Biopolymer extrusion coatings on cardboard for sustainable packaging

Abstract

The topic of research was to find more sustainable and environmentally friendly food packaging solutions to replace fossil-based and non-degradable materials. Five bioplastics with different properties were selected for the work, which were extrusion coated onto the cardboard substrate. The aim of the thesis was to study the properties of selected materials related to packaging applications. Furthermore, the effect of the priming treatment of the cardboard, i.e. dispersion coating, regarding adhesion between the layers was investigated. The most important properties of the food packaging materials include sufficient barrier performance, durable mechanical and thermal properties and adhesion to the cardboard. The selected materials for the thesis were poly (lactic acid) (PLA), ecovio®, which is a blend of PLA and poly (butylene adipate-co-terephthalate) (PBAT), two grades of poly (butylene succinate) (PBS) and biobased low-density polyethylene (Bio-LDPE). PLA, ecovio® and PBS grades are both biobased and biodegradable, whereas Bio-LDPE is manufactured from renewable resources, but it is not biodegradable. The materials were processed in pilot-scale extrusion coating line to prepare samples, which were later tested in the laboratory according to the standards. The results show that Bio-LDPE had the best adhesion results overall and especially relative to the sample thickness. Moreover, the barrier values for water vapor transmission rate (WVTR) were clearly the best compared to the other samples. The biodegradable materials were at a similar level regarding water vapour barrier performance. Oxygen transmission rates (OTR) were rather poor for all materials, PLA and PBS being the best. The mechanical results show that the elongation of Bio-LDPE was very high, which allows flexible packaging applications. Additionally, PLA had good mechanical strength and hardness but lowest elongation, thus is suitable for more rigid packaging applications. The primer coating produced the best adhesion values for PBS grades, and the improvement was significant considering converting of the materials.