Browsing by Author "Rustal, Claude"

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Open Access
Functionalization of PP for the enhancement of adhesion between polypropylene and polyamide multilayers
(2009) Rustal, Claude; Fritz, Hans-Gerhard (Prof. Dr.-Ing.)
The aim of the present work was the production of a polypropylene/polyamide three-layer film without using any tie-layers. These films could find an application, for instance, in the packaging or medical industries. To promote adhesion between the two immiscible polymers, two strategies were used: addition of compatibilizers in the polypropylene (PP) matrix and direct functionalization of the PP matrix with reactive monomers such as maleic anhydride and glycidyl methacrylate. In the first part of the work, the main concern was the PP functionalization by reactive extrusion, using a corotating close intermeshing twin screw extruder. The grafting formulations were variied and cast films produced in order to study the influence of the functionalization components and process parameters on the materials' properties. In general, the material structure modifications due to monomer grafting induced clear impact on the physical properties. The PP degradation through β-scission during the radical initiated reaction caused a diminution of the mechanical characteristics (tensile strength and elongation) as well as the viscosity of the samples with increasing amounts of monomer and peroxide. The crystallisation behaviour was also influenced, showing an increasing crystallisation temperature. Moreover, the modified PP films showed a higher polarity than the pure resin's ones. In the second part of the study, two-layer films were pressed in order to study the influence of the formulations as well as the process parameters (temperature, time, pressure) on the adhesion properties of the PP/PA bonds. T-peel tests were used for the adhesion characterization. Differences were found between the high molecular weight and low molecular weight grafted PP/PA bonds. Hence, it appeared that the molecular weight of the grafted PP played a predominant role on the adhesion performance of the joints. This could be correlated to the cohesiveness of the PP film. Time and temperature were found to be the most influencing factors among the process parameters because they accelerated the diffusion and flow processes as well as the chemical reactions at the interface. A comparison of the two methods (direct grafting and addition of compatibilizers) in terms of adhesion showed that the second strategy led to better results. This trend was confirmed by the coextrusion trials. The variation of the layers formulations and the process parameters was performed. An improved layer adhesion was achieved by using a special coextrusion die exit system. A further challenging work should be done in order to integrate this two-step process, functionalization and coextrusion, into a one-step process.