【作者】 方辉；

【导师】 王奎升； 冯连勋；

【作者基本信息】 北京化工大学 ， 化工过程机械， 2007， 博士

【摘要】 接枝反应挤出作为现代聚合物加工工艺的一种新方法,与其他加工方法相比,具有诸多优点。就加工设备来说,同向双螺杆挤出机以其优异的输送、混合等性能已成为接枝反应挤出的主要设备。国内外学者对反应挤出的工艺参数(配方、螺杆转速、加料量、机筒温度、加料方式等)进行了大量的研究,而对于螺杆元件和螺杆构型的系统研究未见报道。在接枝反应挤出过程中,各反应物的充分混合是至关重要的,作为挤出机“心脏”的螺杆对混合的作用更是其他条件无法替代的。本文从同向双螺杆挤出机螺杆捏合盘混炼段元件入手,研究了其对接枝反应挤出过程的影响,深入探讨了捏合盘混炼段的混合性能与接枝反应挤出过程之间的关系。主要的研究工作如下:(1)利用专业软件POLYFLOW对七种捏合盘混炼段元件和一种常规螺纹元件进行流场模拟计算,并对模拟结果进行了后处理,分析了各种捏合盘混炼段元件的混合性能;(2)在微观流变学的基础上,结合接枝反应动力学方程,模拟分析了捏合盘混炼段的接枝反应挤出过程;(3)通过MAH熔融接枝LDPE的实验,研究了捏合盘混炼段元件对接枝反应挤出过程的影响;(4)通过充满度、停留时间分布以及不相容体系共混等实验,探讨了捏合盘混炼段元件与接枝反应挤出之间的关系。通过对捏合盘混炼段的混合性能模拟可知,就轴向分布混合性能和剪切性能而言,反向捏合块元件优于正向元件和中性捏合块元件,捏合盘厚度对这两个性能的影响不大,而常规螺纹元件的这两个性能相对较差。从应变分布的模拟结果中可以看出:常规螺纹元件所对应的平均应变水平居中偏差,且分布较宽,因此其混合效果不好;在捏合块元件中,反向元件所对应的平均应变较大,其中KB120所对应的应变分布较窄,而KB150的较宽,故KB120的混合性能最好,而KB150则不利于物料的均一性;中性元件KB90的应变分布较窄,有利于物料的均一性,但是其平均应变较小,对物料的混合效果不好;正向元件中,KB60的混合效果要比KB30差。另外,在相同捏合盘错列角的条件下,随着捏合盘厚度的增加,平均应变稍有增大,但应变分布加宽。在对螺杆元件混合性能模拟分析的基础上,本文结合不相容体系分散相的相态演变理论和接枝反应动力学,提出了微粒反应挤出模型,并对捏合盘混炼段接枝反应挤出进行了模拟分析,结果表明,物料所经历的平均应变大且应变分布窄的元件有利于接枝效率的提高。MAH熔融接枝LDPE的反应挤出实验表明,在相同捏合盘厚度条件下,接枝率的大小与捏合盘错列角不成单调的对应关系,其中KB120最大,KB60最小。而在相同捏合盘错列角条件下,随着捏合盘厚度的增加,各取样点的接枝率均下降,而且捏合盘厚度大于一定值后,各取样点的接枝率甚至小于常规螺纹元件。接枝反应挤出实验结果与模拟结果在趋势上相符合,只有正向输送元件的结果存在一定偏差,这与流道充满度的差异有关。为了探讨捏合盘混炼段元件的混合效果与接枝反应挤出之间的关系,本文进行了填充度、停留时间分布(RTD)以及不相容体系共混的实验研究。研究结果表明,对于接枝反应挤出来说,螺杆元件的建压能力会在很大程度上影响接枝反应挤出的进程,包括反应的起始位置和物料的流动状态等。各螺杆构型所对应的RTD分布和分散混合性能与接枝率有着直接的对应关系,而分散混合性能与流场的剪切应力和剪切速率相关。因此,在接枝反应挤出中,产物接枝率主要取决于物料在挤出机内的停留时间和所经受的剪切速率。由物料所经受的应变为停留时间与剪切速率的乘积说明,接枝反应挤出与物料所经受的应变历程相关。综上所述,适用于接枝反应挤出的螺杆构型应该能够为物料提供较大且分布较窄的应变,而且也有利于物料的均一性。就本文所涉及到的捏合盘混炼段元件而言,具有窄捏合盘厚度、120°错列角的捏合块元件——KB120最适用于接枝反应挤出。更多还原

