K. Helanto: Pilot-scale filler-reinforced biodegradable coatings for paperboard packaging

Abstract: 

Environmental impact and regulation of packaging materials are topics that critically influence the adoption of alternatives to fossil-based systems that are in current use. In this context, paperboards represent suitable renewable and biodegradable options that also have the advantage of recyclability. However, the nature and structure of paperboard-based products limit their use and undermine other competitive advantages. A main reason is the limited barrier properties displayed by paperboard products. Gaining control of the transport of moisture, grease, liquids and gases is the most relevant requirement for packaging materials together with heat sealability. A possible route to achieve barrier control includes consideration of biodegradable thermoplastic polymer coatings, such as poly(lactic acid) (PLA), poly(3-hydroxybutyrate-co-3-hydroxyvalerate) (PHBV) and poly(butylene adipate terephthalate) (PBAT). However, the application of these materials needs adjustments in the processability aspects. They also affect the interactions with the packaged goods and the overall functionality, demanding the adoption of auxiliary components, including plasticizers, nucleating agents and fillers. These subjects are complex and should be examined carefully, not only from the fundamental viewpoint but for actual deployment. This thesis discusses these topics from the perspective of scalable and deployable technologies. 

The effect of mineral fillers on biodegradable polymer coatings for paperboard packaging is examined at a pilot scale. The utilized thermoplastic polymers included PLA and PLA-based blends, PHBV and PBAT. The fillers introduced to the polymer matrices included talc, kaolin and calcium carbonate. Production processes typical of the packaging industry were contemplated, such as injection and compression moulding and pilot-scale extrusion coating. The potential of the packaging materials and their combinations was evaluated from the perspective of processability to the end-of-life. The addition of fillers benefited processability in the extrusion coating process by reducing neck-in and improving adhesion formation. As a drawback, they contributed to the formation of pinholes at lower coating weights. The barrier properties of intact films and coatings were improved, whereas the introduction of the fillers did not significantly impact on the biodegradability characteristics. This thesis provides insights on the filler-reinforcement of biodegradable polymers and their utilization as coating layers. This work is expected to serve as a guide for future developments of sustainable extrusion coatings for paperboard packaging.

Opponent: Technical Service Specialist Dr. Janet Preston, Imerys Minerals, UK

Supervisor: Professor Orlando Rojas,  Aalto University, Department of Bioproducts and Biosystems

Link to electronic thesis: Pilot-scale filler-reinforced biodegradable coatings for paperboard packaging