Foam injection molding of magneto sensitive polymer composites

The purpose of this work is obtaining magneto sensitive foamed parts made by iron microparticles distributed in a flexible polymer matrix. The material adopted is a compound of a thermoplastic elastomer with 20% by weight of iron microparticles. In particular, a masterbatch containing 50% by weight of iron microparticles was obtained by melt compounding in a twin screw extruder and was then diluted with the pure polymer directly in the hopper of the injection molding machine. A conventional injection molding machine was adapted to carry out the microcellular injection molding process. The cylinder of the injection molding machine was modified to host a system for controlling the quantity of gas injected during the batching step. The screw was modified introducing a mixing section in order to improve the dissolution of the gas inside the melt. An aluminum mold was designed and built in order to host an electro-magnet able to apply a magnetic field (up to 0.2 Tesla) during the injection and foaming steps. The samples obtained by foam injection molding achieved a density reduction up to 40% when compared with the corresponding non-foamed samples. In the case of samples obtained in the presence of magnetic field, the iron particles aligned in the direction of the field and organize into fibrillar structures of variable length. The mechanical tests have shown that the samples in which the iron particles are aligned in the direction of the magnetic field have a higher modulus compared to samples in which the particles are randomly dispersed. Furthermore, it was verified that the magnetic field aligned particles induces an anisotropic structural reinforcement. To the best of our knowledge, this work is the first attempt to obtain an alignment of filler particles by a magnetic field applied during foam injection molding