U. S. DEPARTMENT OF COMMERCE

R. P. LAMONT, Secretary BUREAU OF STANDARDS

GEORGE K. BURGESS, Director

MISCELLANEOUS PUBLICATION No. 108

MANUFACTURE AND PROPERTIES

OF A CELLULOSE PRODUCT (MAIZOLITH)

FROM CORNSTALKS AND CORNCOBS

March 20, 1930

ADVANCE COPT FOR "REVIEW

UNITED STATES

GOVERNMENT PRINTING OFFICE WASHINGTON : 1930

For sale by the Superintendent ol Documents, Washington, D. C. - - - Price 5 cents
Bureau of Standards

SEP 1 2 1930

D C \ ()C)
MANUFACTURE AND PROPERTIES OF A CELLULOSE

PRODUCT (MAIZOLITH) FROM CORNSTALKS AND

CORNCOBS

ABSTRACT

Maizolith is a dense, hard, bonelike substance made by cooking cornstalks or corncobs with caustic soda, washing the residue, beating it to a jell, and drying.

The finished product has a modulus of rupture of about 16,000 lbs. /in.2 and a volume resistivity of 3X10° ohms/cm 3

. It is practically unaffected by oil, but

becomes soft on prolonged soaking in water. The optimum conditions for the manufacture of maizolith were found to be

those indicated by the following process: Digest the shredded cornstalks three hours at 40 pounds pressure with 10 per cent of their bone-dry weight of caustic soda; dilute to a 1 per cent solution; wash free of cook liquors; dilute the pulp

to a consistency of 4 per cent, beat for two hours in a combined beating engine

and Jordan refiner and dry at a temperature of 70° C. Cost figures for the process indicate that in a plant large enough to produce

5 tons per day, finished maizolith can be made for about $240 per ton, using

cornstalks as the base material. Maizolith could probably be made at a lower figure than $240 per ton as a by-product of the insulating wall board industry, by utilizing fibers or pith

particles which are too fine or too highly hydrated to be used in insulating board. By utilizing the soft residue from the process of extracting adhesive material from corncobs maizolith could probably be produced at a lower figure than that from either of the processes outlined above. CONTENTS Page

I. Introduction 1 II. Method of manufacture 2

III. Properties and possible uses 2

IV. Optimum conditions for producing maizolith 3 V. Cost of producing maizolith commercially 8 VI . Maizolith as a by-product from other industries 10

I. INTRODUCTION

The work on maizolith is a part of the program on the utilization

of agricultural wastes which has been carried on for the past 10 ye\ars

in the chemical engineering department at Iowa State College under

the direction of Dr. O. R. Sweeney. Since August, 1927, the National

Bureau of Standards has been cooperating with the Iowa State College in the development, on a semicommercial scale, of two or three

of the more promising processes for the utilization of farm wastes. The purpose of the work recorded in this paper was to determine

the optimum conditions for the production of maizolith, to make a study of its properties, and to get an idea of the cost of producing

the material.

Maizolith is a dense, hard, bonelike material, ranging in color

from a golden tan to a deep ebony. It is somewhat heavier and

stronger than the hardwoods, and is a good electrical insulator.

Figure 1 gives an idea of the way in which the material may be

machined and polished,

93841°—30 1
2 BUREAU OF STANDARDS

Maizolith closely resembles cellulith, a material which is made from

sulphite pulp, and which was patented in 1899 by Heinrich Brunswig. 1 Its properties also coincide closely with those of vulcanized fiber, a material which is used extensively in this country to-day. It is not

surprising that the properties of maizolith closely resemble those of vulcanized fiber since the two products are chemically similar; that

is, products which are obtained by drying gelatinized cellulose. In

the case of vulcanized fiber the cellulose is gelatinized by chemical

means, in the case of maizolith, by mechanical means. Any differ- ences found in the properties of the two substances are no doubt

due to variations in the raw materials and in the way the gelatinized

cellulose is handled in converting it into the finished products. The

following brief descriptions of the manufacture of vulcanized fiber and of maizolith will illustrate how the gelatinized cellulose is handled

in the two processes.

II. METHOD OF MANUFACTURE

In the preparation of maizolith, cornstalks which have been

shredded to lengths of 1.5 to 3 inches (or corncobs roughly broken up)

are digested about three hours under 40-pound steam pressure with

caustic soda equal to 10 per cent of the weight of the bone-dry stalks and diluted to a 1 per cent solution. The cooked pulp is then washed

free of the caustic liquors. These cooking and washing treatments

leave a pulp that for all practical purposes may be considered pure

cellulose. The pulp is then diluted to a consistency of about 4 per

cent and is gelatinized by treatment in a beating engine and a Jordan

refiner, two standard pieces of paper-mill equipment, until a jelly- like mass is obtained. This jell is boiled to remove air bubbles, placed

in a mold with a perforated bottom and having a plunger top which

exerts a pressure of about 0.5 lbs. /in. 2 on the jell, and dried in the

mold at about 70° C. The time for drying sheets one-half inch thick

is about 10 days. On drying, the maizolith shrinks to about one- fourth of the volume it occupied when molded.

