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MODIFIED WOODSBy

R. M. SEBORG, Chemist

HAROLD TARKOW, Chemist

and

A. J. STAMM,2-Chemist

Forest Products Laboratory, ! Forest Service

U. S. Department of Agriculture

Abstract

Chemical and physical treatments of wood are described that modify the

dimensional stability and mechanical properties of wood. The main emphasis,

together with commercial applications, is given to the product made by

phenolic -resin impregnation.

Introduction

Considerable research has been done to improve the utility of wood by

modifying its properties by chemical, thermal, and compressive treatments.

Some of these treatments involve permeating the wood with synthetic resinforming chemicals; one consists of forming a cellulose derivative of the

type used in plastics; another takes advantage of the plastic properties of

lignin; and still others, although the materials they employ have no more

plastic properties than the original wood, form cross linkages of the type

sought in plastics. Because of these various methods of modifying wood, it

appears desirable to consider each method and its product collectively.

I

-The original article by A. J. Stamm, "Modified Woods," first appeared in

the 1948 edition of Modern Plastics Encyclopedia.

Now research professor, School of Forestry, North Carolina State College,

Raleigh, N.C.

:-'jaintained at Madison, Wis., in cooperation with the University of

Wisconsin.

Report No. 2192 (Revised)
Dimensional Stabilization

Most of the efforts to modify wood have been directed toward increasing its

dimensional stability under varying conditions of temperature and humidity

that reduce the stability of the wood in service. The successful procedures

for this purpose have involved one or more of the following methodsi

(1) Coating the external or internal surfaces of the wood with water-insoluble

materials to retard the rate of moisture loss or gain; (Z) depositing bulking

agents within the cell walls to block normal shrinkage; (3) chemically

replacing the hygroscopic hydroxyl groups of cellulose and lignin with less

hygroscopic groups; and (4) forming chemical cross bridges between the

structural units.

It is possible to reduce both the final equilibrium swelling and shrinking and

the rate of swelling and shrinking by the last three methods. Unfortunately,

however, reductions in the final swelling and shrinking have not been

attained by the coating method. All known coatings that adhere to wood allow

the passage of some moisture. Internal coatings are in general less effective

than external coatings, as it is impossible to coat completely all of the

microscopically visible capillary structure (38). ± One thick, continuous

surface film is more effective in blocking the passage of water than numerous

imperfect internal films. On the other hand, while good surface coatings,

such as synthetic resin varnishes and aluminum paints, do retard the rate

of moisture absorption sufficiently to minimize the steepness of moisture

gradients within the wood and subsequently to reduce the stresses that cause

grain raising, warping, and checking (4, 11), they do not prevent the

aggravating swelling, such as that of drawers and doors, that occurs during

prolonged periods of high relative humidity.

Superficial internal coating of wood with so-called "water-repellants" has

been advocated. The effectiveness of these materials in stabilizing the

dimensions of wood is, however, less than that of the better surface coatings,

so that their range of usefulness is limited (5).

The second method for stabilizing the dimensions of wood is to keep the wood

in a partially or completely swollen state by the bulking action of chemicals

deposited within the cell-wall structure. This can be accomplished by

impregnating the wood with water-soluble chemicals such as water-soluble

salts (33), sugars (2,36), and polyethylene glycol (39), or with waterinsoluble chemicals. Of the water-soluble chemicals used to stabilize wood,

-Underlined numbers in parentheses refer to Literature Cited at the end of

this report.

Report No. 2192 -2-
only polyethylene glycol is used commercially. The treatment of wood with

polyethylene glycol and its applications will be discussed later.

The treatment of wood with water-insoluble chemicals can be accomplished

either by (1) replacing the water in the wood by a mutual solvent for the water

and for the wax or resin with which the wood is to be treated, and then

replacing the mutual solvent with the wax or resin; or (2) by insolubilizing

a water-soluble material within the cell-wall structure. Procedure No. 1

has been successfully carried out on small specimens of wood by using

ethylene glycol monoethyl ether as the mutual solvent, or intermediate

replacing agent, and various waxes as the final bulking agent (35, 41).

This procedure, although reasonably effective for reducing the swelling and

shrinking, is, however, too involved for commercial use. Procedure No. 2

involves the formation of water-insoluble synthetic resins within the cellwall structure of the wood. This is accomplished by impregnating the wood

with a water-soluble resin solution and then heating the wood to insolubilize

the resin (43). This latter procedure (resin treatment) has proved quite

practical and is at present the most important commercial method of

dimensionally stabilizing wood (32, 45,46).

Resin Treatment

Many resin-forming systems have been tried, but none has been found so

effective as a water -soluble phenol -formaldehyde resinoid. The molecules

of the water-soluble resinoids have been formed from the phenol and

formaldehyde molecules with such slight polymerization, or change in

character of the molecules as they are formed in the new resinoid substance,

that they remain small enough to penetrate the cell-wall structure readily;

and because of the high polarity of the slightly polymerized phenol and

formaldehyde molecules, the wood is swollen beyond its maximum swelling

in water. Such swelling is indicative of selective adsorption of the phenolformaldehyde resinoid within the intimate cell-wall structure (45,46).

Some commercial phenol resinoids have been shown to be suitable for making

uncompressed resin-treated wood (impreg) and compressed resin-treated

wood (compreg). In addition to this, alcohol-soluble phenol-formaldehyde

resinoids that have been slightly polymerized have also been successfully

used (6,9). Alcohol-soluble resins that are appreciably advanced, however,

do not penetrate the cell-wall structure and are deposited only in the coarse,

microscopically visible structure. Because of this lack of penetration, they

do not bulk the fiber and can minimize swelling and shrinking only by

retarding the rate of moisture absorption, as do coatings. Such resins have

been used in Europe in making the equivalent of compreg, but they are not

used in the United States.

Report No. 2192 -3-
Resorcinol resin can be substituted for phenol resin, but it is considerably

more expensive. Its only advantages are that the resin can be set at lowe.

temperatures and, since no acid or alkaline catalyst is needed, it offers the

possibility of obtaining a product with somewhat better electrical resistance

prope rtie s.

Cresols can be substituted for part of the phenol, but because of their lower

solubility in water they are less suitable than straight phenol and are more

expensive in the United States. Substituting furfural for formaldehyde also

reduces the water solubility of the treating system. Furfural -aniline and

furfural -alcohol systems have been tried and found to give fairly good

dimensional stabilization, but they are difficult to cure completely within the

wood. Melamine -formaldehyde resins have not been thoroughly studied as

impregnating agents for wood, because their cost is higher than that of

phenol resins and there is little likelihood that they would impart superior

properties to the wood.

Urea -formaldehyde is the only resin-forming system other than the phenolformaldehyde system that has received serious consideration for the bulking

treatment of wood. When dimethylolurea and urea are dissolved in formalin

and buffered at a pH of about 8 and cured within the wood, they stabilize

its dimensions about half as much as a water-soluble phenol-formaldehyde

resinoid in the same concentration (19). A 13-percent phenol-resin content

of the wood gives it the same dimensional stabilization as a 30-percent urearesin content. This greater stabilizing effect of phenol resin offsets any

price advantage that the urea resin may have. Urea-resin-forming systems

are further inferior to phenol systems in plasticizing the wood (before curing),

in preventing springback in compressed wood (20), and in ease of distribution

throughout the wood (21). Only a limited amount of urea-resin-treated wood

has been made commercially.

Phenol-Resin-Treated Wood (Impreg)

The term "impreg" is applied only to phenol-resin-treated wood in which the

resin has been cured within the cell-wall structure without the application of

pressure to cause compression. Impreg has been made almost exclusively

from veneer to avoid the difficulties encountered in treating large specimens

of wood. Unlike the treatment of wood with preservatives and fire retardants,

it is not enough merely to treat an outer zone of the wood when making impreg;

the resin must be distributed uniformly throughout the entire cell-wall structure to be fully effective. Furthermore, partial treatment would set up

stresses between the treated and the untreated zones, because of the

permanent bulking effect caused by the resin-forming chemicals. These

Report No. 2192 -4-
stresses would result in checking or honeycombing of the wood at the junction

between treated and untreated wood.

For these reasons, the treatment of lumber or the treatment of freshly felled

logs has not met with the success that some investigators have claimed. It

has been found that veneer of almost any species and solid wood of species

less resistant to penetration by resinoid solutions, in lengths up to 1 or

2 feet, can be treated adequately (46). With the exception of the sapwood of

a few species, wood cannot be adequately treated in lumber sizes (21). Even

if lumber could be treated adequately, the increase in cost would make the

material prohibitively expensive.

Methods of Treatment

Three different methods of treating wood to form impreg have been used.

These methods are: (1) Soaking in an aqueous phenol-formaldehyde resinforming system; (2) immersing under pressure in a resinoid solution in a

cylinder; and (3) applying water-soluble phenol resins with a glue spreader.

