Volume 4, Number 3
Jul 1991

A Selective Glossary for the May Issue

The May issue had more technical term in it than usual, and a glossary could not be compiled in time to include it. Some of the key terms and more interesting concepts are defined below, under the article or item in which they were used. The definitions of cure and anionic trash were submitted by David A. Smith.

Smith's Letter to the Editor, p. 13

AKD - Alkyl ketene dimer, a synthetic sizing agent introduced in the 1950s and used in the form of an emulsion. It is effective at pH levels above 6 or 6.5.

ASA - Alkenyl succinic anhydride, a synthetic sizing agent first patented in 1963. It is more reactive than AKD and cures more quickly. It is effective at pH levels above 5. Both AKD and ASA are used to size alkaline paper.

Clothing - Any of the endless belts, usually of woven monofilament cloth, m which the web of paper is formed or carried through the sections of the paper machine. Includes forming fabrics (sometimes still called "wires"), dryer fabrics (or dryer felts or screens), and press felts.

Cure - Completion of the reaction between an additive and the fiber, usually as a result of temperature and storage time. Polyamide epichlorohydrin wet strength resin generally reaches 75% of its maximum efficiency before it comes off the machine. It will generally reach 100% in two weeks at room temperature. Then it is fully cured and reacted with the fiber. AKD, a reactive size, is also slow in reacting with the cellulosic carboxyl groups, so it has to cure over a period of than. To predict the eventual degree of sizing, the oven test (10 minutes at 105° C) is used. It speeds the reaction and indicates what the final test will be when fully reacted or cured.

Rosin size and alum combination (aluminate resinate) reacts in the dryer section, melts and the molecules are reoriented to give sizing (water resistance). You have immediate sizing off-machine. The reaction is complete. There is no curing!

M.G. - Machine glazed, said of a paper given a highly glazed surface by drying on a Yankee cylinder, which is a large, stem-heated cylinder with a highly polished surface.

Report of TAPPI Papermakers, p. 9

Anionic Trash - This is a relatively new term and simply means debris consisting of wood fiber, synthetic fibers, pitch, some fillers, coating contaminants, inks, dyes, pigments, etc., which are anionic in character, that is, carrying a negative charge. Many of these contaminants come from the pulp itself (pitch and bleaching residuals including process chemicals such as dispersants, defoamers, and talc) and recycled fiber contaminants (inks, coatings, latex, fillers, starches, polymers, process chemicals, fines, etc.). The problem becomes more severe as the system becomes more closed.

The "trash" can be measured using a combination of procedures including conductivity instruments and the zeta meter.

There are also cationic materials in anionic system which are positive and tend to neutralize the anionic materials.

When you have an abundance of anionic materials, which is most generally the case, you have anionic excess or trash, with the result that cationic polymers such as retention aids or wet strength resins are wasted when they are added to the system, because they have to react with the anionic materials rather than with the cellulose.

Progress in Preservation, p. 15

Maillard Reaction - Sometimes called "browning reaction." A complicated series of reactions involving carbohydrates and proteins, brought about by heating or long storage, responsible for the surface browning of bakery products and meats. It often causes browning of photographs made with albumen or gelatin emulsions, and may also affect handmade paper sized with gelatin.