Potential Applications of Hybrid Layered Double Hydroxide (LDH) Particles in Pulp and Paper Production

Functionalization of papermaking pulp fibers using inorganic particles was investigated as a novel approach. Different layered double hydroxide (LDH) particles were used in peroxide bleaching of thermomechanical pulp (TMP) and in oxygen bleaching of eucalyptus kraft pulp. LDH particles were also tested as binding sites for optical brightening agents (OBA) that are commonly used in paper production. The surface chemistry of LDH-treated pulps was examined using X-ray photoelectron spectroscopy (XPS) and apparent contact angle with water. Adsorbed LDH was not detected by XPS on the fiber surfaces after the bleaching trials, but it had a clear impact on the processes. LDH particles modified with terephthalate anions decreased the consumption of hydrogen peroxide and increased opacity by 3 units in TMP. Unmodified LDH particles enhanced the selectivity in oxygen delignification of kraft pulp, leading to 10% gain in ISO brightness and reduction of 2 units in Kappa number in comparison with conventional processes. Paper strength properties were unaffected in the presented system. After bleaching with LDH, the amount of anionic groups on pulp surfaces was increased. Also, the retention of OBA onto TMP fibers was improved with modified LDH particles. LDH proved to have great potential for current and prospective applications in pulp and paper manufacture.