All methods can be used for treating veneer, but only (1) and (2) can be used

for solid wood.

Method No. 1. -- The simplest method of treating wood with resin is to soak

it in an aqueous phenol-formaldehyde system that is resin-forming. Green

wood is used rather than dry, because the resin-forming chemicals diffuse

best into the green, swollen wood structure (45,46). When thin veneer is to

be treated, it is not so important that the wood be green, because sufficient

solution is taken up by capillarity to swell the structure completely.

Unfortunately, this method is very slow, except in the case of very thin

veneer, because the rate of take-up of chemicals varies inversely as the

square of the thickness. For example, the heartwood of green sweetgum

veneer 1/32 inch thick absorbed about 35 percent of its ovendry weight of

resin-forming chemicals from a solution containing 30 percent solids after

the veneer soaked for 1 hour at 100" F. If the veneer had been 1/8 inch

thick, it would have taken approximately a 16-hour soaking.

Method No. 2. -- A more rapid means of treating, especially for thicker

veneer, is the cylinder impregnation method, which involves either pulling

a vacuum or applying a pressure, or both (38, 46). It has been shown that

very little, if any, improved treatment is obtained by pulling a vacuum

before applying pressure when treating veneer. Because the vacuum step

causes a loss of volatile formaldehyde from the inappreciably condensed

resin solutions generally used, it has been avoided. The most satisfactory

procedure is to immerse the veneer in the resinoid solution in a container

slightly larger than the sheets of veneer, and to make sure that both faces

Report No. 2192 -5-
of each ply are wetted as they are placed in the container so that no spacers

between plies will be necessary to ensure contact of the surfaces with the

solution. The plies should be weighted down and the liquid level above the

veneer adjusted so that the veneer will still be immersed after it has taken

up the desired amount of resinoid solution.

The container is then placed in a treating cylinder, in which an air pressure

of 25 to 100 pounds per square inch is applied for 15 minutes to 5 hours, or

even overnight. Cottonwood and basswood l/16 inch thick can be treated in

15 minutes at 25 pounds per square inch, while birch and the sapwood of

maple in the same thickness require about 5 hours at 75 to 100 pounds per

square inch. Other suitable species can be treated adequately under

intermediate conditions.

It has been found desirable to have the veneer take up a weight of resinoid

solution equal to the air-dry weight of the wood. In the case of birch and

maple, this is practically equivalent to filling the void capillary structure

completely (treating to refusal), while in the case of spruce and cottonwood

only 1/3 to 1/2 of the void capillary structure need be filled. This take-up

of solution will require the use of a slightly greater resinoid concentration in

the solution than the final resin content desired in the wood. A final resin

content of 30 percent of the air-dry weight of the wood can be obtained by

using a solution of about 35 percent resinoid concentration. A solution with

this concentration remains sufficiently fluid to permit thorough treatment of

the wood. It might seem advisable to treat the veneer with smaller amounts

of more concentrated resinoid solutions so as to have less solvent to remove

from the wood. The treatment, however, is never so completq and uniform

as when a relatively dilute solution is used.

Method No. 3. -- Veneer has also been treated successfully with water-soluble

phenol resins, when low resin contents are sought and the optimum of resin

distribution is not required, by applying the slightly diluted resinoid to the

veneer with a glue spreader. The amount taken up can be increased by

repeating the process several times of putting the veneer through the

spreader, and then allowing it to diffuse and dry.

Drying

When a product with maximum dimensional stability is desired, veneer

treated by any of the foregoing methods should be stacked under nondrying

conditions for a period long enough to insure uniform diffusion of the resinoid

throughout the structure. The diffusion time, before drying, will depend upon

how uniformly the resinoid is distributed during the treating process.

Veneer treated by the simple soaking method will require practically no

Report No. 2192 -6-
diffusion time, whereas veneer with a coarse capillary structure only half

filled or less than half filled by cylinder treatment, will require a deadpiling period of about I day under nondrying conditions. The treated veneer

can then be dried in a commercial veneer roller dryer or in a kiln that has

circulating air.

If dried in a veneer dryer, the treated veneer should first be dried at 175* to

260* F. for approximately 30 minutes, which will result in a moisture

content of about 10 percent. An initial low temperature (below the boiling

point of water) is used to prevent the solution and the dissolved resin from

being forced to the surface of the wood by the steam pressure developed in

the wood at high temperatures. The resin in the dried, treated veneer is

then cured by heating at a high temperature. This is a time -temperature

reaction; at 3100 F. the curing time is approximately 30 minutes. When

kiln dried, the treated veneer should be stickered to allow adequate circulation between the plies. The time required to dry and cure the resin depends

on the maximum temperature that can be maintained in the kiln and may vary

from a few days to a week or more.

Properties of Impreg

Impreg has a number of improved properties compared to those of normal

wood and ordinary plywood. When 30 to 35 percent of resin on the basis of

the ovendry weight of the untreated wood is formed within the structure, the

hygroscopicity and equilibrium swelling and shrinking of the wood are reduced

to 25 to 35 percent of normal. The reduction in swelling and shrinkage is

accompanied by a marked *reduction in grain raising and surface checking.

Figure 1 shows what can be done in protecting the surface of Douglas -fir

plywood by a suitable treatment of only the face plies.

The treatment also imparts to wood considerable resistance to decay, termite and marine -borer attacks. Figure 2 shows a Douglas -fir plywood

specimen with resin-treated faces and an untreated core ply that was inserted

in the ground for 1 year in a field in Mississippi where termite action is

severe. The termites cleaned out the untreated cores completely up to the

ground line and left the faces virtually untouched. Similar core material

that had its edges protected with a preservative treatment withstood termite

action and decay for about 3 years. Similar ground exposure panels with all

their plies treated with 30 percent of phenol resin had an average life of

12.4 years as compared to that of 1. 9 years for an untreated panel. Panels

treated with 15 percent resin had an average life of 6.8 years. Impreg

specimens with all their plies treated (30 percent resin) showed little or no

attack by marine borers after 4 years' exposure to sea water in Pensacola

Bay, Fla.

Report No. 2192 -7-
Decay-culture tests on phenol-resin-treated wood blocks show growth of

fungus on the surface of the treated blocks as well as on the control blocks,

even though the loss in weight of the treated blocks is negligible in contrast

to that of the controls (38). This growth indicates that decay resistance is

not due to the presence of a toxic agent, such as an excess of either phenol

or formaldehyde. When an excess of either of these chemicals is present,

fungi shun the block. The decay resistance of impreg presumably results

from either the reduced hygroscopicity whereby insufficient water is

permitted to enter the cell-wall structure to support decay, or from a

chemical change occurring within the wood that makes it no longer susceptible

to fungus attack, or from both. Experience to date has indicated that any

treatment that appreciably reduces its hydroscopicity also imparts decay

resistance to the wood.

The treatment of wood with phenol resin cuts down the passage of water

vapor through the panels to a marked extent (44), and greatly increases

its electrical resistance (57) and its resistance to most chemicals, with the

exception of strong alkalis. Contrary to many publicity claims, resin treatment has a negligible effect in improving fire resistance. Fire-resistant

salts, however, may be incorporated in the wood with the treating resin and

be fixed by it in the wood structure to give good fire -retardant properties.

Only a few of the strength properties of wood are increased significantly

by a resin treatment; moreover the toughness, Izod impact, and tensile

strength parallel to the grain are decreased significantly (8), facts that are

contrary to many of the publicity claims for resin-treated wood. The only

properties that are increased appreciably more than the specific gravity

are hardness, compressive strength and stiffness perpendicular to the grain.

A sugar pine specimen, with a resin content of 47 percent on the basis of the

ovendry weight of the untreated wood, increased in hardness by 85 percent (31).

To become as hard as sugar maple, the hardness of sugar pine would have

to be increased 3.8 times. Thus it would hardly pay to treat such wood with

resins if the primary objective were to increase its strength properties.

When increases in strength are sought, the wood should be compressed as

described later.

Applications

Impreg was manufactured during World War II only for military uses, one

of which was for housings for electrical-control equipment, in which the

improved electrical properties of impreg were utilized. Another use was

for treating veneer faces that would be applied to a redwood core for

laminated aircraft-carrier decking. In service tests for such purposes,

Report No. 2192 -8-
impreg showed its superiority to the normally used edge-grain Douglasfir (14). The chief current application for impreg is for making pattern and

die models. Irnpreg has practically replaced mahogany lumber for this use

in the automobile industry (32).

