Fundamental research on foaming of elastomers with water as physical blowing agent and description of mechanisms of foaming

原则上，水是聚合物材料的合适发泡剂。在热塑性弹性体和热塑性弹性体领域，已经开展并发表了许多研究项目。对于化学交联弹性体的挤出，科学研究尚不清楚。其原因是众多配方成分如何影响水的吸附和解吸、吸水率不足以及水在基质中的均匀分散等问题尚未得到解答。在这项研究项目中，将研究用水发泡丁腈橡胶和三元乙丙橡胶化合物的新方法。为此，粉状吸湿性填料被装入水并混合到橡胶胶料中。水用作发泡剂。为了量化在储存过程中水分从化合物中扩散出来或水分扩散到混合物中的情况，对选定的样品在不同储存时间后的水分含量进行了分析。由于硫化和发泡反应的协调对所产生的泡沫结构有很大的影响，除了设备结构和工艺参数的影响外，还考察了不同的硫化动力学，重点考察了它们对挤出样品的泡沫结构和表面质量的影响。此外，为了全面描述水的脱附，对不同负载和成核样品的发泡行为进行了评估。除了工艺和材料调查外，还考察了附加成核剂的使用，以便找到发泡行为的分析描述。本研究项目的结果为水在橡胶加工中作为发泡剂的可能应用提供了科学的证据。

In principle, water represents a suitable blowing agent for polymer materials. In the field of thermoplasts and thermoplastic elastomers, numerous research projects have been conducted and published. For the extrusion of chemically cross-linked elastomers, scientific investigations are not yet known. Reasons for this are the yet unanswered questions on how numerous recipe ingredients influence water adsorption and desorption, an unsufficient water absorption and a homogeneous dispersion of water within the matrix.In this research project, novel approaches are to be examined for foaming NBR- and EPDM-compounds with water. For this, powdery hygroscopic fillers are loaded with water and mixed into the rubber compound. The water serves as blowing agent. In order to quantify peliminary diffusion of water out of the compounds or a diffusion of humidity into the comopund while storing, selected samples are analysed with respect to their water content after different storing times.As the coordination of vulcanisation and blowing reaction represents a substantial influence on the resulting foam structure, different vulcanisation kinetics are examined apart from the influence of equipment configuration and process parameters with focus on their influences on foam structure and surface quality of extruded samples. Furthermore, the foaming behaviour of differently loaded and nucleated samples is evaluated in order to describe desorption of water comprehensively.Apart from process- and material investigations, the use of additional nucleating agents is examined in order to find an analytic description of the foaming behaviour.Results of this research project allow scientifically substantiated statements on possible applications for water as blowing agent in rubber processing.