Multilayer coextrusion reveals interfacial dynamics in polymer blending

A multilayer coextrusion line is constructed and interfaced with a series of layer multiplication dies which are capable of making multilayer sheets with number of layers ranging from 2 to 2048 layers. One unique aspect of this process is the large amount of interfacial area generated in a fast and well controlled manner, and the rheological properties of the components do not interact with the interfacial area generation up to the point of layer breakup. These coextruded multilayers provide a model system to decouple interfacial dynamics from component rheology.; A novel technique is developed to measure the interdiffusion coefficient of two polyethylenes with different molecular weight. These two polyethylenes are coextruded into 256 layers. The interdiffusion is followed by monitoring the increase of apparent viscosity of the multilayers. Finite element method is used to solve the interdiffusion in the multilayers, and the concentration dependent interdiffusion coefficient is calculated by fitting the measured apparent viscosity.; Interfacial reaction kinetics in a miscible pair of polyethylene-graft-maleic anhydride/polyethylene-co-glycidyl methacrylate (PE-MA/PE-GMA) and an immiscible pair of polystyrene-co-maleic anhydride/polyethylene-co-glycidyl methacrylate (PSMA/PE-GMA) are also studied using rheological measurement on coextruded multilayers of these polymers. The obtained kinetics is in agreement with that from FTIR spectroscopy measurement on the same system.; Comprehensive rheological measurements are done on coextruded multilayers of polypropylene/polysyrene (PP/PS) with 8, 32 and 64 layers. These measurements show strong evidence of slip at the melt interfaces of PP/PS when shear stress is above a critical value. The slip velocity is calculated and appears to be dependent on shear stress. A modified Ellis model is used to describe the relation of slip velocity to shear stress.; In addition to rheological measurements, the slip at the melt interface of PP/PS is also directly visualized. A technique is developed to imbed carbon black particles (about 1 μm) across the interface of a PP/PS bilayer sample. After shear, particles on each side of the interface move away from each other due to slip. The estimated slip velocity agrees with our rheological measurement. These studies provide the first reliable experimental evidence for slip.