Phenol -Resin -Treated Compressed Wood (Compreg)

Compreg is resin-treated wood that is compressed while the resin is being

formed within its structure (47). Although a number of different resins have

been tried in making this material, none has proved so successful as phenolformaldehyde. There are two quite different types of compreg: (1) an old

form, developed in Europe, that is composed of wood treated with a spiritsoluble phenol resin prepolymerized to a stage at which it does not penetrate

the cell-wall structure and does not bond to the polar groups of the wood and,

as a result, does not stabilize the dimensions of wood appreciably; and

(2) a new form (developed by the U.S. Forest Products Laboratory) that is

composed of wood treated with a water-soluble, phenol-formaldehyde

resinoid, as in the case of impreg, so as to form the resin throughout the

cell-wall structure of the wood and to bond it to the active polar groups of

the wood. The new form of compreg is much more stable than the old,

but tends to be more brittle. All of the cornpreg now being made in the

United States is either of the new type or of an intermediate type.

The term "compreg" should be reserved only for woods that are truly

treated and not be given to laminated compressed wood that may have been

impregnated by only a very small amount of glue -line resin. Untreated

compressed wood is preferably called "dense wood" (24, 27), when made

from solid wood, or "superpressed plywood" (3, 26,56T when made from

veneer. "Dense wood" corresponds to the German material, Lignostone,

and "superpressed plywood" is similar to the German product, Lignofol (13).

English Jicwood and Jablo are of the superpressed-plywood type. The

German equivalent of compreg is known as Kunstharzschichthols (13).

Veneer for making compreg can be treated by any of the methods given under

phenol-resin-treated wood (impreg). The amount of resin used and the

uniformity of its distribution will depend upon whether maximum dimensional

stability or maximum impact strength is sought. To obtain the maximum

dimensional stability, about 30 percent of resin on the basis of the ovendry

weight of the untreated wood, distributed uniformly throughout the structure,

is desired (47). To obtain the maximum impact strength, 10 to 20 percent

of resin, with an appreciable proportion of it at the surface, is desired.

Report No. 2192 -9-
An important advantage of compreg is that it can be made from a great variety

of woods, including such normally inferior species as cottonwood, to give a

product with properties that approach the optimum values.

Assembly, Compression and Cure

The term ttcompreg" is commonly used to designate material compressed to

a specific gravity of 1. 3 to 1. 4. Compreg can, however, be made with any

specific gravity between that of impreg (about 18 percent higher than that of

the original wood) and these high values. It is suggested that the term

"semicompreg" be used to designate the material of intermediate specific

gravity.

When veneer is treated with at least 30 percent of a phenol-formaldehyde

penetrating resinoid, it can be made up into high-density parallel-laminated

compreg without the application of bonding resin between the plies, as

sufficient resin is exuded from the plies under compression to give a good

bond (6). When cross-banded compreg is made, the dried plies should be

spread with a small amount of hot-press phenol bonding resin. When

treating-resin contents lower than 30 percent are used and when the product

is to be compressed only to the semicompreg stage, a thin glue spread of

about 15 pounds per 1, 000 square feet should be used. When water-soluble

glues are spread on the plies, the veneer should again be dried to a

moisture content of 2 to 4 percent before assembly.

The pressure required in pressing compreg depends upon the resin and its

volatile contents, the degree of precure of the resin, and the distribution of

the resin throughout the structure, as well as the species of wood. Compreg

with a specific gravity of 1. 3 to 1. 4 can be made from veneer of most species

containing 30 percent of a water-soluble phenol -formaldehyde resinoid on the

basis of the weight of the dry untreated wood, by applying pressures of

1, 000 to 1, 200 pounds per square inch and a temperature of 300* F., when

the volatile content of the resinoid is between 2 and 4 percent (45, 47).

The pressure required to make semicompreg varies with the nature of the

treating resin, as in the case of full. compreg, and to a greater extent with

variations in the species. When most of the softwoods (coniferous woods)

and the softer hardwoods (deciduous woods), such as cottonwood, basswood,

and aspen, are treated with a stabilizing resinoid, they can be compressed

to two-thirds to one-half of their original thickness under pressures as low

as 250 pounds per square inch to give a product with a specific gravity of

0.7 to 1. 0 (47). Under this pressure, the same woods in the dry untreated

form or when treated and precured will compress only 5 to 15 percent.

Because of this increased plasticization of the treated but uncured wood,

Report No. 2192 -10-
plywood with semicompreg faces and either an untreated or a treated and

precured uncompressed dry core can be made in a single assembly and

compression operation without significantly compressing the core (48).

Compreg should be made up from dry treated but uncured veneer with a

residual volatile content between 2 and 4 percent. The drying of the treated

veneer must be done at temperatures (175* F. or less) which will not set

up or cure the resin in the veneer as is done in the final drying ( 30 minutes

at 310* F. ) of treated veneer for impreg. The curing of the resin in the

treated veneer to be used for compreg is done during the heating and densification process. When thick panels are made, moisture content values near

2 percent should be approached to avoid subsequent checking of the product.

Thinner material and semicompreg can be made up at a slightly higher

moisture content without subsequent checking. Compreg compressed to

specific gravities above 1. 35 is more subject to checking than a lower

specific gravity product. Hence, the highest specific gravities should be

avoided. The center of the wood should be held at a temperature of 300* F.

for 30 to 40 minutes to obtain complete cure of most of the resins. Thicker

material should be cured at a lower temperature to avoid a building-up of

the temperature at the center of the panel by the exothermic resin-curing

reaction.

Properties of Compreg

The water absorption by compreg, determined according to Military Specification (55) (a 3- by 3/8-inch specimen by 1 inch in the fiber direction after

a 24-hour immersion in watez) will range, for products of high specific

gravity, from less than 1 percent for the best stabilized compreg to 6 percent

or more for the less stabilized compreg. In all cases, a decrease in specific

gravity will result in increased water absorption.

Small blocks of the dimensionally stable form of compreg that is compressed

to a specific gravity of 1. 35 will swell only 4 to 7 percent in thickness upon

prolonged immersion in water at room temperature (47). Blocks 4 inches

square by 1/2 inch thick hardly came to swelling equilibrium when soaked

in water at room temperature for a year. When dried to the original

moisture content (about 2 percent) the stabilized material will practically

regain its original compressed dimensions, an indication that the loss of

compression is negligible.

The older form of compreg made with appreciably prepolymerized resin will

not only swell about three times as much in thickness as the stable form, but

will swell much more rapidly and also lose a large part of its compression

(47). The more rapid swelling of the less stable form is presumably due to

Report No. 2192 -11-
the fact that water is sucked into the structure as it recovers from compression, with the result that water is distributed throughout the structure

much more rapidly than by diffusion alone. The combined swelling and

recovery from compression of the specimen of the older form of compreg

1 inch long in the fiber direction may be as much as 20 to 60 percent in

several weeks. Thin cross sections will give these values in I day. Onehalf to two-thirds of this dimensional change may be due to recovery from

compression.

Because compreg swells so slowly, the old 24-hour water-absorption test

has little meaning. A new rapid equilibrium swelling and recovery test

(developed by the Forest Products Laboratory) is included in a recent

Military Specification (55). In this test, cross sections 1/8 inch wide by the

thickness of the panel by 2 inches long are measured in the thickness

direction of the original panel, then soaked in water at 70" F. for 24 hours,

and again measured in the same direction. These thin sections come

virtually to swelling plus recovery equilibrium in this period of time.

Tests have shown that when the equilibrium swelling plus recovery does not

exceed 12 percent increase in thickness, which is the newly specified

maximum, the tendency for the particular compreg to washboard in service

(exhibit uneven swelling plus recovery) without a surface finish is negligible.

Most of the compreg now made in the United States will meet this specification, although the earlier material would not.

Like impreg, compreg is fairly resistant-to decay, termites and marine

borers (38,47. Its improved electrical resistance is similar to that of

impreg (2)l. Its resistance to the passage of water vapor is appreciably

greater than that of impreg because of the practical elimination of the capillary

structure (417. The acid resistance is also improved to some extent beyond

that of impreg, due to the fact that it is more difficult for acid to penetrate

the structure (4D. The resistance of compreg to flaming is somewhat

greater thaii that of impreg because of its greater density, and it can be

further improved to some extent by incorporating phosphate salts in the

treating solution.

A high degree of polish can be imparted to any cut surface of stabilized

compreg or semicompreg with a specific gravity of about 0.8 or higher by

merely sanding the surface with fine sandpaper and then buffing it. This

potential polish exists throughout the structure. All that is necessary to

bring it out is to smooth the surface. This easy way of restoring the finish

would be an advantageous property of compreg or compreg -faced furniture

or flooring. The natural finish is highly resistant to such organic solvents

as alcohol and acetone, which destroy most applied finishes.

Report No. 2192 -12-
Compreg has a higher coefficient of thermal expansion than normal wood,

largely because of its high degree of compression. The increase is mostly

in the direction of compression and is generally about 50 percent. The

increase in the thermal-expansion values can be calculated from the resin

content and degree of compression (58).

The strength properties of compreg, with the exception of the toughness and

the Isod impact, are increased about in proportion to its increase in specific gravity. Table 1 gives strength data for parallel-laminated birch

compreg and semicompreg made with three different commercial resins (9).

