Study On Structural Properties Of Reinforced Rubber Prepared By Continuous Mixing Via Volume Elongational Deformation

Rubber-based nanocomposites are widely used in transportation,aerospace,marine equipment,construction industry,electronic appliances,etc.due to their unique high elasticity.However,the mixing of rubber and nano-reinforced fillers is an extremely complex physicochemical changing process.At present,the rubber processing industry adopts a batch mixing process in stages,processes and batches,which has the problem of the long mixing cycle,high labor intensity,large environmental pollution,large unit energy consumption,and poor batch average.The traditional rubber mixing process dominated by the shear deformation flow field has to extend the mixing time and increase the mixing process to obtain a uniformly dispersed nano-filler compound,resulting in low processing efficiency,high energy consumption,and severe chain breakage.Too much reduction of the molecular weight of rubber will damage the mechanical properties of rubber products.With the increasingly prominent energy problem and the urgent demand for high-performance rubber products,developing new technologies for rubber mixing with high efficiency,low energy consumption,and continuity equipment is imminent.In this paper,for the first time,a rubber mixing process method based on the volumetric elongational deformation flow field is proposed,a new technology of one-step continuous mixing and extrusion of compounds with volumetric elongational deformation biaxial eccentric rotor extruder?BERE?is successfully developed.Through simulation analysis and rich experiments,the dispersion and distribution behavior of nanoparticles in the rubber matrix as well as the interaction between the nanoparticles and the rubber molecular chain in the volumetric elongational deformation flow field were studied in-depth and in detail.The relationship between the dispersion and distribution of nanoparticles and the properties of vulcanized rubber composites is studied.Polyflow simulation was used to analyze the velocity field and pressure field distribution of the compounds as well as the mixing index and the first principal stress distribution probability in the spiral section and straight section of the BERE cavity.It was found that the velocity in the compounds flow direction diverges first and then convergent elongational flow,the melt has the fastest speed at the bottom of the biaxial eccentric rotor near the meshing position,and the strongest squeezing effect.The mixing index,elongational deformation index and squeezing effect produced by the straight section are higher than the spiral section,and the first principal stress increases with enlarging the BERE speed,compounds modulus and zero shear viscosity.The dispersion mechanism of nanoparticles in the volume elongational deformation flow field was expounded.Nature rubber/carbon black?NR/CB?compounds were fabricated through internal mixer batch mixing process dominated by shear deformation flow field and BERE one-step continuous mixing and extrusion new technology dominated by volumetric elongational deformation flow field,respectively.Compared with internal mixer processing,BERE one-step processing exhibits stronger extension and weaker shear,leading lower Payne effect of the compound,good dispersion of CB within short mixing time?1.5 min?,increasing of NR molecular weight by 23%,smaller Mw/Mn,more bound rubber content and stronger interaction between NR and CB;the comprehensive mechanical properties of the vulcanizate are comparable to or even exceed those of the vulcanizate prepared under the optimum conditions?80 r/min mixing for 8 min?of the internal mixer.Compared with the vulcanizate prepared by mixing for 2 min at 50 r/min in an internal mixer,the tensile strength,elongation at break,modulus at 500%and tear strength of vulcanizate prepared by the one-step method are significantly improved,highlighting the advantages of the new technology of BERE one-step rubber continuous mixing and extrusion dominated by volumetric elongational deformation flow field.The effect of different rotational speed,temperature,sulfur feeding position and CB content on the properties of the NR/CB system in BERE one-step continuous mixing and extrusion process were studied.It was found that the dispersion of CB in NR matrix can be improved by increasing the rotational speed of BERE to enhance the first principal stress,the tensile strength,elongation at break and tear strength of vulcanizate increased first and then decreased with the increase of BERE speed,getting maximum at 50 r/min.By reducing the fourth zone temperature and increasing the rotational speed of BERE,the volumetric elongational