Application of Nano-sericite to a Colloidal Silica Microparticle Retention System

Sericite is a mica mineral mined in southeastern Taiwan, a naturally swelling inorganic layered material having high negative charges on the plate surfaces and a high aspect ratio, it was found to be a functional filler pigment enhancing retention of fines and chemicals in papermaking wet-end. In this study, we examined the effect of using nano-sericite in a nanoscale colloidal silica micro- particle retention system on the drainage, first-pass retention (FPR) and ash retention. Under a typical colloidal silica micro-particle retention dosage and calcium carbonate filler loading of 25%, dynamic drainage jar (DDJ) was used to evaluate the effect of adding to the microparticle system varying amounts of nano-sericite at 0, 300, 400, 500, and 3500 mg kg-1 to dry pulp on the wet-end performance. The experiments were conducted in 2 stages, with trial and error tests in the first stage; including a condition of mixing 500 mg kg-1 nano-sericite (to dry pulp) with 3000 mg kg-1 colloidal silica (to dry pulp) before adding to paper stock. The second stage was the optimization of the initial best conditions. The results indicated that incorporating nano-sericite could act as a complimentary agent to the dual system, under adequate conditions, not only ash retention was enhanced; drainage time was reduced as well. Premixing of the nano-minerals gave better results than the separately added system. A 4-stage reaction mechanism was proposed to explain the results. Overall, when sericite dosage was under 400 mg kg-1 to dry pulp, the first-pass retention attained was 80.1~83.5%; and ash retention increased with increasing nano-sericite dosage which reached 54.0% at 400 mg kg-1 to dry pulp level. And at nano-sericite dosage of 500 mg kg-1 to dry pulp, these retentions were 85.8% and 66.9%, respectively.