The water-soluble resin B gives lower water absorption, swelling and

recovery properties than alcohol-soluble, low -molecular -weight resin A,

but also a lower Izod impact strength. The other strength properties do not

vary significantly with the different resins.

Comnpreg made with higher resin contents has greater compressive -strength

values but lower tensile and Izod impact values (8). Many of the strength

properties of compreg, such as the modulus of rupture and the modulus of

elasticity in static bending and shear, are but slightly affected by manufacturing variables and degree of cure, whereas the water-resistance

properties continue to be improved with a more complete cure (31). The

toughness and Izod impact values of compreg, however, vary considerably

with variations in the manufacturing technique and curing time (_8). For this

reason, one of these two tests should be regularly made.

The regular American Society for Testing and Materials hardness tests for

wood cannot be applied to compreg, as embedding the steel ball to the depth

required splits the wood. The hardness can, however, be expressed in

terms of the slope of the linear load-penetration curve. In this way it is

possible to make correlative measurements on both normal and densified

wood by the same method. The hardness has been shown to increase rapidly

with an increase in the specific gravity of the wood.

The resin has a minor effect upon the hardness. The hardness of untreated

compressed wood is about 20 percent less than the values for normal resintreated wood of the same specific gravity. Compreg may be 10 to 20 times

as hard as normal wood.

The abrasion resistance of compreg is significantly higher than that of normal

wood, chiefly because of the compression of the wood.

Report No. 2192 -13-
Fabrication. and Molding

Due to its increased hardness and the presence of the resin, compreg is

more difficult to machine than normal wood. In appreciable thicknesses, it

should be cut with special saws such as those used for cutting brass or plastics. Machine speeds should in general be lower than for cutting normal

wood. Compreg machines nicely and can be turned on a lathe using metalworking tools with greater precision than normal wood.

Compreg is more brittle than normal wood and most metals, although it is

considerably tougher than the ordinary molding plastics. Because of its

brittleness, objects made from it should have rounded fillets rather than

sharp edges. This is true of threads cut in compreg.

Compreg can be glued to itself or to normal wood with both hot-press and

room -temperature -setting, nonacidic resin glues. The compreg surfaces

to be glued should be lightly sanded to remove the surface gloss before

gluing (45), and when the panels are thick these surfaces should be milled

plane so as to ensure perfect contact. Glue spreads of 15 to 27 pounds per

1,000 square feet should be applied. Gluing pressures should be adequate

to get good contact, generally 150 to 250 pounds per square inch.

A simple method of molding compreg was developed by the Forest Products

Laboratory and used during World War II by manufacturers for short stubby

"club" propellers used for testing motors on the ground, and for an airplane

antenna mast, both of which were in large production. The method consists

of assembling dry but uncured resin-treated veneer with a hot-press phenol

glue under a pressure of 150 to 250 pounds per square inch at 200" to 250" F.,

which is inadequate to cure the treating resin and only partially adequate to

cure the glue (47). Although the shear strength of such a block is not great,

it is sufficiently strong to permit the block to be carved or turned in such a

manner that each of its final dimensions is obtained in one direction. The

thickness of the uncompressed block at right angles to this direction is,'

however, made from 1. 5 to 3 times the final dimension, depending upon the

original specific gravity of the wood. The block is then heated to about

250" F. by means of high frequency, placed in a split mold, and pressed,

in the direction in which it was carved, to 1. 5 to 3 times the final dimension

with the mold heated to 270" to 300" F. A slight squeeze-out, or flash, that

occurs at the parting line of the two halves of the mold must be removed.

The remaining surface requires little or no further finishing. When a

product with a uniform specific gravity is sought, the number of times the

carved thickness should exceed the final thickness must be kept constant

over the entire object. By varying this thickness multiple from one part of

the object to another, variations in ispecific gravity between any desired

parts of the object are obtainable.

Report No. 2192 -14-
A more generally applicable means of molding compreg after precompression

without the use of a press has recently been developed (52). This method,

known as expansion molding, consists of precompressing dry but uncured

resin-treated wood at about 200* to 240* F. At this temperature the wood is

plasticized by the resin-forming chemicals but the resin does not cure in

the short period involved. If the pressure is released while the wood is hot,

it springs back immediately. If cooled under pressure, however, the wood

retains its compression for months when kept dry. This uncured material

is cut to templates and laid up to fit and fill a mold. The mold is then locked

in the closed position and heated. The tendency for the wood to expand and

release the pent-up stresses exerts back pressure as high as 750 pounds per

square inch against the mold.

The precompressed resin-treated veneer can be prepared by feeding single

heated plies into a rapidly operated press, the platens of which are kept

cold. When 1/10-inch thick veneer is used, it need be in the press only

about 15 seconds to be pressed completely and cooled.

Metal inserts or surfaces can be molded to compreg by this expansionmolding method. The method can also be used for gap filling and for applying

pressure in making various kinds of joints. In this case, the material into

which the precompressed resin-treated wood is inserted acts as the mold.

Applications

Solid compreg was used chiefly during the war for trainer-plane adjustablepitch propellers, motor-test propellers, antenna masts, spar and connector

plates, refrigerator blocks for ships, and tooling jigs. The flight propellers

were carved from glued-up blocks of compreg made up from compreg panels

1-1/4 inches thick. Compreg, because of its high compressive strength,

was found to make excellent spar and connector plates. For this purpose,

the cross-banded product is usually used. Its combined load-bearing and

thermal -insulating properties were taken advantage of in using it for

supporting blocks for refrigerators. Compreg was found extremely useful

for aluminum drawing and forming dies, drilling jigs, and jigs for holding

parts in place while welding, because of its excellent strength properties$

dimensional stability, low thermal conductivity, and ease of fabrication.

Solid compreg shows promise for use in silent gears, pulleys, waterlubricated bearings, fan blades, shutters, bobbins and picker sticks for

looms, instrument bases and cases, electrical insulators, tool handles,

knife handles, and various novelties (59) (Fig. 3). Compreg has better

strength properties than fabric-reinforced plastics, and it should be significantly cheaper because veneer is cheaper than fabric on a weight basis and

Report No. 2192 -15-
because half as much resin is used per unit weight of compreg as for fabric

laminates. Compreg may thus replace fabric laminates in a number of uses.

Compreg and semicompreg show their best promise for future use as facing

materials for ordinary plywood. These facing materials may find external

use in house, trailer, and box-car panels and in boat siding, and internal use.

in panels, furniture and flooring. A test floor has been laid at the Forest

Products Laboratory consisting of tongue-and-groove panels 10 inches

square, composed of 3-ply semicompreg faces of yellowpoplar compressed

from a 3/16-inch to a 1/8-inch thickness, a single back ply 1/16 inch thick

of impreg to balance the construction from a swelling standpoint, and a

5-ply Douglas-fir core 1/2 inch thick, with all plies glued with phenol glues.

The floor has a very attractive greenish-tan natural finish. It is in

excellent shape after 10 years' service. Such a floor would be more expensive

than the normal strip oak floor. It is, however, hoped that it will require

less service to keep in good condition. The original finish can be restored

by sanding with fine sandpaper, and then buffing.

Sta)pak

Resin-treated wood in both the uncompressed (impreg) and compressed

(compreg) forms is, unfortunately, more brittle than the original wood. To

meet.the demand for a tougher compressed product than compreg, a

compressed wood containing no resin was developed by the Forest Products

Laboratory (29,30). It will not lose its compression under swelling conditions as will ordinary compressed untreated wood. This material, named

staypak, is made by modifying the compressing conditions to cause the lignin

cementing material between the cellulose fibers to flow sufficiently to

eliminate the internal stresses.

Staypak is not so water resistant as compreg, but it is twice as tough and

has higher tensile and flexural properties. The natural finish of staypak is

almost as good as that of compreg. Under weathering conditions, however,

it is definitely inferior to compreg. For outdoor use staypak should have a

good synthetic resin varnish or paint finish. The heat treatment used in

making staypak is not sufficiently severe to give the wood a significant

reduction in hygroscopicity. Staypak, consequently, is only slightly more

resistant to decay, termites and marine borers than normal untreated wood

of the same species.

Staypak can be used in the same way as compreg where extremely high water

resistance is not needed. It shows promise for use in propellers, tool

handles, forming dies, connector plates, and picker sticks and shuttles for

Report No. 2192 -16-
weaving where high impact strength is needed. It is not being manufactured

commercially as yet. Similar material in a less dimensionally stable form

has, however, been in production in England and Germany for some years.

Staybwood

Heating wood under drying conditions at higher temperatures (200 ° to 600* F.)

than those normally used in kiln drying has been shown to reduce the hygroscopicity and subsequent swelling and shrinking of the wood appreciably.

The stabilization, however, is always accompanied by loss of mechanical

properties. Toughness and resistance to abrasion are most seriously affected.

