Recycling kaolin from paper waste and assessment of its application for paper coating

In the cellulose industry, the paper coating process plays an essential role in reducing manufacturing costs while increasing the quality of the products. Given that cellulose products are being used increasingly, the ability to recycle and reuse these materials might be highly beneficial in this industry. Thus, kaolin—one of the most commonly utilized ingredients in the cellulose industry that has a major impact on the final quality—was recycled from paper waste for this study. Then, to confirm the successful recycling process, the particle distribution, morphology, and chemical composition of recycled kaolin were analyzed by DLS, SEM/EDS, FTIR, XRF, and XRD. The related results verified the recycled kaolin's high purity and crystallinity. Subsequently, coatings with thicknesses of 30, 60, 90, and 120 μm were applied to paper using a suspension of recycled kaolin. Their mechanical properties (burst strength and tensile strength), permeability (air passage, the amount of which indicates the porosity of the paper structure), wettability (the contact angle can reveal the wetting ability of the paper), and water absorbance (the Cobb test) were then assessed. The pertinent findings demonstrated that applying a coating considerably improves paper quality. So, a coating with a thickness of 30 µm is superior to uncoated paper. In addition, among all the coating thicknesses, the treatment with the best mechanical strength, permeability, contact angle, and Cob value values had a coating thickness of 120 µm. The corresponding values for the tensile index, burst index, air passage amount, and contact angle are 70kNm/kgr, 3.61kPa m2/gr, 680 ml/min, and 46֯ ±2. Consequently, the 120 µm-thickness treatment was determined to be the most effective one in this investigation.