【作者】 黄勇；

【导师】 尹红；

【作者基本信息】 浙江大学 ， 化学工程与技术， 2021， 硕士

【摘要】 聚对苯二甲酰己二胺/聚己二酰己二胺(PA6T/66)属于半芳香族共聚酰胺,具有优异的耐高温性能、低吸水性、尺寸稳定性、高强度和刚度及优良的耐化学药品性能。PA6T/66连续化生产过程分为成盐、预聚和后缩聚三个阶段,在后缩聚阶段将PA6T/66预聚物泵入双螺杆挤出机(TSE)进行反应挤出(REX),预聚物继续缩聚增长从而提高分子量。挤出机内流场复杂,操作参数众多且相互耦合,实验手段难以探明PA6T/66反应挤出过程机理。论文采用计算流体力学(CFD)方法对双螺杆挤出机中的PA6T/66反应挤出过程进行模拟研究,从挤出机内流变、反应和混合三者之间的相互作用出发,探究螺杆配置和操作参数对PA6T/66反应挤出过程的影响,以期为PA6T/66反应挤出过程提供理论指导。论文首先探究PA6T/66流变性能与剪切速率、剪切温度和端氨基含量之间的关系,并构建PA6T/66流变学模型。运用核磁共振和红外光谱对PA6T/66进行结构表征,差示扫描量热结果显示PA6T/66的熔融温度为303℃、玻璃化转变温度130℃,热重分析结果显示PA6T/66的初始分解温度为392.84℃、最大分解温度为457.69℃。利用高压毛细管流变仪构建PA6T/66的流变学方程,探究PA6T/66粘度与剪切速率的关系并拟合实验数据,结果表明:PA6T/66出现剪切变稀现象,非牛顿指数n=0.2504,Bird-Carraeu模型在参数较少的情况下可获得较高拟合精度。采用Arrhenius模型拟合PA6T/66粘度随温度变化的实验数据,发现粘流活化能随剪切速率增大而减小。探究端氨基含量对PA6T/66流变性能的影响,结果表明端氨基含量减小,剪切粘度曲线上移,拟合方程所得到的零剪切粘度也更大。论文针对PA6T/66连续化生产工艺难点——后缩聚阶段,即耦合了流动、传热、传质和化学反应等问题的反应挤出过程,采用三维数值模拟方法模拟PA6T/66预聚物在共转双螺杆挤出机内的缩聚过程。采用分段模拟方法对PA6T/66反应挤出过程进行建模,模拟水的脱除过程。耦合PA6T/66缩聚反应动力学和流变学模型,得到挤出机温度、剪切速率和粘度场分布。研究螺杆转速、壁面温度、进料量与预聚物进料状态对缩聚反应进程的影响并计算各组分沿挤出过程的演化。结果显示,增大螺杆转速,PA6T/66反应程度略微下降。增大机筒壁面温度可提升缩聚反应速率,促进反应进程。增大进料量会缩短停留时间,延缓反应进程。多组分竞争反应条件下,预聚物分子量和组成显著影响缩聚反应速率,进而影响反应进程。挤出机内的混合状况对反应挤出过程有较大影响,利用基于有限元的计算流体力学方法构建双螺杆挤出机的三维混合模型,采用网格叠加技术(MST)求解变化的计算域以获得挤出机内的速度和剪切速率分布,采用粒子示踪方法计算不同操作条件下的混合指数和混合效率。模拟结果表明捏合块与逆转元件出现较大程度漏流,输送元件所受应力随导程增大而减小。分散混合研究结果表明螺杆转速或进料量增大,平均混合指数变小,但最大混合指数变大,表明挤出机内PA6T/66分散混合效果变差,但部分粒子经历的最大拉伸作用更强。分布混合结果表明PA6T/66粒子在挤出机内经历拉伸和压缩作用,捏合块元件的瞬时混合效率最高、分布混合性能最强。停留时间演化结果表明沿挤出方向死区时间变长,停留时间分布变宽,平均停留时间呈线性增加趋势,无因次方差增大,轴向混合效果变强。更多还原

