The machine direction of paper. The direction in which most fibers lie in a sheet of paper.
Groundwood Pulp
A mechanical wood pulp produced by pressing a barked log against a pulpstone and reducing the wood to a mass of relatively short fibers.
Hardwood
Wood obtained from a class of trees known as Angiosperms, such as birch, maple, oak, gum, eucalyptus, and poplar. These trees are characterized by broad leaves and are usually deciduous in the temperate zones.
Hardwood Pulp
Any pulp made from a hardwood or mixture of hardwoods by either a chemical or mechanical process.
Headbox
On fourdrinier machines: A large flow control chamber which received the dilute paper stock or furnish from the stock preparation system and by means of baffles and other flow evening devices, maintains sufficient agitation of the mixture to prevent flocculation of the fibers, spreads the flow evenly to the full width of the paper machine and provides delivery of stock to the fourdrinier wire uniformly across its full width. The height of the liquid in an open headbox or the air pressure in a closed headbox provide the requisite speed of flow of the stock onto the fourdrinier wire.
Holdout
The extent to which a paper or board surface resists penetration by aqueous or nonaqueous fluids. Where the fluid involved is water or water vapor this property is usually termed Sizing. Nonaqueous fluids of concern include printing inks, lacquers, and various oils or waxes.
Hydrophilic
Readily wetted by water.
Hydrophobic
Water repellent; not wetted by water.
Hygroexpansivity
The change in dimension of paper that results from a change in the ambient relative humidity. It is commonly expressed as a percentage and is usually several times higher for the cross direction than for the machine direction. This property is of great importance in applications where the dimensions of paper sheets and cards or construction board are critical.
Integrated Mill
A paper or board mill that produces substantially all its own pulp. A partially integrated mill is one that produces some but not all of its pulp. A non-integrated mill is one that has the luxury to purchase quality pulps in the open market.
Internal Bond
The force with which fibers are bonded to each other within a sheet of paper or paperboard.
Kraft Pulp
Pulp produced by a process where the active cooking agent is a mixture of sodium hydroxide and sodium sulfide. The term “kraft” is commonly used interchangeably with “sulfate” and is derived from a German word that means “strong”.
Lignin
The noncarbohydrate portion of the cell wall of plant material; it is usually determined as the reside after hydrolysis with strong acid of the plant material, after removal of waxes, tannins, and other extractives. Lignin is amorphous, has high molecular weight, and is predomininantly aromatic in structure. It is not one compound, but varies in composition with the method of isolation and with the species, age, growing conditions, etc., of the plant. It is more or less completely removed during chemical pulping, but it is not removed by mechanical pulping. Bleaching of the pulp further removes or modifies any remaining lignin. Left in pulp, lignin causes yellowing over time.
M Weight
The weight in pounds of 1000 sheets of paper.
Machine Direction
The direction of paper parallel with the direction of movement on the paper machine. It is also called the grain direction. The direction at right angles to the machine direction is called the cross-machine direction or simply cross direction.
Machine Finish
Any finished obtained on a paper machine. It may be that of the sheet as it leaves the last drier or as it leaves the calender stack. It may also be a dry or water finish.
Machine Glazed
The finish produced on a Yankee machine, where the paper is pressed against a large steam-heated, highly polished revolving cylinder, which dries the sheet and imparts a highly glazed surface on the side next to the cylinder, leaving the other side rough – i.e., with the texture of the felt used on the machine.
Mechanical Wood Pulp
Any wood pulp manufactured wholly or in part by a mechanical process, including stone-ground wood, chemi-groundwood and chip mechanical pulp. Uses include newsprint printing papers, specialty papers, tissue, toweling, paperboard, and wallboard.
Mercerization
The process of treating vegetable fibers with an alkaline reagent, with or without tension, so as to increase their diameter, density, strength, luster, and receptiveness to dyes. Increases porosity as well.
Moisture Content
The percentage by weight of water in sawdust, pulp, pulpboard, paper, or paperboard.
Mullen
Bursting strength. So called from the name of the instrument used in the test.
Nip
The “line” of contact between two rolls, such as press, calender, or supercalender rolls. Owing to the compressibility of the felt and/or the web of paper, the “line” of contact is actually a narrow zone. Wet nip refers to those at the presses; dry nip usually refers to those at the calendars.
Opacity
The property of a sheet that obstructs the passage of light and prevents seeing through the sheet objects on the opposite side. This property is especially important for printing papers.
pH
The measure of acidity or alkalinity of a material: paper with a pH below 7.0 is considered acidic; paper with a pH above 7.0 is considered alkaline. An expression of the hydrogen-ion concentration, and thus the acidity or alkalinity, of an aqueous solution. The pH value is the negative logarithm, to the base ten, of the hydrogen-ion concentration. A pH of 7 represents a neutral solution; decreasing pH values below 7 represent increasing acidity, and increasing values above 7 represent increasing alkalinity. The pH values of hot or cold aqueous extracts are empirically correlated with properties of paper such as its permanence, its reaction with the fountain etch in offset printing, and others.
Point
One thousandth of an inch. It is used in expressing the thickness of paper or board.
Porosity
The property of having connected pores or minute interstices through which fluids may pass. It is dependent on the number of pores and their distribution in size, shape, and orientation. The porosity of paper is commonly evaluated by measuring its air permeability.
Press
In a paper machine a pair of rolls between which the paper web is passed for one of the following reasons: (1) Water removal at the Wet press; (2) Smoothing and leveling of the sheet surface at the Smoothing press; (3) Application of surface treatments to the sheet at the Size Press.
Pulper
A machine designed to break up, defiber, and disperse dry pulps, mill process broke, commercial waste papers, or other fibrous materials into slush form preparatory to further processing and conversion into paper or paperboard. It normally consists of a tank or chest with suitable agitation to accomplish the dispersion with a minimum consumption of power. It may also be used for blending various materials with pulp.
