Premixing Effect of Precipitated Calcium Carbonate with Isolated Soy Protein on Properties of Recycled Writing and Printing Paper

Paper is considered as a composite product of lignocellulosic fibers and mineral and/or organic additives. The lignocellulosic fibers shortage together with economical, technical and environmental aspects ever increased mineral fillers application in papermaking. The filler utilization in recycled pulp involve more benefits which is highly considered, recently. Therefore, effects of precipitated calcium carbonate (PCC) and its premixing with isolated soy protein (ISP) on paper properties recycled from writing and printing papers were investigated.

Pulp recycled from printing and writing papers was received from Atrak Pulp and Paper Co. stock preparation point without any additive. PCC (10, 12 and 15% based on O.D paper mass) and ISP (10 and 15% based on PCC mass) were added individually and as premixed composite to the recycled pulp. Laboratory hand sheets (60 g/m2) were made and have been compared according to SEM images, opacity, brightness, caliper, grammage, bulk and burst strength.

SEM images revealed fillers presence in paper structure and its flocculation due to the ISP polymer usage. Increasing of filler addition replacing the recycled fibers reduced caliper, grammage and burst index of paper continuously and also increased the bulk and brightness, continuously. Individually addition of ISP and without filler increased grammage and caliper and reclined burst index, with no effects on the other properties. PCC-ISP premixing drastically improved caliper, bulk and the paper grammage, but opacity and brightness were stable compared to ISP unemployment.

PCC-ISP premixing enhanced bulk, caliper, grammage, brightness and in some cases burst strength of paper from recycled printing and writing papers. Retention behavior of ISP polymer proved by scanning electron microscopy observations, in addition to the physical properties. The retention role is an important benefit regarding to several aspects of economical due to higher productivity, environmental due to the biomaterial loss reduction, and also processing features because of blockage and shutdown decrease and production rate increment. Lipophilic part of ISP is probably resulted in fiber bonding hinder and uneven the structure strengthening.