Press‐formed paperboard food packages were heated and cooled to study the humidity effect on the packages with a series of dimension measurements. The empty packages in the form of trays were pre‐dried or preconditioned before their packing with oatmeal, and heating humidity of the packages was altered to find the optimal storing and heating conditions for improving the dimensional stability of the trays. The dimension measurement results showed aggravated dimensional stability of the trays during the heating and cooling. Pre‐drying and low heating humidity were observed to reduce the impact of the humidity effect on the packages, and the humidity effect was linked to the material moisture content change. The dry storing and heating humidity were concluded to enhance the dimensional stability of the press‐formed paperboard food packages. Use of the dry storing condition was found necessary to mitigate the humidity effect in the heating and cooling of the food packages.

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Dimensional measurements were recorded to observe the durability of press-formed paperboard trays used for food processing via heating and cooling of the paperboard trays containing oatmeal. A set of the studied press-formed paperboard trays were dried before being heated, and a set of the paperboard trays were heat-sealed before being cooled to compare the effects of drying and sealing on the durability of the tray. In addition, empty trays were heated to observe the impact of food processing conditions on its durability via leak tests with a colouring solution as well as optical analysis of the material coating on the surface of the trays. The drying process of the trays was observed to improve the dimensional stability of the trays while being heated, and heat-sealing the trays yielded a major positive impact on the dimensional stability of the trays while being cooled. The leak tests and optical analysis results on the heated empty trays showed a negative durability impact from the food processing conditions. It was concluded that adjusting the heat-sealing parameters and food processing conditions is necessary in order to achieve improved durability of the press-formed paperboard trays for food processing purposes.

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The dimensional stability of press-formed paperboard trays was investigated during heating and cooling of trays packed with oatmeal. Female mold tool temperature, dwell time, pressing force, and blank holding force were altered in the press-forming of the trays to observe their impacts on the dimensional stability. Dimensional measurements of the trays showed reduced tray width, and the trays exhibited distortions on the tray flange and outer wall. The results showed smaller effects on the tray length, parallel to the machine direction of the material. Improved dimensional stability of the trays was found with a 180 °C female mold tool temperature, a 600-ms dwell time, a 150-kN pressing force, and a 1.44-kN blank holding force. The optimal press-forming parameters were concluded to enhance bonding of the paperboard fibers during the press-forming. The optimization of the press-forming parameters was found necessary to reduce the observed negative response of the material to the challenging environmental conditions in the production of prepared food.

The press-forming process and the effects of parameter variation on the forming process have attracted great interest lately. The dimensional accuracy of the formed trays and the rigidity and stability of the packages are crucial factors for functionality in packaging lines, especially in fast operating machinery. The torsional stiffness of trays must be at a sufficient level to ensure the functionality in subsequent processes and logistics. The objective of this study was to develop and build a device for measuring the torsional stiffness of whole tray packages, to verify its functionality and to investigate the effect of heat load transferred to paperboard material on the torsional stiffness of the formed trays. The operation of the novel torsional stiffness tester was confirmed, and the tester was found to be suitable for measuring the thermal response of the sample materials and the effect of the fibre direction. Thus, the analysed material does not need to have a homogeneous stiffness property since the differences are noticeable in the measurement results. In addition, the results indicate that tray blanks should be die cut in the machine direction of the paperboard. The torsional stiffness of the tray packages increases, and the outer dimensions decrease as a function of the heat input. The first feature is desirable for packaging functionality and the second feature can be compensated by competent packaging design. To conclude, the use of higher mould temperatures is recommendable if the integrity of the package material is not compromised.

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Liquid package board (LPB) packages typically have the smallest global warming potential compared to other package solutions, but recycling of the integrated plastic and aluminum fractions of the packages is still limited. In the fiber recycling process the plastic and aluminum fractions with some residual fibers are concentrated to the repulping reject (Polyal). This study investigates composition and properties of repulping rejects from recycling of separately collected LPB packages. The rejects were modified in different ways, hot pressed, grinded and finally compounded with a twin screw extruder. Compositions of the compounds were characterized with Differential Scanning Calorimetry (DSC) and Thermogravimetric Analysis (TGA) and their properties were studied with tensile testing and melt flow rate (MFR) measurements. All studied compounds had relatively good processability and mechanical properties. Properties of compounds were improved by extraction of residual fibers