INSULATING BOARDS AND BLANKETS

Both insulating boards and insulating blankets or quilts are sometimes made of wood pulp. Among the types of this base it is estimated that 80 percent use ground-wood pulp, that 20 percent use sulphate pulp, and that not more than 2 percent use sulphite pulp. The semichemical process, developed by the Forest Products Laboratory (U.S. Forest Service), Madison, Wis., has been found to be particularly adaptable to the making of wood-pulp insulation.

Insulating boards and blankets (1) should have low thermal conductivity, (2) should be moisture resistant, (3) should be fire resistant, and (4) should be vermin and insect resistant. The wood-pulp product, when chemically treated, answers all of these requirements. At least 14 types of insulating board and at least one type of insulating blanket are now being made of wood pulp. The blanket is made of ground-wood pulp and pulp-mill screenings. It is dark brown in color, fluffy in texture, and the fibers are matted tightly so that it can expand after being put in place.

VULCANIZED FIBER

Vulcanized fiber, or hard fiber, made by treating an unsized, unloaded rag or wood-pulp paper with zinc chloride, is a product with which we are all familiar; though few of us realize, perhaps, that this hard-fiber product is in any way connected with paper. The pulp is given a special beating and the zinc chloride treatment; subsequent washing, drying, and aging sometimes take as long as 6 months. Soft papers shrink into the harder fiber products.

Vulcanized fiber is used as electrical insulation, also for handles, bushings, cogs, gears, angle plates, and trunk fiber, and for barrels, boxes, and baskets, where a hard, durable product is desired. Some types of this fiber are as hard as steel.

PLASTICS

Wood pulp, as almost everyone knows, is frequently molded into such articles as picnic plates, egg-case fillers, bottles, and jars. It is probably not so well known, however, that wood pulp may be the base of the beautiful powder-puff box, glove box, or pastel-colored backs of the toilet articles so much admired. In the nitrocellulose type of plastics wood pulp is frequently used as the base material. In that pink, green, or purple-colored bathroom drinking cup, too, and in that pastel-colored brooch, buckle, or clip, there may be large proportion of wood pulp; for the urea-formaldehyde type of plastic frequently uses a highly refined wood pulp, finely cut, as a filler.

SHIPPING CONTAINERS

The shipping container of today is frequently made of paperboard. Indeed, the growth in the use of the paperboard container has been so rapid and the use of this type of container has become so extensive that the subject could not well be omitted here.

The fiber shipping container was introduced to the commercial world only about 28 years ago. In 1910 there were but 20 manufacturers of such containers in the whole United States. By 1935 this number had grown to 132 companies, cperating 217 plants. Today many

products of the corner grocery or the corner drug store come from the manufacturer in fiber containers. Canned goods, electric-light globes, cured meats, bottled goods, and toilet paper are some of the products received in fiber shipping containers. Efficient design and ease of opening have been factors in extending the use of the fiber or paperboard container.

Fiber shipping containers fall into two general classes: (1) the corrugated-board container and (2) the solid-fiber container. The corrugated container is made from a board constructed by firmly fastening, between two liners, a corrugated or fluted inner member made of

Figure 8.-Apples are now packed in fiber containers. Fiber containers are also used for packing eggs, dressed poultry, celery, tomatoes, grapes, and numerous other agricultural products.

straw, kraft, or similar pulp. The solid-fiber container is made from a board constructed of two liners between which is pasted solid chipboard, making a flat, laminated board.

Not all paperboard containers are made of wood pulp, however. As a matter of fact, until recently strawboard had been used almost exclusively in the manufacture of the corrugated sheets, and until recently paperboard containers had never been entirely of woodpulp. Southern mills are producing more and more container board of kraft pulp, however, and it is probable that the use of kraft board in shipping containers will continue to increase. Liners may be made of kraft pulp, but they may also be of "jute." The "jute liner," the type most commonly used today, is made of a mixture of kraft pulp and waste papers.

OUR COMPARATIVE PRODUCTION AND CONSUMPTION

World production of wood pulp in 1936 approximated 23,000,000 short tons. Of this amount the United States produced 5,700,000 tons, or approximately 25 percent. The United States imported approximately 2,300,000 tons of foreign-produced pulp to add to the domestic supply and exported less than 200,000 tons. It is quickly seen, therefore, that for the year 1936, our domestic consumption of wood pulp not only exceeded domestic production, but that it approximated one-third of the world production. It is also seen that relatively little wood pulp was exported.

