Characteristics of rare earth heat stabilizer for PVC
Rare earth ions have many 4f and 5d vacant orbital electron levels.As coordination center ions,they can accept the lone electron pairs of 6~12 electron ligands.At the same time,they have large ionic radii,which makes it possible to form coordination bonds with different bond energies of 6~12 and complex bonds,which makes them capable of forming ionic bonds with 3 or 4 HCL.It can also bind to unstable chlorine atoms on PVC chains.In addition,the energy range between the valence electron energy level of rare earth elements and the empty electron energy level is small,such as 6s electron energy 6.0(relative value),4f electron energy level 6.1,5d electron energy level 6.4,so their electrons are easy to transition from the ground state to a relatively high energy level under the action of external forces(light,heat,etc.),such as 4f or 5d energy level in the empty orbital.It is in an excited state,and then returns to the ground state by emitting fluorescence and releasing energy,resulting in the following properties of rare earth thermal stabilizer:
(1)Heat stability function and transparency.The stabilization effect of rare earth stabilizer is better than that of metal soap stabilizer.It has good heat resistance,is not polluted by sulfur,and is stable in storage.Rare earth elements can absorb ultraviolet rays of 230~320mm,which is one of the factors of pvc aging.Therefore,rare earth stabilizer has the rare weather resistance of other heat stabilizer,which is suitable for outdoor products such as Windows.The rare earth ion pole may form coordination bonds with the unstable chlorine atoms on two pvc chains at the same time,thus increasing the pvc intermolecular force,enhancing the transfer of shear force during plasticization,promoting plasticization,and increasing the toughness of the finished product.
(2)Coupling function.Rare earth ion is a kind of hard cation which is not easy to polarize and deform.It has strong complexing ability with oxygen in metal hard base containing oxygen such as filler CaCO3,so it can improve the affinity for CaCO3 in PVC.The action of coupling agent is conducive to the combination of CaCO3 and matrix resin,especially for high-filling materials,the coupling effect is more obvious.Because of this feature,it appears to have the characteristics of processing AIDS and internal lubrication during processing,which can promote the plasticization of resin,show the effect of excellent impact modifier in the products,and increase the toughness of PVC.This effect was evident at low temperature,which inhibited the detcl degradation of PVC.Due to the unique coupling function and compatibilityof rare earth composite stabilizer,it can form ionic coordination with inorganic or organic ligands,so that the CaCO3 is coated by PVC and evenly distributed in the PVC matrix.
Internal and external lubrication,plasticizing and processing AIDS.The addition of rare earth thermal stabilizer can make the PVC composite system melt blending torque decreased,the material and metal cavity easy to peel off after mold opening,the material glass transition temperature decreased by about 3℃,indicating that the rare earth thermal stabilizer has internal and external lubrication,plasticizing,processing aid.
Enhance the function of brilliance.Rare earth elements are characterized by f and d vacant orbitals,which are prone to electron transition.Therefore,excitation spectra(200-400nm)and emission spectra(400-700nm)appear under ultraviolet radiation.The fluorescence spectra of PVC sheet can confirm that the rare earth thermal stabilizer has fluorescence effect.However,due to the peak range of emission spectrum,it is bluish,so attention should be paid to color matching.Rare earth has the property of absorbing ultraviolet light and then releasing visible light,so it can reduce the damage of PVC molecules caused by ultraviolet light,improve the outdoor aging performance of PVC products,or reduce the amount of anti-aging agent under the same conditions,and save production costs.
Rare earth composite stabilizer low toxicity or non-toxic,rare earth composite stabilizer of low lead(or lead-free)products can reduce(or avoid)due to the use of lead salt sulfide pollution and free lead catalytic titanium dioxide caused by discoloration problems,so as to improve the performance of PVC products.
Mechanism of rare earth stabilizer improving mechanical properties of products.Rare earth elements have many empty orbitals as the central ion to accept the lone pair electrons of the ligand.Meanwhile,rare earth metal ions have a large ionic radius,which makes it form a variety of ligand or integrand with organic matter and inorganic matter in PVC formula,increasing the interaction force between molecules.The physical entanglement increases,the compatibility between components is enhanced,and the inorganic substance is well wrapped,so the strength and toughness of the material are improved.The improvement of plasticizing uniformity also contributes to the improvement of mechanical properties.
Stabilizing effect of single rare earth and complex rare earth stabilizer.The stabilization effect of single rare earth and complex rare earth stabilizer is obviously better than that of calcium salt,zinc salt and their mixtures,and also better than that of lead salt stabilizer.But the early stability(early pigmentation)is poor.Adding zinc stearate to rare earth stabilizer can solve this problem.
Synergistic effect of rare earth stabilizer.Generally speaking,there is a strong synergistic effect between rare earth stabilizer and other stabilizers or co-stabilizers,while there is no obvious synergistic effect between rare earth and rare earth.The synergistic effect of rare earth is not only manifested in the great improvement of stability,but also in the further improvement of initial chromism.Rare earth element substitution replaces allyl chloride,and because of its strong coordination ability,it can complex 12 chlorine atoms,thus showing better long-term stability.However,the activation energy of rare earth combined with chloride ion is higher and the reaction rate is slower,showing the initial coloring property,while zinc soap has the characteristics of good thermal stability in the initial stable period,so the combined use of the two is better.
