U. S. DEPARTMENT OF COMMERCE

DANIEL C. ROPER, Secretary NATIONAL BUREAU OF STANDARDS

LYMAN J. BRIGGS, Director

NATIONAL BUREAU OF STANDARDS MISCELLANEOUS PUBLICATION M148

SEPARATION OF CORNSTALKS INTO

LONG FIBERS, PITH, AND FINES

By

E. R. WHITTEMORE, C. B. OVERMAN,

and BAKER WINGFIELD

Issued May 4, 1935

UNITED STATES

GOVERNMENT PRINTING OFFICE

WASHINGTON : 1935

For sale by the Superintendent of Documents, Washington, D. C. - - - - Price S cents

SEPARATION OF CORNSTALKS INTO LONG FIBERS,

PITH, AND FINES

By E. R. Whittemore, C. B. Overman, and Baker Wingfield

ABSTRACT

The wet method of separating pith from cornstalks was modified to produce

three fractions of useful materials. The method consisted in a preliminary coarse shredding, preferably in a wet

condition to minimize the production of fine material, washing the shredded

material with water to remove most of the loose dirt, breaking the pith free from

the shell and inner fibers by a wet mechanical treatment, separating the pith,

"fines", and dirt from the long fibers by wet screening, and separating the pith

from the fines and dirt by water flotation. Data on the ash of the various fractions and the thermal conductivities of pith and pith board are given, together with a discussion of the uses to which the

materials may be put. The yields are 42.5 percent of long fiber, 5 percent of

pith, and 22.5 percent of fines. CONTENTS

Page

I. Introduction 1 II. Mechanical separation 2

1. Shredding 2

2. Washing 2

3. Breaking 3

4. Separation of long fiber 3

5. Separation of pith and fines 4

III. Handling of products 6 IV. Analyses of the materials 6 V. Cost and uses 7

I. INTRODUCTION

For a number of years, the National Bureau of Standards, in

cooperation with the Engineering Experiment Station of Iowa State

College, conducted investigations on agricultural wastes as a source of

papermaking fibers. One of these annual wastes studied was cornstalks. Experiments with cornstalks soon made it evident that the physical

characteristics of different portions of the stalks cause different

degrees of reactivity to the same chemical or mechanical treatment.

A separation of these parts would simplify the pulping process of the

material more suitable for papermaking fiber. The stalks can be separated into two main constituents, the outer

shell, which contains fibers suitable for papermaking, and the parenchymatous tissue or pith. Two general methods for the separation

have been investigated, the dry and the wet. The dry method,

120814—35 1
2 Miscellaneous Publications, National Bureau of Standards

patented 1 in 1899, cut the pith free from the outer shell with a special

machine. The wet method 2 was used by workers in plant chemistry- investigations 3 and by G. N. Seidel, a member of the Bureau staff, working on insulation lumber from cornstalks. The wet method

consisted in breaking the pith loose from the shell in a beater, screening

the pith through a no. 8 screen fastened to a rotary washer, and col- lecting the pith on a fine screen. The breaking and screening were

accomplished in the presence of water. This method produced a good separation of the constituents and had the advantage over the

dry method of producing an outer-shell fiber free from dirt as well

as from leaf membrane. The method, however, was slow and made

no attempt to separate the dirt and fine material from the pith.

The following method is a modification of the wet method and

separates the stalks into three fractions.

II. MECHANICAL SEPARATION

The mechanical separation consists in preliminary shredding and

washing of the stalks followed by operations which break the pith

free from the fiber, screen the pith and other materials from the

fibers with water, and separate the pith from the fines and dirt by

flotation in water.

1. SHREDDING

The baled stalks were broken open and fed into an ensilage cutter

fitted with 12-inch blades. The stalks were reduced to lengths of

from 1 to 3 inches at the rate of 300 pounds per hour. In this work,

the stalks were shredded in an air-dried condition since it was neces- sary to store the material for some time. In practice, it would be

better to shred the stalks wet to reduce the formation of fine, broken

fiber that would be lost in the subsequent washing treatments.

2. WASHING

Sixty pounds of shredded stalks were added to 250 gallons of water

in a 300-gallon thresher tank, figure 1. The mixture was agitated

for 10 minutes, agitation stopped, and the water drained, leaving

the stalks in the tank. Fresh water was added, the mixture agitated,

and then drained as before. When the agitator was stationary, most

of the stalks rose to the top of the water and permitted a large proportion of the water to be discharged before a mat of stalks formed

over the outlet pipe. The small amount of stalks passing through the

discharge pipe was caught on a no. 4 screen and returned to the tank.

This was repeated until the wash water was practically clear, requiring 4 to 5 washes. In the last step, the agitator was kept in motion

to permit the stalks to discharge with the water. The stalks were

collected behind the removable grating shown in figure 1. This prewashing of the stalks is advisable to remove most of the

dirt and prevent its being ground into the fibers by the action of the

attrition mill in the next step. Mechanical dusting of the stalks

will not remove the dirt as effectively as wet washing unless the

stalks are dry.

