U. S. DEPARTMENT OF COMMERCE

DANIEL C. ROPER, Secretary NATIONAL BUREAU OF STANDARDS

LYMAN J. BRIGGS, Director

NATIONAL BUREAU OF STANDARDS MISCELLANEOUS PUBLICATION M147 PAPERMAKING QUALITY OF

CORNSTALKS

By

CHARLES G. WEBER

MERLE B. SHAW

MARTIN J. O'LEARY

Issued February 18, 1935

UNITED STATES

GOVERNMENT PRINTING OFFICE

WASHINGTON : 1935

or sale by the Superintendent of Documents, Washington, D. C. - - - - Price 5 cents'

PAPERMAKING QUALITY OF CORNSTALKS

By Charles G. Weber, Merle B. Shaw, and Martin J. O'Leary

ABSTRACT

Study of the papermaking quality of cornstalks was made at the National Bureau of Standards to find the practical possibilities of utilizing this form of waste farm product as a raw material for paper. Special mechanical preparation

of the stalks was found essential for successful pulping because of certain struc- tural peculiarities of the type of plant stem. The best results were obtained by

using only the outside shell or cortex, which had been separated from the re- mainder and shredded by mechanical processes. The cortex was pulped without difficulty by both the kraft-sulphate and the

caustic-soda processes. The use of unbleached pulps in the manufacture of brown

wrappings was investigated, but the papers did not compare favorably with

wood-fiber wrapping papers. A bleached pulp suitable for use in medium grades

of white writing papers and greaseproof specialties was made by the caustic-soda

process. Papers made from this pulp had fair strength and satisfactory color, formation, and cleanliness. However, higher costs due to low yields of pulp

based on the amount of cornstalks used, place them at a disadvantage with wood

as a raw material at present. CONTENTS

Page

I. Introduction 1

II. Structural characteristics of cornstalks 2

III. Experiments in pulp and paper manufacture 3

1. Mechanical preparation of stalks 3

2. Pulp and papermaking 3

IV. Discussion of results 4

1. Effect of mechanical preparation of stalks 4

2. Brown wrapping papers 7

3. White papers 7

V- Summary and conclusions 9

I. INTRODUCTION

The utilization of cornstalks for paper has received much publicity,

mainly because of the relatively large supply of readily available

fibrous material for which the farmer has no profitable use. For

many years cornstalks have been proposed as a source of cellulose,

and particularly cellulose pulp for paper. However, although many

investigators 1 have experimented with cornstalks and numerous

patents 2 have been granted for methods of making paper pulp from

them, no successful commercial developments have resulted. Despite

the numerous experiments recorded in the literature, the published

results were somewhat lacking in detail. Published information did

not indicate clearly the most satisfactory pulping methods or the

quality of pulp that could be produced from the material. Therefore,

in order to determine definitely the papermaking quality of cornJ West, Papermaking Materials, p. 224, Lockwood Trade J. Co. (1928). 'Hossman, Cornstalks in Papermaking, Paper Trade J. 91, no. 23, 51 (1930). 107028—35 1
2 Miscellaneous Publications, National Bureau of Standards

stalks, it was necessary to make a thorough investigation of the

pulping of this material by the processes adapted to crop plants.

Some preliminary small-scale pulping experiments made in the branch

laboratory of the National Bureau of Standards at Ames, Iowa, in

cooperation with Iowa State College, indicated that the stalks could

be pulped in the conventional type of equipment.3 These experiments were followed by an extensive investigation at the Bureau with

laboratory-scale and semicommercial-scale equipment, using stalks

shipped from Ames.