【Abstract】 Grafting reactive extrusion is a new method in modern polymer processing, and compared with other processing technologies, there are lots of advantages. As for the process equipment, co-rotating twin-screw extruder depending on its excellent performance in transportation and mixing has become the main equipment used in grafting reactive extrusion (GRE). By now, many experts had done a number of researches on grafting recipes and processing conditions such as rotation speed of the screws, throughput, temperature of the barrel and feeding mode. There is no systematical research about screw element and screw configuration. However, the mixing among the monomer, initiator and polymer melt is very critical in the manufacturing of high grafting products, and the screw, a core component of an extruder, would have significant impacts on the GRE process.Focused on the kneading-block mixing element (KBME) in co-rotating twin-screw extruder, the effect upon GRE was researched in the thesis, and the relationship between the mixing property of the kneading-block mixing zone (KBMZ) and the GRE was investigated. The main research work consists of: (1) Seven kneading blocks and one normal screw element were simulated by using the CFD package, POLYFLOW, and the mixing property of each screw element was analyzed; (2) Based on the microscopic rheology, combined with the kinetics of grafting reaction, the process of GRE in the KBMZ was simulated and analyzed; (3) The experiment of the GRE for LDPE-g-MAH was performed to investigate the influence of KBME; and (4) The experiments of filling ratio, residence time distribution (RTD) and immiscible polymer blends were carried out to explore the relationship between the KBME and the GRE.According to the simulation of the mixing property for KBME, the axial distributive mixing property and the shear property of reversed kneading blocks are better than those of neutral and forward ones, and those of normal screw element are worst, whereas the kneading disc width has few impacts on these two properties. In addition, based on the simulation of strain distribution, some conclusions were drawn: the mixing property of the normal screw element is the worst owing to the smaller mean strain and the wider strain distribution; the mean strains of the kneading block KB120 and KB150 are better, and the KB120 has the best mixing property due to its narrower strain distribution, but the KB150 is not favorable to the uniformity of the material because of its wider strain distribution; the strain distribution of the neutral element KB90 is much narrower, which would benefit the uniformity of the material, while its mean strain is smaller, which would result in the bad mixing of the material; as to the forward kneading block, the mixing ability of KB60 is worse than that of KB30. Furthermore, with the increase of the kneading disc width, the mean strain increase little, but the strain distribution becomes wider.Based on the simulation of the mixing property for the screw elements and combined the microscopic rheology with the kinetics of grafting reaction, the model of particulate reactive extrusion was put forward in this thesis. According to the analysis of the GRE in KBMZ, a conclusion was drawn that the screw element which could provide large mean strain but narrow strain distribution could improve the grafting efficiency.The result of the GRE for LDPE-g-MAH showed that as to the kneading blocks with the same kneading disc width, the grafting degree of the element KB120 is the largest, while that of KB60 is the smallest. With the increase of the kneading disc width, the grafting degrees of the specimens from each sampling point would decline. Moreover, as the kneading disc is wide enough, the grafting degree for the kneading block is even less than that for the normal screw element. In addition, the trend of the simulation is good agreement with that of the experiment in the GRE. There is some deviation for the forward element, which results from the difference of the filling ratio between the simulation and the experiment.In order to explore the relationship between the mixing property of KBME and GRE, the experiments of filling ratio, residence time distribution (RTD) and immiscible polymer blends were performed in this thesis. Seen from the results of these experiments, the ability of building pressure for the screw element would affect the GRE process, such as the initial position of the reaction and the flow state of the material. The RTD and dispersive mixing property for each screw configuration have direct impact on the grafting degree. And the dispersive mixing property is related to the shear stress and the shear rate. So the grafting degree of the extrudate depends on the residence time and the shear rate. Moreover, the strain equals to the multiple of the residence time with the shear rate. Therefore, the GRE would correlate to the strain course experienced by the material.Generally, the screw configuration suited to the GRE would provide large strain but narrow strain distribution. And the narrow strain distribution would favor the uniformity of the material. As for the KBME investigated in this work, the kneading block with the narrow kneading disc and the staggering angle 120°, that is KB120, is most suitable for the GRE.更多还原