1 G. R. Sherwood, U. S. patent, no. 627882.

2 H. Kumagama and K. Shimomura, British patent no. 299740; Ohem. Abs. 23, 3574 (1929).

3 C. J. Peterson, E. H. C. Fang, and R. M. Hixon, Iowa State Coll. J. Sci. 7, 17-24 (1932).
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'] Mechanical Separation of Cornstalks

3. BREAKING

The washed stalks were passed through a 24-inch attrition mill at the rate of 100 pounds per hour together with water at 30 gallons per

minute. The discharge of loosened pith and long fiber bundles was

caught on a no. 30 screen. The attrition mill proved to be the best

type of mill for producing the desired action. The mill consisted of

two corrugated steel disks mounted on horizontal shafts. The disks

revolved in opposite directions at 1,800 rpm and were enclosed in a

steel shell. Pressure was exerted on the adjacent faces of the disks

by springs attached to the shaft of one of them. The compression in

the springs was regulated by an adjusting screw. The feed was made

through a hopper connecting to openings around the shaft of the nonadjustable disk. The tension of the springs of the attrition mill was

Figure 1.

Thresher tank. adjusted to give the least cutting action on the fibers and still break

the pith free. The breaking operation also loosened the residual dirt

in the stalks.

4. SEPARATION OF LONG FIBER

One hundred pounds, dry weight, of the milled stalks were transferred to the thresher tank and the screening hopper, figure 2, was

fitted tightly into the top opening of the tank. A continuous stream

of water, 10 gallons per minute, and a small amount of compressed air were introduced into the bottom of the tank. The water, under continuous agitation, carried the pith, fines, and dirt through the screen, D, and into the hopper trough, A, where it was discharged through B

into the pith separating barrels. The operation required about 90

minutes. At the end of the separation, the long fiber, consisting chiefly

of cortex and practically free of pith, fines, and dirt, was discharged in

the same manner as the washed stalks.

t The screening hopper, figure 2, consisted of wooden side walls partially covered by a galvanized-iron top, C. Spaced beneath the top was 6 square feet of no. 4 galvanized-iron screening, D. The screen was attached to the walls and to the top of the wall adjacent to the

solid-bottomed discharge trough, A. The agitator paddles in the

thresher tank worked counter-clockwise, considering the end view in
4 Miscellaneous Publications, National Bureau oj Standards

figure 1, and caused the charge to flow from the back toward the front

at the screen surface.

5. SEPARATION OF PITH AND FINES

The overflow water, carrying the pith and fines, was led into the top

of a 50-gallon barrel, about 18 inches in diameter, illustrated in figure

3, which shows the details of the separation. From the side-wall pipe,

the water was led into a 100-gallon barrel, about 23 inches in diameter,

and then into a box with a no. 30 screen bottom. The settled fines were washed from the barrels at the end of 2 or 3 charges of milled

stalks. Practically all of the pith was recovered from the top of the

first barrel.

Figuke 2.Screening hopper.

The separation depends upon the fact that the fines will water-log more readily than the pith during the process and will settle in water

while the pith floats. Figure 3 is a schematic representation of the

present set-up of the flotation process. Figure 4 is a proposed modification of the arrangement. The reversal of the sizes of the settling

tanks is in order to have a greater capacity for settling in the first step. It will be noticed in the representation of materials gathered, figure 3, that the first settling contains practically no water-logged pith.

Unless there is to be a further separation of the water-logged pith and

the short fibers or a differential use of the two types of fines, it would

be more logical to have the main settling area in the first step. Further experimentation with the correct rate of flow of water through

this area might lead to the elimination of the second tank entirely.
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Present system of pith flotation.

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SETTLING FINES SEPARATION OF PITH [TiT- 33° ZZj TWfTvS

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Figure 4.

Suggested system of pith flotation.
6 Miscellaneous Publications, National Bureau of Standards

III. HANDLING OF PRODUCTS

The long fiber from the separation process is ready for processing

into papermaking fibers, etc., without additional treatment.

The pith can be utilized in a wet condition for some purposes, but

for others it must be dried. The pith recovered from the top of the

flotation barrels contains about 95 percent of moisture, which is reduced to 60 or 70 percent by subjecting sacks of the material to a pressure of 400 pounds per square inch. The pressed pith is then

fluffed out by passing it rapidly through a swing-hammer mill. The

final drying is accomplished by a current of hot air over or through

thin layers of the pith.

The fines, when desired in a dry condition, can be treated in a manner similar to the pith. IV. ANALYSES OF THE MATERIALS

The efficiency of the operation in removing the dirt from the cornstalks is as follows:

Ash in the various fractions Material: Ash {percent)

Shredded stalks 4 6. 1 Long fibers 2. 9 Pith 5 4. Fines 6. 2

* O. R. Sweeney and L. K. Arnold, Iowa State Coll. Exp. Sta. Bui. no. 98 (1930), list data showing the ash of cornstalks to vary from 3.6 to 10.5 percent.

