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

分析了挤出发泡实验中的泡沫结构与物理发泡剂、改性应变硬化聚合物熔体的化学配方以及挤出工艺参数的关系。聚合物熔体拉伸性能的关联只能与气泡和结构的建立有关，因为没有关于气泡中拉伸速率的真实信息，所以只能定性地、不够纯粹地影响聚合物熔体的拉伸性能。对于泡沫塑料建筑，不能为了控制泡沫化过程中聚合物的拉伸粘度和应变硬化而对聚合物进行选择性的改性。基于这些流变学和工艺特有的缺陷，为了描述泡沫塑料过程，有必要开发或建立基于物理特别是流变学的模拟模型，以便更好地预测泡沫塑料的泡沫化过程。采用实验验证的气泡形成模型和流变本构方程，其参数可以用合适的流变学测量系统来识别改性聚合物熔体的发泡。采用旋转流变仪、毛细管流变仪和拉伸流变仪对化学改性PLA型进行流变性表征。为了描述挤出发泡过程中的气泡形成过程，应确定拉伸速率下的拉伸粘度，并建立和应用扩散模型。现有的含发泡剂聚合物熔体的气泡形成模型必须采用时间和应变相关的拉伸粘度函数，并考虑拉伸粘度和应变硬化与气泡生长的关系。为此，可以采用分子应力函数(MSF)模型，其参数可以通过单轴拉伸实验来确定。该模型能较好地描述实际气泡形成过程中的等轴拉伸流。

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.