Process validation and optimization of a two-step two-component direct bonding between thermoplastic and rubber

Sebastian Huber

Research output: ThesisMaster's Thesis


The objective of this master’s thesis was the optimization of a two-step two-component (2C) direct bonding process between a semi-crystalline thermoplast (PA 612) and a rubber-blend (HNBR/NBR). The two steps mentioned above included the manufacturing of the thermoplastic inserts by injection molding and the direct bonding process by transfer molding. To define the limitations of the process chain to be optimized, the Six Sigma-tool “Process Mapping” was applied. Furthermore, the most determining factors to be analyzed were worked out by the application of the Six Sigma-tool “Ishikawa-diagram”. Afterwards, the optimization of the two-step 2C direct bonding process was done by 4 fractional factorial or full-factorial experiments with two levels per factor. By means of tensile tests and microscopical analyses of the fracture surfaces, the adhesion quality of the 2C-parts was analyzed. Besides, the microscopical analyses were quantified by a self-developed rating system. All results were evaluated by the same mathematical software which was applied to implement the design of the experiments. The results of the experiments lead to the conclusion that a contamination of the components by foreign particles interferes most with the bonding process. In addition, PA 612 tends to water absorption which works against a high adhesion quality as well. Thus, the components must be produced and stored under appropriate conditions. Moreover, the results of the experiments validate the assumption that interdiffusion is the most dominating bonding mechanism between PA 612 and HNBR. Thus, the mobility of the polymer chains of the rubber must be guaranteed for an appropriate time during the bonding process. Besides, a high pressure during the bonding process affects the appropriate approach of the polymer chains of both materials for the interdiffusion. Consequently, the interactions of temperature, pressure and time are the determining factors during the direct bonding process. As a result, lower vulcanization temperatures in combination with longer curing times lead to optimal bonding properties. Nevertheless, the pressure must also be in a certain range to guarantee a complete filling of the cavities by the rubber and to avoid residual stresses in the interfaces between the components. In consideration of postprocessing of the 2C-parts, the results illustrate that post curing causes a significant increase of the rubber’s mechanical properties. Before the bonding process, chemical and physical aging of the materials should be avoided to achieve good bonding properties. Considering the manufacturing of the thermoplastic inserts, the results lead to the assumption that the bonding behavior of the inserts can be influenced by the variation of the processing parameters. To conclude, the results of the experiments point out that the two-step 2C direct bonding process between PA 612 and HNBR shows a high potential for industrial applications. Nonetheless, there is still a high number of other factors which should be analyzed to provide a profitable mass production.
Translated title of the contributionProzessvalidierung und Optimierung einer zweistufigen Zwei-Komponenten Direktbindung zwischen Thermoplast und Elastomer
Original languageEnglish
Awarding Institution
  • Montanuniversität
  • Marksteiner, Albin, Co-Supervisor (external), External person
  • Lucyshyn, Thomas, Supervisor (internal)
Publication statusPublished - 2020

Bibliographical note

embargoed until 05-05-2025


  • direct bonding
  • composite
  • elastomer
  • polyamide
  • HNBR
  • thermoplast
  • compound
  • adhesion
  • 2C
  • components
  • rubber
  • interdiffusion
  • interface
  • adhesion strength
  • vulcanization
  • bonding
  • transfer molding
  • injection molding

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