The semicommercial-scale equipment consisted of a rag duster; rag

cutter; rotary boiler; 50-pound, copper-lined, wood-tub beater with

manganese-bronze bars and plate and equipped with one washing cylinder ; jordan refiner, 4-plate screen ; and 29-inch Fourdrinier papermaking

machine with a 33-foot wire, two presses, nine 15-inch dryers, a 7-roll machine stack, and a reel. Detailed descriptions of this equipment

have been given in previous articles. 4 5

II. STRUCTURAL CHARACTERISTICS OF CORNSTALKS

Certain structural characteristics of cornstalks present serious diffi- culties in reducing them to a satisfactory paper pulp. The most

serious obstacle lies in the different character of various parts of the

stem which consists essentially of two distinct portions, the outside

shell or cortex, and the soft, bulky pith inside. The cortex, which is very much harder at the joints or nodes than in the portion between

the nodes, contains a high percentage of fibers of papermaking quality;

while the spongy pith consists principally of thin-walled, oblong cells known to be of little value for paper. The fibers comprising the dif- ferent parts of the stalk differ greatly as to length, and the longest do

not compare favorably with the more commonly used wood fibers. This is shown by the comparison in table 1. Detailed information on

the physical structure of cornstalks is contained in a previous article

by Lofton. 6 Table 1.

Comparison of fiber lengths

Cornstalks Woods

Cortex Nodes Leaf

sheath Spruce Hemlock Yellowpine Poplar

Fiber length (millimeters) 1.65 0. 62 1. 17 2. 69 3. 62 3. 17 1.46 The concentration of chemicals necessary to disintegrate the differ- ent parts of the stalk differs very much. The cortex requires a much

stronger cooking liquor than the pith, and unless thoroughly broken

by preliminary mechanical treatment, the nodes require much more

drastic cooking than the remainder of the cortex. Therefore, if the

entire stalk is cooked for the purpose of producing fibers, the concentration of chemicals necessary to pulp the cortex practically destroys

3 The authors gratefully acknowledge the assistance of B. Wingfield, E. R. Whittemore, and C. B. Overman in making the preliminary experiments and preparing the cornstalks for the work done at the Bureau.

* Tech. Pap. BS 21, 323 (1925) T340.

s Paper Trade J. 89, no. 19, 60 (Nov. 7, 1929).

e Paper Trade J. 91, no. 5, 39 (July 31, 1930).
Papermaking Quality of Cornstalks 3

the thin-walled pith cells, and the concentration required to soften

uncrushed nodes greatly overcooks the remainder of the stem. The

difficulties presented by the structural characteristics of the stalks and

by the excessive amounts of dirt always present in field-gathered

cornstalks made it essential to study the efficiency of different mechanical treatments before cooking, as well as different cooking conditions.

III. EXPERIMENTS IN PULP AND PAPER

MANUFACTURE

1. MECHANICAL PREPARATION OF STALKS

Three different kinds of mechanical treatment were used to prepare

stalks for cooking with chemicals in the rotary digester. Pulping tests were made on the entire stalks cut into short lengths and dusted; on

the entire stalks shredded; and on the outside shell or cortex only,

well shredded to break up the hard nodes.

Cut stalks were prepared by first agitating them in. a rotary duster,

covered with a no. 5 wire screen, to remove the loose dirt; then reducing them to approximately 1-inch lengths in a rag cutter. The loss in

dusting was 5 percent, and since the moisture content of the baled

stalks was 10 percent, the yield of cut stalks was approximately 85

percent on a dry basis.

The shredded stalks used were prepared at Ames, on the conventional farm-type shredder, before shipment to the Bureau. No data were obtained on the loss in shredding, but, inasmuch as it is known

that dirt and other fine material are removed in the process, the dry

basis yield of shredded stalks was estimated to be the same as for the cut and dusted stalks. The outside shell or cortex was processed in the branch laboratory

at Ames, by a method developed there. The process consists essentially in shredding the stalks and washing them thoroughly; breaking

the pith loose in an attrition mill; and separating the cortex from the

pith and extremely short-fibered, fine material by wet screening and

water separation. The yield of dry cortex was 43 percent based on

the weight of baled stalks containing dirt and 10 percent of water. The cortex was in much better condition for pulping than whole stalks

in any form, because it consisted principally of fibers suitable for

paper, and much of the dirt had been washed out in the wet separation

process.