Under conditions that cause a reduction of 40 percent in shrinking and swelling,

the toughness is reduced to less than half that of the original wood. Extensive

work was done to minimize this loss without success. Because of the

reduction in strength properties from heating at such high temperatures,

wood that is dimensionally stabilized in this manner is not used commercially (54,37,40,42).

Acetylated Wood

Treating Method

The chief disadvantage of stabilizing the dimensions of wood by forming

synthetic resins within its structure is that the resins embrittle the wood

appreciably. For some uses, such as in aircraft, this is very serious.

Efforts were therefore made to find some other bulking agent *that would

preferably react with the hydroxyl groups of wood without embrittling its

fibers. Acetylation appeared to be a likely means of accomplishing this

purpose, from the standpoints of both methods No. 2 and No. 3 given on

page 2.

Acetylation, as it is normally practiced on cellulose with acetic anhydride,

requires a swelling agent, such as acetic acid, to open up the structure, and

a catalyst, such as sulfuric acid, to promote the esterifying reaction.

Mineral acids such as sulfuric, however, promote hydrolysis and breakdown

of the cellulose chains. This hydrolytic effect, if kept within bounds, is not

harmful in plastic and rayon manufacture, but it would defeat one of the chief

objectives of acetylating wood by breaking its structural bonds and embrittling

its fiber.

Report No. 2192 -17-
It was found that pyridine acts as an excellent catalyst for the acetylation

reaction without degrading the wood (49, 50, 53). It was also found that the

acetylation can be carried out to advantage in the vapor phase (49, 50, 53).

As with the treatment with resins, adequate treatment could only be made

on veneer. The treatment is carried out in an acid-resistant air-tight

chamber or kiln at atmospheric pressure. The spaced veneer is first dried

in the chamber operated as a kiln. Air intakes are closed, and a mixture of

liquid acetic anhydride and pyridine is introduced into a tray beneath the

load. Air is circulated over the tray and through the load at a temperature

of 80" to 120" C. until acetate groups equal to 18 to 25 percent of the weight

of the wood are formed in the wood (50, 53. The tray is then drained.

Heated air is circulated through the load and then through a condenser to

remove the excess acetic anhydride, the pyridine, and the acetic acid

formed in the reaction, and is then circulated back through the load until the

wood is free from odor.

Properties

In the .above way, the highest dimensional stabilization thus far attained by

any treatment has been realized. The equilibrium swelling and shrinking

have been reduced to as little as 20 to 30 percent of normal (53). The

specific gravity of the wood is increased by only 6 to 12 percen't. The wood

is not darkened, as it is with resin treatments, and in the case of some

species is bleached. High decay, termite and marine borer resistances are

attained. Moisture transfusion through the wood is reduced to about one -

fifth of normal. Most of the strength properties of wood are unaffected, but

its toughness and Izod impact are frequently increased by 10 to 20 percent

(53). This increase is an especially desirable feature of this treatment.

It has been shown that the dimensional stabilization achieved by this method

results more from bulking the fibers than from reducing the hygroscopicity

by replacing hydroxyl groups with acetate ,groups (50).

Experimental work (10) has been carried out to determine the suitability of

this treatment for wood in lumber-size dimensions.

Polyethylene -Glycol -Treated Wood

The dimensional stabilization of wood with polyethylene glycol also stabilizes

by bulking the fibers and thus keeps the wood in a partially swollen condition.

This treatment, however, differs from most of those previously described

in this report in that polyethylene glycol is used in the treatment of green or

waterlogged wood in contrast to other methods in which air -dried wood is

primarily used.

Report No. 2192 -18-
Oa SIMNIC CHEMISTRY

I FRAGMENTS ASTIA

DEPUTY FOR WIIENCE A TECHNOLOJOY

U ~~74 1L 6

I ANAYS "MIS .15 -1-C-S 3852.

33.71 Ia 0 --N-C(,S)--

am65. 3 C Il. 7 I sN-C(S)-

07,: 4 4C [ TI - R O sc.20 2 --S-CN 3984

3111. IC 2611.5 3 -- N-CzS 244

2146 0C HAi.OGENS 463.10 1 9-44rERo 327.7 4 POLY USAGE 0S3

2m2. 7 7C 1m. 7 F 4860.14 2 3, 4M 3-7.6 5 MISIC. 323.

39a, 8 sc 09215. s Cl 4363. 3 sm

331.5 3 9C 0724.: 9 b 48463. I 4 sM 5251

124. 5 II IC 2511. II I 488.3 17 5 7+M w

0210. 1 01 Is 04 0421 asL AT 4463.21 O-CONT.

0m3. M VT M"AL 2214.5 07 0 POL.Y USAGE 4M3. 2 7 N-CONT.

l NCNIEMINAL 414.22 8 OTHI t-CONT. 327.2 6 N,C,O 10101

2 POLY USA. , 401. IS 4452.5 7 l€.C(-oC0-- iSIS.

4163.12 '' 2 0- 1 -*-(.o)-o- I".

49U3. 1 J2 s+ 5361.5 aN-C(=O)-N= 023

0210, I 3 A L CARSONYL 4M6. 16 0 I m 0783. 71 11 -C(-O)-N- 0

3 0 1 5,6 4 1C~ a 4 ,5. 2 CU I F U S3 ED 2 6 13 . 2 3 14 12 --N - C O 0 2 3 9

75 5 3 mono 4863.24 2 SPIRO 1222.5 IS 0 --- CN

IIII.71 5 SCa6 4 C-S 463.23 3 POLY USAGE 3207.4 I POLY USAGE

10741 7 X 5011. NC 327.3 2 MISC.

3 m7a:78 9 1. 7 9 7 8 *C 1C M4. =4 0 . 5 9 O COES) noR IN G ) Ic O -N - 3 6HU .

2*4. 75 9 SC S6M.311 7 S- (RING) ,N33

2am.75 11 70S S I ITCAMN~ 3634

692 71 0232 sc 3451.5 9 'WER 328 0 3u 1111.1 3311.75 01 0i SC 9C 13.0 3M:8 M 4 5 N--TER 3, 4M 0717. 122.3 3 4 C,N CN 3634 64

1247.5 I i0C 00.5 II POLY USAGE 3233. Is 5 sM 223.75 5 -N-C

0210. 2 04¢ 000.4 jI MIsc. 32. 16 7 S 0239.2 6 -N-CN 36U. 01 20 3 T 3294:.17 4 7+M 2150.5 7 -N-C(N)-N- 3634 0210.17 4 NONTEI NA. 3296. 20 9 0-CONT. 077. S -- =C=N- 36 0210.5 6 POLY 32n6.23 zo I -< 'T. 0797.75 9 POLY USAGE 36U 0210.19 I PLY 3296. 21 1112 OTH3ER-CONT. 0797.5 II MISC. 31.:I 12 0 IN

321.112 I 2H 3634

0604.3 08 0coon 3236.313 2 3461313

0604.1 I -COO-ESTER 36. 24 3 SALT

0211.2 7 ALKYIES 004.2 2 COOH 3298.19 4 IND 332

30.7 S 8 C 004. 7 3 CARSOXY HALIDES 323.36 5 FUSED 15 12 OH,SN 332

301.0604.6 4 F-CO 325.23 6 SPIRO 14 0 H 3617.

06.5 3 S2C 06.5 5 5 ClC-O 3238. 7 POLY USAGE SH 3634

307.5 S n 0 004.4 5 Se-C 'O. 2 POLY USAGE 3634

395. 0747. 08 2 4C3634 s 04 0 004. M 6 7 I-C0O

02113 I 640 4EEON. F'* 0. (S)I

0211.7 2 TERMINAL 0162.5 9

021.4 3 NONTERMINAL 060. 4 II METAL SALTi 6475.10 6 O-HETERO 3298.27 3 N,O (5)

0211.5 4 POLY a 146.7 0812 POLY USAGE 3475.13 3,4M 2391.2 4 N-OH 067

0233.6 5 POLYUSAGE 0116.5 06 0 MISC. 475.14 U1 5M 266.75 5 N-SH

3475.15 12 12 sM 3295.5 6 - N02 [Z ] 3475.16 30 7+M 32M.75 7 -N= 4530

3475.19 I N-CONT. 3299.25 S -- 0no

S IIENZENE 3475.22 2 S-CONT. 326.5 9 N-N3O2 7 MONOSUR 3475.20 3 OTHER--CONT. 329. 29 1 POLY USAGE

.11 s DISI J00.1 1 S-..OR

070.2 2 TRISUB S00.32 2 TIO ACIDS (CXXH) 3475.11 4 3298.27 16 12 MISC.

