Study On The Application Of Rare Earth Compounds In Natural Rubber Formulation

Zinc oxide（ZnO）is a vital component in the process of rubber sulfurization and serves as a crucial raw material for the production of rubber.ZnO plays a pivotal role in formula design as an essential activator,vulcanizing agent,and reinforcing agent in rubber formulations.China consumes a significant amount of ZnO annually in the rubber industry.However,there are often dispersion issues with ZnO in rubber formulations,causing a large amount of ZnO to leach into the environment as soluble zinc ions.This phenomenon is harmful to human health and can damage aquatic ecosystems.Many European and American countries classify ZnO as an environmentally hazardous substance and restrict the import of zinc-containing products.As a result,reducing the amount of ZnO used in rubber formulations and improving its activation efficiency have become urgent issues that need to be addressed in the rubber industry.This article mainly focuses on the application of a series of rare earth compounds synergistically enhancing ZnO in natural rubber（NR）formulations.The effects of different rare earth compound/ZnO ratios,types of promoting systems,and reinforcing systems on the comprehensive performance of NR composites were studied in this manuscript.The specific research contents of this article are as follows:Firstly,this article investigated the effects of a series of rare earth compounds,including lanthanum oxide（La₂O₃）,lanthanum cerium sulfide[（LaCe）₂S₃],cerium sulfide（Ce₂S₃）,and samarium sulfide（Sm₂S₃）,on the comprehensive properties of NR composites,such as vulcanization performance,mechanical performance,wear resistance,and aging resistance.The results showed that La₂O₃ and（LaCe）₂S₃ were much better than Ce₂S₃ and Sm₂S₃ regarding vulcanization properties,mechanical properties,wear resistance,and aging resistance.The tensile strength and aging coefficient of La₂O₃ in NR formulation were 2.2 MPa and 24.9%higher than those of Sm₂S₃ after five days of aging,and the tear strength and crosslinking density were 5.5k N·m^-1 and 6.8%higher than those of Ce₂S₃,respectively.Regarding wear resistance,（LaCe）₂S₃ performed much better than other rare earth compounds in NR formulation.Therefore,two compounds La₂O₃ and（LaCe）₂S₃,were mainly selected for further study in the following sections.Secondly,this article thoroughly investigated the application of rare earth compound La₂O₃ in NR formulations,specifically studying the effects of La₂O₃ dosage,La₂O₃/ZnO ratio,reinforcing system,and promoting system on the comprehensive properties of NR.The results showed that the addition of La₂O₃ not only shortened the vulcanization time and improved the mechanical properties,aging properties,and packing dispersion of NR materials.The addition of La₂O₃（3 phr）increased the tensile strength by 1.9 MPa,enhanced the crosslinking density by 4.8%,reducedΔG’by 14%,and boosted the aging coefficient by 4.8%after five days of aging.In terms of promoting system selection,the performance of La2O3 as a substitute for part of ZnO in neutral CZ promoting systems was superior to that in acidic DM and M promoting systems.In the CZ promoting system,when the ratio of La2O3/ZnO was 2/3 and the substitution amount of ZnO was 60%,the crosslinking density of vulcanized glue increased by 3.2%,and the vulcanization time t₉₀ decreased by 1.20 min.In addition,the aging coefficient after five days of aging was increased by 7.3%compared with the original formula due to the principle of La³⁺free radical trapping.The maximum rate of heat loss temperature T_max was increased by 8.9℃.In the reinforcing system,La2O3 could also effectively reduce the amount of ZnO in the white carbon black filling system.In particular,when the La2O3/ZnO ratio was 3/2,compared to the original formulation,the vulcanization time T90 of NR materials was reduced by 0.69minutes,the crosslink density was increased by 14.8%,and the tensile strength and tear strength were increased by 6.7 MPa and 16.6 k N·m-1 respectively.Additionally,E’was increased by 13.0%,and DIN wear resistance was reduced by 9.0%.Finally,this paper extensively studied the application of rare earth compound（LaCe）₂S₃ in NR formulations,specifically investigating the effects of（LaCe）₂S₃/ZnO ratio and reinforcing system on the comprehensive properties of NR.The results showed that the substitution of（LaCe）₂S₃ in the carbon black system is better than that in the white carbon black system.In the carbon black system,when the（LaCe）₂S₃/ZnO ratio was 2/3,compared to the original formulation,the vulcanization time T90 of NR materials was reduced by 1.48 minutes,the tear strength increased by 4.3 k N·m-1,E’was increased by 6.1%,the aging coefficient after 5 days of aging was increased by4.5%,and the maximum rate of heat loss temperature Tmax was increased by 5.0℃.In the white carbon black filling system,（LaCe）₂S₃ can effectively reduce only 40%of the ZnO content in the NR formulation while also maintaining its original mechanical properties.However,if the substitution amount exceeds 40%,the addition of（LaCe）₂S₃ may quickly lead to a decrease in both the mechanical and aging properties of NR materials.