Enhanced Internal Coating Structure and Light Reflectance of Coated Papers: A Sludge Valorization Process

Abstract

Paper mill sludge (PMS) is a high-volume waste of the pulppapermaking industry, containing cellulose fibers. This paper introduces cellulose nanofibers extracted from PMS (CNFs PMS ) and their application in paper coatings using a wire-wound coating method to enhance internal and optical properties of paper. Three factors were investigated: (i) CNFs PMS amount, (ii) number of layers, and (iii) surface treatment via a 4 × 2 × 2 factorial design. The experimental responses were tracked by fundamentally important internal properties including porosity, air permeability, thickness, roughness, and optical properties of brightness, gloss, and CIE L*a*b* color coordination. The results showed that CNF PMS enhances porosity to 91 mL/ min, permeability to 0.5 × 10 −3 μm 2 , and gloss to 29.5 at 1 wt % CNFs PMS applied in two layers with 500 pli calendering. Roughness improves to 2 μm at all levels of CNFs PMS applied to two layers with 500 calendering. CNFs PMS prevents a decrease in brightness and improves lightness, suggesting more colors can be produced in printing applications. The utilization of PMS for papermaking applications can add value to these underutilized residues and open a new revenue stream by reusing it as a high-value material.

Impact of optical brightening agents on alkali‐based inks in packaging: A comparative study on color accuracy

“…Paper samples with different porosity index can affect the absorption rate and ink leveling, causing a change in color appearance and colorimetric readings. 12 When a substrate has a high porosity, it can absorb liquids more quickly and deeply into the paper fibers, changing ink film thickness and leading to different colorimetric readings compared to a less porous substrate. Using Equation 1, the porosity index was found to be 0.12 for OBA paper and 0.09 for the non-OBA paper.…”

“…In the printing industry, color management is often achieved based on color space defined by the International Commission on Illumination (CIE) in 1976 by 12 This process is incorporating colorimetric coordinates into printing process control initiatives is commonly referred to as "printing to the numbers". 11 However, physical properties of various substrates, including basis weight, porosity, wettability, together with optical properties such as brightness, whiteness, color, and lightness can also have impact on color reproduction capabilities.…”