Enhancing optical and mechanical properties of white top testliner through size press application of functional additives

Abstract

This study investigates the enhancement of the optical and mechanical properties of recycled White Top Testliner (WTT) papers through size press application of functional additives. Starch-based formulations containing nano ground calcium carbonate (nano-GCC), optical brightening agent (OBA), and textile dye (TD) were applied to the paper surface using a laboratory-scale size press. The treated papers were evaluated in terms of whiteness, brightness, yellowness index, breaking length, burst index, and physical properties in accordance with ISO and ASTM standards. Under the studied conditions, TD resulted in the highest measured improvements in ISO whiteness (67.6 %) and brightness (72.7 %), while nano-GCC mainly contributed to increased thickness and grammage, supporting mechanical reinforcement. OBA showed limited contribution to ISO whiteness but was effective in reducing yellowness (−16.05). Overall, the results demonstrate that size press application of advanced additive formulations can enhance both the optical appearance and structural performance of recycled-based testliner papers, providing a viable approach for improving the quality of sustainable packaging materials.