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

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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.