Our position with respect to paper is even more impressive. We produce nearly half of the world's total production of paper and con

Figure 9.-Production of paper and paperboard in the United States, 1909-1936.

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sume slightly over half of this production. We consume annually over 200 pounds per capita, a figure which far exceeds that of any other nation in the world.

The population of the United States is steadily increasing, and our per capita consumption of paper is increasing. We would expect, therefore, to see just what is shown in figure 9, namely, an increasing production of paper. From 1909 to 1936 the production of tissue paper, of book paper, and of wrapping paper increased gradually and consistently. The increase in the production of paperboard, however, has been almost phenomenal. The item that has pushed up the paperboard production is container board, used extensively in packaging. There is no way of telling to what heights the production of container board may rise.

4 World Wood Pulp Statistics, published by United States Pulp Producers Association, 122 East 42d St., New York, N. Y.

PRESENT-DAY MANUFACTURING METHODS

RAW MATERIAL

It is physically possible to make pulp for paper from any plant the fibers of which will felt or mat to form a sheet. In early times paper was actually made, on an experimental basis, from potato vines, thistles, cabbage stalks, corn husks, and a wide variety of other products. Pulp for paper and paperboard is also made from waste

paper.

FACTORS INFLUENCING SELECTION

Though, technically, pulp for paper can be made from a wide variety of raw materials, numerous practical and economic factors must be considered. A plant or material might, for instance, make a suitable pulp; but (a) it might not occur in sufficiently large quantities for practical use; (b) it might not contain a sufficiently high proportion of the desired fibers to make its commercial use feasible; or (c) the cost of collecting the raw material and transporting it to the place of manufacture might be too high. In deciding on the type of raw material to be used for paper, major factors to be considered are (1) dependability of supply, (2) cost of collection, (3) cost of transportation to the pulp mill, (4) seasonableness of supply, (5) cost of storage, particularly where the raw material supply is seasonal, (6) deterioration of stock during storage, and (7) the yield of usable fiber per ton or per cubic foot.

CHIEF MATERIALS USED

The more important types of raw materials which are used or advocated for use in pulp for paper are (1) wood, principally of spruce, pine, true fir, and hemlock; (2) waste paper; (3) stem or bast fibers, such as flax, hemp, cornstalks, and straw; (4) seed-hair fibers, such as cotton; (5) leaf filler, such as sisal, manila hemp, and pineapple-leaf fiber; and (6) fruit fiber, such as the fiber of the cocoanut. Some of the economic factors mentioned weigh heavily against the practical use of some of these raw products for pulp. By and large, wood fibers, cotton or linen fibers, waste paper, and straw are the raw materials which are today most used by our domestic paper-making industry.

MANUFACTURE OF PULP

The three major types of pulp used in paper manufacture are wood pulp, rag pulp, and straw pulp. In this discussion passing mention will also be made of pulp from jute, hemp, cornstalks, flax straw, and cotton linters; however, from the standpoint of quantity, wood pulp is by far the most important pulp manufactured. Rag pulp comes next in quantity manufactured, but there is a wide gap between the amount of wood pulp manufactured annually in the United States and the amount of rag pulp manufactured. There is also a gap

between the annual output of rag pulp and of straw pulp, but this difference is relatively small.

WOOD PULP

The wood for pulp is received at the pulp mill in the form either of pulpwood or of unbarked logs. Pulpwood is usually 4 feet in length. It may have been barked or peeled in the woods prior to delivery to the mill; or it may be received with the bark on and have to be barked in the barking drums. At the northern mills, pulpwood may be seasoned when received, or it may be green. In the South, where warm temperatures are so conducive to fungus attack, pulpwood is used almost as fast as cut, hence is used in a near-green condition.

Figure 13.-Barking drum of the tumbling-barrel type. The blocks of pulpwood enter at one end and, as they are tumbled against one another, gradually work their way along the drum to the discharge end. The bark falls through the slots which run lengthwise of the drum.

Logs, when received, are of standard lengths and are unbarked. In the Pacific Northwest it is common practice to receive hemlock logs in this form. The log is cut into short lengths and is barked by tumbling in a barking drum; or if too large for such handling, it is broken down into smaller sizes on a head saw, and the bark is removed afterwards.

There are, of course, exceptions to and variations in these general practices; as, for instance, with the mill using sawmill waste. By and large, however, the above practices prevail.

PULPING PROCESSES

Wood is pulped by five commercial processes, one of which is purely mechanical, three of which are strictly chemical, and one of which is semichemical. These are known as (1) the mechanical or ground