Correlation between process conditions and mechanical film properties in foamed multilayer blown films

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In the context of packaging with films, specific mechanical properties are of paramount importance. This can be achieved through the implementation of optimized manufacturing processes and the efficient utilization of raw materials. The foam extrusion process has the potential to enhance material efficiency. The foam structure impacts the mechanical properties due to replacing force-conducting material. Blown film extrusion represents a predominant production process in the packaging field, offering the potential for cost-effective mass production. Integration of these processes gives rise to intricate behavior patterns, attributable to interactions between the conditions governing the blown film and those governing foam extrusion. This affects the density reduction and the mechanical properties of the material. This study’s objective was to identify the significant parameters affecting mechanical properties and to gain insight into the mechanisms influencing the foam blown film process. The results demonstrated that combining foam and blown film extrusion markedly reduces the resulting film density, with a potential savings of up to 40% in plastic at 7% blowing agent content. The optimal conditions to produce small-cell foam structures include high die pressure gradients, which can be achieved by lowering the blown film die head temperature or increasing the mass flow rate of the foamed middle layer. Tensile stress and Youngs modulus decrease with increasing blowing agent content, as the gas-filled cells reduce structural integrity. Thinner films often show higher tensile strength due to better molecular orientation. At the same time, the mass ratio influences the mechanical properties by changing the polymer structure and cell distribution, which optimizes or weakens the mechanical properties. The study presents significant insights into the blown film foam extrusion process and investigates the correlations between density reduction and the resulting mechanical properties.