Study On The Rheological Behavior Of Millable Polyurethane And Its Combination With Natural Rubber

Millable polyurethane(MPU)has a series of advantages such as high strength,high abrasion resistance and excellent solvent resistane.It can also be processed by rubber processing and molding,so it is more used as a special rubber.However MPU generates a large amount of heat due to hysteresis under high-frequence dynamic conditions.The accumulated heat can destroy the structure of MPU,which also limites the application of MPU under dynamic conditions.The microphase separation structure has an important effect on the performance of polyurethane(PU),and the low content of hard segment in MPU makes its microphase separation structure different from conventional PU materials and difficult to measure and characterize.In this thesis,MPUs with different R values,different hard segment contents and different isocyanate structures were synthesized by prepolymer method with PTMG as soft segment and 3-allyloxy-1,2-propanediol as chain extender.The structure of MPU was characterized by IR,~1H-NMR,TG,rotary rheometer,mooney viscometer,and the influence of different structures on the processing rheological properties and microphase separation structure of MPU was studied.The pretreatment method was used to prepare MPU/NR composites to solve the problem of large dynamic heat generation of MPU,and the vulcanization kinetics of the MPU were studied in depth through the rheological method.The mechanical properties,wear resistance,dynamic mechanical properties and micro-morphology of MPU/NR vulcanizates were characterized by SEM and DMA.The main research results are as follows:FTIR and ~1H-NMR results indicate that the required MPUs have been synthesized.TG results show that,when the isocyanate is MDI and the hard segment content is 20%,the thermal stability of the MPU decreases as the R value increases;when the isocyanate is MDI and the R value is 0.93,as the content of the hard segment increases,the thermal stability of the MPU decreases;when the R value is 0.93,the hard segment content is 20%,the thermal stability of MPU is as HMDI>MDI>TDI.Mooney viscosity data shows that when the isocyanate is MDI and the hard segment content is 20%,the Mooney viscosity of the MPU increases as the R value increases;when the isocyanate is MDI and the R value is 0.93,MPU's Mooney viscosity also increases with the hard segment content.When the R value is0.93,the hard segment content is 20%,the MPU Mooney viscosity is:TDI>MDI>HMDI.Among the synthesized MPU,the MPU with MDI and 0.93 R value and 20%hard segment content has the best processing performance.FTIR results show that with the increase of R value and hard segment content,the degree of hydrogen bonding increases.For different isocyanate structures,the degree of hydrogen bonding of MPU is HMDI>TDI>MDI.The variable temperature infrared shows that the elevated temperature can destroy the hydrogen bond formed by the carbonyl group in the MPU,and the hydrogen bond destruction temperature may start at 84?.Rotational rheological data shows that with the increase of R value and hard segment content,the viscoelastic transition point moves to higher temperature.The transition point temperature of MPU with different isocyanate structure is TDI>MDI>HMDI.As the temperature rises,the first derivative curves of the loss modulus have two obvious turning points,the temperature of the first turning point is between 84-90?,and the temperature of the second turning point is between 136-146?.With the increase of R value and hard segment content,both MPU shear viscosity and zero shear viscosity increase.When the isocyanate structures in MPU are different,the zero shear viscosity is:TDI>MDI>HMDI.When the R value is 0.91 and 0.93,the TTS master curves are not offset,when the R value is0.95 and 0.97,the TTS master curves are offset significantly and the offset temperature is140?.When the hard segment content is 20%,the TTS main curve is not offset,while the hard segment content is 21%and 23%,the TTS main curves are offset.And the TTS master curvesare offset when the isocyanate structure is HMDI and TDI.The failure of the master curve of TTS shows that with the increase of R value and hard segment content,the degree of microphase separation increases,and the temperature at which the separation starts is around 140?.The Han curve is less sensitive to MPU microphase separation and cannot characterize the degree of microphase separation well;the Cole-Cole curve can more accurately reflect the phase difference between the soft and hard segments in the polyurethane.and blended with NR.There is no crosslinking structure when the pretreatment time is 2min,which has a good pretreatment effect.The vulcanization kinetics research results show that when the pretreatment time is 0min,2min,4min,the activation energy of the induction period is 82.71KJ/mol,71.87KJ/mol and 81.77KJ/mol respectively,indicating that the pretreatment has improved reactivity of MPU during the induction period and solved the problem of the mismatch between MPU and NR vulcanization.After pretreatment,the cross-linking density and mechanical properties of the MPU and NR blend rubbers can also be improved,and the wear resistance and dynamic performance can be improved.When the blend ratio is 75/25 and the pretreatment time is 2 min,the tensile strength of PMPU/NR is57.3%higher than that of unpretreament,the fatigue life is extended by 119.1%,and the fatigue temperature rise is reduced by 40.5%,wear resistance of Acron is reduced by 34.6%,indicating that pretreatment can improve the mechanical properties of MPU/NR and improve the wear resistance and dynamic performance.DMA data shows that when the blending ratio is 75/25,compared with MPU/NR,the loss factor at 0?of PMPU/NR is slightly improved,and the loss factor at 60?is significantly reduced,indicating that pretreatment can effectively reduce the rolling resistance of the blend rubbers.