Reactive rotational molding process of PP/PA6 bilayer systems: experimental investigations

Rotational molding has been regarded as a plastic molding method with great potential. The process offers virtually stress-free products having no weld lines or material wastage, and utilizes relatively inexpensive molds. Yet its widespread growth is hindered due to long production cycle times, which are limited by the time required to heat up and cool down the mold and the product. This presentation is about the study of making multilayer PP/PA6 parts with the reactive rotational molding process. Different studies have already been made in the past about rotational molding or about reactive process of monolayer part. The aim of this work is to reduce cycle time by making a layer via anionic polymerization of caprolactam, and them to compare each process. This presentation is divided into two parts: the first part deals with rheological, dieclectric aland thermal analysis to investigate the effect of mixtures and the crystallization/polymerization effect; the second part deals with the processing of bilayer parts. Firstly, different mixtures of catalysts and activators were investigated by Rheology and thermal analysis in order to determine which mixture would be the most appropriate for the rotational molding process: 2–2 (2% of activator and 2% of catalyst), 3–3, 4–4 and 6–6. In the second step, different processing investigations have been done in order to study the influences of the parameters like oven time or cooling time. An experimental analysis of heat transfer in reactive rotational molding process was also lead. By using an instrumented mold associated with a radio transmission data acquisition system, we demonstrate that the rotational parts of the bilyar PP/PA6 (reactive way) can be obtained with optimised conditions in correlation with the results of rheology and dielectric measurements. Moreover, the results allows us that it is possible to make bilayer reactive part with the rotational molding process by using less energy in a shorter time.