0570.1H 5061.5 3 SG-O 3475.12 5 2+0 0 1 ORTHO 5001.4 4 C--S 3475.18 6 IND

0570.14 04 12 META c. l-- 3475.17 7 FUSED

0570,7 5 PAR5000.20 6 SAC-HALOGEN 3475.23 a SPIRO

0570.20 I SYM-TRISUB 80.37 7 Sec-B. 3475.21 9 POLY USAGE 463 0 SO(N)

0570. N 2 POLYSul 503.7 I 7 SU--Co 463. 25 170S 0=5-0

dWz- ) 3 IND 500. I 8 Sac-C! 4860.75 1 OzS:O

0570.12 4 FUSED 5060.16 9 S-c-F 4860. 25 2 S03H

0570.18 5 POLY USAGE SM. 21 II SC-I 4499.5 3 S-0

m. 14 091 2 POLY USAGE 4460.5 4 SO2--N

50W .313 10 0 MISC. 4063.27 5 POLY USAGE

j 4963.26 6 MISC.

122.10 5 CYCLOALIKANES

123 .11 7 3,4M L ] 1225.12 S SM

12n.33 9 SM 3475.26 70,S

122. 14 II 7+4 3468.75 8 --0-

12n.16 05 is SAT 3537.5 9 --0-0-

1225.21 0b 0 UNSAT S13. 10 12 -8--

t225. Is I 3ICYCLO 1398.25S 17 12 -5--

122. 17 2 nD 5257.5 I --S--S122.16 3 FUSED 3475.27 I PLY USAGE

122. 20 4 SPIRO 3475.27 2 misc.

1225.18 5 POLY USAGE
ENISTRY

9 A TKC KNOLSGY

10l [T V FoF, 3237.5 I1 NCS 0236.15 3 AMNES 2140 115v m igr

DT Mo.is ". N-C-S 3602.5 4 M2- (PR) 0au ALKALI

6IM. 75 14 0 -N-C(- S)-g 4442.5 5 -NH- (SWc) 0B77 2 C.

3M.7 I -- €(-ws)-m S6.5 6 --N a (T9N) ion 3 p.

SM.20 1 2 -4--CN 3904.5 7 -N4 (QUAT) 2767 4 Li

am1.5 3 -NoC:S 344L 5 1 N 360 K

43.0 I S-HETERO 3297.7 4 PI.Y USAGE 05.5 9 -4p - 4312 6 4.

4863.14 2 3. 4M 3237.6 5 MISC. 130.5 II NN (NIN-) 4345 7 R

43. I 3 sm 5 In.s -N-N-- 1134 3 Cu

483.16 4 GM 5251.5 1 0 N-N'1- 0. Aw

483.17 5 7 M -- l I1412 15 1I An

413.21 6 O-CONY. 1NA34 2 PU OAMIES

4663.2( 7 N-CONT.

4863. I OrHE*-CIT. 3237.2 6 N,C,O low.$ 3 -- Fi2 2141 GROU Ii

463.11 9 Is 4462.5 7 N(-O)-N-N- 1663.6 4 -- NP 026 25 0 ALKALINE

4663.12 II 2S 0710. 6 a -.- C(-O- 1684.5 5 I"N-Nr

- on I *

4963.12 1012 3-8 536M.5 9 =N.-C( =O)-Nz 02.4 6 SALT 0 - 1* a Se

4m3. 19 n O1 07M.71 II -ClO)--- 0233.9 7 POLY USAG a7m CA

4363.18 I FUSED 2663. 2 14 12 -- C-O 023M.7 i MISC. 45 4 Me

4M3. 24 2 SPIRO 122.5 Is 0 -- O-Cm 4110 5 R

48.23 3 POLY UGE 3237.4 1 POLY USAGE 6 C. on

3237.3 2 MISC. aUS 7 c am7 He

N HE---O1[ 3634.2 3 PHOSPHORUS RAD. *66 ZN

3434.16 I1 P:O,SO 3 63~4.|1 12 I P p= ,20

3298.10 4 N-4STERO 0737. 3 C,N 3634.17 20 0 P=O, S, 20 2142 11 GOUP III

326. 14 5 3, 4M 1223.5 4 CH 3634.1 I S-POs 000 ILIZ A.

326. 15 6 SM 213.75 5 --NC 3634.15 2 SP-F 0252 26 0 A.

32M6.16 7 6M 023.2 6 -#4-C-t 3634.14 3 S-P-F m I a^

3266.17 734 2150.5 7 - --C(-N)--N- 3634.11 4 O:P(N) (c---F 2467 2 I.

3298.20 9 O-COT 0737.5 a -N=C=N- 3634.10 5 O=P,(F). 2H .707 3 IA

3296.23 II S-COl. 0797.7 6 P.CLY USAGE 3634.13 6 O:P(P) 02 4410 4 Sc

3238.21 1 12 OTER-CON . 0737.5 11 MISC. 3634.12 7 O-P-F s 5 T,

329.11 12 0 IN 3634.2 Z PS-IITO 35) S3 9 Y

3236.12 I .N 3634.24 P,S--(4S)

3298.13 2 3+14 1224.75 n CYCLIC P

3298.24 3 SALT 3632. 25 20 12 P(+3) 2143 7 GROUP IV 3230.19 4 IND 2072. 6 .G

3298.18 5 FUSED 91 Is 12 O, Sm 3632.75 21 0 P(+5) 2072 a G9

3235.25 6 SPIRO 3.4 I 0 ON 3617.5 1 P04 2201 9 Hr

3298.22 7 POLY USAGE I sm 3634.21 2 P-MISC. 2719 II P.

3 . 7 -. E 2 POLY USAGE 3634.25 3 PS-MISC. 51213 26 2 S

3634.22 4 POLY USAGE 5139 27 0 Ti

5590 I Z7

4475.10 6 0-HETERO 3298.27 3 NO (8) 2144 2

3475.13 9 3, 4M 2391.2 4 = N-CoH 0667 5 .... ._. 0330 3 go

3475.14 II 5M 298. 75 5 = N--SH 0610 4 Be

3475.15 12 12 6M 329.5 6 -NO2 3267 5 No

3475.16 13-0 7+M 3219.75 7 -440 4530 6 6 P

3475.19 1 N-CONY. 3233. 8 .N-NO 4356 7 TA

3475.22 2 S-CONT. 326.5 9 N-#402 5361 8 V

3475.20 3 OTHER-CONT. 323. 0 II POLY USAGE

3475.11 4 F-0 326. 27 16 12 MISC.

3475.12 5 2+0 2145 9 GROUP VI

3475.18 6 IND _ duO II CHALCOGENS

3475.17 7 FUSED , (N) 3781 27 12 Po

3475.23 8 SPIRO OUS 4457 "3IIC 28 0 Sc

3475.21 9 POLY USAGE 4863.2 7 S, (N) 0935 1 Co

4860.75 I OS O 3122 2 Mo

460. 25 2 SOSH 2_ IL 5277 3 W

4M. 5 3 SO 0 0

4860.5 4 802-N I I

463.27 5 PC.Y USAGE 2 2 2146 4 GROUP VII

4163.26 6 MISC. 3 3 5223 5 TRANS. ELEM.

4 4 06132 6 Co

2604 7 In [o-] 66 2607 8 Fe

7 7 3276 9 N. 6 6 3456 II 0.

3475.26 7 OS 3 3 3432 2112 P.

346.5 9 -- 0- II nI 3744 20 0 P36. 3 -S-- 12 12 4277 I R.

