The Performances And Action Mechanism Of Polymer Latexes Modified By Different Function Groups

With the development of cementing industry,the object of oil and gas exploration gradually changes from simple structure to complicated structure.In this complex conditions,neat cement can not meet the requirements of cementing technology.Therefore,it is necessary to improve various application performance of cement-based composites by adding some admixtures.Polymer latexes is one of indispensable cement admixtures,among which styrene-butadiene latex（SBR）is the research emphases.However,the available SBR faces many problems,such as poor tolerance to temperature and salt,unqualified dispersibility and deficient toughening properties,which lead to the flocculation and demulsification of polymer latex.In order to solve the aforementioned problems,it is necessary to graft some specific functional monomers to the SBR.Whereas,the influence of SBR on cement hydration is determined by active functional groups grafting on the surface of latex particles,which will further influence various performances of cement-based composites.On basis of the principle of molecular structure design,two kind of styrene butadiene rubber latex possessing good stability was synthesized by separately grafting2-acrylamido-2-methyl-propane sulfonic acid（AMPS）or acrylic acid（AA）&S to the surface of SBR latex particles via miniemulsion polymerization.In this paper,SSBR latex was synthesized using AMPS as functional monomer,and for CSBR,the functional monomers were AMPS and AA.The two latexes were analyzed by means of infrared spectroscopy（FTIR）,thermogravimetric analysis（TGA）,particle size distribution and transmission electron microscopy（TEM）.The results revealed that the two kinds of latex products were the target products and had good thermostability.The thermal decomposition temperature of SSBR latex and CSBR latex separately was 350℃and 375℃.Both the two polymer latexes possessed clear core-shell structure.The particle size distribution of the two latexes was homogeneous,and the average particle size was about 150 nm.The stability,fluidity,rheological property,control filtration ability,initial and final setting time,compressive and flexural strength,triaxial stress and strain of the two latex modified cement-based composites were investigated.The test results showed that:the latex can not only improve the stability,fluidity,rheological property,setting performance and filtration reduction property of the cement slurry,but also improve the toughness and deformation ability of the cement paste.In addition,compared with SSBR latex modified cement slurry,CSBR latex modified slurry with more excellent comprehensive performance.The action mechanism of the two kind of latexes was investigated by means of isothermal calorimetry,X-ray diffraction（XRD）,scanning electron microscope（SEM）,total organic carbon apparatus（TOC）,Zeta potential,inductively coupled plasma emission spectrometer（ICP-OES）and conductivity test.The results showed that SSBR latex and CSBR latex can not only adsorb onto the positive surfaces of aluminate phases through electrostatic attractive forces.Meanwhile,the abundant Ca²⁺in pore solution can adsorb onto the negative surfaces of silicate mineral phases and provide additional adsorption sites for anionic latex particles.Therefore,the two latexes can both be adsorbed onto the surface of the negatively charged silicate mineral phase via the bridging effect of Ca²⁺.Due to adsorption and chelation,both SSBR latex and CSBR latex delayed the hydration process,increased the hydration degree,filled the pores and cracks,increased the densification and comprehensive performance of cement paste.In addition,the calcium-complexing ability of CSBR latex was stronger than that of SSBR latex,which lead to the adsorption capacity of CSBR latex on mineral surface is higher than that of SSBR latex at the same dosage and CSBR latex modified cementitious composites possess superior performance.