The Influence Of Formula On Dynamic Mechanical Properties Of Natural Rubber

Natural rubber is widely applied to automotive tires,shock absorbing sealing products,bridge and housing shock absorbing products due to its high strength,elasticity,adhesion,and outstanding comprehensive processing performance.For damping products,it is necessary to control the dynamic and static stiffness ratio to meet the need to avoiding resonance,while for damping products,it is necessary to improve the damping characteristics of the rubber to achieve the purpose of dissipating energy.Therefore,the purpose of this article is to study the influence of formula on the dynamic mechanical properties of natural rubber,providing a reference basis for the formulation design of vibration damping and shock absorbing products.The effects of sulfur content and sulfur/accelerator content of the vulcanization system on the dynamic mechanical properties of natural rubber were studied.The results indicated that increasing sulfur content when the contents of other ingredients and accelerator remaining constant,or increasing the content of sulfur/accelerator when keeping their ratio（1:1）didn’t change the loss factor（tanδ）,storage modulus（E’）and damping properties obviously,which also cause the increasing of static stiffness,the decreasing of dynamic and static stiffness ratio,and improving the mechanical properties of natural rubber vulcanizate obviously.The effects of the type and amount of carbon black,inorganic filler,and kaolin content of the reinforcing filler system on the dynamic mechanical properties of natural rubber were studied.The results indicated that the type and amount of carbon black have significant influence on the mechanical properties,tanδ,E’,static stiffness and dynamic and static stiffness ratio.The tanδ,E’,static stiffness,and dynamic and static stiffness ratio of natural rubber vulcanizates filling Kaolin,Ca CO₃,and Fly ash in their high elastic state were obviously lower than the vulcanizate filling N220.As the surface area of carbon black increasing,and amount of N330 increasing（within50phr）,the tanδ,E’of high elastic state NR vulcanizate increasing,static stiffness and dynamic and static stiffness ratio increasing significantly.The tanδ,E’,static stiffness and dynamic and static stiffness ratio ofvulcanizates filled with three kinds of inorganic filler were similar.As the amount of Kaolin increasing,the tanδof high elastic state NR didn’t change a lot,E’and static stiffness increasing,while the dynamic and static stiffness ratio decreased at first,and then increased,when the amount of Kaolin is 10-20 phr,the dynamic and static stiffness ratio is the smallest.Theeffects of the types of operating oil and the amount of aromatic oil of plasticizer system on the dynamic mechanical properties of natural rubber were studied.The results showed that the effects of operating oil on tanδof NR vulcanizate at high elastic state was minimal,E’had a slight decrease,andstatic stiffness decreased obviously.Aromatic oil could increase the dynamic and static stiffness ratio of NR vulcanizate,while naphthenic oil and paraffin oil could reduce the dynamic and static stiffness ratio of NR vulcanizate.As the amount of aromatic oil increasing,the Tg of NR tended to increase,the tanδat high elastic state increased,E’decreased,the static stiffness decreased significantly,and the dynamic and static stiffness ratio fluctuated in a small range.The effects of three kinds of hindered phenols（AO-60,HP-1098,and AO-4426）and the amount of AO-60 on the dynamic mechanical properties of natural rubber were studied in this paper.The results show that all three hindered phenols could effectively improve the loss factor and dynamic and static stiffness ratio of NR under high elastic state,with AO-60 being the most obvious.NR filled with AO-60 had a higher tanδ,lower E’and static stiffness,larger dynamic and static stiffness ratiounder high elastic state.With the increase of the amount of AO-60,the tanδof NR at high elastic state increased,E’and static stiffness decreased,the dynamic,static stiffness ratio increased,and the damping properties increased.The mechanism of hinder phenol AO-60 affecting the dynamic mechanical properties of NR was investigated in this research.The results indicated that,AO-60existed in NR in the form of small aggregate and large aggregate.As the amount of AO-60 increasing,the content of large aggregate increasing.When adding more than50phr AO-60,obvious gap appeared between large aggregate and NR,and holes appeared when adding more than 70phr AO-60 in NR.As the parking time increaseing,AO-60 in amorphous form transformed to its crystalline state.The AO-60 molecule in aggregates which closely contacted with NR formed hydrogen bond between each other.Under dynamic action,hydrogen bond opening and recombination consumed more energy,resulting in high damping properties of the filled rubber.Adding too much AO-60,gaps and holes were resulted in the decreasing of damping properties,storage module and mechanical properties.The amount of AO-60 in natural rubber should not exceed 50phr.