Study On The Performance /thermal-athermal Effect Of Microwave Synthesis Of Polycarboxylic Ether Superplasticizer

Concrete,the “backbone” of the construction industry,is the most extensively used artificial civil engineering materials in the world.With the continuously innovation of concrete materials and it's related technology,more and more high performance concrete is appearing,the concrete is turn to be high fluidity,high strength,low pollution and easy workability.The use of polycarboxylic ether superplasticizer(PCE)reflects the "green,energy saving and sustainable development" concept of concrete development.As the consumption of world energy and the deterioration of the environment,building energy conservation has become the focus of the world attention.The PCE conventional heating synthesis(CHS)technology are time and energy consuming,process complexity,and other shortcomings.While the PCE microwave assisted synthesis(MAS)technology is popular for its clean,efficient and targeted feature.Based on realistic industry demand and research status above,MAS-PCE were synthesised by single focused microwave apparatus in this paper.The preparation process,the thermal-athermal effects in the reaction system,the micro polymerization kinetics of adsorption-dispersion and rheological properties of MAS-PCE reaction system were investigated.The detailed research contents are as follows.(1)The influence of MAS-PCE process parameters on the dispersion energy,were characterized by cement paste fluidity compared with CHS-PCE,the conclusions were as following.In 2.5<n(AA): n(TPEG)6 range,with n(AA): n(TPEG)increased,initial and by-1h fluidity of the fresh cement paste with MAS-PCE or CHS-PCE increased first and then decreased,when n(AA): n(TPEG)was 3.0,MAS-PCE,CHS-PCE initial and loss 1h fluidity reached the optimal.As the H2O2 dosage was from 0.12% to 0.28%,Adding MAS-PCE,fresh slurry initial fluidity increases gradually,by-1h fluidity showed increased at first and then to maintain the same trend;adding CHS-PCE fresh slurry initial fluidity and by-1h fluidity showed a trend of first increased and then decreased.As the dosage of H2O2 were 0.28% and 0.20% respectively,the by-time fluidity reached maximum(317mm,270mm).As Vc was from 0.06% to 0.30%,with the increasing of Vc dosage,the initial and by-time dispersion properties of cement paste of MAS-PCE and CHS-PCE were both increasing firstly and decreasing finally.When the dosage of Vc was 0.24%,the initial and by-time dispersion properties of MAS-PCE were the optimal performance(313mm,310mm).When the dosage of Vc was 0.18%,the initial and bytime dispersion properties of cement paste of CHS-PCE were the best(305mm,279mm).As the TGA was in the range from 0.12% to 0.26%,Adding MAS-PCE,fresh slurry initial fluidity increases gradually,by-1h fluidity showed increased and then decreased trend,adding CHS-PCE fresh slurry initial and by-1h fluidity showed a trend of first increased and then decreased.As the TGA were 0.18% and 0.24% respectively,the initial and bytime dispersion properties of MAS-PCE and CHS-PCE were the optimal.As the polymerization temperatute(T)was from 30 ? to 70 ?,the initial cement paste dispersion properties of MAS-PCE are ahead of CHS-PCE.When the polymerization time was from 10 min to 50 min,the initial dispersion properties of cement paste of MASPCE were better than CHS-PCE,the initial and by-time dispersion properties of MASPCE was the optimal as the polymerization time was 30 min.With the increasing of microwave power from 200 W to 1000 W,the initial and by-time dispersing performance of MAS-PCE was gradually increasing therewith.In a higher power,the initial dispersion performance is more superior.In all conditions,the addition of MASPCE,the initial cement paste by 1H dispersion properties are better with CHS-PCE.Accoring to the single factor analysis above,the optimal microwave assisted reaction process parameters for the synthesis of superplasticizer were: n(AA):n(TPEG)=3,Vc=0.18%,TGA=0.18%,H2O2=0.20%,P=1000W,T=50? and t =30(15,16,14)min respectively.(2)The reaction dielectric constant was computed by artificial neural network inversion method.The dielectric properties of the reactants were evaluated by the real part and imaginary part of dielectric function,and the tangent value of loss angle.Then the microwave thermal effects of mixed solution was expounded.The results were as following.The microwave thermal effects are obvious as the TPEG/AA/TGA/H2O2/Vc solution system were at low concentration or low temperature.The polarization ability of mixed solution would be reduced with the addition of TPEG/AA/TGA/H2O2/Vc in the electromagnetic field.The addition of H2O2 and Vc could improve the transformation efficiency of mixed solution from microwave energy to heat energy.The addition of TPEG/AA/TGA/H2O2/Vc could improve the transformation ability of the mixed solution from electromagnetic energy into heat energy,which means the thermal effect of mixed solution was improved.