* H. W. Wiley, U. S. Dept. Agr. Chem. Bui. no. 50 (1898), gives the ash of pith as 4.52 percent. The average content of ash in the combined long fiber and pith

amounts to 3 percent, and, considering that in the cornstalks there is present constituent ash amounting to about 2 percent, it is evident

that most of the dirt has been removed from these fractions. The

high ash content in the fines is to be expected as the dirt loosened

during the attrition mill treatment will settle with the fines. A partial chemical analysis of the different portions of cornstalks is given in table 1 . These data were reported by Hooper 6 and indicate

that the chemical difference in the pith, vascular bundles, and shell is small and that their differences in properties are " largely due to the

original mechanical subdivision of the tissues".

Table 1.

Composition of shell, pith, and inner vascular bundles

Tissue

Specific gravity at 25° C

Lignins Pentosans

CellulQsic pulpPentosans

in pulp

Cellulose by differ- ence

Pith 1.52 32.0 27.7 50.1 12.2 37.9 Inner vascular bundles 1. 515 35.2 26.4 50.2 13.1 37.1

Shell 1. 52 33.5 25.9 55.9 16.6 39.3 The yields of materials obtained by the wet separation process are given in table 2, together with yield data presented by Peterson

Fang, and Hixon,7 using the wet separation with a beater.

8 F. E. Hooper, Plant Physiol. 6, 531-539 (1931) table 1, p. 536.

7 C. J. Peterson, E. H. Fang, and R. M. Hixon, Iowa State Coll. J. Sci. 7, 17-34 (1932).
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'] Mechanical Separation of Cornstalks

Table 2. —Yields of fractions in the wet separation of cornstalks Wet separation method 1 Wet separation with a beater 2

Material Percent Material Percent Long fiber 42.5

5.0

22.5 30.0

Fibrous material 6326

92

Pith

Fines Water soluble Loss. .- Loss and difference

1 Data obtained in this investigation.

* Data obtained by Peterson, Fang, and Hixon. footnote 7.) The two sets of data do not agree. There are a number of reasons

for this disagreement. The stalks used by Peterson, Fang, and Hixon

were freed from leaves and loose dirt before the separation was begun,

the separation was performed on small batches of 1 to 2 pounds of

stalks and the fraction reported by them as pith material was the material passing through a no. 10 screen and retained on a no. 60 screen. Wiley,8 on the other hand, gives the yield of pith from the whole cornstalk, not including the corn or cob, as 10.3 percent.

The size of the batches used in this investigation was between 100

and 200 pounds and consequently offered opportunities for errors in

sampling the wet masses. The authors made one yield determination on the beater method on a large scale, starting with approximately

100 pounds, in which the stalks were separated into three fractions.

The results of this run gave a 70-percent recovery and indicated that

the beater and attrition mill methods were comparable on a large

scale. The products from these two methods were quite similar.

The disadvantage of using a beater lies in its high consumption of

power compared with the combined power used by the attrition mill

and the separating tank.

V. COST AND USES

The cost and yield figures are given in table 3. The power costs

are based on power consumed by the small equipment used in the

experimental work. The water costs are based on pumping and

filtering the volume of water used since fresh water would be expensive

at ordinary prices.

Table 3.

Cost data

Stalks Long

fiber Pith Fines

Tons 1.00 0. 425 0. 05 0.225 Power at 1 cent a kilowatt hour $0. 75 .38

$0. 09

.05 .15

$0. 40

.20 .69 Water at 0.8 cent a 1,000 gallons Fuel for drying. Total 1. 18

2. 65

.29

5. 90

1.29 Cost a ton $2. 76 5. 73

s H. W. Wiley, U. S. Dept. Agr. Chem. Bui. no. 50 (1898), gives the ash of pith as 4.52 percent.
8 Miscellaneous Publications, National Bureau oj Standards

To these costs would have to be added those for labor, raw material,

overhead, etc. The values given in table 3 have been apportioned

between the three products according to the weight of each.

The three components of cornstalks have many possibilities for

utilization in industry. The chemical analysis of each fraction is very nearly the same, but the differences in physical characteristics

give them a wide range of usefulness. The long fiber, after suitable

treatment, has the possibility of economical use in making paper,

insulation board, and pressboard. The pith has interesting possibilities as an insulating material. Tests by the heat and power division of the National Bureau of Standards indicate that its thermal

conductivity is as low as that of cork, while its density is much less. In a wet condition the pith can be beaten, molded into boards or blocks and dried. These boards have approximately the same thermal

conductivity as the original material, but with a greater density. In

the granular and molded forms pith can be used as insulation material

in refrigerators, refrigeration cars, house insulation, and because of its low density it might find application in airplane insulation. Further,

it might find an outlet as a substitute for ground cork in the manufacture of linoleum. Pith is easily nitrated and it is possible that it might be valuable as a raw material for the manufacture of explosives.

The fines should find outlets as material for pressboard, insulating

material, and possibly as a substitute for wood flour in the manufacture of linoleum.

The authors acknowledge their appreciation for the cooperation

and the assistance of the members of the staff of the Iowa State

College Experiment Station in this work; particularly to Dr. O. R.

Sweeney, in whose laboratory the work was carried out, and to Charles

W. Miller for his assistance and suggestions in the actual experimental

work.

Washington, January 12, 1935.

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