Synthesis And Performance Study Of Two Novel Thermal Stabilizers For Poly(Vinyl Chloride)

Environmentally friendly additive plays an important role on improving greenization of PVC industry.Calcium,zinc and rare earth heat stabilizers are the most common heat stabilizers for PVC.At present,prolonging the time for“burning zinc”?a larger amount of zinc salt will accelerate the degradation of the resin?and increasing the initial whiteness of the sample are the key to broadening the applicability of metal soap heat stabilizers.In order to balance the initial whiteness and“zinc burn”,preparation and synthesis of new heat stabilizer through optimizing the combination of ligands and metal ion has become a hot research method in this field.Then,we selected two metal ions,Zn???and La???,which are commonly used in industrial thermal stabilizers,and Gly,a polyhydroxy-organic ligand,and synthesized two compounds named La-Gly and Zn-Gly?Gly=trishydroxymethyl-glycine?as rigid PVC thermal stabilizers by referring to the work of other researchers.The thermal stability was tested when PVC was stabilized with the compound alone and compared with other traditional stabilizers.The results of infrared spectroscopy showed that cooridination bonds were formed between La???and Gly.Through high resolution mass spectrometry?HRMS?,we found that the ratio of La:Gly was 1:1.In addition,we proved that La-Gly could be used as a heat stabilizer for PVC using thermogravimetry since its structure is stable at the processing temperature of PVC.The thermal stability of La-Gly to PVC resin was evaluated by dehydrochlorination test,static aging test and dynamic aging test.,and the results showed that compared with traditional heat stabilizers?barium stearate,calcium,zinc heat stabilizers?,La-Gly possessed more overall performance:La-Gly was a long-term heat stabilizer with excellent performance.When used alone,the static aging time was 140 min,which was much higher than that of the sample stabilized with LaSt₃?40 min?.As the increase of the amount of La-Gly,the thermal stability of PVC could be improved.When the sample was stabilized with 2.0 g La-Gly,the static aging time was180 min,and the induction time and stable time obtained from the dehydrochlorination tests reached 91.9 min and 119.7 min respectively.According to the results of dynamic aging tests,when the addition amount of La-Gly is 0.9 g,the sample showed the best processing performance and excellent dynamic thermal stability,of which dynamic aging time is 24.2 min.A synergistic effect was found between La-Gly and zinc stearate?ZnSt₂?.When La-Gly/ZnSt₂ was 0.9/0.6,the sample had the best thermal stability and the totally-turning-black time is 140 min with slightly improvement in initial whiteness.No synergistic effect was observed between La-Gly and?-diketone.The structure,thermal stability of Zn-Gly and the thermal stability of PVC stabilized with Zn-Gly were also studied systematically.It was found that Zn-Gly could efficiently retarded“zinc burn”when used alone.In addition,there were synergistic effects between Zn-Gly and pentaerythritol?Per?and between Zn-Gly and?-diketone.The sample stabilized with Zn-Gly/Per?0.9/0.6?showed the longest aging-time of 210 min.When?-diketone was used with Zn-Gly,the sample presented the best initial whiteness but no improvement in the long-term stability.The totally-turning-black time of the sample stabilized with Zn-Gly/DBM?1.2/0.9?was 190 min,but its color was deep during the degradation.When Zn-Gly was used in combination with trimethylolaminomethane?Tris?,the sample had good initial whiteness and long-term thermal stability.The maximum aging time was 170 min when Zn-Gly/Tris was 0.3/1,2.