Preparation Of Cysteine Rare Earth Complexes And Their Applications In Natural Rubber

Three new cysteine rare earth complexes were synthesized as lanthanum cysteine,cerium cysteine and cerium cysteine.The successful synthesis of the products was verified by elemental analysis,infrared spectroscopy,thermal analysis,ICP analysis and other tests,and the molecular formula of the products were determined as La（C₃H₇NO₂S）₃Cl₃·3H₂O,Ce（C₃H₇NO₂S）₃Cl₃·3H₂O and La_0.35Ce_0.65（C₃H₇NO₂S）₃Cl₃·3H₂O.The three cysteine rare earth complexes were applied to natural rubber to study the effects of cysteine rare earth complexes on the curing characteristics,crosslink density,curing rate and thermo-oxidative aging properties of natural rubber,and the vulcanization mechanism and anti-aging mechanism of the complexes were investigated.At the same time,cysteine lanthanum cerium was used to replace some of the existing auxiliaries to explore the maximum proportion of existing auxiliaries it could replace in order to achieve cost savings.The addition of cysteine rare earth complexes can effectively prolong the scorch time t₁₀ of the vulcanization process,shorten the normal vulcanization time t₉₀ and promote the cross-linking of rubber vulcanization.The best vulcanization performance was achieved at an addition level of 1 part.Kinetic calculations of natural rubber vulcanization showed that when the addition of cysteine rare earth compound gradually increased,the reactivity of cross-linked precursors increased and the activation energy decreased during vulcanization;the activity of cross-linked degradation decreased and the activation energy increased.When lanthanum cysteine cerium was substituted for part of accelerators and activators,it was found that the vulcanized rubber could maintain the vulcanization performance comparable to that of the blank rubber when the accelerator M was substituted with equal mass of the compound;the performance of the vulcanized rubber decreased significantly when the accelerator DM was substituted with equal mass of the compound.When lanthanum cysteine partially replaced zinc oxide,the vulcanization level of the vulcanized rubber could all be maintained at a high level.As a result,when 1 part of lanthanum cysteine was added to further replace all the processing aids in equal proportion,it was found that the stiffness,crosslink density and scorch time t₁₀ of the vulcanized rubber were basically unchanged and the positive vulcanization time t₉₀ was reduced when the substitution amount was 10%.However,when the substitution ratio gradually increased,one part of lanthanum cysteine cerium could not compensate for the decrease of vulcanization performance due to the reduction of other processing aids.Compared with the blank rubber compound,the natural rubber vulcanizate added with cysteine rare earth complex reduced the generation of thermal oxygen products.From the results of thermal analysis,it was known that rare earth cysteine complexes could increase the characteristic temperature of thermo-oxidative degradation of natural rubber vulcanizates and increase their thermal oxidative stability.Calculating the activation energy of thermo-oxidative degradation by Kissinger method and Fynn-Wall-Ozawa（FWO）method found that rare earth cysteine complexes could increase the activation energy of thermal oxidative degradation,making the thermo-oxidative degradation of vulcanizates more difficult.Among them,the activation energy of thermo-oxidative degradation of blank rubber was E_a=73.328 k J/mol,and the activation energy of thermo-oxidative degradation of vulcanized rubber with the addition of lanthanum cysteine,cerium cysteine,and cerium cysteine were 87.706 k J/mol,79.054 k J/mol,and 82.790 k J/mol,respectively,which indicated the strongest protection against thermo-oxidative degradation of lanthanum cysteine.