Study On Segregation Behavior Of Vulcanization System In Rubber Blends

In this paper,dynamic mechanical analysis,low-field solid-state nuclear magnetic resonance crosslinking density meter,SEM-EDS,dynamic and static mechanical testing,and vulcanization curve were used to study the segregation of different vulcanization systems（sulfur vulcanization systems,peroxide vulcanization system）in rubber blends.The results showed that the sulfur vulcanization system was easy to segregate in the polar NBR phase of NR/NBR blends,which was obvious in NR70 blends,and there was co-crosslinking at the interface between NR and NBR phase;For all NR/NBR blends at any sulfur contents in this work,the t_c10 became shorter,vulcanization rate became faster and the glass transition temperature of NBR was higher with the reduction of NBR content.When the NBR was the continuous phase（the NR content is not more than 30phr）,the crosslinking density of blends increased with the increase of NR content in NR/NBR blends,but the crosslinking density of the blends was reduced to a minimum when NR content got up to 50phr in NR/NBR blends.And then the crosslinking density continued to increase with the increase of NR content in blends.When NBR was continuous phase,NR with a smaller crosslinking density plasticized the NBR phase,making relative equilibrium stress and stress at 300%strain of NR30 the smallest;when NBR was dispersed phase,NBR with a larger crosslinking density reinforced the NR matrix,making NR90 the largest tensile strength.DCP was segregated in NR phase of NR/NBR blends and the co-crosslinked NR-NBR structure existed at the interface of NR and NBR phase.When the content of NR phase was less than 50phr,DCP was saturated in NR phase;when the content of NR phase was more than 50phr,the phenomenon of segregation was manifested.The t_c90 of NR/NBR blends increased first and then decreased with the increase of NR content,of which that of NR30 was the longest.The crosslinking density of the blends increased slowly with the increase of the NBR content,when the NBR content was less than 50phr,and it increased sharply with the increase of the NBR content when the NBR content was more than 50phr.The NR phase with relatively higher crosslinking density endowed the blends larger tensile strength,of which NR30 owned the largest tensile strength.The NBR phase with a relatively lower crosslinking density imparted the blends larger elongation at break,of which NR50 owned the largest elongation at break.The sulfur vulcanization system was easy to segregate in the SBR phase of NR/SBR blends,which was obvious when the NR content was up to 70phr and sulfur content reached 3.25phr.The crosslinking density of NR70,NR90 was larger than other blends.The SBR with a large degree of vulcanization reinforced the NR matrix as"reinforced microspheres"and the smaller the size of the SBR phase,the more significant the reinforcement effect,making NR90 the biggest hardness.The distribution of crosslink points was affected by the sulfur content and the blending ratio.The relative equilibrium stresses of NR70 and NR50 were the smallest when NR/SBR blends were cured by 2.25phr and 3.25phr sulfur,respectively.