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Conventional multi-material multi-layer flexible packaging offers excellent properties. However, it has recycling challenges, necessitating a shift to mono-material multi-layer flexible packaging for example all-polyethylene (PE) packaging which can be tailored through various synthesis and processing methods for different layers. In this work, we study how the key molecular properties (number-average molecular weight (M n), weight-average molecular weight (M w ), molecular weight distribution (MWD), comonomer content (short chain branching)) and machine direction orientation (MDO) process draw ratio (MDX) influence the final morphology and mechanical properties of MDO-PE films which are intended as the outer layer of mono-material all-polyethylene multi-layer flexible packaging. Five PE grades and various blends were extruded and blown into films. Selected blown films were machine direction oriented to obtain the final MDO-PE films. Furthermore, one selected PE blown film was processed at different MDO process draw ratios while keeping other process parameters constant. From the molecular properties point of view, the higher molecular weight fractions provide a higher possibility for uniform stretching whereas lower molecular weight fractions provide a higher natural draw ratio and therefore higher modulus and stiffness enhancement. Further, the results show that increasing MDO process draw ratio leads to more fibrillation and increased crystallinity. Consequently, the tensile modulus and stiffness at the higher draw ratios increase as well and are comparable to conventionally used polymers in outer layers of multilayer flexible packaging. Thus, this work demonstrates that MDO-PE films with enhanced modulus can provide sufficient stiffness for the design of outer layer of mono-material multi-layer all-PE packaging which presents higher potential for mechanical recyclability. [ABSTRACT FROM AUTHOR]

In this paper, the role of extensional viscosity in different paper coating processes was evaluated. Numerical models for the various coating application processes (blade coating, film coating, and curtain coating) were constructed to calculate the extension rate. Different rheological methods were employed to measure extensional viscosity versus extension rate for model coating colour systems. Pilot coater trials were carried out to study the performance of each model coating colour in curtain, blade and film coating. It was demonstrated that extensional viscosity of model coating colours depends on the rate of extension, and colours can be extension thickening or extension thinning. With the numerical calculation results of extension rate in coating application processes, the extensional viscosity test results of model coating colours were matched to their performance in pilot coater experiments. It was shown that increasing the extensional viscosity measured at the appropriate extension rate that exists in blade or rod metering increased blade or rod load. Misting in film coating was reduced by low extensional viscosity measured at the appropriate extension rate. Cratering in curtain coating was reduced by increasing extensional viscosity measured at the appropriate extension rate. It was further concluded that the extensional viscosity can be used to predict the coating performance only if it is measured at the prevailing extensional rate of the specific coating process speed.