2 was consumed. This effect can prolong stability time and blacking time. When the ratio of epoxidized zinc oleic acid ester/ epoxidized calcium oleic acid ester was 1/3, stability time reached to 120min. The stability time was incresed 5 times than the zinc oleic acid ester was added separately. At the same time, blacking time came to 120 min, indicating that in this ratio thermal stability was the best.Moreover, soybean protein isolate (SPI) and its individual complex with zinc stearates (ZnSt2), calcium stearates (CaSt2), calcium/zinc compound thermal stabilizers (Ca-Zn), epoxidized calcium (zinc) oleate of various ratios as environmental friendly thermal stabilizer on the processing thermal stability of PVC were investgated by means of congo red test, conductivity test, visual color comparison, TGA test, FTIR analysis and mechanical analysis. The results showed that SPI was an auxiliary stabilizer. In the condition of a certain amount of primary Ca-Zn or epoxidized calcium (zinc) oleate, there was a synergistic effect between SPI and Ca-Zn stabilizers. When Dioctyl phthalate (DOP) was used as plasticizer, and Ca-Zn/SPI reached to 4/10, the stability time was 172min, twice as Ca-Zn was added separately, the blacking increased from 120min to 180min. When epoxidized soybean oil (ESO) was used as plasticizer, and epoxidized zinc oleic acid ester/epoxidized calcium oleic acid ester/SPI was 1/3/10, the stability time was 392.5min, 1.7 times as SPI was not added, the blacking increased from 240min to 400min. SPI was a long-term thermal stabilizer, which could reduce the release of HCl, the increase of the acid chloride carbonyl (COCl) stretching band in FTIR spectra suggested that amide(CONH)band may break and chloride carbonyl (COCl) band partly generated at the latter stages of degradation.