【Abstract】 Poly(hexamethylene terephthalamide)/Poly(hexamethylene adipamide)(PA6T/66)is a semi-aromatic copolyamide,which has excellent high temperature resistance,low water absorption,dimensional stability,high strength and stiffness,and excellent chemical resistance.The PA6T/66 continuous production process is divided into three stages:salt formation,pre-polymerization and post condensation.PA6T/66 prepolymer was pumped into twin screw extruder(TSE)for reactive extrusion(REX),and the prepolymer continued to polycondensate to increase molecular weight.It is difficult to investigate the mechanism of PA6T/66 reactive extrusion process by experiment method because of the complex flow field and numerous operating parameters coupling in the extruder.In this thesis,computational fluid dynamics(CFD)was used to simulate the PA6T/66 reactive extrusion process in twin screw extruder.Based on the interaction among rheology,reaction and mixing in extruder,the influence of screw configuration and operating parameters on the reactive extrusion process of PA6T/66 was explored,in order to provide theoretical guidance for the reactive extrusion process of PA6T/66.Firstly,the relationship between PA6T/66 rheological properties and shear rate,shear temperature and terminal amino content was explored,and the rheological model of PA6T/66 was established.The structure of PA6T/66 was characterized by NMR and IR,the melting temperature and galss transition temperature of PA6T/66 were 303℃ and 130℃ by DSC.The initial decomposition temperature and maximum decomposition temperature of PA6T/66 were 392.84℃ and 457.69℃ by TGA.The rheological equation of PA6T/66 was established by high pressure capillary rheometer,the relationship of PA6T/66 viscosity with shear rate was studied and the experimental data were fitted.The results showed that PA6T/66 has a shear thinning phenomenon,non newtonian index n=0.2504,Bird-Carraeu model can obtain a higher fitting accuracy under the condition of fewer parameters.The Arrhenius model was used to fit the experimental data of PA6T/66 viscosity changing with temperature,the results show that activation energy of viscous flow decreases with the increase of shear rate.The effect of terminal amino content on the rheological properties of PA6T/66 was investigated,the results show that with the decrease of terminal amino content,the shear viscosity curve moves upward,and the zero shear viscosity obtained by fitting equation is also bigger.In this thesis,a three dimensional numerical simulation method is used to simulate the post condensation process of PA6T/66 prepolymer in a corotating twin-screw extruder,aiming at the critical procedure of PA6T/66 continuous production process,which is the reaction extrusion process coupled with flow,heat transfer,mass transfer and chemical reaction.The process of PA6T/66 reaction extrusion and the water removal were modeled by subsection simulation method,the extruder temperature,shear rate and viscosity distribution were obtained by coupling PA6T/66 polycondensation reaction kinetics and rheological model.The influences of screw speed,barrel temperature,feeding rate and prepolymer feeding state on the polycondensation reaction process were studied,and the evolution of each component along the extrusion process was calculated.The results showed that the reaction degree of PA6T/66 decreased slightly with the increase of screw speed.The rate of polycondensation can be increased and the reaction process can be promoted by increasing the barrel temperature.Increasing the feeding rate will shorten the residence time and delay the reaction process.Under the condition of multi-component competitive reaction,the molecular weight and composition of prepolymers significantly affect the polycondensation rate and the reaction process.The mixing condition in extruder has a great influence on the reaction extrusion process.In this thesis,a three-dimensional mixing model of the twin screw extruder was constructed by using computational fluid dynamics based on finite element method.The velocity and shear rate distribution in the extruder were obtained by using mesh superposition technique(MST)to solve the changing computational domain.Particle tracing method was used to calculate the mixing index and mixing efficiency under different screw revolution,feed rates and screw configurations.The simulation results show that the kneading block and the reversing element have the largest leakage flow.The stress of the conveying element decreases with the increase of the screw lead.The results of dispersive mixing show that with the increase of screw speed or feed rate,the average mixing index decreases,the maximum mixing index increases correspondingly,which indicates that PA6T/66 dispersive mixing effect in extruder is worser,but some particles experience stronger maximum stretching effect.The results of the distributive mixing show that PA6T/66 particles experience the stretching and compression effect in the extruder,and the instantaneous mixing efficiency and distributive mixing performance of kneading block elements are the highest.The results of residence time evolution show that the dead time increases along the extrusion direction,the residence time distribution becomes wider,the average residence time increases linearly,the dimensionless variance increases and the axial mixing effect becomes stronger.更多还原