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Effect of Lanthanum Cyanurate as Novel Organic Thermal Stabilizers for Polyvinyl Chloride Mei Li, Zaiyong Jiang, Zhaogang Liu, Yanhong Hu, Mitang Wang, Haiou Wang Material and Metallurgy Institute, Inner Mongolia University of Science and Technology, Key Laboratory of Inner Mongolia Autonomous on New Technologies of Modern Metallurgy and Application of Rare Earth Inner Mongolia, Baotou 014010, People'

s Republic of China Lanthanum cyanurate was synthesized by reacting cy- anuric acid and lanthanum nitrate at basic condition and was characterized by elemental analysis and Fou- rier transform infrared spectroscopy.

Its application as thermal stabilizer for poly(vinyl chloride) (PVC) was investigated by Congo red test and discoloration test. In comparison with other heat stabilizers, including lanthanum stearate, calcium stearate, and zinc stea- rate, lanthanum cyanurate exhibits high stabilizing effect with excellent initial color of PVC. The stability time reaches the maximum (80 min) when the percent- age of lanthanum cyanurate in PVC is 2.5%. The combination stabilizers (LaC3N3O3/Zn(St)2 obviously increase the complete discoloration time of PVC in comparison with the stabilizer of Zn(St)2. The stability time of PVC increases from

14 min (stabilized by zinc stearate) to

26 min (stabilized by LaC3N3O3/Zn(St)2). LaC3N3O3 also shows a slightly stronger effect on ten- sile strength of PVC than La(St)3. Therefore, the LaC3N3O3 can be used to replace La(St)3 and serve as a costabilizer to improve stabilization ef?ciency of cal- cium/zinc stabilizers for PVC. POLYM. ENG. SCI., 53:1706C 1711, 2013. ?

2012 Society of Plastics Engineers INTRODUCTION Polyvinyl chloride (PVC) is one of the ?ve commonly used thermoplastic materials. It has the advantages of superior mechanical and physical properties, high chemi- cal and abrasion resistance, and widely utilized in durable applications [1]. However, in PVC applications have a main drawback or limitation that it easily undergoes severe thermal degradation at a relatively low tempera- ture. The fact that HCl is produced during the thermal degradation of PVC leads to many problems, discoloration and the deterioration of mechanical properties for instance [2, 3]. Proper amount of stabilizers need be added so as to restrict the degradation of PVC during the thermal processing [4, 5]. At present, the commonly used stabil- izers in industry mainly include lead salts [6], organic tin [7, 8], soap salts [9, 10], rare earth element-based stabil- izers [11, 12], organic antimony, and organic auxiliary agent [13, 14]. Although basic lead compounds and or- ganic tin compounds have great stabilization, they should be restricted when applied in PVC on account of their toxicity. Nevertheless, rare earth element-based stabilizers which emerged in recent years are nontoxic and environ- mentally friendly. It has bright prospect to exploit a high-ef?cient per- formed and nontoxic rare earth heat stabilizers [15]. Recently rare earth compounds, such as stearates [12], salicylates, laurates, and palmitates [16], have been used as PVC thermal stabilizers. Nevertheless, only rare earth stearate has been widely applied in industrial production. However, the low compatibility between rare earth stea- rate and PVC becomes a challenge problem and it needs to be further improved in the process of PVC. In recent years, majority research works have mainly focused on either improving the compatibility of rare earth stearate and PVC by adding additives or forming a new compound by introducing a special functional group. The latter has not been fully exploited. Here, we present a cir- cular rare earth cyanurate synthesized via a simple reaction between organic weak acids and rare earth compound. Moreover, we report that lanthanum cyanurate has a long- term thermal stability and can enhance the thermal stability when used with other thermal stabilizer together. EXPERIMENTAL Materials The PVC (SG3) was supplied from the Puyang Chen- gyi Plasticizer Co., Henan, China. Lanthanum nitrate was prepared by reacting lanthanum oxide (Inner Mongolia Baotou Rare Earth High Technology Co., China) with Correspondence to: Mei Li;