Study On The Preparation Process Of Polyamide 12 Powder

Polyamide 12 powder is widely used in various industries such as machinery,medical treatment and chemical industry due to its advantages of light weight,corrosion resistance and high mechanical strength.In this study,solution crystallization thermodynamics of polyamide12,melting crystallization kinetics of polyamide 12 and the effects of technological conditions on the preparation process were studied by means of experiment and simulation.Specific research contents are as follows:Firstly,the preparation process of polyamide 12 powder by atmospheric pressure method was studied.The product was characterized by X-ray powder diffractometry(PXRD),differential scanning calorimetry(DSC)and polarizing microscope.Then,the effect of stirring speed and TiO₂ addition on the morphology dependent particle size of polyamide 12 powder was explored experimentally.It was found that with the increase of stirring speed,the sphericity of the obtained polyamide 12 powder decreased,the particle size distribution became narrower and the average particle size decreased;with the increase of TiO₂ addition,the crystallinity and melting point of polyamide 12 powder became lower.The CFD method was used to simulate the effects of different paddle types and crystallization kettle parameters on the stirring and mixing of polyamide 12 powder in the preparation unit.It was found that the average flow velocity and average shear rate in the stirring flow field of the propulsion impeller and four-broad-blade impeller were smaller than those of the fullzone agitator;with the addition of baffle,the average velocity and the average shear rate in the agitated flow field of propulsion impeller and four-broad-blade impeller will increase.The phase transformation process of polyamide 12 in ethylene glycol was studied by cloud-point method.The phase diagram of polyamide 12 solution with the concentration range of 1%?30%was monitored and analyzed online by imaging method.It was found that the liquid-liquid phase separation would occur when the temperature dropped to 190°C,and the solution would crystallize when the temperature continued to drop to about 150°C.The melting crystallization kinetics of polyamide 12 powders prepared with different TiO₂dosage was studied by DSC.In this study,The Avrami equation and TF(Turnbull-Fisher)equation were selected to analyze the melting isothermal crystallization process of the samples.The isothermal crystallization activation energy and equilibrium melting point of polyamide 12powder prepared with different TiO₂ dosage were calculated.It was found that in the temperature range of 155°C to 162°C,with the decrease of crystallization temperature,the crystallization rate of polyamide 12 is accelerated.The non-isothermal crystallization process of polyamide 12 powder was analyzed by Mo's method and the activation energy of non-isothermal crystallization was calculated.It was found that the crystallization rate of polyamide12 increased with the increase of cooling rate.