【作者】 宗原；

【导师】 戴干策；

【作者基本信息】 华东理工大学 ， 化学工程， 2011， 博士

【摘要】 热塑性复合材料轻质、高韧性、低能耗、耐化学腐蚀、成型方便、制造周期短、对环境友好,在环保意识逐渐增强的今天,得到极大的关注,其产品在国民经济及国防建设中的应用日益广泛。本文以聚合物常用改性方法即共混与复合为起点,对实施热塑性复合材料加工的基本设备——挤出机中的关键问题进行了计算分析。进而以新型热塑性复合材料——轻质热塑性复合片材的制备为主要研究对象,针对热塑性复合材料工业制备过程中的几个关键问题,探讨了复合材料微观相态结构、流变行为以及加工条件这三者之间的相互关系,以期为典型热塑性复合材料工业制备技术的开发及优化提供必要的基础。全文由三部分组成,即多相聚合物系流变学、挤出机螺槽中流动的数值模拟以及预混粉体浸渍技术中相关多相流动及其模拟分析。首先,选择弹性体增韧PET复合体系和石墨填充聚合物体系分别作为聚合物共混体系及粒子填充聚合物体系的代表,并借助力学性能测试及微观结构观察,着重分析了聚合物复合体系的流变行为与相态结构间的关系,讨论了聚合物复合体系的结构及加工工艺对其性能的影响。其次,针对纤维增强复合材料的制备过程,将单螺杆挤出机简化为三维方腔,利用粒子轨迹跟踪技术和有限元法研究了螺杆转速、螺槽深度以及聚合物流变行为对其混合特性的影响。并讨论了导致纤维发生断裂和分散的因素。为此,提出了适合加工长纤维增强热塑性复合材料的流场特征,给出了改善单螺杆挤出机混合的措施。最后,采用喷动流化床预混与双钢带压机浸渍的技术路线制备轻质热塑性片材。为了揭示喷动流化床内纤维分散机理,利用大涡模拟方法,对四种不同结构喷动流化床的流体动力学进行了数值模拟,分析了内构件对流型分布、湍流特性的影响,同时利用流变仪测量了纤维束的内聚力,为纤维束的筛选建立了标准。研究结果表明,内构件(导流筒和圆盘型挡板)的加入大大地改变了喷动流化床内的流场分布,这种独特的组合流场有助于纤维的分散。采用大涡模拟的基本思想,研究了喷动流化床内纤维的分布情况。通过求解组分质量守恒方程,借鉴絮团强度的概念,发现各区域的纤维浓度与流场特征密切相关,絮团的大小直接取决于纤维间的相互作用力及流场中的湍动程度。并且,提出了喷动流化床内纤维絮团产生的机理以及减少絮团的措施。应用REV尺度的格子Boltzmann方法,模拟了热塑性树脂沿轻质毡厚度方向的流动过程,考察了加压方式、载荷、温度、双钢带压机结构等对浸渍的影响。结果表明,与平板压机相比,双钢带压机通过施加高低交替的压力更能有效地浸渍轻质毡使浸渍时间缩短了10～15%。另外发现,浸渍不仅与树脂最大浸渍速度有关,还取决于片材在高压区的停留时间。通过增加载荷或升高温度均可提高树脂最大速度,而片材在高压区的停留时间则对压机辊柱直径及载荷更为敏感,仅依靠调节钢带运行速度不能达到缩短浸渍时间的目的。更多还原

【Abstract】 Owing to the advantages of low weight, high toughness, low energy consumption, chemical resistance, convenient forming, short manufacture and environment-friendly, polymer composite has attracted great attention and its application has been widely increased in the important projects of national economy. Concerned with typical industrialized manufacture of the polymer composites, several key issues were investigated in this thesis, including the microscale structure of the composites, rheological behavior and processing conditions. The relationship between them was discussed in order to provide foundation for the development and optimization of industrialized manufacture process.The thesis consisted of three parts, namely rheology of multiophase polymer system, numerical simulation of the flow field in the screw’s channel and the multiphase flow relating to the technology of premixing of resion powder with long glass fiber and impregnation. Firstly, toughened PET composites and graphite filled polymer composites were selected on behalf of the compounding and filled system, respectively. With the help of mechanical testing, SEM observation, the relationship between rheological behavior and the microscale structure of the composites was emphasized. The effects of the composite’s structure and processing condition on properties were investigated.Secondly, aimed at the manufacturing of glass fiber reinforced composites, the single-screw extruder was simplified as a 3D rectangle cavity and the flow field of it was simulated by means of FEM and particle tracing technology. The effects of rotating speed of the screw, depth of the channel and viscoelastic behavior of the polymer on the mixing performance were evaluated. In order to apply the single-screw extruder in the manufacture of long fiber reinforced composites, appropriate flow field was suggested and approaches to promote the mixing performance was put forward.Thirdly, the maufacure of light-weight reinforced thermoplastic sheet (LWRT) was conducted by premixing of resin powder and long glass fiber in internally spout-fluid bed and impregnation in double-belt press. In order to illuminate the dispersion mechanism of fiber bundle in the spout-fluid bed, LES method was employed to simulate the hydrodynamics of the spout-fluid bed with different structures. These spout-fluid beds were installed with some internals and the effects of the internals on the flow distribution and turbulence characteristic were discussed. In addition, the cohension strength of the fiber bundle was measured by ARES and the purpose of it was to establish a criterion for fiber evaluation. The results showed that the addition of the internals had significantly modified the flow field. The combination of several sub flow was benefit to the dispersion of fiber bundles and the mixing of resion powder and long glass fiber was improved.In view of the basic idea of LES, the species transport model was employed to study the distribution of fiber in the spout-fluid bed. With the concept of flocculation intensity, it was found that the distribution of fiber in each region has close relationship to its flow field and the size of the floc was directly determined by the interaction of the fibers and turbulence in the flow field. On this basis, the mechanism causing fiber flocculation and measures to avoid it were put forward.The lattice Boltzmann method at representative elementary volume (REV) scale was used to simulate transverse impregnation for LWRT and the effect of press mode, loading, temperature and the geometry of the rollers on impregnation were investigated. The results showed that the double-belt press was more effective in shortening impregnation time by 10～15% owing to its undee pressure distribution. Besides, it was found that impregnation was determined by not only the maximum impregnation rate but also the residence time in the area with higher pressure. The maximum impregnation rate could be improved by enhancing loading and increasing the temperature as well. The residence time was more sensitive to the diameter of the roller and loadings. However, it was impossible to shorten the impregnation time only by adjusting the motion of the belt.更多还原