(3)The athermal effects of microwave was investigated through the diversity of activation energy Ea,the pre exponential factor A of Arrhenius equation and the electromagnetic effect factor If of MAS-PCE and CHS-PCE.The microwave thermal effect was analyzed accoriding to the simulation of hydrodynamic radius Rh of PCE molecules in the pore solution through the analysis of polymer molecular weight and itsdistribution,the conclusion was as following.Compared with CHS-PCE,with the apply of microwave energy to the PCE polymer reaction system,the reaction activation energy Ea decreased from 46.83 k J/mol-1 to 35.07 k J/mol-1,A and the effective particle collision probability of anti-body response was greatly improved,the number of active sites was increased therewith.If was always above 1 under varied microwave polymerization temperature,it indicated that,the electromagnetic wave promote the chemical reaction of MAS-PCE,and the athermal effect of microwave was exsisted.Compared with CHS-PCE,the Mw and Mn was reduced in MAS-PCE,but the initial and by-time dispersion properties of MAS-PCE were better than CHS-PCE,this phenomenon was caused by the athermal effects of microwave,also the optimize of PDI in MAS-PCE.MAS-Rh and CHS-Rh were both firstly increased and then decreased under varied process parameters(H2O2,Vc,TGA,n(AA):n(TPEG),t and T): the relatively small MAS-Rh can better contact adsorption sites,improve the dispersion performance,which proved that the alteration of heating mode would not affect this law but affect the relative fluid dynamic radius.Accoring to the FTIR characterization analysis of the PCE molecular structure,MAS-PCE increased the formation amount of high molecular weight and improved the uniformity of block polymerization molecular,which belonging to the nonthermal effects of microwave.(4)The relation curve of reactant conversion and reaction time under varied conditions was measured by dilatometer method,remember the reaction order was calculated by the linear fitting of PCE reaction,the kinetics of MAS-PCE/CHS-PCE microscopic polymerization was proposed.The kinetics equation of PCE microscopic polymerization was: Rp=1.27×1014exp(33.27/RT)[TPEG]4.1385[AA]2.4898[H2O2]0.8348[Vc]2.3077[TGA]1.542;The kinetics equation of conventional thermal polymerization was: Rp=7.64×107exp(-46.83/RT)[TPEG]1.1995[AA]1.1186[H2O2]0.7677[Vc]0.8739 [TGA]0.6578.As TPEG was from 0.1985 mol·L-1 to 0.3967 mol·L-1,the MAS-PCE polymerization rate was 8.9~74.06 times than that of CHS-PCE.In the range of 0.7434 mol·L-1 to 1.4869 mol·L-1 of TPEG,the MAS-PCE microwave polymerization rate was about 16 times than that of CHS-PCE.In the range from 1.4869 mol·L-1 to1.7842 mol·L-1 of AA,the MASPCE was superior to CHS-PCE obviously,the MAS polymerization rate was 38.34~51.57 times to that of CHS-MAS.In the range from 0.0283mol·L-1 to 0.0660mol·L-1 of H2O2,the MAS-PCE polymerization rate was 14.42~16.90 times of conventional polymerization rate.As Vc was from 0.0027mol·L-1 to 0.0135mol·L-1,the microwave polymerization rate was 8.93~83.78 times of conventional polymerization rate,which reflect the advantages of microwave polymerization.In the range of 0.0103 mol·L-1<[TGA]< 0.0310 mol·L-1,the microwave polymerization rate was 18.74~55.65 times of conventional polymerization rate.With the increasing of polymerization temperature,the MAS polymerization rate and CHS polymerization rate were both increasing therewith,but the advantages of MAS polymerization showed a downward trend due to the decrease of the thermal effect of microwave,the microwave polymerization rate was 18.74~55.65 times of conventional polymerization rate.(5)The study of the adsorption-dispersion/rheological properties on fresh cement paste with MAS-PCE/CHS-PCE indicated that: with the increase of W/C,the saturated adsorption amount of PCE in the fresh cement paste decreases and the equilibrium concentration of the corresponding PCE was gradually reduced,but meanwhile the initial fluidity increases.It indicated that,the flow size correlates was inverse proportional relationship with saturated adsorption amount for the same PCE.In the range of 0.30<W/C<0.40,PCEm and PCEc isotherm adsorption in fresh cement paste was nonuniform multi-molecular layer adsorption,the adsorption mode was Tenpkim model.At the constant W/C,the yield stress of PCEm was more sensitive than PCEc,PCEm had small yield stress in few dosage,which indicating that PCEm has excellent dispersion performance in small dosage.Under certain conditions of water-cement ratio,the fresh fluid model slurry gradually shifted from HB model into R-BH or BH model with polycarboxylate super plasticizer content increases,and fresh slurry water cement ratio was larger,more close to the BH model of slurry.PCEc and PCEm of fresh cement paste had good dispersion due to the mixing PCEm can significantly reduce the plastic viscosity of the slurry.With the PCE content increasing,as decreases and the greater the dispersion ability of slurry,which Indicating PCEm has obvious advantages compared with PCEc.Finally the universal law of “microwave polymerization molecular thermal/athermal effect-micro dynamics-structure-performance of PCE systhesised by MAS were revealed.The theories of microwave target polymer and design of PCE molecular by MAS were established.They provide functional PCE by MAS with theoretical and technical support.