Flexo printability of agro and invasive papers

Countries with scarce soft and hardwood resources have been utilizing the non-wood based lignocellulosic biomass (mainly straw or bagasse), besides for bioenergy also for paper production. The increasing demand for wood-based bio solutions (energy and chemicals like lignin) have put cellulose for paper making under pressure. Paper producers are actively looking for alternatives for these purposes, especially for fibre-based packaging. In this study we have tested the flexo printability of six different papers partly made from invasive plants: Japanese Knotweed, Black Locust, Canadian Goldenrod, dedicated crop Miscanthus, and agro-residue Tomato stems and from industrial waste jute bags fibres. All the papers were produced on a pilot-scale paper machine. Fibre and paper properties were analyzed to determine the flexo printability, runnability and durability parameters. We have measured the paper smoothness and roughness, fibre orientation, formation index, surface energy, penetration dynamics and coefficient of friction were determined for runnability and additionally print gloss, mottling and ink rubbing were determined to test printability and durability. From the measured paper properties surface roughness/smoothness, surface energy and short time limit liquid absorption had the largest correlation with printability parameters, while the coefficient of friction and formation index did not correlate with the printability and convertibility parameters. All samples were printable with water-based flexo printing technology. Samples with lower surface energy had lower porosity and liquid penetration was slower, while samples with higher surface energy were more porous, which resulted in higher print gloss. These characteristics influenced the colour differences where consequently where the highest colour difference after ink rubbing had the Jute fibre paper which had low surface energy and porosity. [GRAPHICS] .

Automated summary

This study tested the printability of six different papers made from invasive plants and industrial waste, and found that the surface roughness/smoothness, surface energy, and liquid absorption had the largest correlation with printability parameters.