2. PULP AND PAPERMAKING

In this study of cornstalks, the lime, caustic soda, and sulphate or

kraft pulping processes, three well-known operations adapted to the

pulping of crop plant materials, were investigated. A series of

laboratory-scale experiments made in the branch station at Ames

were followed by 8 laboratory-scale and 15 semicommercial cooks

(pulping experiments), and 16 paper-machine runs at the National

Bureau of Standards. Data on the semicommercial-scale pulping

experiments and the accompanying paper-machine runs are given in table 2.
4 Miscellaneous Publications, National Bureau of Standards

IV. DISCUSSION OF RESULTS

1. EFFECT OF MECHANICAL PREPARATION OF STALKS

The most satisfactory results were obtained by using the cortex of

the stalks. The pulps made from this were not only stronger but were

cleaner and worked much better on the paper-machine. Those from

the entire stalks were very dirty, even after excessive washing, and the

fibers tended to stick to the paper machine wire. As no mineral filler was used in an}7- of the papers, their comparative cleanliness is indicated by the ash contents; low ash content is indicative of low dirt content. While the cortex constitutes only 43 percent of the gross weight of the entire stalks, the average pulp yields, using cortex, were

only approximately 5 percent less than the yields from the entire

stalks in either the cut or shredded form. Inasmuch as twice as much

digester capacity and chemicals are required to pulp the cut or shredded stalks constituting 85 percent of the original stalks, as for the

cortex constituting 43 percent, the economy of using the cortex alone

is apparent.

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Papermaking Quality of Cornstalks

Quality

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6 Miscellaneous Publications, National Bureau of Standards

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Paper-making Quality of Cornstalks 7

2. BROWN WRAPPING PAPERS

The brown wrapping paper having the most satisfactory strength

and cleanliness was made in machine run no. 1079. This paper,

however, was much inferior to a commercial no. 2 kraft wrapping,

which would be a competitive paper. The superiority of the kraft

may be seen by comparing the properties of the cornstalk paper with

the United States Government Printing Office specification requirements for no. 2 kraft as shown in table 3. Table 3.

Comparison of cornstalk wrapping paper with no. 2 kraft requirements

Paper stock Ratio of burst- ing strength to weight

Folding endur- ance average

Spec. GPO no. 2 kraft Percent

70

51

Double folds500 Cornstalk paper, MR1079 93 The yield, 23.7 percent, could doubtless be improved slightly

by using a finer screen for dusting the cortex; probably 25 percent can be obtained. Using that figure, 4 tons of stalks would be

required for sufficient cortex to make 1 ton of pulp. At an estimated 7 cost of $7.15 per ton for baled cornstalks at the mill, and $1 per ton

for separating the cortex, the cost of stalks would be $32.60 per ton

of pulp, which is approximately four times the cost of the pine wood

required for a ton of no. 2 kraft. In addition, the manufacturing

costs would be much higher for cornstalks. Cornstalk material is so

light and bulky that it is impossible to charge a satisfactory amount

into a digester of ordinary capacity, as compared with wood. This

would necessitate greater expense for digester equipment, and result

in greater cost of chemicals, because the larger volume of liquor

necessary to cover the bulky digester charges would mean liquor

dilutions that would greatly increase the cost of recovery of chemicals.

Also the handling costs would be much greater for the light bulky

cornstalk material.

From a consideration of the poor quality of the paper and its relatively high cost, the utilization of cornstalks for ordinary wrapping

papers does not appear to have commercial possibilities. Even if the

cost of wood were to be increased to four times current prices, cornstalks could not compete successfully with wood for use as a raw

material for this class of paper.

3. WHITE PAPERS

Bleached writing paper of fair quality was made from cortex that was thoroughly dusted before cooking. The best paper of this type was made in machine run 1077. This paper had fair strength

together with good color, formation, and cleanliness, and it was

considered suitable for many of the purposes for which sulphite

writing papers are commonly used. That the strength requirements

of the United States Government Printing Office specification for

sulphite writing paper of comparable weight were exceeded by this

paper is shown in table 4.

