The Research On Softening Deformation Behavior Of Pitch Materials Based On Thermomechanical Analysis

Mesophase pitch P₁,P₂ and isotropic pitch P₃ were determined by improving the thermomechanical analyzing method to determine the thermal deformation of pitch.The optimum test conditions such as particle size and pressure are analyzed.By further reducing the amount of samples in test,a thermomechanical analysis with microquantities method was established to simplify the measurement of pitch softening deformation.Based on the measurement,The thermal deformation properties of high temperature separated pitch and two-phase pitch were studied by thermomechanical analyzer.Melting Points of Magnesium,Zinc,Linear Low Density Polyethylene and Nylon 66 were determined through micro-analysis.For determination its applicability in metal and polymer materials.Three kinds of pitch grind particles P₁,P₂ and P₃ were analyzed by thermomechanical method.The softening temperature relationship was P₂>P₁>P₃.Taking P₁ as the research object which sample particles were prepared by knife flattening,wood file frustration and wire scraper peeling.The effects of particle size and probe pressure on Thermomechanical curves were analyzed respectively.A smooth and accurate thermomechanical curve of 40⁶0 mesh pitch particles prepared by wood file under 1500 mN pressure is determined.The standard deviation is smaller,and the repeatability and accuracy are higher compared with the grinding sample.The amount of test samples was further reduced.Three,four and five sample particles were selected for analysis（less than 1 mg）,and the thermomechanical curves of P₁ under different particle sizes and pressures were analyzed.Unlike the typical thermomechanical curves,the thermomechanical curves of pitch measured by micro-method have only one softening peak but no flow peak.The magnified photos show that the pitch has not filled the bottom of the crucible after thermal deformation.and there is no gap between the crucible and the probe.So there is only one downward stage on the TMA curve.The softening temperature of four particles samples at 30⁴0mesh measured at 1500 mN pressure has a high repeatability with the thermomechanical method,which can simplify the softening process of pitch by thermomechanical method.Based on the improved thermomechanical method to test the thermal deformation of pitch,the different positions of high temperature centrifugal pitch and two-phase pitch were tested.The softening temperature of the lower sample of high temperature centrifugal pitch is higher than that of the upper sample and the interface part.Thermomechanical method can be used as a means to evaluate the phase separation effect of pitch.When the mesophase content of two-phase pitch is low,the softening process of isotropic pitch is dominated by isotropic pitch,which shows the softening peak of isotropic pitch on the thermomechanical curve.When the content of isotropic pitch is low,the softening process of isotropic pitch and the softening process of mesophase pitch can be determined by thermomechanical method respectively.The linear low density polyethylene（LLDPE）,nylon 66（PA66）and magnesium and zinc（Mg,Zn）were determined by microanalysis.The thermomechanical curves showed obvious characteristic temperature points,which were close to the theoretical melting point.It is feasible to determine the melting point of other materials by micro-method.