TWO MATERIAL PUSH-PULL PROCESSING OF COMPATIBLE AND INCOMPATIBLE POLYOLEFINS
Júlio Viana, Dimitre Tchalamov, Antonio Cunha
University of Minho
Portugal
Keywords: Push-Pull, two-component, orientation
Mechanical performance of injection moulded parts can be enhanced significantly through special methods like two component injection moulding or live in-mould manipulation. The former combines the solid state properties of two polymers into a single part and the latter directs the microstructural development towards higher levels of overall molecular orientation. An interesting combination of these two methods can be achieved with two material Push-Pull. The technique is based on a two component injection moulding machine fitted with a special mould whose cavity is fed through two independent runner systems. The elevated level of orientation is achieved by continual reciprocating action of the two machine units which exposes the solidifying material to an alternating shear field. The technique normally involves single polymer and is used for enhancing the orientation of molecules and fillers. However in case that two different polymers are used a part with alternating layered structure can be created. The mechanical properties of such mouldings are expected to be determined by the high level of molecular alignment in the alternating layers of the two materials as well as the relatively large interfacial area.
In this work two material Push-Pull processing was performed using two combinations of polyolefins. In the first case two grades of polypropylene were fed into each of the units of a two component injection moulding machine. The produced parts featured alternating oriented layers of the two chemically compatible materials. In the other experiment a pair of polymers with poor interface bonding was chosen. Polypropylene and high density polyethylene were the two constituents of the moulded layered structures.
Optical reflection and polarized light transmission microscopy were used to characterize the morphological and microstructural development respectively of the produced parts. Mechanical properties were evaluated through three point bending and instrumented falling weight impact tests. The role of the polymer pairs and their compatibility was assessed.