Paul D. Fleming

Use of nanoparticle binders for paper coatings: A review

The growing interest by many industrial segments to use sustainable materials has stimulated the development of new biopolymer materials. Some of the biomaterials that have a use in papermaking and coating industry are cellulose, coating starches (modified low molecular weight grades of the native material), chitosan, soy protein, alginate, casein, zein, lecithin and cellulose derivatives such as methyl cellulose and carboxymethyl cellulose (CMC), among others (Klass, 2011). Paper grades sometimes need to be coated with these materials to improve paper printability, surface characteristics or to add extra functional properties. Printability is the main quality for high quality colour reproduction, increased ink gloss, uniform appearance or preventing print defects. It is greatly affected by paper porosity since the rate and depth of ink receptivity depends on it. Porosity is measured by the number and size of the voids within the coating layer. The voids can be controlled with different pigments, binder types, dispersing agents and additives in the coating layer.

Rheological Properties of Coating Colors Containing Biobased Latex

This paper focuses on the understanding of basic properties of water-swollen crosslinked starch nanoparticles as a function of crosslink density. The extent of their water swelling is decreased with increasing particle crosslink density and solid concentration and vice versa. This study elucidates the unique rheological properties of starch nanoparticle dispersions and paper coating formulations in comparison with water-soluble cooked starch and synthetic latex counterparts. These rheological studies extend over many decades of shear rates, using several different rheometers. Low shear viscosities were obtained using a Cannon-Fenske viscometer and a TA AR-2000 stress rheometer with double concentric cylinder geometry. Intermediate shear rate rheology was evaluated with a Hercules rheometer. High shear rates were studied with ACAV A2 ultra-high shear capillary and slit rheometers. Unlike conventional cooked and soluble starch solutions, starch nanoparticle latex dispersions are colloids that consist of internally crosslinked particles. With increasing intra-particle crosslink density these biobased colloids have been found to behave much like petroleum based synthetic latex colloids. However, at ultra-high shear their rheological properties are relatively more shear thinning compared to hard particles, including synthetic latex and pigment particles, which exhibit shear-thickening and dilatancy. The implications of the rheological data on high-speed coater runnability are discussed.