The Rare Earth Compound Stabilizer Impact On The Efficiency Of Pvc Heat Stabilizers

Up to date, Poly(vinyl chloride) (PVC) has been widely used because of outstanding properties, especially in the field of plastic PVC plays a very important role. However, during the process of machining PVC is prone to degrade and release Hydrogen Chloride (HCl) due to the defect structure with unstable chloride in the main chain of PVC. As a result, thermal stabilization of PVC is very poor so that in the course of application thermal stabilizer must be incorporated. Traditional thermal stabilizers mainly include lead salt, metal soap and organotin stabilizers, which have strong stabilization efficiency, but these stabilizers have high toxicity and cost. Hence, they are gradually replaced by non-toxicity rare earth stabilizer. Nevertheless, rare earth stabilizer can not be used solely as a result of the poor initial stabilization effect. Consequently, the stabilization effect of complex stabilizer with rare earth stabilizer and other co-stabilizers will be researched and try to use rare earth complex stabilizer to replace poisonous heavy metal thermal stabilizers.The synergistic effects between lanthanum stearate (LaSt₃) and Ca/Zn stabilizer or pentaerythritol (PeE) have been proved through thermal, mechanical and rheological behavior testing. It is found that LaSt₃ has an obvious synergistic effect with zinc stearate (ZnSt₂) and at the ratio of 8/2 there exists the best synergistic effect, which is comparable to the synergistic effect of Ca/Zn stabilizer. Moreover, thermal stabilization time of La/Ca/Zn stabilizer is far longer than those of La/Zn stabilizer and Ca/Zn stabilizer, which is comparable to that of lead salt stabilizer. At the low Ca/Zn ratio, addition of LaSt₃ can obviously improve tensile strength and reduce dynamic storage modulus. While at the high Ca/Zn ratio, incorporation of LaSt₃ has no noticeable effect on the tensile strength and dynamic storage modulus. In addition, the synergistic effect between LaSt₃ and PeE has been proved by Congo red testing and rheological behavior testing and at the La/PeE ration of 8/2 the synergistic effect reaches maximum. PeE can not be used solely because of poor stabilization effect, while addition of LaSt₃ can markedly improve thermal stabilization time of PeE. However, due to poor initial stabilization effect of LaSt₃ and PeE, addition of ZnSt₂ can remarkably restrain initial coloration and La/PeE/Zn complex stabilizer represents excellent thermal stabilization effect.The influence of LaSt₃ and Ca/Zn stabilizer on the stabilization effect of dibutyltin dilaurate (DBTDL) has been explained in the framework of ionization potential of metal. Due to the lower ionization potential of La than Sn, the substitution ability of LaSt₃ to the main chain of PVC is weaker than DBTDL. As a result, addition of LaSt₃ has no obvious effect on the stabilization effect of DBTDL. While Zn has a higher ionization potential than Sn, the substitution ability of ZnSt₂ is stronger than DBTDL. Hence, addition of Ca/Zn stabilizer markedly reduces the stabilization effect of DBTDL.The influence of hyper branched polymer H20 on the rheological behavior was studied by rheological testing. It is found that with the addition of H20, there exists a best content of H20 when complex viscosity reaches minimum in that at the high content the dispersion of H20 is not very good which will restrain the ability of reducing complex viscosity. Moreover, at high temperature the dispersion of H20 will be better than that at low temperature. As a result, the best content of H20 at high temperature will be higher than that at low temperature. At the same time, the influence of H20 on PVC with low molecular weight will be stronger than that with high molecular weight due to the better dispersion of H20 in the composite with low molecular weight. Additionally, the influences of hyper branched rare earth stabilizer (H20-g-La) on thermal and rheological properties have been studied. It is found that thermal stabilization behavior is similar to LaSt₃, that is, H20-g-La has excellent long-term but poor initial stabilization effect. Moreover, comparison of thermal stabilization effect of H20-g-La and LaSt3, H20-g-La has a better stabilization effect. However, H20-g-La can not effectively reduce complex viscosity like H20 in that the synthesis of H20-g-La destroys the original structure of H20.