The source of cellulose in the vulcanized fiber process is unloaded,

unsized, rag paper. The surface of this paper is gelatinized by run- ning it through a bath of warm zinc chloride, after which the gelatinized paper is rolled up and pressed on a heated hollow drum.2 The

material so formed may be left in the form of a tube or may be cut and pressed into sheets. After removing the fiber from the drum it is washed in progressively weaker solutions of zinc chloride until all traces of chlorides are removed. This washing treatment is very

slow, requiring from three weeks for sheets one-eighth inch thick to

six months for sheets 2 inches thick. If all traces of chlorides are not

removed, a very inferior grade of vulcanized fiber is obtained. .After washing, the fiber is dried, during which operation the sheet shrinks

to about one-half its size in the wet state.

III. PROPERTIES AND POSSIBLE USES

Some physical properties of maizolith are tabulated in Table 1. The strength tests were made in the civil engineering department of

'U.S. patent 622325.

2 Allen Rogers, Manual of Industrial Chemistry, 3d ed., p. 1059.
MANUFACTURE OF MAIZOLITH 3

Iowa State College. The specimens for the various tests were of the

following dimensions: Compressive strength, a cylinder 0.7 inch long

by 0.35 inch in diameter; shearing strength, a bar 0.089 by 1 by 2.33

inches; tensile strength, a rod 3 inches long, turned to 0.375 inch in diameter for 0.5 inch at each end and 0.187 inch in diameter over the

remainder of its length; modulus of rupture, a bar 0.375 by 1 by 2

inches.

Table 1.

Some physical properties of maizolith

Strength Electrical properties Miscellaneous

Modulus of rupture. Compressive

Shearing

Lbs./in.t

16, 000

17,000

8,000

7,000

Dielectric constant at frequency of 6 kc per second, 7 to 9. Surface resistivity, 7X109 ohms per cm 2 at relative humidity of 45 per

cent, temperature of 26° C. Volume resistivity, 3X109 ohm-cm 3 Phase difference, about 3° at frequency

of 6 kc per second.

Brinnell hardness, 15 to 30. 1 Specific gravity, 1.3 to 1.5. Water absorption, 20 to 35 per cent of the original weight in 24 hours.

Oil absorption, 0.09 to 0.13 per cent of the original weight in 24 hours. Tensile

i This hardness falls in the series for brasses and bronzes. The electrical tests were made by A. A. Aardal 3 in the physics

department at Iowa State College. The dielectric constant and phase

difference were measured at a radio-frequency of 6 kc per second, a temperature of 26° C, and a relative humidity of about 45 per cent. The phase difference, which is 3°, indicates that the material will not

heat excessively when used as an electrical insulator. The product

of the dielectric constant and the phase difference, 24, indicates that

the material would be suitable for radio work.

The Brinnell hardness test was made by using a standard Brinnell

hardness-testing machine on a test specimen measuring 1 by 1 by

0.25 inch.

The water and oil absorption tests were carried out by immersing

pieces of maizolith in water or oil at room temperature. The pieces

immersed in water swelled and softened perceptibly after about 15

hours. On drying again they returned to their original hardness, but

were apt to develop surface cracks and checks. The samples immersed in oil showed no visible change in physical properties. \ Maizolith has been used, on a small scale, in the manufacture of

the following articles: Noiseless gears, rods, tubes, refillable fuses,

rings, disks, wheels, bearings, screws, and nuts

IV. OPTIMUM CONDITIONS FOR PRODUCING MAIZOLITH

A study of the above-outlined method for the manufacture of

maizolith indicates that the factors which probably have the most

important bearing on the quality of the maizolith produced are: (1)

The raw material; that is, whether the raw material is corncobs or cornstalks; (2) the ratio of caustic soda to the bone-dry weight of

stalks; (3) the duration of cooking; (4) the consistency of the pulp at the time of beating; (5) the H-ion concentration at the time of beating; (6) the duration of beating; and (7) the drying temperature.

The effect of each of these factors was studied by holding six factors

3 Unpublished paper by A. A. Aardal, physics department, Iowa State College.
4 BUREAU OF STANDARDS

constant and varying the seventh through a definite range. The

values for the constant factors were 100 per cent cornstalk pulp; 10

per cent caustic soda based on the weight of bone-dry fiber; enough

water to dilute the caustic soda to a 1 per cent solution; a cooking

period of three hours at atmospheric pressure ; washing until the pH

of the pulp was 5.5: beating for six hours in a pebble mill: consistency

Figure 1.

