Interfacial Instabilities and Mechanical Strength of Three-layer (PP/HDPE/PP) Symmetric Polymer Melts

n experimental apparatus has been developed for observing interfacial stability and deformation of multilayer pressure driven channel flows. The interface instability of a co-extrusion flow of polyethylene and polypropylene is studied experimentally in aslit geometry.This is performed by introducing disturbances of controlled wavelength and amplitude on three-layer symmetric (A-B-A) polymer melts and followed by a series of extrudate mechanical testing. In this study variations ofmechanical properties as well as wave interlocking have been related to the conformation of the interfacial waves. By investigating the growth of interfacial waves and tensile stress of extrudate samples, a relationship between interfacial instability and mechanical properties of polypropylene (PP) and high density polyethylene (HDPE)systems has been established. It is shown that instabilities are associated with interfacial waves, and it turns out that its amplitude is known as a mechanism for controlling the strength of three-layer polymer products. It is also demonstrated that the mechanism of interfacial strength is related to interfacial instabilities as well as theinterfacial wave interlocking. By considering that the instability is controlled by modal wave it may be possible to forecast the quality of final products in the co-extrusion process.