deformation can be enhanced to break and diffuse the agglomerated CB,which can significantly improve the dispersion and distribution of CB in NR matrix.The molecular weight of NR in the NR/30phr CB system prepared at 50 r/min and 90-80-50-60?is large and the interaction between NR and CB is strong,the vulcanizates prepared at 50 r/min with a temperature of 90-80-50-30 or 90-80-50-60?both have excellent static comprehensive mechanical properties,while the vulcanizates prepared at 90-80-50-60?have higher wet sliding resistance.Adding sulfur from the first or second feeding ports has little effect on the processability of the compound,the dispersive distribution of CB and mechanical properties of vulcanizates,as well as the scorch time T_c10 is not shortened,still leaving enough scorch safety period.The wet sliding resistance of NR/CB vulcanizates increased with the increase of CB content while the dynamic heat generation also increased,achieving the best comprehensive mechanical properties at 40phr CB.The effect of different Si69 modification methods,SiO₂ content and BERE process on the properties of NR/SiO₂ system were studied.Increasing the rotating speed and decreasing the processing temperature is beneficial to strengthen the volume elongational deformation,breaking and dispersing the SiO₂ aggregates,furthermore,increasing the content of Si69 is beneficial to improve the interaction between SiO₂ and NR,thus significantly improving the dispersion distribution of SiO₂.As a result,the Payne effect of the compound decreased and increased with the increase of Si69 and SiO₂ content respectively,and decreased with the increase of BERE speed.The Mooney viscosity increased and decreased with the increase of SiO₂ content and BERE speed respectively,DMA analysis showed that the dynamic heat generation decreased and increased with the increase of Si69 and SiO₂ content respectively.The tensile strength and elongation at break increased with the increase of BERE speed,the tensile strength increased first and then decreased slowly with the increase of Si69 content reached the best at 10wt%Si69,also the tear strength increased with the increase of Si69 content;the best comprehensive mechanical properties of NR/30phr SiO₂ vulcanizate modified by 10wt%Si69were prepared at the speed of 50 r/min and the temperature of 90-80-50-30?.The effect of different CB content and BERE process on the properties of solution polymerized butadiene styrene rubber/carbon black?S-SBR/CB?system were studied.CB shows a good dispersive distribution in its vulcanizate,the particle size and standard deviation of CB aggregate decrease with the increase of CB content,and the proportion of CB aggregate area shows normal distribution and moves to small aggregate with the increase of CB content.The best dispersion of CB is obtained at a speed of 50 r/min and a temperature of 90-80-50-30?with adding sulfur from the first feeding port.The tensile strength and modulus at?100%,300%and 500%?increase with the adding CB content.The elongation at break,300%/100%and tear strength first increase and then decrease with the increase of CB content,achieving a maximum 300%/100%and tear strength at 40phr CB.The effects of different SiO₂ and Si69 contents on the properties of S-SBR/SiO₂ system were studied.The?G?of S-SBR/SiO₂ blends increased and decreased respectively with the increase of SiO₂and Si69 content,and the Mooney viscosity increased with the increase of SiO₂ content;when the content of Si69 is 10 wt%,SiO₂ can achieve uniform dispersion and distribution;the tensile strength,elongation at break and modulus at?100%,300%and 500%?of S-SBR/SiO₂vulcanizate increased with the increase of SiO₂ content,and the tensile strength,modulus at?100%,300%and 500%?and 300%/100%increased with the increase of Si69 content,achieving maximum tear strength at 10 wt%Si69 content.Based on the Polyflow simulation analysis and abundant experimental results,it is shown that the new technology of BERE one-step rubber continuous mixing and extrusion dominated by volumetric elongational deformation flow field has significant advantages over the internal mixer batch mixing process dominated by shear deformation flow field,solving the problems which are hard for traditional rubber batch mixing process and preparing the rubber nanocomposites with uniform distribution and dispersion of nanoparticles,greatly maintained the length of rubber molecular chain and good mechanical properties.The results of this paper provide a new,efficient and continuous one-step mixing and extrusion integrated solution for the rubber processing field,and provide important theoretical support and experimental basis for the application and promotion of this new technology.