In-situ Polymerization of Polyamide
Using a newly developed and servomotor-powered high-pressure RTM injection unit, Engel exhibited In-situ polymerization of e-caprolactam for the first time at an open house held in August. An articulated robot first placed a prepared fiber preform into the injection mold. Next, the fibers were impregnated with caprolactam. This involved the use of two vertical plasticizing units arranged in parallel: one contained caprolactam with a catalyst, the other held caprolactam mixed with an activator. Engel developed this in-situ polymerization technique in conjunction with the Fraunhofer Institute for Chemical Technology (ICT), Pfinstal. Thanks to the low viscosity of the caprolactam, even the finest fiber filaments can be wetted without damage and Incorporated into custom-shaped fiber structures while also beginning oriented in the direction of load.
The use of monomeric lactam to produce finished parts and semi-finished goods was investigated between 2006 and 2008 in a joint research project conducted by the Fraunhofer ICT AND IAP institutes. Major benefits of the process include the numerous processing options and great design freedom when it comes to molded parts. Compared to a thermoplastic melt, the monomer melt has a relatively low viscosity. This makes it possible to combine very long flow paths and thin walls when injection molding. It is further possible to produce very large semi-finished goods and finished parts with nonuniform wall thicknesses. This reduces the time and effort needed for post-molding operations. Since the final product is a thermoplastic, in contrast to what is obtained with most other reactive polymer systems, the material contained in the finished parts or semi-finished goods can be reclaimed at the end of the lifecycle. BASF is currently developing caprolactam systems containing special activators and catalysts with the objective of matching the polymerization reaction to the requirements of the parts to be manufactured.
In a research project conducted at the Institute for Plastics Processing, reactive extrusion of PA6 with cellulose fibers was investigated in twin-screw extruders. This process is also based on the anionic ring-opening polymerization of e-caprolactam. During tests, it was possible to impregnate the cellulose fibers with the low-viscosity reaction mixture continuously. This has a beneficial effect on the mechanical properties, especially the rigidity of the material.