Analysis of the bubble building in with blowing agent loaded polymer melts

根据物理发泡剂、改性应变硬化聚合物熔体的化学配方以及挤出工艺参数来分析挤出泡沫实验中的泡沫结构。聚合物熔体的拉伸性质的相关性只能用气泡和结构的建立来影响，这是不充分的、纯粹的定性的，因为不存在关于气泡中的拉伸速率的可靠信息。没有选择性的改性的聚合物可以采取泡沫建筑物，以他们的拉伸粘度和应变硬化的一个受控的泡沫建筑过程。基于这些流变学和过程的具体缺陷，为了描述泡沫过程的发展或物理，特别是流变学为基础的模拟模型，以更好地预测泡沫建筑物的发泡改性聚合物是必要的。应采用经实验验证的气泡形成模型和流变本构方程，其参数可通过使用合适的流变测量系统确定。应使用旋转、毛细管和拉伸流变仪系统对化学改性PLA型进行流变特性分析。应测定拉伸速率下的拉伸粘度，为了描述挤出发泡过程中的气泡形成过程，必须发展和应用与气泡兰德等双轴拉伸聚合物熔体相关的扩散模型。现有的含发泡剂的聚合物熔体中气泡形成的模型必须用时间和应变依赖的拉伸粘度函数和扩散模型之间的关系来增强。应考虑拉伸粘度和随气泡增长的应变硬化。为此，可以应用分子应力函数（MSF）模型，其参数可以由单轴拉伸实验确定。该模型能较好地描述真实的气泡形成过程中的等双轴拉伸流动。

Foam structure in extrusion foam experiments is analyzed dependent on physical foam agents, on chemical formulation of the modified strain hardening polymer melts and on the process parameters of the extrusion. The correlation of the extensional properties of the polymer melt can be effected with the bubble and structure building only insufficiently, pure qualitatively, because no realible informations exist about the extensional rates in gas bubbles. No selective modification of the polymers can be taken for foam buildings in order to their extensional viscosity and strain hardening for a controlled bubble building process.Based on these rheological and process specific deficits in order to describe the foam processes is necessary the development or a physical and especially rheological based simulation model for a better prediction of the bubble building in for foaming modified polymers. An experimentally verified bubble building model and a rheological constitutive equation, its parameters can be identified on for foaming modified polymer melts using suitable rheometrical measuring systems, shall be taken. The chemically modified PLA-type shall be characterized rheologically by using rotational, capillary and extensional rheometer systems. Extensional viscosity at extensional rates shall be determined, which are relevant for at the bubble rand equibiaxially stretched polymer melt and a diffusion model shall be developed and applied in order to describe the bubble building process during extrusion foaming.Existing models for the bubble building in with blowing agent loaded polymer melts must be enhanced with a time and strain dependent extensional viscosity function and the relation of the extensional viscosity and the strain hardening with the bubble growth shall be taken into account. For this reason the molecular stress function (MSF) model can be applied and its parameters can be determined from uniaxial extensional experiments. The equibiaxial extensional flow in real bubble building process then can be described correctly with this model.