7 Sweeney and Arnold, Bui. 98, Iowa State College.
8 Miscellaneous Publications, National Bureau of Standards

Table 4.

Comparison of cornstalk writing paper with sulphite writing paper

requirements

Weight

25X40:

500 Bursting

strength Folding endurance

Sulphite writing, GP0 specification Pounds54

56

Points

25

30

Double folds30 Cornstalk paper, MR1077 47 Chemical analyses were made to find the purity of the writing

papers. Results of alpha cellulose, 8 copper number,9 and resin 10 determinations are contained in table 5. Table 5.

Chemical tests 1 of cornstalk writing papers

Paper Alpha

cellulose Copper number Resin

MR1076

Percent

72. 66

77. 51 1.311. 07

Percent

2. 06 MR1077 2.12

i These tests were made by the methods of the Technical Association of the Pulp and Paper Industry. The alpha-cellulose content of the papers was somewhat low

although that of MR1077 compared quite favorably with commercial

sulphite papers and the copper number was much lower than is commonly found in sulphite papers.

A greaseproof type of paper was also made from the bleached pulp

in machine run 1078, using waste paper from machine runs 1076

and 1077. In the commercial manufacture of greaseproof papers

the parchment-like properties are obtained by drastic mechanical

treatment in the beater and that procedure was followed in the preparation of stock for this paper. The paper was somewhat comparable in character to commercial papers commonly used for wrapping

butter, lard, and similar products, and it was very satisfactory as regards strength, formation, color, and cleanliness. No attempt was made to obtain a high degree of grease resistance; however, this

could doubtless be accomplished by the special processes employed

in the manufacture of commercial greaseproof papers.

According to the data obtained, 5.2 tons of cornstalk would be

required for sufficient cortex to make 1 ton of pulp for white papers.

Allowing $7.15 per ton of cornstalks at the mill, and $1 per ton of

stalks additional for separation of cortex, the cost of stalks would be

$42.38 per ton of pulp. This is approximately 60 percent higher than

the cost of the spruce wood required for a ton of sulphite (2 cords),

and to this cost differential must be added the higher conversion

costs caused by smaller digester charges, higher handling costs, and

greater consumption of chemicals.

8 The alpha-cellulose content of cellulosic material is that part which is insoluble in a sodium hydroxide

solution of mercerizing strength (17.5 percent NaOH) under certain specified conditions, and is regarded

as a measure of the amount of unmodified cellulose. High alpha cellulose is indicative of good fiber quality.

9 The copper number indicates the amount of copper reduced from alkaline copper solution by the modified cellulose present. High copper number is indicative of the presence of harmful impurities.

i° The resin content of paper indicates the amount of rosin sizing, plus the natural resins present.
Papermakingr Quality of Cornstalks 9

V. SUMMARY AND CONCLUSIONS

The low strength of cornstalk fibers, together with the comparatively high raw-material and manufacturing costs, appears to pre- clude at present commercial success in utilizing domestic cornstalks

for ordinary wrapping papers and similar unbleached papers.

White pulp of satisfactory quality for medium grades of writing

papers, and bleached wrapping specialties such as butter and lard

wrappers was produced. However, the commercial manufacture of

this type of pulp does not appear feasible at the present time on

account of the relatively high costs of raw materials and conversion.

Before the process can be of commercial interest under present conditions, it will be necessary to find profitable uses for the pith and

fine fibrous material which are left after separating the cortex. If these or other byproducts 11 could be made to pay the cost of separating the cortex and one-half the raw material costs, reducing the

cost of the cortex to about $18 per ton of pulp, it is possible that the

cortex could be used profitably for bleached pulp.

Washington, November 19, 1934.

11 Materials obtained experimentally from cornstalks that may ultimately be of commercial interest include xylose, alcohols, adhesives, lignin, maizolith, furfural, plastics, and low-density thermal and

sound-insulating material from the pith and fines.O