Panu Tanninen

Characterisation of Pulsed-Fibre-Laser-Perforated Polymeric Food Package Films

A packaging material requires a proper interaction with regard to water vapour transmission between the product and the outside environment. For many fresh food products such as bakery goods, fruits, and vegetables, microperforation is utilised to extend the shelf life of the foodstuff and to provide better food quality. The microperforation potential of five commercial polymeric films has been evaluated using a pulsed fibre laser technique, and significant differences were found between the films in the penetration of the laser beam and in the diameter of the perforation. Breathable polymeric packaging films were prepared with an average laser power of 20 W and a pulse duration of 200 ns. The numbers of holes (80 μm in diameter) in the films were approx. 2000 holes/m2 and 4000 holes/m2. As expected, the number of perforations affected the water vapour transmission (WVT): the WVT was 11 g/m2/d for unperforated film, and 60 g/m2/d for the film with 4000 holes/m2, indicating that the fibre laser can be used successfully for microperforating this type of polymeric films. However, microscopic and microtomographic analyses revealed major differences in hole formation behaviour and in the wall structures of the microperforations.

Effect of blank pre-conditioning humidity on the dimensional accuracy and rigidity of paperboard trays

Abstract Optimization of storage conditions is essential for successful converting of paperboard. This paper investigates the effect of blank moisture content on the dimensional accuracy and rigidity of press-formed paperboard trays. The trays were manufactured from uncoated, pigment-coated and extrusion-coated paperboards and multi-layer materials using fixed process parameters. Because of the different layer structures and coatings, the paperboards showed different hygroscopic behavior. Prior to converting trials, the bursting strength of paperboards under different moisture conditions was assessed. It was found that the moisture content has only a minor influence on bursting strength, but moisture affects blank curling tendency and dimensional accuracy of the tray. A high blank moisture content led to a loss of the dimensional stability and load-bearing capacity of trays, although based on earlier knowledge it is evident that the moisture content should be high for successful press-forming. As expected, a low blank moisture content increased the prevalence of ruptures in forming but the resulting trays were stiffer and their dimensional accuracy was better. It was suggested that the increased stiffness is related to a more efficient moisture removal during the press-forming, so that the fiber network is more effectively consolidated due to e. g. the formation of hydrogen bonds.