133.25 17 12 --- 4373 2 Ru

5257.5 18 r 0 

3475.2 I IPOLY USAGE

3475.27 2 MISC.
DESCRIPTORS

APPLICATINS STRUCTURES, SYSTEMS & FIEDS 9PRT

003 ACOUSITIC INSULATION4 0141 62 12 AIRCRAFT 0058 8 ADHESION

0055 1 ADDITIVES 06w 63 0 *O..OGICAL WARFARE 01112 7 CHEMICAL BONDS

0060 2 ADHIESIVES 0604 I IONuCS, 8 CHEMICAL

038 3 ARMOR 0902 2 CHEMICAL WARFARE 128 9 DENSITY

0592 4 BINDERS 3 ELECTRICITY a ELECTRONICS 1464 11 ELASTICITY

060 5 CHEMICAL WARFARE AGENTS 4 IR & UV DETECTORS 1523 f[Jj ELECTRICAL

03w 6 COATOMS 5 LASERS & MASERS 2164 66 0 MAGNETIC

1129 7 COO..ANTII 2909 6 METALLURGY 2945 I MECHANICAL

1436 8 DRU15 7 OCEANOGRAPHY 3116 2 MOL.ECULAR STRUCTURE

4107 9 RADIOPROTECTIVE 372 8LAM PHYSC 3117 3 MOLECUL.AR WEIGHT

1452 II DYES 4066 9 RADIOma..OGY 3427 4 OPTICAL

1501 60 12 ELECTRIC INSULATION 4319 11 ROCKET MOTORS 3683 5 PHOTOSENSITIVITY

11I 0 EXPLOSIVES 4464 63 12 SEMICONDUCTOR DEVICES 6 PHYSICAL CONSTANTS

1972 I FUELS 040W-PROPELLANT) 500.5 64 0 SHIPS 7 PHYSICAL

4327 2 ROCKET PROPELLANTS 4679 1 SPACECRAFT 8 RADIANT 0

0607 3 EPROPELLANTS 2 OTHERS 4256 9 RESONANCE 0

2040 4 GASEOUS 4628 11 SOLUBILITY 01

2341 5 HYBRID MISCELLANEOUS 66 12 STEREO ISOMERISM 1

2396 6 HYPERGO..IC 1051 3 COMPATIBILITY 67 0 STRUCT ,IAL ISOMERISM 12

278 7 LIQUID 106 4 CONTAMINATION 4891 I SURFACE I

4624 a SOLID lies 5 CRYOGENICS 5024 2 TENSILE 2

5093 19 TI4IXOTROPIC 2041 6 GASES 5062 3 THERMODYNAMICS 2

2351 II HYDRAULIC FLUIDS 2231 7 HAZARDS 5188 4 TOXICITY V

2818 61 12 LUBRICANTS 2304 8 HICGH-TEMPERATURE 5445 5 VISCOSITYV

3466 62-0 OXIDIZERS 2749 9 LIGHT 6 OTHERS 2

3594 I PESTICIDES 2786 11 LIQUIDS 3 3740 2 PLASTICIZERS 3365 64 12 PRODUCTION PRC4SE

3827 3 POWER SUPPLIES 4034 65 0 RADIATION EFFECTS 0003 7 ALATION 34

1 4 RADAR AISOEBERS 4664 I SPACE ENVIRONMENT 08110 8 CHEMICAL ANALYSIS 34

5 RSIN~S 4737 2 STABILITY 0695 9 CHEMICAL EQUILIBRIUM 3 1 6 SEALANTS 4737 3 STORAGE 1023 11 COLORIMETRIC ANALYSIS 41.

4465 7 SEMICONDUCTORS 5036 4 TEST EQUIPMENT 1031 67 12 COMBUSTION 4

505 8 TEXTILES 5 OTHERS 1144 68 0 CORROSION 4

5067 9 THERMAL INSULATION 4137 I REACTION KINEI CS

I1 OTHERS 2 SPECTROGRAPHIC ANALYSIS

3 OTHERS

CHEMICAL IDENTIFIERS

?o/ MW 3~~4
om 6 ADHESION

002 7 CHEMICAL BONDS

* CHEMICAL -1 C AD [ It I t 1oI

1281 9 DENSITY

IONICS 1484 II ELASTICITY 74 75 75 77 71 79 10

1523 ELECTRICAL

2864 66 0 MAGNETIC -2 5

2945 I MECHANICAL

3116 2 MOLECULAR STRUCTURE

3117 3 MOLECULAR WEIGHT

3427 4 OPTICAL

3683 5 PHOTOSENSITIVITY

ES 6 PHYSICAL CONSTANTS 7 PHYSICAL. CHEMICAL REACTIOS GENERAL CLASSES OF MAT-ERIALS J

PHADIALH~ik A

SRADIANT 0050.5 4 ACYLATION 0210 700 ALKALOIDS 4256 IRESONANCE 0211.1 5 ALKYLATION I CELLULOSE COMP. 4628 11 SEOLULITY 0831 6 CATALYSIS 0883.5 2 CHELATES 67 120IL STEOISOMMERISM 1133 7 COPOLYMERIZATION 1054 3 COMPLEX COMP. 0 STRUCTURAL ISOMRISM 1252 8 DECOMPOSITION 1057 4 COMPOSITES 4891 I SURFACE 1682 9 FLUORINATION 1224.25 5 CYCLIC METALS

5024 2 TENSILE 2213 II HALOGENATION 1641 6 ENZYMES

5082 3 THERMODYNAMICS 2375 68 12 HYDROGENATION 1741 7 FATTY ACIDS

5188 4 TOXICITY 2381 69 0 HYDROLYSIS 1930 8 FREE RADICALS 5445 5 VISCOSITY221 60HDOYI 2590 I ION EXCHANGE 2324 9 HORMONES 6 OTHERS 2992 2 METALATION 2361.5 II HYDROCARBONS

PROCSSES 3291 3 NITRATION 2693 70 12 LAMINATES

0003 7 ABLATION 3463 4 OXIDATION-REDUCTION 3000 710 METALORGANICS

0690 8 CHEMICAL ANALYSIS 3636 5 PHOSPHORYLATION 3741 1 PLASTICS

0695 9 CHEMICAL EQULIIUM 3674.5 6 PHOTOLYSIS 1691 2 EXPANDED

12 103 1 i cHE CO IMTRI M. ALYSIS AN YSIs 3736 4180 7 POLYMERIZATION RECOMBNATION 2253 3 HEAT-RESISTANT 5m 4 THERMO

0311 67 12 COMBUSTION 4858 9 SUI.FATION 5087 5 THERMOSETTING

1144 68 0 CORROSION

4137 1 REACTION KINETICS 9 9 12 OTTERS 474 7 PTEROIDS

2 SPECTROGRAPHIC ANALYSIS

3 OTHES 8 OTHERS

CHEMICAL IDENTIFIERS

P- 3
To obtain a high degree of dimensional stability, a penetration of the chemical

throughout the wood is required, leading to a uniform uptake of 25 to 30

percent of chemical. The time necessary for this uptake depends on the

thickness of the wood and may require weeks. This treatment has been

effectively used in the treatment of walnut gunstocks (22).

Another application of this chemical is to reduce the checking of green wood

during drying. For this application the polyethylene glycol is used as a

seasoning agent and a high degree of penetration is not required. This method

of treatment has been used to advantage to reduce checking during drying of

small wood blanks or turnings (23).

More recently, it has been shown that the excessive cracking and distortion

that old, waterlogged wood undergoes when it is dried can be substantially

reduced by treating the wood with polyethylene glycol. The process was

used to dry 200-year-old waterlogged wood boats raised from Lake George,

N.Y.

Formaldehyde -Treated Wood

All. of the other methods thus far described for permanently stabilizing the

dimensions of wood, with the exception of heating to high temperatures,

involve either bulking the fibers, chemically making the product less hygroscopic, or both. Another general method for stabilizing wood is that of

forming cross links between swelling units. It has been shown that heating

dry wood in the presence of formaldehyde vapor and of a mineral-acid

catalyst will appreciably stabilize the dimensions of wood, presumably as a

result of the formation of acetal cross linkages in the wood (34, 51). High

degrees of dimensional stabilization have been obtained with an increase in

weight of as little as 3 to 6 percent. The dry vapor is generated by heating

paraformaldehyde suspended in a mineral oil. The reaction can be carried

out in the same type of chamber or kiln as used for acetylation. The chamber

should be provided with a means of spraying small amounts of acid into the

chamber to act as catalyst. Unfortunately, the acid a catalyst tends to

embrittle the wood and seriously detracts from the process.

Nuclear Irradiation of Wood

Numerous attempts have been made to modify the hygroscopic characteristics of wood by radiating with gamma rays and beta particles. Paton and

Hearmon (25) exposed wood to I06, 107, and 108 roentgens of Cobalt-60

Report No. 2192 -19-
gamma rays. Small but measurable reductions in moisture regain were

observed. However, this is always accompanied by moderate to severe

losses in mechanical properties (15, 17). Attempts have also been made to

polymerize monomers in impregnated wood with nuclear radiation. Kent (12)

describes properties of wood treated with vinyl type monomers which were

polymerized by gamma radiation. Substantial improvement in properties

are reported. Some of these (swelling) are time dependent and suggest the

improvements are due to the massive loadings of polymer. Russion

workers (7) have reported similar results. Some of their data pertain to

samples having 120 percent polystyrene.

Surface Densification

Besides methods that involve the impregnation or densification of the total

wood, there are, however, methods which involve densification of only part

of the wood, generally the outer surface. One patented process (16) involves

the densification of the edge portion of desk legs and the edge portions of

table and desk tops by the application of heat and -pressure through forming

dies. Local densification has the advantage that the major portion of the

wood retains its normal characteristics and so is easier to work and is

better adapted for connection with other untreated wood parts.

Another patented process (Q) involves modification of surface properties by

polishing at speeds which cause -local heating of the wood surface. The aim

of this process is to provide a better surface for surface finishes. Increased surface hardness can be obtained in flat panels by heating the surfaces to the desired depth and then applying sufficient pressure to

compress the more readily compressible heated area. Cooling of the

densified wood while still under pressure is necessary to avoid springback.

Report No. 2192 -20-
Literature Cited

I. Alexander, G. E.

1958. U. S. Patent 2,827,935.

2. Bateson, B. A.

1939. Sorbitol in Wood Treatment. Chemical Trade Jour. 105:98.

(Aug. 4. )

3. Bernhard, R. K., Perry, T. D., and Stern, E. G.

1940. Superpressed Plywood, Bonded with Thermosetting Synthetic -

Resin Adhesives. Mech. Eng. 62(3):189-195.

