Advances in printing technology have posted serious problems for the deinking industry. When ink is fused, as in laser printing and the photocopy process, when water resistant binders are included in coatings or ink formulations, and when varnishes are applied to printed papers, conventional methods fail to disperse inks and specks. The objective of this article is to review different approaches available for removing these inks and specks. Copying processes, coatings, and varnishing processes are discussed prior to discussing deinking and speck removal processes.

Deinking ideally involves intense mechanical, chemical, and thermal action needed to detach non-dispersible inks from fibers. The detached ink is then removed by screens, cleaners, washing, and the flotation process. If higher brightness and cleanliness are desired, high-consistency dispersion, together with bleaching or the use of agglomerating chemicals (for photocopy-laser toners), may have to be considered. For coating specks, increasing the pH. increased pulping time, and removal by cleaners are typically used to reduce the number and size of specks. Varnish specks can be more difficult to remove than coating specks, as they are resistant to chemical treatment and are not easily removed by centrifugal cleaners. Flotation removal holds promise for removing varnish specks if particle size is controlled.

A variety of adhesive contaminants (“stickies”) are encountered in wastepapers. They are broadly classified as hot melts, pressure-sensitive adhesives, and lattices. Their properties and control methods are discussed. Specifically, control methods include furnish selection, improved pulping and deflaking, well-designed screening and cleaning systems, and dispersion and additives to detackify or stabilize stickies, or both. A new technology is also discussed regarding it's possible application for controlling stickie contaminants. Test methods for measuring stickies are also reviewed.

When faced with bleaching recycled fibers, the technologist must consider the usual factors associated with the bleaching of virgin fibers plus additional factors introduced by recycling. The lignin content of the furnish and the products to be made determine whether delignifying or lignin-preserving agents are to be used. Factors introduced by recycling include mixed lignin contents, dyes, residual ink particles and carrier chemicals, contaminants, color reversion, and hornification (which affects accessibility of chromophores to bleaching reagents). In addition, the technologist must be concerned with the environmental impact of the bleaching operation.

Dithionite and formamidine sulfinic acid are effective lignin-preserving reductive bleaching agents for recycled fibers. Hydrogen peroxide is an effective lignin-preserving oxidative agent, but heavy metals and enzymes catalyze its decomposition. Chelating agents have an important role in decreasing metal content. For some delignification and effective removal of organic chromophores, oxygen and ozone show promise. Research on the use of oxygen-based oxidative bleaching agents is intense because of their favorable environmental attributes.

Microbial enzymes can enhance the properties of virgin pulps and secondary fibers. Enzymes added to pulp slurries at key steps during fiber processing alter structure and composition of native substrates in specific ways. Lipases hydrolyze fatty acid esters thereby facilitating depitching and deinking. Cellulases remove fines and change surface properties, thereby enhancing drainage, deinking, and contaminant removal of secondary fibers. The binding domains of cellulases exfoliate or roughen the surface of cellulose fibers. This feature may be used to enhance inter-fiber bonding. Xylanases and ligninases enhance lignin and chromophore removal thereby facilitating bleaching of kraft pulps. Microbial xylanases reduce chemical demand for bleaching by 35 to 50% in softwood and hardwood pulps, respectively. Many extracellular microbial enzymes are stable at 50 to 60°C and between pH 4 and 7, and some function well at greater extremes. In some instances crude enzymes can be used, but by cloning and expressing pure enzymes at high titers more precise and economical applications can be achieved.

This paper discusses the use of a new rhombohedral precipitated calcium carbonate (PCC) morphology and existing PCC morphologies in wood free, wood containing, and recycled paper. The new material has properties that mimic TiO2 with respect to morphology, particle size, particle size distribution, and surface area. TiO2 is widely used by the paper industry as a functional filler for opacity and brightness. The new PCC rhombohedral morphology can be used in place of TiO2 for many applications greatly reducing the cost of production.

The physical properties of the new PCC morphology as well as application as a paper filling pigment will be discussed.