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

根据物理泡沫剂、改性应变硬化聚合物熔体的化学配方和挤出工艺参数对挤出泡沫实验中的泡沫结构进行了分析。由于没有关于气泡中拉伸速率的可靠信息，聚合物熔体的拉伸性能与气泡和结构的形成之间的关联只能是不充分的、纯定性的。为了使聚合物的拉伸粘度和应变硬化达到可控的造泡过程，不能对聚合物进行选择性改性。基于这些流变性和工艺特异性缺陷，为了描述泡沫过程，有必要开发一种物理的，特别是基于流变性的模拟模型，以便更好地预测发泡改性聚合物中的气泡形成。采用实验验证的造泡模型和流变本构方程，利用合适的流变测量系统，可以确定发泡改性聚合物熔体的参数。化学改性pla型应通过旋转、毛细管和拉伸流变仪系统进行流变学表征。应确定拉伸速率下的拉伸粘度，这与气泡和双轴拉伸聚合物熔体有关，并应开发和应用扩散模型，以描述挤出发泡过程中的气泡形成过程。现有的含发泡剂聚合物熔体气泡生成模型必须增加随时间和应变变化的拉伸粘度函数，并考虑拉伸粘度和应变硬化与气泡生长的关系。因此，可以采用分子应力函数（MSF）模型，并通过单轴拉伸实验确定其参数。用该模型可以较好地描述实际造泡过程中的等双轴拉伸流。

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.