4. Browne, F. L.

1933. Effectiveness of Paints in Retarding Moisture Absorption by

Wood. Ind. Eng. Chem. 25(8):835-842.

5. , and Downs, L. E.

1945. A Survey of the Properties of Commercial Water Repellents

and Related Products. Forest Prod. Lab. Rept. No. 1495.

6. Burr, H. K. and Stamm, A. J.

1945. Comparison of Commercial Water-Soluble Phenol-formaldehyde

Resinoids for Wood Impregnation. Forest Prod. Lab. Rept.

No. 1384, Revised.

7. Dickey, David E., and McEwen, John E.

1960. Slide Rule Simplifies Xenon Computations. Nucleonics 18:88.

8. Erickson, E. C. 0.

1947. Mechanical Properties of Modified Wood. Forest Prod. Lab.

Rept. No. 1639.

9. Findley, W. N., Worley, W. J., and Kacalieff, C. D.

1946. Effect of Molding Pressure and Resin on Results of ShortTime Tests and Fatigue Tests of Compreg. Trans. Amer.

Soc. Mech. Eng. 68:317, (May).

10. Goldstein, Irving S., et. al.

1961. Acetylation of Wood in Lumber Thickness. Forest Prod.

Jour. 11(8):363-370.

Report No. 2192 -21-
11. Hunt, G. M.

1937. Effectiveness of Moisture-Excluding Coatings of Wood. U.S.

Dept. Agr. Circular No. 128.

12. Kent, J. A.

1962. Radiation Monomers Improve Properties of Wood. Nucleonics

20:94.

13. Kollenen, F.

19-36. Technologie des Holzes. Julius Springer, Berlin, Germany.

14. Kuenzel, J. G.

1947. Wood Has Big Role on Modern Warships. Part I, Wood

2(5):14-16, 41; Part II, Wood 2(6):26-27, 37.

15. Lawton, E. 3., Bueche, A. M., and Balwit, 3. S.

1953. Irradiation of Polymers by High-Energy Electrons. Nature

172:76.

16. Lundstrom, C. B.

1949. U. S. Patent 2,488,301.

17. Mater, Jean

1957. Chemical Effects of High Energy Irradiation of Wood. Forest

Prod. Jour. 7(6):208-209.

18. Millett, M. A., Seborg, R. M., and Stamm, A. J.

1943. Influence of Manufacturing Variables on the Impact Resistance

of Resin-Treated Wood. Forest Prod. Lab. Rept. No. 1386.

19. , and Stamn, A. J.

1946. Wood Treatment with Urea Resin-Forming Systems. Modern

Plastics 24(2):150-153, 202, 204, 206.

20. , and Stamm, A. J.

1947. Wood Treatment with Urea Resin-Forming Systems. Modern

Plastics 24(6):159-160, 208, 210, 212.

21. , and Stamm, A. J.

1947. Wood Treatment with Resin-Forming Systems. Modern

Plastics 25(l):125-127.

22. Mitchell, H. L., and Wahlgren, H. E.

1959. New Chemical Treatment Curbs Shrink and Swell of Walnut

Gunstocks. Forest Prod. Jour. 9(12):437-441.

Report No. 2192 -22-
23. Mitchell, H. L., and Iverson, E. S.

1961. Seasoning Green -Wood Carvings with Polyethylene Glycol -1000.

Forest Prod. Jour. 11(l):6-7.

24. Olson, C. G.

1934. U. S. Patent 1,981,667.

25. Paton, J. M., and Hearmon, R. F. S.

1957. Effect of Exposure to Gamma Rays on the Hygroscopicity of

Sitka Spruce Wood. Nature 180:651.

26. Plesheimer, L. J.

1929. U. S. Patent 1,707,135.

27. Sears, C. N.

1900. U. S. Patent 646,547.

28. Seborg, R. M., and Inverarity, Robert Bruce

1962. Preservation of Old, Waterlogged Wood by Treatment with

Polyethylene Glycol. Science 136(3516):649-650.

29. , Millett, M. A., and Stamm, A. J.

1945. Heat Stabilized Compressed Wood (Staypak). Mech. Eng.

67(1):25-31.

30. , and Stamm, A. J.

1941. Compression of Wood. Mech. Eng. 63(3):211-213.

31. , and Stamm, A. J.

1945. Effect of Resin Treatment and Compression Upon the Properties

of Wood. Forest Prod. Lab. Rept. No. 1383, Revised.

32. , and Vallier, A. E.

1954. Application of Impreg for Patterns and Die Models. Forest

Prod. Jour. 4(5):305-312.

33. Stamm, A. J.

1934. Effect of Inorganic Salts Upon the Swelling and Shrinking of

Wood. Amer. Chem. Soc. Jour. 56, 1195-1204.

34.

1959. Dimensional Stabilization of Wood by Thermal Reactions and

Formaldehyde Cross-Linking. Tappi 42(1): 139-144.

35.

1936. U. S. Patent 2,060, 902.

Report No. 2192 -23-
36. Stamm, A. 3.

1937. Treatment of Wood with Sucrose and Invert Sugar. Ind. Eng.

Chem. 29(7):833-835.

37.

1942. U. S. Patent 2,296,316.

38.

194. Modified Woods. Amer. Wood Preservers' Assoc. Proc.,

Vol. 42, 150-167.

39. •

1959. Effect of Polyethylene Glycol on the Dimensional Stability of

Wood. Forest Products Jour. 9(10):375-381.

40. , Burr, H. K., and Kline, A. A.

1946. Staybwood--A Heat Stabilized Wood. Ind. Eng. Chem.

38(6):630-634.

41. , and Hansen, L. A.

1935. Minimizing Wood Shrinkage and Swelling; Replacing Water

in Wood with Nonvolatile Materials, Ind. Eng. Chem.

27(12):1480-1484.

42. , and Hansen, L. A.

1937. Minimizing Wood Shrinkage and Swelling; Effect of Heating in

Various Gases. Ind. Eng. Chem. 29(7):831-833.

43. , and Seborg, R. M.

1936. Minimizing Wood Shrinkage and Swelling; Treating with

Synthetic Resin-Forming Materials., Ind. Eng. Chem.

28(10): 1164-1169.

44. , and Seborg, R. M.

1938. The Anti-Shrink Treatment of Wood with Synthetic ResinForming Materials and the Application in Making a Superior

Plywood. Southern Lumberman 157(1985):157-162.

45. , and Seborg, R. M.

1941. Resin-Treated, Laminated, Compressed Wood. Trans. Amer.

Inst. Chem. Eng. 37:385 (June).

46. , and Seborg, R. M.

1943. Forest Products Laboratory Resin-Treated Wood (Impreg).

Forest Prod. Lab. Rept. No. 1380, Revised.

Report No. 2192 -24-
47. Stamm, A. J., and Seborg, R. M.

1944. Forest Products Laboratory Resin-Treated, Laminated, Compressed Wood (Compreg). Forest Prod. Lab. Rept. No.

1381, Revised.

48. , and Seborg, R. M.

1944. U. S. Patent 2,354,090.

49. Stamm, A. J., and Tarkow, H.

1947. Dimensional Stabilization of Wood. Jour. Phys. and Colloid

Chem. 51(2):493-505.

50. ,and Tarkow, H.

1947. U. S. Patent 2,417,995.

51. ,_and Tarkow, H.

1951. U. S. Patent 2,572,070.

52. , and Turner, H. D.

1945. U. S. Patent 2,391,489.

53. Tarkow, H., Stamm., A. J., and Erickson, E. C. 0.

1946. Acetylated Wood. Forest Prod. Lab. Rept. No. 1593.

54. Tiemann, Harry D.

1920. Effect of Different Methods of Drying on the Strength and

Hygroscopicity of Wood. The Kiln Drying of Lumber,

Chapter 11. 3rd edition edited by J. P. Lippincott Co.,

Philadelphia, Pa., 256-264.

55. U. S. Department of Defense

1951. Wood: Impregnated Compressed. Military Specification

MIL-W-2872, Aug. 23.

56. Walsh, F. L., and Watts, R. L.

1923. U. S. Patent 1,465,383.

57. Weatherwax, R. C., and Stamm, A. J.

1945. The Electrical Resistivity of Resin-Treated Wood and

Laminated Hydrolyzed-Wood and Paper-Base Plastics.

Elec. Eng. 64:833.

58. _ and Stamm, A. J.

1947. Coefficients of Thermal Expansion of Wood and Wood

Products. Trans. Amer. Soc. Mech. Eng. 69:421, (May).

59. Young, S. H. A., and Palese, R. A. M.

1945. Molded Wood. Modern Plastics 22(9):100-104, 196.

Report No. 2192 -25- 1.5-32
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