Oil and grease barrier properties of converted dispersion-coated paperboards

Sami-Seppo Ovaska Oil and grease barrier properties of converted dispersion-coated paperboards Lappeenranta 2016 92 pages Acta Universitatis Lappeenrantaensis 719 Diss. Lappeenranta University of Technology ISBN 978-952-335-008-3, ISBN 978-952-335-009-0 (PDF), ISSN-L 1456-4491, ISSN 1456-4491 Changes in consumer habits and the replacement of solid trans fats in foodstuffs with unsaturated fats have increased the demand for low-cost grease-resistant packaging materials worldwide. Taking into account the global aim to reduce our dependence on oil-based plastics, new bio-based solutions are needed to meet the demand for sustainable packaging solutions, and the development of such materials was the focus of the work reported in this thesis. Pigmented dispersion barrier coatings were prepared using a blade-coating technique on commercial solid bleached sulphate paperboard. The coatings consisted of a bio-based component, hydroxypropylated starch or hydroxypropyl cellulose, a styrene-butadiene latex binder, and talc. The grease resistance in terms of time taken for a model grease to penetrate the coated paperboard varied between a few hours and several days, depending on the coating composition and on the ambient temperature during the test. Particular attention was given to coatings that prevented oil to penetrate the whole 24 h test period described in ISO 16532-1. The feasibility of producing barrier-coated boards was studied from the viewpoints of the finishing and converting processes and their end-use applications. The findings suggested that corona treatment should be used with caution if the board is to be printed, since it may cause a drastic decrease in oil penetration time due to strike through that occur if the voltage of the discharge is sufficiently high to change the electrical conductivity of the sample. The oil barrier was impaired regardless of whether the uncoated or the coated side of the board was treated with corona. Moreover, the coatings did not prevent the occurrence of reverse side effects. Unexpectedly, contact angle determinations suggested that exposure to heat in converting processes may even improve the oil repellency of dispersion coatings containing pigments due to the migration of latex towards the outer surface. Migrated latex also induced self-healing of the coating, according to scanning electron microscope (SEM) images that indicated the disappearance of pinholes. The oil and grease resistance (OGR) was, however, dependent on the oil viscosity and fatty acid composition. Particularly with moderately grease-resistant samples, the penetration time of pure coconut and rapeseed oils was considerably longer than that of their mixtures. Finally, press forming of paperboard led to a decrease in oil penetration time, but none of the studied coating compositions completely lost their barrier properties. The developed coating formulations seem to have a potential in many commercial sustainable packaging applications in a transitional period before implementation of completely bio-based coatings on an industrial scale. Potential uses may include e.g. instant meal trays and fast food packages, but particular attention should be paid to the effects of converting and finishing processes on the physical and barrier properties of the materials.