Articles made from maizolith of 2 per cent in pebble mill; drying temperature of 60° C. The

variable factor was then plotted as abscissas against the moduli of rupture of the resulting maizolith samples as ordinates. The effects of the individual factors are shown graphically in Figures 2 to 8, inclusive.

Figure 2 indicates that corncobs and cornstalks give about equally

good maizolith but that mixtures of the two yield an inferior product.

From this it would seem that the particles of cornstalk fiber are of such a nature that they adhere to each other more firmly than they
MANUFACTURE OF MAIZOLITH 5

do to corncob particles, and that the corncob particles adhere to each

other more closely than they do to cornstalk particles.

/OO 80 60 40 20 O Sta/ks

O 20 40 60 SO /OO - Cobs

Composition Percent

Figure 2.

Strength of maizolith made from cornstalks and corncobs Figure 3 shows that the optimum amount of caustic soda to use in cooking the pulp is from 9 to 11 per cent of the bone-dry weight of

• 3OO00

Percent of Caustic Soda

Figure 3.^

Effect of percentage of caustic soda used in cooking on the strength of maizolith cornstalks or corncobs. The alkali is diluted to a 1 per cent solution.

The time of cooking, according to Figure 4, should be about 16 hours
6 BUREAU OF STANDARDS

at atmospheric pressure. Although no corresponding series of runs has been made for pressure cooking, experience in the laboratory at

/600O

/2O00

eooo

4-OOQ

O 4 8 /2

f 16 20 24 28

Duration of Cooking Period in Hours Figure 4.

Effect of duration of cooking on the strength of maizolith Ames indicates that three hours' cooking under 40-pound steam pres- sure is sufficient. The calculations for the amount of water to be

2O0OO

4

gI

/ZOOO

fOOO

Figure 5. Percent Wafer- To Weight Cellulose

-Effect of consistency of cellulosic materials at time of beating on the strength of maizolith added to the pulp, after cooking and washing, to make the pulp up to any given consistency shown in Figure 5, were based on the general
MANUFACTURE OF MAIZOLITH 7

experience that 40 per cent of the total bone-dry weight of the cornstalk or corncob is removed by the cooking and washing operations.

tQOOO I I I I I

1 1

I 1

pfi of Time of deofing

Figure 6.

Effect of the pH of the mixture during the beating process on the strength of maizolith Figure 6 indicates that the strength of maizolith increases as the pH

at time of beating is decreased from 9 to 5. The optimum pH is evi3OOO0 -

O 6 /2 /a 24 30 36 f£ 48 Duration of Beating Process in tjrs. Figure 7.

Effect of duration of the beating process on the strength of maizolith dently some value lower than 5 ; and experiments are nowr under w

T ay

to determine this point. The optimum time of beating is 12 to 18

hours as shown by Figure 7. The beating experiments w

r ere carried
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out in a 4-liter porcelain pebble mill, running at 60 r. p. m. Subsequent experiments have developed a beating method which produces

a satisfactory jell in two hours. The cooked and washed pulp is placed in a beating engine, which is connected with a Jordan refiner so that pulp may travel continuously under the beater roll, through

the Jordan, and under the beater roll again. The valve connecting

the beater to the Jordan is left closed for the first half hour, during

which time the pulp is subjected simply to the action of the beater.

The valve is then opened and the pulp is given the combined beaterJordan treatment for one and one-half hours, at the end of which time

it is found to be gelatinized to the proper degree for making maizolith.

Work is under way at the present time to obtain data which will make it possible to construct a curve for the beater-Jordan machine

similar to Figure 7, for the pebble mill. At the present time it is

24-COOt

2.0000

.Q

l

ure leooo

/2OO0 o3 8OO0

Modal 400O

(

o s

o\

0/

/o

o

3 o

)

Dry/hy Temperature °C Figure 8.

Effect of the temperature of drying on the strength of maizolith known merely that two hours in the beater-Jordan combination gives a pulp which is satisfactory. Whether or not this length of beating

treatment is the optimum remains to be worked out. Figure 8

indicates that the best drying temperature is about 70° C. The drying oven was operated at a relative humidity of 75 to 80 per cent. No provision, other than natural convection, was made for circulating

air.V. COST OF PRODUCING MAIZOLITH COMMERCIALLY

Figure 9 shows a suggested layout for a plant to produce 5 tons of maizolith per day. Figuring on the basis of a 50 per cent yield,

which experiments have shown may be expected, the plant would

require a storage space for 108,000 bales of stalks. This figure assumes a harvesting season of three months ; that is, storage space is needed for a 9-month supply of stalks. From the storage piles the

baled stalks should be carried by a slat conveyor to a shredder.
MANUFACTURE OF MAIZOLITH 9

