Process Control for Biowax Impregnation of Recyclable Packaging Papers with Enhanced Water and Oil Barrier Properties

The industrial processing of innovative packaging papers with enhanced barrier properties has become ever more challenging due to the more stringent regulations on single-use-plastics (SUP), with extended applicability to coated papers. Although traditional packaging papers are based on renewable sources, they do not provide water and oil resistance and require the deposition of extruded polymer films or dispersion coatings that interfere with the paper recycling process. In this study, the impregnation of paper with biowax rendered barrier properties with enhanced water and oil contact angles. However, the close control of processing conditions on an industrial pilot line is critical in producing optimized product quality. Therefore, the effects of material grades and processing conditions were more closely monitored through design of experiments, allowing us to increase product performance and enhance flexibility for processing different material grades. In particular, variations in surface properties of the base paper, wax content, and control of processing temperatures were related to the oil and water contact angles. It was concluded that variations in base paper roughness should be considered for the efficient uptake and impregnation of wax, while contact angles are a good indication of the penetration of wax in the paper bulk. The increase in oil contact angles up to 60° further relates to the enhanced grease barrier properties of the impregnated paper. Although an improvement in water contact angles up to stable values of 116° was obtained, this is not predictive for a similar improvement in oil contact angles, while it perfectly relates to the wax coverage and surface roughness. The relations between performance in barrier properties and wax coverage on both impregnated and non-impregnated paper sides are finally confirmed through a qualitative description by spectroscopic analysis.