Interface Design Of Styrene-Butadiene Rubber/Clay Nanocomposites Prepared By Gel Compounding Method

Styrene butadiene rubber(SBR)has low raw rubber strength and needs to be filled with inorganic fillers for reinforcement.Clay is a natural layered silicate mineral with abundant reserves and low cost in China,and replacing carbon black or silica for rubber reinforcement can reduce the dependence on oil and gas resources.To achieve efficient clay nano-reinforcement,it is necessary to overcome the interlayer forces of clay to disperse it in the rubber matrix at the nano-scale.The gel compounding method is an environmentally friendly,low-cost,and suitable method for the preparation of nanocomposites in solid rubber,but the compatibility between non-polar lipophilic styrene-butadiene rubber and polar hydrophilic clay gel is poor,and a reasonable interface modification design is required to obtain nanocomposites with good dispersion of clay in rubber.For the principle and characteristics of gel compounding method,this modified the clay gel with a macromolecular modifier butadiene-styrene-vinyl pyridine rubber(VPR),hydrophilically modified the SBR with three quaternary ammonium modifiers containing non-polar groups,polar groups,and unsaturated double bonds,and improved the compounding process characteristics to prepare SBR/clay NC with high-performance.The gel of organic clay was firstly prepared by using the adsorption between the positively charged bupyrene rubber macromolecule and the negatively charged clay sheet layer,and then the nanocomposites were prepared by using the gel compounding method.The vulcanization and XRD results showed that the clay was successfully modified by VPR,which not only reduced the adsorption of vulcanizing agent,moreover,the VPR macromolecular structure is inserted into the clay layer spacing.The compatibility of SBR and clay is improved,TEM and SEM show that the layer of clay in the composite are still uniformly dispersed and the layer are clearly spaced at high dosage,and the thin layer are tightly embedded in the matrix,indicating that the interface between the two is enhanced.The mechanical properties of the SBR/VPR/clay NC reached the highest at 40 phr of clay,with tensile strength and elongation at break of 16.3 MPa and 778%,respectively.The DMA also showed that the modulus of the material was much higher than the other composites,and excellent interfacial interaction was obtained.Secondly,in order to solve the problem of difficult mixing of clay gel with rubber,Hexadecyl trimethyl ammonium chloride(CTAC)was directly modified to SBR with gel compounding technology to prepare nanocomposites(NC).The contact angle of SBR was reduced from 88° to 21° after adding CTAC,and the hydrophilic SBR/CTAC complexes made the gel compounding process easier.The vulcanization curves showed that CTAC has promoted the vulcanization rate of the composites;XRD showed that the clay layer spacing expanded and intercalation structure has appeared,and the macromolecular intercalation structure decreased with increasing clay dosage;TEM demonstrated that the clay was dispersed in the rubber matrix in monolayer or thin multilayer.In addition,DMA and SEM also showed the enhanced interfacial force between filler-rubber,so the mechanical properties of SBR/CTAC/clay NC were significantly improved,and the tensile strength of the composites with 10 and 40 phr of clay added reached 9.43 MPa and 14.0 MPa,respectively,which were 6 and 9 times of pure SBR,and the reinforcement effect was even better than that of commercial organic clay(OC).It is shown that this modification method makes the filler network and filler-rubber network greatly optimized and effectively improves the clay dispersion and compatibility problems with nonpolar rubber.Then,the amphoteric surfactant Cocoyl ammonium propyl betaine(CAPB)containing three polar groups,carbonyl,amino and carboxyl,was directly modified with the rubber matrix.The results showed that the addition of CAPB not only greatly improved the hydrophilicity of SBR,but also promoted the peeling and intercalation of clay layer by ion exchange with clay;the reaction rate and cross-link density increased due to the activation of the vulcanization reaction of SBR/CAPB/clay NC.TEM shows that the excellent hydrophilicity of the rubber matrix makes the clay dispersion of the composite better than other methods,and the spacing between clay layer is significantly expanded;in addition to the advantages of CTAC modification,hydrogen bonding between polar groups and clay reactive groups will reinforce the physical cross-linking network,which makes the filler-rubber interfacial interaction significantly enhanced.The tensile strength of the composites reached 14.9 MPa and 16.3 MPa at 20 phr and 40 phr of clay,respectively,and the elongation at break reached a maximum of 846%;SEM and DMA also demonstrated the enhanced interfacial interactions.Finally,On the basis of CAPB,a surfactant Methacryloyloxyethyl trimethyl ammonium chloride(DMC)containing a double bonding group was designed to modify the rubber directly.The contact angle of SBR was reduced from 88° to 47°after the addition of DMC,and the hydrophilicity was improved.The results of vulcanization curves showed that DMC improved the vulcanization delay phenomenon and accelerated the vulcanization reaction rate;XRD showed that the clay layer spacing increased in SBR/DMC/clay NC,and macromolecular intercalation peaks with layer spacing of 4.58 nm and 10.1 nm appeared in 10 phr of dosage,however,the intercalation structure gradually decreased with the increase of filler parts.TEM and SEM also confirmed the intercalation and dispersion structure of the filler.This modifier not only improves the filler-rubber compatibility,but also the double bonding groups reacted to become cross-linking points during the vulcanization process,increasing the chemical cross-linking density of the composite.The highest tensile strength and elongation at break were achieved for the composite with 30 phr of clay,which were 17.6 MPa and 803%,respectively,equivalent to 11.1 and 4.2 times of pure SBR.It indicates that the rising hydrophilicity of the matrix and the double bonding groups make great contributions to disperse the gel filler,strengthen the interface and increase the cross-linking network.