Figuring on a 24-hour day this shredder should have a capacity of onehalf ton of dry stalks per hour. The shredded stalks should be

conveyed to a storage hopper mounted above the digester and arranged

so that the stalks can be discharged into the digester. The hopper

should have a capacity for a 4-hour output of 2 tons of shredded

stalks. The digester should have a capacity of 1,200 cubic feet. The 2 tons of stalks in the digester are cooked under 40-pound steam

pressure for four hours with 10 per cent of their bone-dry weight of caustic soda diluted to a 1 per cent solution. From the digester the

pulp is pumped to a storage tank having a capacity of 5,000 gallons,

where it is diluted to a consistency of 5 per cent. From this tank it

is pumped to a continuous suction filter to wash out the material

in the pulp which has been dissolved by the treatment in the digester.

H h

R. R.

-I V RR. H

Note-. Storage Space is drawn to smaller scale than rest of drawing

T

F'n/shed Product Storage

Dryer

Molds Steam

Kettle

Storaoe Hopper

Shredder ^—1 D/9 esfer Stoh9

e Tank M'*'"?

t Tank vTpBeater^

JU

WO' Figure 9.

Flow sheet for maizolith factory

The pulp from the first filter is broken up, diluted, and pumped to another filter, where the washing operation is completed. After this operation the pulp is given the combined beater and Jordan treatment

for two hours as previously described. Two 1,000-pound beaters

and two No. 1 Jordans are required to handle the pulp.

From the beaters the pulp passes to a 300-gallon steam kettle in

which it is boiled one hour to remove air bubbles. The boiled pulp

is poured into a tray 3 by 3 feet by 3 inches deep and dried in an

atmospheric shelf dryer. Figuring on a drying time of 10 days, this dryer would have to accommodate 3,560 trays. This could be done

m a drier 45 by 32 feet by 12% feet high, if the drier shelves were 44

feet long by 31 feet wide, and the shelves were spaced 6 inches apart.

Based on the process outlined above for making maizolith, quotations have been secured from manufacturers of the required equipment which indicate that a plant to produce 5 tons of the material

per day would involve a capital layout of about $325,000. On the
10 BUREAU OF STANDARDS

basis of this capital requirement and estimated cost for the various

steps in the process, maizolith could be produced for about $140 per

ton. This figure includes charges for raw material, cost of production

depreciation of equipment, and manufacturing overhead.

The figure of $140 represents the cost per ton of maizolith as it comes from the drier in a rather rough form. If a charge of 75 per

cent, or $100, is added for the cost of machining, a total of $240 is obtained as a very rough estimate of the cost of a ton of the finished

product.

Maizolith, manufactured as a by-product of the cornstalk insulation

board industry, or the corncob adhesive industry, could probable be

produced at a figure lower than $240 per ton. VI. MAIZOLITH AS A BY-PRODUCT FROM OTHER

INDUSTRIES

In the process of making an insulating wall board from cornstalks,

it may be necessary before forming the board to remove the fibers which are smaller than a certain size. If this is the case these small

fibers would make an excellent raw material for the manufacture of maizolith. Experiments conducted at the experimental insulating

board plant at Ames indicate that a plant producing 150,000 square

feet of insulating board per day would furnish enough fine material

to make 3,000 pounds of maizolith per day. This fine material would

be put through the same process as that outlined above for the cornstalks except that instead of being passed through the shredder they

would be run through a filter and then to the digester. This modification of the process would then reduce the cost of the raw material and

the shredding and add the expense of filtering and hence make the

total cost less than that outlined above.

The process of extracting an adhesive material from corncobs is one which gives promise of soon becoming commercial.4 5 In this process corncobs are steam digested for a short time. The liquor

which is drained off shows good adhesive properties when concentrated. This treatment leaves 55 per cent of the cob as a soft residue,

in ideal condition for conversion into maizolith. This process would

be the cheapest of the three, since the cost of raw material and beatingwould be reduced, and expense of the shredding eliminated.

Since the demand for a low-priced material which combines strength,

hardness, and electrical insulating properties is continually increasing, it seems probable that maizolith, which can be produced cheaply,

and which has the desired properties, may soon play an important

part in supplying this need.

Washington, December 18, 1929.

4 T. R. Naffziger, Iowa State College, The Manufacture of an Adhesive Material from Corncobs, unpublished thesis; 1928. ^ „,

6 Frederick B. LaForge, The Simultaneous Production of Pentosan Adhesives and Furfural from Lorncobs and Oat Hulls, J. Ind. Eng. Chem., 16, p. 130; 1924. O


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